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.

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.

The boiling point of liquid hydrogen is very low, at −253 °C under atmospheric pressure, which causes boil-off gas (BOG) to occur during storage and transport due to heat penetration. Because the BOG must be removed through processes such as re-liquefaction, venting to the atmosphere, or incineration, related studies are required to estimate the heat transfer of storage and transport devices and to improve insulation to reduce BOG generation. In this study, a vaporization analysis was performed on a vacuum-jacketed valve used in liquid hydrogen storage and transport devices to calculate the amount of BOG generation considering the flow characteristics at the vena contracta and the saturation temperature. At a pressure of 1 bar in the liquid hydrogen storage tank, the maximum fluid flow velocity and minimum static pressure occurred at the vena contracta, with values of 62.9 m/s and −0.4 bar, respectively, and the BOG generation rate was estimated as 0.132 m3/h, where the saturation temperature was minimized at 19.3 K. Furthermore, through case studies, when the pressure in the liquid hydrogen storage tank increased to 1.5 and 2 bar, the static pressure and saturation temperature decreased, and the BOG generation rate increased to 0.221 and 0.283 m3/h, respectively.

Lithium tantalite (LiTaO3) is a representative multifunctional single-crystal material with electro-optical, acoustic, piezoelectric, pyroelectric, and nonlinear optical properties used as a substrate for surface acoustic wave (SAW) devices. To enhance SAW device performance, thinner LiTaO3 substrates with improved surface roughness are desired. Chemical mechanical polishing (CMP) is employed to achieve the desired surface roughness after grinding. However, the thinning process increases the risk of substrate fracture, especially at the edges, resulting in edge chipping. Edge chipping can lead to complete substrate failure during SAW device fabrication, requiring an effective wafer geometry to prevent it. The study utilizes scratch tests and finite element analysis (FEA) to identify the optimal edge shape (C-cut, trimmed, and thinned) for preventing edge chipping on LiTaO3 wafers. The C-cut edge refers to the rounding of the wafer’s edge, while the trimmed edge refers to the machining of the wafer’s edge to be perpendicular to the wafer surface. As a result of the scratch tests, we observed edge-chipping lengths of 115 and 227 μm on the C-cut and trimmed edges, respectively, while the thinned edge (half C-cut) resulted in complete wafer fracture. In the finite element analysis (FEA), edge-chipping lengths of 80, 120, and 150 μm were obtained on the C-cut, trimmed, and thinned edges (half C-cut), respectively. In conclusion, it has been confirmed that the C-cut, trimmed, and thinned edge shapes are effective in preventing edge chipping. However, considering that the C-cut edge shape becomes thinner through grinding, using the trimmed edge shape appears to be the most effective.