fiESIGN E’ARAMETERS m A SYSTEM FER MOVERS SURFACE. M033?!) RE. FROM BLUEEERRIES Thesis for the Degree of m s: héECt-fiem STATE U N I‘JE‘RSEW jEFFREY K. MOWRY 1972 ABSTRACT DESIGN PARAMETERS IN A SYSTEM FOR REMOVING SURFACE MOISTURE FROM BLUEBERRIES By Jeffrey K. Mowry Blueberries which are mechanically harvested are subjected to continuous deterioration prior to being packaged for the fresh market. Water handling could improve product quality by reducing detrimental effects. Cold water would rapidly cool the fruit. In addition. water would minimize bruising by cushioning the berries and would assist in removing extraneous material. Prior to packaging. the water must be removed from the blueberry surface since water on packaged blueberries decreases shelf-life. The primary objective of the research presented was to investigate the influence of air velocity. water temperature. air temperature. and relative humidity on the rate of surface moisture removal from blueberries in air flow. .The experiments were conducted such that a relationship between surface moisture removed and time could be determined. The ranges of the parameters in- vestigated were: air velocity. 200-800 ft/min; water temperature. “5-750F3 air temperature. 62-87OF; and relative humidity. 16-50%. Jeffrey K. Mowry The data obtained from these experiments were fit to least square-exponential curves from which sur- face moisture removal rate constants were obtained. The rate constants were also fit to least square- exponential curves to determine the influence of each parameter. An increase in air velocity or air tempera- ture resulted in an exponential increase in the rate constant. while an increase in relative humidity ex- ponentially decreased the rate constant. An increase in water temperature was assumed to exponentially increase the rate constant. although the relationship was insig- nificant at the 5% level. A systems design equation for predicting the surface moisture removal rate constant was obtained by multiple linear regression. The increase of the pre- dicted rate constant from the systems design equation. over the experimental range of each parameter. was greater than that predicted by respective exponential equations. This was very evident with water temperature and relative humidity variables and probably resulted from the influences of the parameter constants on the multiple linear regression. In a commercial operation. the surface moisture would probably be removed from blueberries on a conveyor within a tunnel. Air temperature was found to be the most influential parameter on tunnel length. A 25% in- crease in air temperature resulted in a “1% decrease in Jeffrey K. Mowry tunnel length. Similar increases in air velocity and water temperature resulted in decreases of only 1h and 12%. respectively. in tunnel length. A 25% increase in relative humidity increased tunnel length by uo%. DESIGN PARAMETERS IN A SYSTEM FOR REMOVING SURFACE MOISTURE FROM BLUEBERRIES By {C'\ Jeffrey K. Mowry A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science and Human Nitrition 1972 ACKNOWLEDGEMENTS The author is deeply indebted to Professor D.R. Heldman for his invaluable assistance and encouragement throughout the course of this research work. Many hours of consultation given by him were essential in the completion of this study. Sincere gratitude is also expressed to Professors F.W. Bakker-Arkema and C.L. Bedford for their constructive criticisms of the manuscript and to Professor R.C. Nicholas for his help on the statistical analysis. The author also wishes to thank the members of the Michigan Blueberry Growers Association. especially Murlin R. Hansel. for their support which made this study possible. ii TABLE OF C LIST OF TABLES . . . . . . . . LIST OF FIGURES . . . . . . . LIST OF SYMBOLS . . . . . . . INTRODUCTION . . . . . . . . . LITERATURE REVIEW . . . . . . Historical Development Harvesting . . Shelf-life and Quality ONTENTS of Mechanical of Blueberries Effect of Mechanical Harvesting on Shelf-Life and Quality . . . . . . Potential for Improving Quality of Mechanically Harveste Handling of Blueberries EXPERIMENTAL PROCEDURES . . . Laboratory Equipment . Measurement Systems . Experimental Procedures RESULTS AND DISCUSSION . . . . Data Analysis . . . . Influence of Air Veloci Influence of Water Temp Influence of Air Temperature . . Influence of Relative Humidity . Systems Design Equation . . . . Implementation of Design Equation CONCLUSIONS . . . . . . . . . . REFERENCES . . . . . . . . . . APPENDIX A . . . . . . . . . . .APPENDIX B . . . . . . . . . . ii d Blueberries . in Water . . . ty 0. erature i Page iv viii com 12 l7 18 18 20 22 26 26 33 36 39 #8 53 55 58 75 TABLE 1. 2. A.1. A.2. A030 A.“. LIST OF TABLES Page Parameter variables investigated with corresponding parameter constants . . . . . 2b Surface moisture removal rate constants obtained for experimental parameter variables . . . . . . . . . . . . . . . . . 33 Comparison of time. required to remove 90% of the surface moisture. obtained experimentally with that predicted by the corresponding exponential equation and by the deSign equation 0 o o o o o o o o o o o u? Tunnel lengths computed for given sets of parameters 0 o o o o o o o o o o o o o o o 50 Fraction of water. r. vs time. t. obtained with varying air velocity . . . . . . . . . 58 Fraction of water. r. vs time. t. obtained with varying water temperature . . . . . . 59 Fraction of water. r. vs time. t. obtained with varying air temperature . . . . . . . 60 Fraction of water. r. vs time. t. obtained with varying relative humidity . . . . . . 61 iv Figure 1. 2. 3. 4. 5. 7. 9. 10. LIST OF FIGURES Michigan Blueberry Growers Association grading and packing standards - fresh pack (Hansel. 1971) . . . . . . . . . . . Plexiglass tunnel. with basket removed. . Schematic view of laboratory system for removing surface moisture from blueberries o o o o o o o o o o o o o 0 Determination of surface moisture removal rate constant. k. at air velocity variable oof 800 ft/min (constants: Tw =h5° F. Ta =76°F. RH=l6%). . Determination of surface moisture removal rate constant. k. at water temperature Page variable of h5°F (constants: u=800 ft/min. Ta =76° F. RH=19%). . . . . . . . . . . Determination of surface moisture removal rate constant. k. at air temperature variable of 620F (constants: u=800 ft/min. Tw =u50F. RH=13%). . . . . . Determination of surface moisture removal rate constant. k. at relative humidity variable of 26% (constants: u=800 ft/min. Tw =u5° F. Ta=76°F). . . . . Influence of air velocity. u. on the surface moisture removal rate constant. k 0 O I O O O O O O O O O D O O O I O O I Influence of water temperature. Tw' on the surface moisture removal rate COUStaNt’ k c o o o o o o o o o o o o o 0 Influence of air temperature.T . on the surface moisture removal raTe ConStant. k 0 o o o o o o o o o o o o o o 10 19 21 28 29 30 3h 37 #0 LIST OF FIGURES (Continued 0 o 0) Figure 11. 12. 13. A.l. A.2. A.3. A.4. A.5. A.6. A.7. A.8. Page Influence of air temperature on sur- face moisture removal rate constant. k. USing an Arheniu3-type pIOt o o o o o o “'2 Influence of relative humidity. RH. on the surface moisture removal rate constant,k................1W Influence of parameter increases on tunnellength..............51 Determination of surface moisture removal rate constant. k. at air velocity variable of 200 ft/min (constants: Tw=h5°F. Tg=76°F. Rkléyo) O I O I O O O O O O O O O O O O O O 62 Determination of surface moisture removal rate constant. k. at air velocity variable of #00 ft/min (constants: Tw=h5°F. Tg=76°F. Rk16%)ooooooooooooooooo063 Determination of surface moisture removal rate constant. k. at air velocity variable of 600 ft/min (constants: Tw=h5°F. T =760F. Rlfil6‘7o). O 0 O O O O O O O O O O 0 0a. 0 O .6“ Determination of surface moisture removal rate constant. k. at water temperature variable of 55°F (constants: u=800 ft/min. Ta=760F.RH=19%)ooooooooooooo65 Determination of surface moisture removal rate constant. k. at water temperature variable of 65°F (constants: u=800 ft/min. Ta=76°F. RH=19%) . . . . . . . . . . . . . 66 Determination of surface moisture removal rate constant. k. at water temperature variable of 75°F (constants: u=800 ft/min. Ta=760Fka19%)ooooooooooooo67 Determination of surface moisture removal rate constant. k. at air tempgrature variable of 72°F (constants: u=800 ft/min. TquOF' RH=13%) o o o o o o o o o o o o o 68 Determination of surface moisture removal rate constant. k. at air tempgrature variable of 82°F (constants: u=800 ft/min, '1‘quon Rh13%) o o o o o o o o o o o o o 69 vi LIST OF FIGURES (Continued . . .) Figure Page A.9. Determination of surface moisture removal rate constant. k. at air temperature variable of 87°F (constants: u=800 ft/min. Tw=nSOF P. RH=13%) o o o o o o o o o o o o o 70 A.lO. Determination of surface moisture removal rate constant. k. at relative humidit variable of 16% (constants: u=800 ft min. TW=u50 F. Ta =760F)o o o o o o o o o o o o o 71 A.ll. Determination of surface moisture removal rate constant. k. at relative humidit variable of 36% (constants: u=800 ft min. nguso F. Ta =760F) o o o o o o oo o o o o o 72 A.12. Determination of surface moisture removal rate constant. k. at relative humidit variable of 50% (constants: u=800 ft min. TW =u50 F, Ta 3760 F) o o o o o o o o o o o o 73 A.13. Unsteady-state temperature distributions in a sphere (Foust et al.. 1960) . . . . 74 vii a: 'U'USL“ LIST OF SYMBOLS computed water fraction at time. t=0 surface area. ft2 conveyor belt width. ft correlation coefficient blueberry capacity of commercial system. pints blueberry capacity of experimental system. pints energy of activation. BTU/mole surface heat transfer coefficient. BTU/hr- ftZ-OF surface moisture removal rate constant. l/min mass transfer coefficient. l/hr tunnel length. ft rate of water vapor transfer. lb/hr 2 water vapor pressure in air. lb/ft water vapor pressure at the surface. lb/ftz rate of heat transfer. BTU/hr fraction of water remaining on the basket + blueberries universal gas constant. BTU/mole-OR relative humidity. % time. min air temperature. OF surface temperature. oF viii LIST OF SYMBOLS (CONTINUED . . .) O Tw water temperature. F a air velocity. ft/min wt weight of the basket + blueberries at a given t1me interval wD initial dry weight of the basket + blue- berries where dry implies absence of surface moisture wo initial wet weight of the basket + blue- berries Ti absolute air temperature. OR )5 latent heat of vaporization. BTU/1b ix INTRODUCTION In 1971. Michigan ranked first in the United States in the production of highbush blueberries. Vaccinium corymbosum. with an estimated value between 6 and 8 million dollars (Howell et al.. 1971). Of the 31 million pounds harvested. about 32% was fresh marketed (anon.. 1971). Approximately 75% of the highbush blue- berries were harvested mechanically - either by straddle row harvesters (50%) or by hand held vibrators (25%) (Howell et al.. 1971). The advantage of mechanical harvesting over hand picking is that larger acreages are harvested more quick- ly with less expense. The mechanically harvested berries. however. are more bruised. vary more in maturity. lose more bloom (waxy surface coating). and require more clean- ing than those that are manually picked. In addition to these problems. the blueberries must be manually sorted for removal of green. decayed. and overripe fruit. This could result in longer periods of exposure to heat in the packing house if adequate numbers of inspectors are not employed to handle the blueberries at the rate the fruit is being mechanically harvested. In the fresh market. these factors will probably decrease the product shelf-life and may reduce market appeal for the blueberries. 2 One approach suggested to minimize detrimental effects is a water handling system. The main advantage of such a system would be the rapid cooling of har- vested blueberries. thereby retarding microbial and fungi growth. resulting in increased shelf-life. Cool- ing also decreases respiration to prevent rapid deteri- oration of the fruit (anon.. 1971). Additional benefits may be derived from a water handling system. In addi- tion. water should cushion the berries to decrease bruising. It could act as a lubricant to reduce loss of bloom normally caused by the blueberry rubbing against an object or other blueberries. Water would wash off exuded juice collected on blueberries from overripe fruit. In addition. water could be used to sort green berries. twigs. leaves. and other forms of trash collected in the mechanized harvest. Finally. a properly designed water sorting system should significantly reduce or even eliminate potentially long periods of heat exposure in the packing shed for the mechanically harvested blue- berries. The major obstacle preventing the use of a water handling system is the moisture to be removed prior to packaging for the fresh market. Stiles and Abdalla (1966) stated that surface moisture on picked blueberries en- hanced mold growth. Heldman et a1. (1971) reported that the shelf-life of blueberries increased as the amount of surface moisture removed increased. with blueberries 3 which were not exposed to moisture displaying the longest shelf-life. Whether 100% of the surface moisture must be removed to attain maximum shelf-life has not been established. but if the surface moisture removal system is designed to be 100% efficient. maximum shelf-life should be obtained. The implementation of a surface moisture removal system would not only allow fresh market blueberries to be handled in water. but would allow blueberries moistened by rain or dew to be harvested resulting in a uniform and uninterrupted harvest. Surface moisture could feasibly be removed from blueberries by an air flow system. The system. to be commercially feasible. must be designed to accommodate or improve upon present sorting rates and the blueberries leaving this system must be equal to or exceed present shelfblife expectancies. Therefore. the surface moisture removal rate must be known before the system can be designed. It is expected that this rate will be a function of air velocity. air temperature. relative humidity. and water temperature to which the blueberries are exposed. The objectives of this investigation were: 1. To design and construct a laboratory apparatus for measuring surface moisture removal rates with independent regulation of air velocity. air temperature. relative humidity. and water temperature. 2. 3. u. 5. 4 To evaluate the influence of each of the above parameters by obtaining and compar- ing moisture removal rate constants. To derive an expression that describes the rate of change of the surface moisture removal rate constant for each parameter. To derive a systems design equation which will incorporate the overall influence of air velocity. air temperature. relative humidity and water temperature on the sur- face moisture removal rate. To illustrate the use of the systems design equation in construction of a commercial system to remove surface moisture from blue- berries e LITERATURE REVIEW Higtgrical Development of Mechanical Harvesting The harvest season in Michigan for highbush blueberries extends from July through September with the dates of harvesting varying with variety and weather (Johnston. 1970). An acreage of one variety must be picked 3 to 7 times over a 6 to 8 week period to obtain maximum yield (Stiles and Abdalla. 1966). Stiles and Abdalla (1966) reported that blue- berries harvested manually were deposited either directly into the market container or into a pail. The advantage of the latter method was that the harvests could be examined for foreign material and green and overripe berries before filling the market containers. This procedure. however. resulted in increased handling of the fruit promoting increased loss of bloom. Stiles and Abdalla (1966) stated that mechanical harvesting was introduced to compensate for a decreasing supply of labor and an increase in wages. In 1958. USDA engineers developed hand-held vibrators to aid in the harvesting of highbush blue- berries (Monroe and Levin. 1966). The first units were powered by portable electrical generators driven by gasoline engines. but they could not be easily moved around. To alleviate this problem. an air compressor 5 6 was used in place of the generator in 1960. but was very noisy resulting in battery powered vibrators in 1963 (Gaston. 196“). With a hand-held vibrating unit. 1 man could have harvested as many blueberries as 8 men could have picked by hand (Nelson. 1966). Gaston (196h) discussed the need to mechanize the filling of lugs in the field and to reduce the need for qualified operators of the hand-held vibrators. Monroe and Levin (1966) reported that preliminary investigations on mechanical harvesters began in 1959. These investiga- tions led to the conclusion that this harvester must remove. collect. and deposit ripe blueberries into lugs with minimum damage to the bushes. The first mechanical harvester was towed by a tractor and subsequent models were self-propelled beginning in 1960 (Monroe and Levin. 1966). The initial blueberry removal structure was a vibrating angular unit. but this unit failed to remove the berries because of cane resiliency. Modifications to this system resulted in little improvement of the harvest. The next removal structure incorporated was a vertical rotating shaft with rubber flails. This unit failed because the flails damaged the bushes excessively. The third removal structure consisted of 2 rotating vertical spindles. each with a number of horizontal struts. The spindles revolved and vibrated horizontally and vertically with one spindle on each side of the bush. This 7 over-the-row machine harvested 90% of the ripe berries with little damage done. Over-the-row harvesters were used to harvest blueberries in Michigan beginning in 1965 (Howell et al.. 1971). Monroe and Levin (1966) stated that labor costs were: 8¢/1b for manual picking. 3.5¢/1b for hand vibrator harvesting. and £¢/lb for over-the-row harvest- ing. The over-the-row harvester. which required 3 men to operate. produced a daily harvest equal to that of about 120 manual pickers (anon.. 1968). Nelson (1966) estimated the cost of an over-the-row harvester to be approximately $30.000. Stiles and Abdalla (1966) reported that hand-held vibrators shook the branches detaching the blueberries which fell into canvas catchers positioned beneath the bush and then the fruit was transferred manually into field lugs. Over-the-row harvesters vibrated the whole bush removing the blueberries. The fruit then fell onto flexible baffles which closed in around the bush (Monroe and Levin. 1966). The berries then fell onto a conveyor which transported the fruit into field lugs. Blueberries harvested from either the hand-held vibrator or the over-the-row harvester required more cleaning than those harvested manually because of ex- cessive foreign material. green berries. and damaged and overripe fruit (Stiles and Abdalla. 1966). A pneumatic winnower. incorporating an air stream. removed the 8 foreign material and green berries. but the damaged and overripe fruit had to be removed manually. (Nelson (1966) stated that one pneumatic cleaner could efficiently handle the harvest from 8 hand-held vibrators (600 1b/hr). but that h of these cleaners were needed fbr each over- the-row harvester.) The inspected fruit was conveyed to a filling tray where the blueberries dropped into con- tainers for the fresh market. Shglf-life and Quality of Blueberries Hruschka and Kushman (1963) reported that the shelf-life of blueberries was one week. or less. and that this shelf-life was very short compared with other fresh products. Stiles and Abdalla (1966) stated that blue- berries. high in quality. could be stored for 2 days at 75°F (no relative humidity given) and 1 week at 40°F. 85% RH. The shelf-life could be extended from 2 to h weeks if these berries were stored at 32°F. 85% RH. in pints placed in plastic lined lugs (Hruschka and Kushman. 1963). At h weeks. some loss in quality could develop. Stiles and Abdalla (1966) reported that the shelf-life was increased to 6 weeks by storing the blueberries at 32°F. 85% RH in sealed polyethylene bags. Turgidity. flavor. weight. and appearance were maintained. but after 6 weeks. off-flavors and off-odors became apparent. Quality was defined by Kushman (1970) as cleaned fruit that looks and tastes good and will remain in this state for a few days. A more complete definition as it 9 applies to blueberries is given in the grading standards of the Michigan Blueberry Association. Figure 1. Ballinger and Kushman (1971) employed storage tests to evaluate quality. The blueberries were placed in pint containers and covered with cellophane. The packaged fruit was then stored for 7 days at 70°F and 85% RH. At the end of this period the blueberries were individually sorted into marketable (ripe) and not marketable (decayed. damaged. etc.) fruit and counted to determine % decayed. Galletta and Mainland (1971) used similar procedures to obtain the amount of decayed fruit. Bowers (1960) discovered that controlled har- vesting and storage produced sugar-acid ratios that correlated linearly to the deterioration and shelf-life of blueberries. Increased sugar-acid ratios increased deterioration and decreased shelf-life. Bowers (1960) stated that this ratio was not a function of ripening alone. The sugar-acid ratio may also be affected by the amount of sunshine. berry size. nutritional status. amount of irrigation. size of yield. pruning practices and. especially. by variety. If the harvest was not controlled. the sugar-acid ratio may also be influenced by the source of the fruit. handling and picking methods. and elapsed time between harvesting and testing. gffect of Mechanical Harvesting on Shelfelife andgguality Galletta and Mainland (1971) compared blueberries harvested mechanically with those harvested manually and 10 MICHIGAN BLUEBERRY GROWERS ASSOCIATION Grading 81 Pack'ng Standards — Fresh Pack GREAT LAKES BRAND GENERAL: All berries packed in 12 pint and 8 quart crates. and bulk cartons shall conform to the following requirements: A. All blueberries accepted by the Association must conform to the general requirements setforth in the Federal Food. Drug and Cosmetic Act. Failure to meet these requirements will he basis for rejection. l B. The following defects shall result in rejection, regardless of the overall condition and character of the fruit: I. The fruit must have 'normal flavor and odor" meaning that the product is free from objectionable flavors and objectional odors of any kind. 2. Excessive insect fragments and blueberry fly infestation. 3. Any form of adulteration or contamination, including chemical residues foreign material, or unclean fruit. C. Marking: — Each crate or carton must be stamped with Grower 5 stamp on one end. 0. Inspection: In addition to the Field Men, the General Manager (or any appointed employee of the general manager) of the Michigan Blueberry Growers Association has authority to Open packages and inspect the pack of any member of the Associa- tion at any time or place. When berries fail to meet the established standards in grade, quality, or fullness of pack, if they have not left the grower's premises, the grower shall repack the berries, so that they will meet the standards. If the inspection is made after the ship- ment has left the grower's premises, a) the shipment shall be excluded from the pool and sold as a separate item. returns being made separately and directly to the grower, or, b) the grower will be notified to pick up shipment for re-packing. QUALITY: Berries shall be mature. firm, well colored, well developed, and not over-ripe; which are free from stems, mold and decay; and from damage caused by dirt or other foreign matter shriveling, moisture disease insects, mechanical or other means. There shall not be more than eight (8) defects per pint; of which not more than two may be soft berries. Soft Is defined as not bleeding or moldy. Red berries are not counted as a defect. SIZE: - Count shall be made on the basis of a standard measuring cup stroked level full and shall not be more than 175 BERRIES PER CUP. If more than 2 pints in any crate are below grade, the crate shall be considered below grade. PACK: - Fruit destined for the fresh market shall be packed as follows: A. 12 Pint Crate I. All pints shall be tightly packed, corners well filled, and well rounded in the center. 2. Filled cups should be settled down on vibrators and/or other mechanical devices or means to insure full pack. 3. Cellophane should be secured tightly with rubber bands. 4. Minimum net weight of berries per 12 pint crate is 11 1/2 pounds (that Is,11-1/2 pounds after deducting weight of crate, cups and other packing material). 8.8 Quart Crate 1. Items 1 - 3 for 12 pint crate also applies to this pack. 2. Minimum net weight of berries per 8 quart crate is 15 pounds (that is, 15 pounds after deducting weight of crate, cups and other packing material). C. Bulk Carton ("10 Pound" Carton) 1. Minimum net weight of berries per carton is 11 pounds (that is, 11 pounds after deducting the weight of the carton). 2. The quality and size requirements for this pack are the same as for crates. 3. The center divider and/or other carton modifications must be put in each carton. Failure to do so will he basis for rejection- (unless the item was not available at the warehouse). LAKE STATE BRAND Prior permission is necessary before the Lake State Brand is packed. Berries shall meet the requirements and be graded in conformity with the GREAT LAKES BRAND except as to size. count shall ‘ not be more than 250 BERRIES PER CUP. All Berries smaller in size than 250 count per cup — Special arrangements must be made -— not to be packed under cellophane -— will be excluded from pool. DEFINITION OF TERMS AS USED IN THESE GRADES: “Well Colored" means that the whole surface of the berry shall he of good blue color. "Well Developed" means that the berries shall not be misshapen owing to frost injury, lack of pollination, insect injury or other causes. ' “Over-ripe" means dead ripe, over mature, past commercial utility. "Damage" means any injury from the causes mentioned which materially affects the appearance, edible or shipping quality. it: - . 1920 ReVIsron Figure 1. Michigan.31ueberry Growers Association grading and packing standards - fresh pack (Hansel. 1971). 11 found that after 7 days at 70°F. 85% RH. the mechanically harvested fruit was 15% more decayed on the average. The leading cause for the higher incidence of decay was believed to be bruising of the fruit during mechanical harvesting and subsequent handling. Galletta and Mainland (1971) also found that blueberries harvested mechanically were on the average 11% darker in color than those harvested manually. due to loss of bloom. Ballinger and Kushman (1971) also reported in- creased levels of decay with mechanically harvested blueberries. Mechanically harvested fruit stored at 70°F. 85% RH. that had not been sorted was 12 to 26% more decayed than manually harvested samples. Mechanical sorting and packaging operations increased the incidence of decayed mechanically harvested fruit an additional u to 13%. Ballinger and Kushman (1971) found significantly more bruised berries from mechanical harvesting than with hand harvesting. confirming the observations of Galletta and Mainland (1971). These investigators also discovered that mechanically harvested berries were covered with juice that had dried and become sticky. resulting in a less appealing appearance of the blueberries. Ballinger and Kushman (1971) conducted a detailed study on the causes of bruising when blueberries were harvested with an over-the-row machine. Once detached. the blueberries fell as much as 6 feet. striking branches and harvester parts. The fruit was then conveyed to the 12 rear of the harvester where the berries fell 10 to 18 in. into a lug hitting the bottom or other fruit. bruising these berries also. Bruising also occurred when these lugs were roughly loaded onto the vehicle for transporting the fruit to the packing house. The lugs may also have bounced around. depending upon the terrain over which the vehicle traveled. causing additional bruising. In the packing house. the blueberries were dumped onto conveyor belts. falling 10 to 15 in. The fruit was then transported to the pneumatic cleaner where the berries were bounced around by the force of the air causing secondary bruising of other berries. When the fruit left the air cleaner. the berries rolled onto the sorting table striking other berries al- ready present. In the mechanized packaging system. the blueberries rolled into the emptying chute where the fruit fell up to 15 in. into pint containers hitting the container bottom or other berries. bruising this fruit also. Potential for Improving anlity of Mechanicallngarvesteg_ Blueberries To improve the quality of blueberries harvested mechanically. several areas of research were undertaken. One approach was to improve the blueberry through breeding. Moore (1966) stated that specific characteristics were strived for in obtaining new varieties. One was large berry size which not only harvested easier. but also had a greater market appeal. Another was firmness which was desired for handling and shipping. Other desirable 13 characteristics included resistance to disease and uniform ripening. especially for mechanical harvesting. Eck (1970) conducted research to determine if Ethrel (2-chloroethy1phosphoric acid) could increase the rate at which blueberries ripen to obtain more ripe fruit in the mechanical harvest. When Ethrel was applied 2 weeks prior to the expected harvest date. the ripe fruit obtained on the first harvest increased 28% with the variety. Weymouth. and 22% with Blueray. The amount of ripe fruit obtained on the second harvest decreased 27 and 22%. for Weymouth and Blueray respectively. com- pared with the second harvest where Ethrel was not applied. There were no significant differences in the percentages of ripe berries in succeeding harvests. Ethrel treated acreages produced significantly smaller fruit in the first 2 harvests except in the first harvest of Blueray. Also. with Ethrel treated varieties. the pH increased while tritratable acidity decreased. Eck (1970) cited the need for further research on the con- centration of Ethrel needed for other varieties (the 2 varieties tested here did not respond the same with identical concentrations of Ethrel). when to apply. how often to apply. and on the effects of multiple applications. Ballinger and Kushman (1970) have suggested that varieties high in acid be developed for longer shelf-life. These investigators found that acid was more effective than sugar in controlling Alternaria and Botgytis. which 1H were reported to be the most common producers of decay in the storage of blueberries. Culture solutions with the same concentration of sugar and acid as found in various stages of ripening in blueberries were used. Ballinger and Kushman (1970) also used blueberry samples. with the berry interior uniformly exposed. In these samples. decay increased from 12% with the small dark green berries to 99% with the overripe. These results were obtained from an average of samples held for 10 days at 75-8OOF and of samples held at 32°F for 21 days followed by storage at 60°F for 6 days. Ballinger and Kushman (1970) verified that the sugar-acid ratio increased as the blueberries ripened from small green to overripe. These investigators also reported that the anthocyanin content highly correlated with the sugar-acid ratio. The anthocyanin content in- creased 12 times from the stage where the blueberry was s red-5 green to the overripe stage. Ballinger and Kushman (1970) concluded from these results that there was a potential for sorting by light transmittance. thus automating the inspection table. Ballinger and Kushman (1971) discovered that light transmittancy was a feasible method for sorting blue- berries while sizing was not. The berries were separated into light classes corresponding to the anthocyanin content using a light transmittance difference meter. These berries were then stored at 70°F. 85% RH for 7 days. 15 The incidence of decay was found to increase as the anthocyanin content increased. These same tests indi- cated that increased berry size did not correspond with an increase or decrease in the incidence of decay. Hamann (1971) tested the possibility of sorting by vibration on the principle that firm berries (ripe) would bounce easier than soft (overripe or damaged) berries. These tests revealed that this method dis- played promise. although significant softening occurred with vibration. Milholland and Jones (1971) stated that cooling the blueberries soon after harvest increased the shelf- 1ife of the fruit. Blueberries stored in 5°C (UloF) air 2 hours after harvest displayed less decay (authors didn't establish how much) than those stored 12 hours after harvest. A reduction in storage temperature from 21°C (69.8OF) to 5°C (41°F) also resulted in a signifi- cant reduction in decayed fruit. Kushman and Ballinger (1962) investigated the possibility of forced-air cooling to improve the rate at which the fruit temperature was decreased. Cooling rates were found to be a function of container type. room temperature. air movement and the manner in which master containers were stacked. Kushman and Ballinger (1962) concluded that blueberries with a maximum temperature of 100°? could feasibly be cooled to 55°F or less within 2 hours compared to a conventional time (authors did not 16 elaborate on the meaning of conventional time) of u to 8 hours. These investigators also reported that some moisture. occurring from dew. was removed. Kushman and Ballinger (1962) cited the dis- advantages of using other cooling methods. In hydro- cooling. the water (not removed) caused loss of bloom and increased the potential for decay. Vacuum cooling caused juice loss through cracks in the skin and the fruit did not cool rapidly. Air-blast cooling was in- effective because the fruit was shielded to some extent by the shipping containers. Kushman and Ballinger (1968) stated that the molded pint paper cup improved the cooling rate. using fbrced-air cooling. over that obtained with wooden pint cups because the former had more ventilating slits. Wooden master containers also allowed more rapid forced- air cooling than could be obtained with corrugated fiber- board boxes because the former containers had more ventilation. Kushman (1971) investigated the possibility of using hot water treatments to control decay in the stor- age of blueberries. This investigator found that berries exposed to 130°F water for 3 min. controlled fungus growth. but this treatment damaged the fruit. A decrease in water temperature resulted in decreased fruit damage. but this temperature decrease also reduced control of fungus growth. At 105°F. this control was very small. 17 Handling of Bluebgrries in Water An extensive searcher the literature has resulted in very little information recovered on handling small fruits in water and subsequent moisture removal. Levin and Gaston (1956) reported that cherries for processing were handled in water from the orchard to the processing plant on a commercial basis. The benefits of such a sys- tem resulted in maintenance of quality. decreased handling costs. elimination of lugs and subsequent problems of maintenance. storage. etc.. and less sorting since cherries handled in water were higher in quality. Before considering any type of handling system. the capacity of the system. the influence of the system on the quality of the fruit. and the cost of the system must be considered (anon.. 1971). The only reference to surface moisture removal was found in the report of Kushman and Ballinger (1962) who commented that before a forced-air system could be used to remove large amounts of moisture from the surface of blueberries. factors such as humidity would have to be considered. EXPERIMENTAL PROCEDURES Laboratory Eguipment A plexiglass tunnel (Figure 2). measuring 6 in. square and 21 in. high. was designed and constructed to facilitate the collection of experimental data. A 3 in. diameter opening. located in the lower portion of the tunnel. allowed the introduction of air flow. The air moved upward through a 15 in. layer of plastic packing material to obtain a uniform distribution of air velocity. The air flow then passed through the bottom of a wire basket containing a single layer of blueberries. The basket was supported by plexiglass rails attached to the sides of the tunnel as shown in Figure 2. To facilitate minimum handling of the basket. a plexiglass support panel was constructed as illustrated in Figure 2. Hooks were fastened to the inside of the door and a handle was attached to the outside. These hooks supported the basket on the panel and allowed easy removal of the panel from the basket prior to weighing. When the basket was inserted into the tunnel. the panel prevented air from escaping through the side before pass- ing through the basket. The air flow source was a 1/3 HP fan which pro- vided a maximum air velocity of approximately 800 ft/min 18 19 Air out Upper rail channel Basket support rail Support panel Figure 2. Plexiglass tunnel. with basket removed. 20 at the outlet of the tunnel. The fan was connected to the tunnel by h alternating segments of flexible and metal tubes as illustrated in Figure 3. The flexible tubes provided for independent positioning of both the fan and the tunnel. One of the metal tubes contained a heating coil for increasing the air temperature. The amount of heat added to the air was controlled by vary- ing the current to the heating coil. Insulation on the outside of the tubing prevented heat loss to the surround- ing air. The second metal tube. connected directly to the tunnel. contained a baffle which could be positioned from the outside to regulate air velocity. The relative humidity of the air flow was in- creased by using 1.5 gallon humidifiers connected to the fan inlet by metal tubing (Figure 3). The increase in relative humidity was a function of the limited amount of control available with each humidifier and the number of humidifiers used. Mgggurement Systems The system utilized for measuring air temperature and relative humidity was an electric hygrometer. Air velocity measurements were obtained by using a hot wire anemometer and water temperature was measured using a mercury-in-glass thermometer. All samples were weighed on a Mettler top loading balance. 21 .mmwunmnozan scum waspmwos commune mcw>osoh now Eopmzm hhopmuonma mo 3ma> nanosecom maummm Hamann Hfloo wcaumom \(Ht - )5 ii Encod- asses ass has poxmmm Emu meoaeasassm .m ouswam ca cs4 22 Experimental Procedures Mechanically harvested Jersey blueberries were obtained from the Michigan Blueberry Growers Association and were frozen at -20°F to prevent further deterioration and/or decay. (Freezing of the blueberries should not effect the rate at which surface moisture can be removed). The size of the berries averaged about 3/8 in. in diameter with an average weight of approximately 0.h grams/berry. Blueberries removed from cold storage were examined frozen for detection of green. cracked. and damaged berries. Stems were also removed while the blue- berries were still frozen to prevent extraction of the berry interior. The inspected fruit was then thawed in water at ambient temperatures where the berries were again examined for cracked. leaky. and overripe fruit. The remaining blueberries were then spread out on paper towels to allow all of the surface moisture to evaporate. Berries that dehydrated during this time were discarded. The blueberries were then placed into the basket in a single layer as close as possible without crushing. An initial dry weight of the basket and fruit was obtained. (In this text. dry weight will imply that all surface moisture was removed.) The basket and blueberries were then placed into a water bath. approximately 1 in. deep. for 1 minute. The temperature of the bath was adjusted by adding ice or hot water and recorded prior to 23 inserting the blueberries. The depth of the water bath was maintained fairly constant in an attempt to hold the amount of moisture accumulated on the basket at a con- stant level. The holding time of 1 min. constant for all experiments. decreased the surface temperature of the blueberries to within 1°F of the water bath (see Appendix B for calculations.) After withdrawing the basket from the water bath. excess water was removed by tapping the basket 10 times on each side using approximately a constant force. This procedure removed the water that would have dripped off during transport of the basket and during the initial stages of the experiment. Before each experiment. the wet basket of blueberries was weighed. inserted into the tunnel. and withdrawn. This operation. accomplished in triplicate. eliminated most of the moisture lost by physical handling. The last weight obtained in this pro- cedure became the initial wet weight. The fan and other applicable equipment were activated and the wet basket of berries was again placed into the tunnel. Periodically. the basket was removed. weighed. and placed back into the tunnel. This procedure required approximately 30 sec. of time. The removal times. constant for all experiments. were 15 seconds. 30 seconds. 1 minute. 1.5 minutes. 2 minutes. 3 minutes. a minutes. 5 minutes. 6 minutes. and at intervals of 2 minutes. if required. for the remainder of the experiment. 2h The experiment was terminated when the weight of the basket and contents equalled that of the initial dry weight. There were 9 sets of experiments containing 4 trials each. In each set. 3 of the a parameters. air velocity. water temperature. air temperature. and relative humidity. were held constant while the fourth was varied. The parameter variables investigated with corresponding parameter constants are given in Table 1. (The air temperature constant chosen was that of room temperature.) Each experiment was conducted in triplicate. Table 1. Parameter variables investigated with corresponding parameter constants. Variables Air Water Air Relative velocit tem . tem . humidit (ft7mini (5F; (5F; (%) Air velocity. ft/min Water temperature. °F - 45.55.65.75 -- 45 76 16 Air temperature. OF . 62.72.8298? 800 (+5 -- 13 Relative humidity. % - 16.26.36.50 800 (+5 76 -- The fraction of water remaining on the basket of blueberries at any time. t. was given by the expression 25 w w rs. 15-9 (1) wo-wD where w was the weight of the basket + blueberries at a t given time interval. wD was the initial dry weight of basket + blueberries.and w0 was the initial wet weight of basket + blueberries. (In a commercial design. surface moisture must be removed from both the blueberries and the conveyer. In the experimental apparatus. the basket simulated the conveyor and. therefore. was included in the weight measurements.) The values obtained for each triplicate of experiments along with corresponding time intervals were analyzed using a Wang Model 700 computer. The data was fit to a least square-exponential curve of the form r = aekt (2) where k was the surface moisture removal rate constant or slope of the curve for a given set of parameters. (Equation (2) was selected because the data seemed to follow a logarithmic form.) A graph of each set of data was then drawn on semi-log paper using the slope. k. and the r intercept. a. RESULTS AND DISCUSSION Data Analysis The results obtained from the experiments are presented in Appendix Tables A.1 to A.4. Equal numbers of data points for each set of 3 experiments were then analyzed by the computer. The least square fit- exponential curves obtained with experimental data from the parameter variables of 800 ft/min air velocity. h5°F water temperature. 62°F air temperature. and 26% relative humidity are illustrated in Figures 4. 5. 6. and 7. respectively. The curves obtained for the remaining parameter variables are presented in Appendix Figures A.1 to A.12. In all the figures. the curve intercepted the vertical axis at values greater than one. This indicated that either there was a lag factor before the surface moisture removal rate became constant or the removal of surface moisture did not occur at a constant exponential rate. The latter factor seemed to be the case after careful examination of Figures 4 to 7 and Appendix Figures A.1 to A.12. In these figures. the majority of water fractions. r. fell below the curves during the first minute of surface moisture removal and also during the period after a water fraction of 0.1 had been obtained. During the remaining time. the majority of these values 26 1.10 1300 Water fraction. r 27 070 l .50 .20 .10 .07 .05 .02 A "KDIID ==11.50g u - - == 0.60 VOTE) 1 g I l I I 2 b 6 8 10 Time, t, min Figure 4. Determination of surface moisture removal rate constant. k. at air velocityovariable of 800 ft/min (constants: T = as F. Ta = 76°F. RH = 16%). " 1.10 1.00 .70 .50 .30 .20 .10 Water fraction, r .01 28 A I 'O-VD = 120558 0 - "0" = 11.20g 9.75s 1.05 -0JHH -00973 I I I I I 0 2 h 6 8 10 Time, t. min Figure 5. Determination of surface moisture removal rate constant. k. at water temperature variable of 45°F (constants: u = 800 ft/min. Ta = 76°F. RH = 19%). 29 1.10 1.00 .70 .50 .30 .20 .10 Water fraction, r .07 .05 .03 .01 A - "O-HD = 10.108 0 a again .'-'= 12.253 Figure 6. Determination of surface moisture removal rate constant. k. at air temperature variable of 62°F (constants: E 2 800 ft/min. 1.10 Water fraction, r 30 A - WO-WD U—W—W 11.70g 12.358 I I I I I Time, t, min Figure 7. Determination of surface moisture removal rate constant. k. at relative humidity variable of 26% (constants: fi = 800 ft/min. _ O _ O Tw — 05 F. Ta — 76 F). 31 were located above the curves. These observations in- dicated that there may have been two surface moisture removal rate periods. In the initial period. where the rate constant (k) would be less than that calculated from the original curve.approximately 90% of the sur- face moisture would be removed (the water fraction would equal 0.1). In the second period. where the rate con- stant would be greater than the computed value. the remaining moisture would be removed. Conclusive evidence that two surface moisture removal periods existed. however. was lacking because there was insufficient data to describe the curve during the second period. In addition. the experimental data seemed to be adequately defined by the least square fit- exponential curves in Figures 0 to 7 and Appendix Figures A.1 to A.12. indicated by the correlation coefficients ranging from -.907 to -.996. significant at the 1% level. Since these coefficients were very close to -l. the data points were located very close to the exponential curves indicating that these curves accurately described the relationship of water fraction. r. to time. t. The probability that these curves did not describe the relationship of water fraction to time was 1 out of 100. evidenced by the significance at the 1% level. One factor which could not be controlled ade- quately for any of the experiments was the initial amount of moisture on the basket and blueberries. An 32 increase in the initial amount of surface moisture would result in consistently higher water fractions causing the surface moisture removal rate constant to decrease. This was very evident in Appendix Figure A.2 where the rate constants for the 3 experiments were significantly different at the 1% level with the rate constant decreasing as the initial amount of surface moisture increased. (The 1% level implied that the probability of making the wrong conclusion was 1 out of 100). The justification for finding an average rate constant using the data from all 3 experiments. was that the initial amount of surface moisture would be expected to vary within a commercial design also. In the latter stages of the replicated experi- ments. differences between water fractions at any given time. t. may have also resulted from variations in the amount of free surface water (water not physically held between the berries and between the berries and the basket) remaining. A summary of the computed surface moisture removal rate constants appears in Table 2. The influence of each parameter on these rate constants was determined by fitting the parameter variables with the corresponding rate constants to a least square-exponential curve. 33 Table 2. Surface moisture removal rate constants obtained for experimental parameter variables. Air Rate Water *ERate AI? RatE’ Rela- Rate veloc- con- temp. con- temp. con- tive con- ity stant stant stant humid- stant it (ft7min) (17min) (OF) (17min) (5F) (I7min) (I7min) 200 -0277 “5 -0601 62 ”01"17 16 -.61+9 uoo -.333 55 -.631 72 -.518 26 -.516 600 -0u65 65 -0699 82 -0678 36 "th7 800 -.575 75 -.695 87 -.751 50 --366 Tw = 45°F 3’: 800 ft/min E = 800 ft/nin.fi = 800 ft/min - ° _ o _ o _ o Ta—76F Ta—76F T—LI5F Tw—LlSF RBI: 16% RH: 19% RH: 13% Ta: 76°F Influence of Air Velocitx The influence of air velocity. 3. on the surface moisture removal rate constant. k . is illustrated in Figure 8. The correlation coefficient of the computed least square fit-exponential curve was .996. significant at the 1% level and showed that the rate constant in- creased exponentially with increasing air velocity. Al- though air velocities in excess of 800 ft/min could not be attained with the experimental equipment. higher air \elocities would probably cause flotation of the blue- berries in the basket and alter the rate constant signi- ficantly. 34 .x .pcmpmcoo mums Hm>08ou mpzpmaoe commune on» do .w .zpaooam> has mo mocozamcH .m ouswam can\oa .s .saaoodoa ad< coo- sow can 006 set so: can ssm _ l a . a _ S. .1 ma. as? u as some .I. as so? u an. t om. mcmsoo.oo~am.o- u a an. arm/I ‘x “quegsuoa sic; renown; canistom eoegxng ll oo.H 35 Air velocity can effect the rate of heat trans- fer. expressed by the equation Q = hAfla-TJ (3) where h is the surface heat transfer coefficient. A is the surface area to which heat is transferred. and Ta and T8 are the temperatures of the air and the surface. respectively. The surface heat transfer coefficient. h. can be increased by an increase in air velocity. 3. as displayed by the following equation presented by Earle (1966) h = 1 + .2113 for 'fi<960 ft/min (LI) h =- 0.53 for Ti>960 ft/min (5) where the surface heat transfer coefficient. h. would be expressed in BTU/hr-ftz-OF. The rate of heat transfer may also be expressed as Q = M71 (6) where M is the rate of water vapor transfer and )\ is the latent heat of vaporization. From equations (3) and (6). an expression for rate of moisture transfer was pre- SGNPGG PY' Earle (1966): M = hA(Ta-TS)/)\ (7) The more familiar form of expressing rate of moisture transfer is probably M = K A(P ~P ) (8) g S a where Kg is the mass transfer coefficient. A is the surface area upon which moisture is removed and PS and Pa are the 36 water vapor pressures at the surface and in the air. respectively. (The rate of moisture transfer. M. predicted by equation (7) will be identical to that given by equation (8) only when the surface temperature. Ts’ is equal to the wet bulb temperature of the air.) The value of Kg was predicted by Earle(l966) in the equation Kg = uh (9) where h is the surface heat transfer coefficient of the airflow. With increasing air velocity. the rate of water vapor transfer should increase as predicted by equations (7) and (8). assuming that temperature and vapor pressure gradients. respectively. remain constant. This would account for the increase of the surface moisture removal rate constant with increasing air velocity illustrated in Figure 8. Igfluence of Water Temperature The surface moisture removal rate constant. k. increased exponentially with increasing water tempera- ture. Tw’ (Figure 9). The maximum water temperature that could be implemented without damaging the fruit was less than 130°F (Kushman. 1971). Relatively high water temperatures. however. would be contrary to a primary objective of a water handling system - cooling of the blueberries. 37 bx .Pcmpwcoo open Hm>oEou onzpmaos commune map so . a .opspmnoasop have: mo mocosamcH .m muswam mo .39 6.35393. have: we on no 00 mm om m: o . L -_ _ _ _ a s? S .. m. 0 *9 .I. a m d «.2. a a l om. m sauna 68 u s m l on. m. u. . u I.Q: m N. .o- .. a a 3398.63 s I m D iIIIIIl... 00. x. #Illlllllllttlllll o nu . I. cm. W. oo.« .38 The correlation coefficient of the least square- exponential curve in Figure 9 was relatively high at -.936. but was insignificant at the 5% level. since the curve was determined from only 4 data points. The in- significance apparently resulted from the slightly larger surface moisture removal rate constant obtained experimentally at 65°F than that obtained at 75°F. which was contrary to the predicted values in Figure 9. This was apparently caused by the relatively large water fractions in experiment 11 at 75°F after 3 minutes. com- pared with those in experiments I and III (Appendix Table A.2). which. as discussed earlier. would effect a decrease in the rate constant. Since the initial amount of surface moisture in all 3 experiments at 75°F water temperature was essentially the same (Figure A.6 in Appendix A). the larger water fractions associated with experiment II probably resulted from significant fluctu- ations in one or more of the parameter values. The exponential increase of the rate constant. k. with increasing water temperature. evident by the equation in Figure 9. was probably a net result of 2 factors. Increasing the water temperature raised the water vapor pressure on the surface increasing the vapor pressure gradient. assuming constant air temperature and relative humidity. This would cause an increase in the rate of water vapor transfer. as predicted by equation (8). and. therefore the rate constant would 39 increase. The difference in the rates of water vapor transfer. however. approached zero since the surface temperature approached the wet bulb temperature of 53.5°F. (Since the surface temperature was not equal to the wet bulb temperature. equation (7) could not be used to describe the increase of the rate constant.) This not only nullified part of the effect of water temperature on the rate constant. but also supports the argument. dis- cussed earlier. that the surface moisture removal rate was not constant fer any of the experiments. The time required for the temperature gradient between the surface and the wet bulb temperature to decrease 50% was calculated to be 3.5 min (see Appendix B). In computing this time. the blueberry surface was assumed to be completely exposed to the air stream.' This was generally not true in the experiments because of physical contact between blueberries and between blue- berries and the basket. The time calculated. however. should be a good approximation illustrating that the temperature gradient was not constant for a given experi- ment. Ipflgence of Air Temperature An increase in air temperature. T . produced an a exponential increase in the surface moisture removal rate constant. k. as illustrated in Figure 10. The correlation coefficient of the least square-exponential curve was .999. significant at the 1% level. Air #0 mm .xm.p:mpmcoo ovum Hm>oeou eugenics mowhusm on» so . a .ouspmuoasop “an we oososamsH .oa enemam ho .ua .ohspmaoaloa om mm om me as on a _ a d in: an. a an as} :1 sasxeu can u m 0H. ma. om. om. Uta/L ‘x ‘iueqsuoa can; rename; sandstom seeping Al temperatures at an air velocity of 800 ft/min could not be varied in the experiments much beyond the range of 62 to 87°F. The limiting factors on increasing the air temperature would be the quantity of heat available and the effect on the blueberries. The latter would not be a factor as long as evaporative cooling prevented heat damage to the fruit. The exponential increase of the rate constant. k. resulted from increases in the rates of heat transfer and water vapor transfer. Increased air temperature difference (between dry bulb and wet bulb) in equation (3) increased the rate of surface heat transfer. An increase in air temperature also raised the saturation vapor pressure which allowed the air to hold a larger capacity of moisture. This increased the rate of water vapor transfer resulting from an increase in vapor pressure gradient as revealed by equation (8). The influence of air temperature on the surface moisture removal rate can also be expressed in an Arhenius-type plot (Figure 11). The exponent of the equation in this figure can be expressed as follows «6810/1;at = 4/31; (10) E = 68101? (11) where E is the energy of activation. R is the universal gas constant. and 7; is the absolute temperature. Since the gas constant. R. has a value of 0.238 BTU/mole-OR. 02 so.“ .poan unharmsa:onuu< cm mafia: .x .vcmpm:oo opmu Hm>osmu ouovmaoe commune so ousvmuoasov has me mucosamcH .HH auswwm nIS w « .méxe Jeanna-Bo. 330mg mo $.82; mm; om; mm; om!" aw; mm; om; _ d a a _ _ 2 Iowa. a. ... a as? a J flit cos n m 18. (on. dkOHQWIflWOH N HmoH' H X .1 0:. ate/L in “iueaeuoo can; Income; eanqetom eaegang “3 the activation energy required for moisture removal. computed from equation (11). was 1621 BTU/mole. Influence of Relative Humiditp The influence of relative humidity on the surface moisture removal rate constant is revealed in Figure 12. An increase in the relative humidity. RH. exponentially decreased the rate constant. k. The exponential curve produced a correlation of .993 with the data. significant at the 1% level. Relative humidities at an air velocity of 800 ft/min could not be varied in the experiments much beyond the range of 16 to 50% RH. An increase in relative humidity of air at a constant temperature resulted in a decrease in the capacity of the air to hold water vapor. This resulted in decreased rates of evaporation since the partial pressure of the water vapor in the air increased with increased relative humidity. This was observed in equation (8) where the amount of moisture transferred to the air per unit time decreased as the vapor pressure gradient decreased. The rate of heat transfer in equation (3) also decreased due to the decrease in the difference between the dry bulb (air) and wet bulb (surface) temperatures resulting from increasing relative humidity. These factors accounted for the decrease in the surface moisture removal rate constant with increasing relative humidity. as described by the equation in Figure 12. .x .pcmpmcoo oven Ha>oEon mpzpmaos oommusm on» :0 .mm .hvaoaasz m>apmaeu no mocosamsH .ma ouswam a .51 $335: 2,3331 2. so on 3 on ON 2 o. L L a L _ _ .11“. as. u a. no? u an east cos n m 40 arm]; “a “queqeuoo age; tuneup; canistem eaeJJng oo.H 45 The k value for 100% RH predicted by the curve in Figure 12 does not appear to be realistic. When the air is saturated with water vapor. the moisture removal rate should be zero because the vapor pressure gradient in equation (8) would be 0. This would indicate that the k value should be an infinitely small number at 100% RH. The relationship at this humidity then would not be the one expressed in Figure 12 and may indicate that the ex- ponential equation in this figure may not be the best one for 0 to 100% RH. Systems Desigp Eguation A multiple linear regression was performed on the parameter variables with corresponding surface moisture removal rate constants (Table 2) utilizing the Wang Model 700 computer. The resulting equation was as follows: k = .959-.ooou75 '13-.00509Tw-.01366Ta+.006lt8 RH (12) Equation (12) can be used with confidence only when the parameters used to determine the rate constant. k. are within the experimental limits. This equation should provide reasonable estimates of the rate constant with air temperature. water temperature.and/or relative humidity values outside these limits. provided the relationships given in Figures 9. 10. and 12. respectively. do not change significantly. (As discussed earlier. air velocities in excess of 800 ft/min probably would change the relationship in Figure 8). 06 The time required to remove 90% of the surface moisture. obtained experimentally. was compared. in Table 3. to the time computed from the surface moisture removal rate constant predicted by the exponential and design equations. (The computation of these time periods will be discussed later.) This comparison was made for the minimum and maximum variables of each parameter investigated. Table 3 shows that the time periods derived from the exponential equations were in excellent agreement with those obtained experimentally. The time periods derived from the design equation were generally in some- what less agreement. with the maximum difference being approximately 1/2 min. This should not be considered excessive. however. since this difference also existed between two experimental time periods. in Table 3. obtained under identical conditions - air velocity of 800 ft/min. water temperature of 05°F. air temperature of 76°F. and relative humidity of 16%. The experimental difference probably resulted from fluctuations in the parameter values. in the initial amount of surface moisture. and/or in the amount of free surface moisture. discussed previously. The average time periods derived from the design equation may be more accurate than those obtained experimentally because all of the experimental variables 97 oo.o om.o ao.o+ sm.o om.c I on we com on a sm.o+ so.m mo.o+ mo.m mm.m I be me com ca spa Icaezn.aom No.OI mo.m ao.o: oo.m mo.n ma I m: com um Ahoy mo.o+ sm.m mo.o+ sm.n ~m.m ma I we com «o .oeo» na< HH.0I o~.m 00.0: mm.m Hm.m ma on I com mm Amov s~.o+ so.s Ho.oI mm.m mm.m as as . com me .asop copes 66.0- as.m No.6I mo.m 66.: as as ms I com Mmas\pmv cm.o- cc.s na.o+ ms.m ~m.m cs as as I com acoao> na< coco N. Ildml . V . oopoao coco copoao Houses mm m a m a gas pm a 03Hm> novosupmm Ieoeuan Iona Incense Iona Iaaoaxm o o I ImmmmmmdMImwmmmm_ IIIImmwmmmmMIIII Hwapcosoaxm I, .mflmldosae mpmmvmsoo moanmdum> .coMpmsdo swamoo on» no use seaweede Hmwpcoconxo wcwocoamouuoo as» an covowooum was» an“: zaampcmswuoqxe cocampno .onspmaos commune one no moo o>oaou op conducts made no comanmaeoo .m canoe A8 and constants were used in the determination of the design equation. This. however. can only be proven by many repetitions of the same experiments. Implementation ofgygsingguation A commercial surface moisture removal wstem for blueberries may be designed from the surface moisture removal rate constant provided that both the capacity of the experimental system. C in pints from which the 8’ rate was obtained. and the product capacity of the com- mercial process. Cc’ are known. The capacity of the experimental system was 2 approximately 90g/.25 ft of blueberries. one berry-layer deep. Assuming 1 pint of fruit weighs 360g. then 1 pint of blueberries. one berry-layer deep. will occupy l ftz. the value of °e° The area calculated here for 1 pint of blueberries probably exceeded the commercial require- ment resulting in less surface water per ftz. This would indicate that less time would be required to remove the surface moisture provided the rate constant remained un- changed. Given a surface moisture removal rate constant. k. the time may be computed from the following equation lepe = k/2.303=(1og rZ-log r1)/(t-t1) (13) where tl,is the initial time. t. at the origin and. therefore. equals 0. In one log cycle. where the slope is negative. 49 - = - ’4 log r2 log r1 1 (l ) so that equation (13) becomes t = -2.303/k (15) where t is the time required to remove 90% of the sur- face moisture (initial log cycle). If the commercial system consists of a surface moisture removal tunnel through which a conveyor belt passes. the length of the tunnel. L. can be calculated from the equation 1.: CeCct/Bw (16) where Bw is the width of the conveyor belt and L is ex- pressed in ft. Assuming a product capacity. Cc’ of 10 pints/min and a conveyor belt 5 ft wide. the tunnel lengths. L. required for given sets of parameters are displayed in Table A. The percent surface moisture removed was then plotted against tunnel length. L. on semi-log paper (Figure 13). In Table 0. an initial set of parameters is represented by Set I. Each parameter was then increased by 25% with the others held constant except where an in- crease in air temperature and in relative humidity effected a decrease in relative humidity and in air temperature. respectively. These increases are displayed by Sets II through V. 50 Table 0. Tunnel lengths computed for given sets of parameters. Air _. ——I '" veloc- Water Air Relative Tunnel §°° III7ETn)temF . :°°I° hui%iit (1/°in) IEIE) lTIII° I 800 60 -.560 0.11 8.22 II 1000 60 80 00 -.655 3.52 7.00 III 800 75 80 no -.637 3.62 7.20 IV 800 60 100 22 -.909 2.03 0.86 V 800 60 73 50 -.399 5.77 11.50 As illustrated in Figure 13. increasing the air temperature. decreasing the relative humidity. effected the largest reduction of tunnel length (01%) with the same surface moisture removal capacity as that required by the original set of parameters. Increased air velocity and water temperature resulted in relatively small tunnel length reductions (l0 and 12%. respectively) of the original length. As expected. increased relative humid- ity with decreased air temperature effected a substantial increase in tunnel length (00%) over that of the initial length. required to remove similar amounts of surface moisture. Unless the tunnel length can be adjusted. the design of the commercial system will have to feature means of regulating the air temperature. air velocity. and/or relative humidity to accomodate for fluctuating 51 0.0 °\ \ 30.0 \ Initial Conditions ( a = 800 ft /min g=wu — O 60.0-— \\ Ta - 80 F \ RH = 00% \ \ \ \ \ \ i: /’ / / ‘8 'o T Surface moisture removed. 1 ‘61 {‘3 'o '0 I l ’/’,/¢5” / /// // // ////////’ I I / I / \ \ \ c \\ 25% increase in relative humidit 98.0 — \ ‘\ yi \ \ \ \ \m— ' 25% increase 99 0 25% Witer temp. \ 25% increase \ increase \\ in air temp. hair ve- \ locity \\ ‘ Initial \\ conditions \ 0 C' J L X °”jo 5 70 25 Tunnel lengfih. 1L. ft Figure 13. Influence of parameter increases on tunnel length. 52 air temperature. relative humidity. and/or water tempera- ture. l. 2. 3. 0. 5. CONCLUSIONS The relationship of the data points for each set of triplicated experiments for moisture removal from surfaces of blueberries was described by a least squares-exponential curve from which a surface moisture removal rate constant was obtained. Increase in air velocity or air temperature in the ranges of 200 to 800 ft/min and 62 to 87°F. respective- ly can be described by an exponential increase in the surface moisture removal rate constant. An increase in water temperature in the range of 05 to 75°F was not significantly related to an exponential increase in the surface moisture removal rate constant. An increase in relative humidity in the range of 16 to 50% was significantly related to an exponential decrease of the surface moisture removal rate constant. The systems design equation can be used with confi- dence to determine the surface moisture removal rate constant only when the parameters used are within the following limits: air velocity. 200-800 ft/min. water temperature. 05-75°F: air temperature. 62-87°F: and relative humidity. 16-50%. The time computed from the surface moisture removal rate constant obtained from the systems design 53 7. 5h equation should be more than adequate to remove a designated quantity of surface moisture. Air temperature is the parameter which has the most significant influence on the time required to remove a specified percent of surface moisture from blueberries in a commercial operation. REFERENCES Anon. 1968. Blueberry Harvester Ready. Agricultural Research. U.S. Dept. of Agriculture. 16(10):l6. Anon. 1971. Marketing Michigan Strawberries. United States Department of Agriculture. Consumer and Marketing Service. Fruit and Vegetable Division. pp. 17-19. Ballinger. W.E. and L.J. Kushman. 1970. Relationship of Stage of Ripeness to Composition and Keeping Quality Highbush Blueberries. Journal of the American Society for Horticultural Science. 95(2)8239-2“2. . and . 1971. Interrelationship of Mechanical Harvesting. Bruising. and Decay of Highbush Blueberries. Proceedings Highbush Blue- berry Mechanization Symposium. North Carolina State University. Raleigh. N.C. pp. 38-47. . and . 1971. Light Transmittancy Versus Si2ing as a Means of Sorting Blueberries for Quality. Proceedings Highbush Blueberry Mechaniza- tion Symposium. North Carolina State University. Raleigh. N.C.. pp. 127-139. Bowers. R.C. 1960. The Relation of Sugar-Acid Ratios to the Ripening and Deterioration of Blueberry Fruit. M.S. Thesis. Michigan State University. East Lansing. Mich. Dixon. W.J. and F.J. Massey. Jr. 1957. Introduction to Statistical Analysis. 2nd edition. McGraw-Hill Book Company. Inc.. New York. Earle. R.L. 1966. Unit Opegations in Food Processing. Pergamon Press. Elmsford. N.Y. Eck. P. 1970. Influences of Ethrel Upon Highbush Blue- berry Fruit Ripening. Hortscience. 5(1):23-25. Fbust. A.8.. L.A. Wenzel. C.W. Clump. L. Maus. and L.B. Andersen. 1960. Principles of Unit Operations. John Wiley and Sons. Inc.. Newaork. 55 56 Galletta. G.J. and C.M. Mainland. 1971. Comparative Effects of Mechanical Harvesting on Highbush Blueberry Varieties. Proceedings Highbush Blueberry Mechanization Symposium. North Carolina State University. Raleigh. N.C. Gaston. H.P. 1964. Developments in Blueberry Harvesters. American Fruit Grower. 84(5)315+. Hamann. D.D. 1971. Sorting Blueberries for Quality by Vibration. Proceedings Highbush Blueberry Mechanization Symposium. North Carolina State University. Raleigh. N.C. Hansel. M.R. 1971. Fruit Quality Standards of the Michigan Blueberry Growers Association. Proceed- ings Highbush Blueberry Mechanization Symposium. North Carolina State University. Raleigh. N.C.. pp. SO-SH. Heldman. DoRo. JOKO MOWry and COM. Hansen. 1971. Feasibility of Systems for Removing Surface Moisture from Blueberries. Proceedings Highbush Blueberry Mechanization Symposium. North Carolina State University. Raleigh. N.C.. pp. 113-126. Howell. G.S.. B.G. Stergios. C. Burton and J.W. Nelson. 1971. The Influence of 2-Chloroethyl-Phosphoric Acid on the Harvester Induced Mechanical Injury- Winter Kill Complex. Proceedings Highbush Blue- berry Mechanization Symposium. North Carolina State university. Raleigh. N.C.. pp. h8-h9. Hruschka. H.W. and L.J. Kushman. 1963. A Longer Market Life for Blueberries. Agricultural Marketing. USDA. 8(6):6. Johnston. S. 1970. Hints on Growing Blueberries. Extension Bulletin 564. Cooperative Extension Service. MSU. Oct. Kushman. L.J. 1970. Automated Blueberry Sorting and Packaging Possibilities. Proceedings of the Southeastern Blueberry Council. N.C. State University. Wallace. N.C.. pp. 30-39. . 1971. Blueberry Decay Prevention with Hot Water and Fungicides. Proceedings Highbush Blue- berry Mechanization Symposium. North Carolina State University. Raleigh. N.C.. p. 150. 5? Kushman. L.J. and W.E. Ballinger. 1962. Forced-Air Cooling of Blueberries. Proceedings of the American Society for Horticultural Science. 81:281-287. . and . 1968. Commercial Forced-Air Cooling of Blueberries in North Carolina. Pro- ceedings of the American Society for Horti- cultural Science. 923788-92. Levin. J.H. and H.P. Gaston. 1956. Grower Handling of Rgd Cherries. U.S. Dept. of Agriculture Circ. 9 l. Milholland. R.D. and R.K. Jones. 1971. The Effect of Temperature Fungicides and Heat Therapy on Post- Harvest Decay of Mechanically Harvested Blue- berries. Proceedings Highbush Blueberry Mech- anized Symposium. North Carolina State University. Raleigh. N.C., pp. 148-159. Monroe. G.E. and J.H. Levin. 1966. Mechanical Harvest- ing of Blueberries. Transactions of the ASAE. 9(1) 314-50 Moore. J.N. 1966. Breeding. Chap. 3. pp. h5-7h. Blueber Culture. P. Eck. ed. and N.F. Childers. co-ed. Eutgers University Press. New Brunswick. N.J. Nelson. J.N. 1966. Mechanical Harvesting of the Highbush Blueberry. Maine Agr. Exp. Stat. Misc. Rep. 118 3 58" 59 o Rohlf. J.F. and R.R. Sokal. 1969. Statistical Tables. W.H. Freeman and Co.. San Francisco. Stiles. N.C. and D.A. Abdalla. 1966. Harvesting Process- ing. and Storage. Chap. 11. PP. 280-301. Blueberry Culture. P. Eck. ed. and N.F. Childers. co-ed. Rutgers University Press. New Brunswick. N.J. APPENDIX A 58 mmo. . moo. Hmo. mmo. mso. mms. omo. moo. wmm. mpa. mma. Hos. Ham. psm. spa. was. mms. mam. pmm. ppm. mmm. .mmp. amp. pam. 2mm. mmm. o.H o.H o.H HHH HH H omm\pm com omo. u I Hos. smo. mmo. ops. was. opo. mmm. mas. osa. me. mom. mmm. omm. ass. mos. mmm. mmm. awn. mmp. opm. paw. one. saw. map. Hmm. mom. mam. o.H o.H o.H HHH HH H omm\wu oom :Ho. . . :po. I I owa. omo. mso. Hmm. :mo. mma. mms. mmH. mam. mmm. pmm. mom. 0mm. mmm. wag. mgp. mom. Hmm. mom. :om. Ham. opm. mop. mzp. mmm. mgm. mmm. Hmm. 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Hmp. asp. mmw. smm. mom. o.a o.H o.H HHH HH H moms m.H Om. mm. o Illlfillll CHE mafia .musvmuonsov Hops: wcHsz> :pHs umcHMpno .p .oan m> H .Houms mo coHpomHm .N.< manna (30 woo. I HHo. Hmo. Hmo. Hoe. HsH. 00H. NmH. mom. mom. mHm. ems. 0pm. ems. opm. mmm. own. mop. mmp. mop. mpm. mom. mwm. o.H o.H o.H MMMI. IMMI .IwII .Hopm I I woo. wmo. smo. smo. mmo. mac. wwo. mpH. mHN. mpH. Hmm. 0H3. mom. ass. Hos. mss. Now. owe. wmm. mpp. imp. pr. 1pm. pow. mwm. o.H o.H o.H HHH HH H momw oso. one. one. mmo. mmo. Npo. omH. mmH. HsH. sow. wsm. msm. mHs. mom. mum. smm. son. mas. Nmo. mso. sHe. mop. omp. pmp. mam. Ham. mam. o.H o.H o.H HHH HH H Hemp one. soc. I pHH. mwo. omo. HmH. mHH. mos. mom. cow. was. mom. mom. Hmm. sow. ass. Hms. 0mm. psm. own. map. moo. mso. msm. map. mpp. paw. mmm. mmm. o.H o.H o.H HHH HH H aomm CHE aoEHp .mhsvauonaov use wcwhha> gas: conuavpo a .oEHv m> .n .Hmpus no coauomum .m.< meme 61 r.“ n all II pHI. mwo. owo. I I mmo. I I aHo. I I I w mmH. ppH. ppH. mmo. mso. Hao. I smo. woo. smo. I I m mom. Ham. Hem. mHH. sao. pmH. smo. ppo. mmH. amo. mHo. Hmo. m aHm. Ham. mom. mom. me. mom. mOH. msH. mHm. sMH. ppo. @mo. s Hss. mos. oas. mmm. mom. HHm. sHm. psm. pmm. Hmm. HmH. HwH. m mam. OHm. amp. was. pps. Hos. 0mm. MHs. sps. ppm. Hmm. mmm. m cam. paw. aHp. mom. mam. mom. pHm. omm. mom. was. mos. Hss. m.H oap. pap. HHm. omp. wep. saw. pmw. wmm. mop. mam. aom. Ham. H ooa. moa. ooa. paw. smw. mmm. mHm. us. Hmm. amp. opp. asp. cm. mma. pma. mma. mma. aHa. mHa. OHa. moa. sHa. paw. paw. mom. mm. o.H o.H o.H o.H o.H o.H o.H o.H o.H o.H o.H o.H o HHH HH H HHH HH H HHH HH H HHH HH H HmHWImmHH pom “mm pom HwH .awHoHEH: o>HpsHoH mcHzHa> :aHz. nocHdvno .9 .oEHv m> .u .Hmpms po coHpomHm .:.< mHowa Water fraction, r 1.10 1.00 .70 .10 62 A - wO—wD 12.758 10.30g O - WO—WD =I.o9 = -0.277 = -o.922 0 J I 11 L l 2 a 6 8‘ 10 Figure A.1. Tine, t, min Determination of surface moisture removal rate constant. k. at air velocity variable of 200 ft min (constants: Tw = 45°F. Ta = 76 F. RH = 16%). 63 1.10 14.20g A—W-W - - = . O a '0 "D 10 1 g Water fraction, r .02 - ° 1 l I 1 I .010 2 h 6 8 10 Time, t, min Figure A.2. Determination of surface moisture removal rate constant. k. at air velocity variable of 400 ftémin (constants: TW '2 “50F, Ta = 76 . RH = 16%). 6h 1.10 1.00 .70 .50 .30 .20 .10 water fraction, r 12.353 11.053 A - WO-WD a - wO-wD .01 L I I I - O 2 8 10 Time, t, min Figure A.3. Determination of surface moisture removal rate constant. k. at air velocity variable of 600 ftémin (constants: TW 2 45°F. Ta = 76 . RH = 16%). 1.10 Water fraction, r 65 .01 0 A - VO-WD = 13075g O - WO—WD = 11.75% = 11.65g 1.05 -O.b31 -O.984 l l l L L 2 a 6 8 10 Figure A.“. Time, t, min Determination of surface moisture removal rate constant. k. at water temperature variable of 55°F (constants: Ti = 800 ft/min. Ta = 76°F. RH = 19%). 66 1.10 — ‘- = 12.10 A "61%) 8 .. .. = 10.0 o "0 WD 5g 0 .. —w = 10.75 1.0 WO g :-I 5 o H .p O m s. e... h 3 .43 a = 1.08 k = -O.699 c = -O.989 l l l l l .010 2 l; 6 8 10 Figure A.5. Time, t, min Determination of surface moisture removal rate constant. k. at water temperature variable of 65°F (constants: G = 800 ft/min. Ta = 76°F. RH = 19%). 67 Water fraction, r 1.10 A - Wo-WD = 11075: D — WO-WD = 11.058 1.0 o — ub—wb = 11.70g = 1.11 = -o.695 = -0.977 I I I I I .010 2 1+ 6 8 10 Time, t, min Figure A.6. Determination of surface moisture removal rate constant. k. at water temperature variable of 75°F (constants: u = 800 ft/min. Ta = 76°F. RH = 19%). 1.10 1.00 Water fraction, r .70 .50 .01 68 A - wO—WD = 12.50: - I- = 1 g 0 0 WC WD 1 9 g I I I I Figure A070 h 6 8 10 Time, t, min Determination of surface moisture removal rate constant. k. at air temperature variable of 72°F (constants: a = 800 ft/min. Tw -.-.- 1450?. RH = 13%). 69 1.10 - 1.0 Water fraction, r 12.70 14.558 13.10g A .. Wo—WD .17.?! a o D O - WO-WD 1.16 -0.678 .0.988 I I Figure A.8. a 6 8 10 Time, t, min Determination of surface moisture removal rate constant. k. at air temperature variable of 82°F (constants: u . 800 ft/min. Tw = 45°F. RH = 13%). 7O 1.10 A - wCHwD = 12.80g o - wb-WD = 11.n5g 1.0 o - wO-WD = 13.15g H E o .H 4.) O a H H H 0 -3 a = 1.13 :2 k = -0.751 c = -0.986 I I I I I .010 2 u 6 8 10 Figure A.9. Time, t, min Determination of surface moisture removal rate constant. k. at air temperature variable of 87°F (constants: u = 800 ft/min. Tw a as F. RH = 13%). Water fraction, r 1.10 71 A-w-w 12.35g 12.40g 11.35g OO DUO 1.13 -006” .0.971 x II II II I I I I Figure A0100 4 6 ' 8 10 Time, t, min Determination of surface moisture removal rate constant. k. at relative humidity variable of 16% (constant : u a 800 ft/min. Tw = #5019. Ta = 76 F). Water fraction, r 1.10 1.00 .70 .50 .30 .20 .10 .02 72 a .. wO—wD = 11.753 — — = 00 0 W0 WD 1 95g _ I I Figure A.1l. 4 6 8 10' Time, t, min Determination of surface moisture removal rate constant. k. at relative humidity variable of 36% (constants: u a 800 ft/min. Tw = as F. Ta = 76°F). 73 1.10 A " "OI-ND = 11.45% A I J I I I__ '010 2 u 6 8 10 Time, t, min Figure A.12. Determination of surface moisture removal rate constant. k. at relative humidity variable of 50% (constants: u = 800 ft/min. Tw = usoe, Ta = 76 F). 7‘} 1.0 0.10“ I 9' I _ 'T‘ - r---- - r --v-- r.-. l . I- = — 4 I r-.<- - ’- C 0.010 “-— ~ - ”s... -4 7'7" I" r1808 8' “h" ’ 33-0.? HH . —-o.4 ' I: 81.0 ./0-4 ' /0.2 10.0 I i “/06 .. .¥- .. . -. w“-.. .- n- .. e.-.- 1......” ---+—..~---IL--—- . l I . ' I T--“.—-?- - ._.l-.‘ --u-- .0.- In"; t "I . 0 0.5 Figure A.1). Unsteady-state temperature dis- tributions in a sphere (Foust et al.. 1960). APPENDIX B APPENDIX B - CALCULATIONS Determination of time. t. from Figure A.13 in Appendix A for: I. II. Surface temperature of blueberries to decrease to within 10F of the water bath temperature. Initial difference between surface temperature and wet bulb temperature to decrease 50%. Constants used in both sets of calculations (thermal and density properties of blueberries assumed to be those of water. since blueberries are 85% water): kt=Oo C =10 p I. l)n= 2) m = 3) Y = LI)x= 35 BTU/lb-ft-OF p: 62.6 lb/ft3 0 BTU/lb-OF r =.- 0.0156 ft (3/16 in.) x/xl = l (for surface of sphere - blueberry) kt/(h)(r) where h = 100 BTU/lb-ftz-OF (from Earle 1966) o.35/(100)(0.0156) 0.22 (T -T_)/(TO-T,.) (86-45)/(76-u5) 0.032 dt/r2= 0.33 (from Figure A.13 - by interpolation) 0.33 = oat/r2 = ktt/pCprZ 0.33 = 0.35t/(62.6)(1.0)(0.0156)2 t: 75 76 The time of 0.84 min would be the maximum time for the surface temperature of the blueberries to decrease to within 1°F of the water temperature at USOF. Increased water bath temperature. T . would result in decreasing this time in Figure II. 1) n 2) m 3) Y as the value of Y would increase as indicated A.13 in Appendix A. x/x1 = l (for surface of sphere - blueberry) = kt/(h)(r) where h = 1 + 0.215 (from Earl. 1966) l + O.21(800/60) = 3.80 = 0.35/(3.80)(0.0156) = 6 = 0.5 LI) x =a(t/r2 = 1.35 l. l. t 2 2 35 = att/r -_- kttgocpr 2 35 = 0.35t/(62.6)(1.0)(0.0156) = 0.059 hr = 3.5 min