The flow distribution in a printed circuit heat exchanger (PCHE) is of great theoretical and practical significance in the Brayton cycle power generation system. For the straight barrel inlet header PCHE, when S-CO₂ flows in the PCHE, the structural types and working parameters of the inlet header and diversion zone may lead to differences in the flow distribution in each channel of the PCHE. This flow distribution difference affects the thermal hydraulic characteristics of the PCHE. A numerical simulation method was applied to explore the flow uniformity of the PCHE and the overall performance and analyze the influence of the type of straight barrel inlet header PCHE. Within each layer, the flow showed an uneven flow distribution, and the optimized inlet header was the tapered type. The results showed that when the taper angle varies from 6° to 9°, the flow distribution in each layer is relatively uniform. The comprehensive heat transfer performance of the straight-channel PCHE can be improved by 17.3–19.7%. Finally, the response surface and a genetic algorithm were combined to optimize the inlet header. The heat transfer performance of the optimized PCHE was improved by 19.7%.

The hybrid heat exchangers (H²Xs) can be used for heat exchange equipment between high-temperature exhaust gas from ships and high-pressure supercritical carbon dioxide (S-CO₂) from S-CO₂ power cycle. We investigate structural stress characteristics of the H²Xs based on thermal-hydraulic performance. Air and S-CO₂ are employed as the working fluids and the Stainless Steel 316 (SS316) as the solid substrate. The thermal-hydraulic performance and structural stress characteristics of the H²Xs is conducted by Fluent and Mechanical, respectively. The results shows the mechanical stress induced by pressure loading and the thermal stress induced by temperature gradient are found to be equally important sources of stress. At the inlet and outlet of the H²Xs, the total stress along all paths is not smooth and continuous, and there will be a significant change due to the change in temperature gradient. The mechanical stress caused by the fluid pressure loss is almost negligible. The change of inlet mass flow rate and temperature mainly affects the stress distribution of the left and right walls on the fin channel. The pressure variation of the diesel engine has little effect on the total stress. Importantly, the total stress intensity of the H²X is mainly affected by the change of S-CO₂ fluid pressure.

Cold starting is the biggest challenge for mechanical equipment in polar environments. Selecting suitable friction pair materials and exploring the wear mechanism are keys to improving the reliability in a low-temperature environment. This study analyzed the tribological properties of the two typical materials of hydraulic motor’s rotor at different ambient temperatures, especially at low temperature. Finally, it explored the wear process and mechanism of two sets of friction pairs. The results showed that the low temperature environment not only affects the viscosity of the hydraulic medium in the hydraulic system and changes the lubrication state between the friction pairs, but also enhances the cold brittleness of metal materials and affects the wear characteristics between the friction pairs. There is a maximum difference of around −20 °C. The wear volume of material QT500-7 sharply increases and reaches a maximum of 0.107 mm³ when the normal force is 20 N, which is 3.65 times as much as the wear volume of the LC2-1. When the normal force is 30 N, the wear volume of materials QT500-7 and LC2-1 are 0.125 and 0.036 mm³, respectively. The wear volume of the former is 3.4 times that of the latter. In addition, it indicates that the impact energy of the material affects its tribological properties since the impact energy of the material QT500-7 decreases sharply, including two consecutive subintervals of sharp decreases from 97.3 J to 42.2 J and then to 18.0 J at the temperature of −10 to −30 °C. The material LC2-1 with stable wear performance is more applicable for being processed and manufactured into parts for low-temperature environmental conditions, as there is no serious fluctuation in the temperature range from −40 °C to room temperature. The research findings are expected to provide a theoretical support for hydraulic motors design, material selection and the maintenance of polar deck machinery. They are of great significance for improving the operational reliability of hydraulic motors for polar ships.