A cryogenic needle valve is used to precisely control the flow rate of working fluids such as liquid hydrogen and liquefied natural gas, making it essential to design the valve with consideration of the cryogenic environment. To prevent freezing of the packing materials, which directly affects leakage, extended bonnet-type valves are commonly used. In these designs, the bonnet length is increased to position the packing farther from the flow path. However, due to spatial constraints, extended bonnet structures are often unsuitable for installation in confined spaces. To address this limitation, a compact-type valve was developed by significantly shortening the bonnet length and incorporating a heat sink capable of providing the required heat transfer performance within the reduced length. In this study, a cryogenic environment test using liquid nitrogen, along with heat transfer analysis, was conducted on the compact-type cryogenic needle valve to evaluate the thermal behavior of its components. A parametric study and size optimization were performed by treating the heat sink's outer diameter and thickness as shape design variables, with the goal of minimizing its size while maintaining the necessary heat transfer performance in the shortened bonnet. As a result of the optimization, the heat sink volume was reduced by approximately 54% compared to the initial design. A cryogenic leakage test was subsequently conducted on a prototype equipped with the optimized heat sink, in accordance with BS6364, confirming that no leakage occurred.

A three-way valve has a multi-port structure with three openings, which allows control of the fluid direction. However, owing to the complicated trim shape of the internal flow, an irregular fluid flow occurs, which hinders precise fluid flow control. In severe cases, cavitation induces mechanical damage owing to abrupt changes in the fluid direction. In this study conducted a computational fluid dynamics (CFD) analysis was performed to estimate the localized cavitation around the bottom plug of the three-way valve. To quantify localized cavitation, the percentage of cavitation (POC) was derived using the vapor volume fraction (VVF). The POC, defined by the cavitation occurrence zone with VVF > 0.5 divided by the volume of the cavitation danger zone, was 34.90%. Cavitation at this POC level could cause mechanical damage; therefore, a size optimization was performed. The lengths of the optimized waist and tail regions of the bottom plug were obtained wherein the POC level decreased by 19.06%. In addition, experiments were conducted using a flow visualization test setup. The experimental results were quantified into the POC employing the image gradients method, and the results were in good agreement with the CFD analysis.