Automated valves are used in the process industry for precise control of process parameters (e.g. flow, pressure, temperature). For the proper process design of a system, it is crucial to ensure that these valves possess the appropriate flow coefficient to effectively regulate the fluid flow within these systems. Although automated control valves are widely available, very few domestic (USA) manufacturers offer automated control valves for cryogenic applications, especially helium systems where there is a need for control valves with precise flow control and low flow regulation (i.e., flow coefficient < 1.0). The present research aims to establish a comprehensive design methodology for developing an equal percent valve plug for use in a cryogenic control valve. The methodology adopts a holistic approach that integrates analytical, computational, and experimental techniques. An analytical model is developed to estimate the geometrical profile of an equal percent control valve plug for use in a commercially available cryogenic control valve. This model serves as the fundamental framework for estimating the valve flow characteristics. Predicted valve flow characteristics from the analytical model are be compared against results obtained from a computational fluid dynamics model (CFD). The implemented CFD model further enhances the understanding of the valve flow characteristics under various operating conditions through characterization of the internal flow across the valve plug profile. Results from both these theoretical models are validated against experimental measurements. Experimental results are obtained using a valve flow characterization test bench, which is designed and built to measure the flow and corresponding pressure drop across developed valve plug profile(s) under different operating conditions. The relationship between the valve lift and the flow coefficient characteristics for the developed profile(s) are captured from the measurements and compared against the theoretical predictions. The developed design methodology can assist cryogenic system designers and operators to generate control valve plug profiles based on a commercial control valve, as needed for efficient process control.
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