This study investigates the thermal performance of diffusion‑bonded hybrid heat exchangers through wind tunnel experiments and numerical simulations. Comparative analysis was conducted on the adaptability of heat transfer and friction factor correlations obtained by different methods for stainless steel plain fins. Results indicate that the thermal load of the heat exchanger increases with rising air‑side velocity，while the pressure loss grows more significantly. When air velocity increases from 8.1 m/s to 28.2 m/s，the thermal load increases by 2.9 times，and the pressure loss escalates by 9.82 times. Within the air‑side Reynolds number range of 2 440≤Re≤8 502，the theoretical thermal load calculated using statistically derived Colburn factor correlations deviates by 0.34%~16.55% from numerical and experimental results. Theoretical pressure loss predictions show less than 3% deviation from measured values. The study verifies the accuracy of the heat transfer/friction factor correlations and numerical models，providing practical guidance for thermal design of single‑phase diffusion‑bonded hybrid heat exchangers.

Aiming at the problems of low head and low efficiency of a high‑speed centrifugal pump used for cooling specific equipment under strict space constraints，a study on cavitation characteristic analysis and inducer wrap angle optimization was carried out.The reliability of the numerical analysis results of the pump was verified by comparing the experimental test results with the simulation calculation results.Based on the basic cavitation equation，cavitation specific speed and suction specific speed methods，the required net positive suction head （NPSH_r） of the pump was initially calculated.Combined with the CFD cavitation flow field simulation，the accuracy of the theoretical calculation results and the critical conditions for cavitation occurrence were clarified.On this basis，an inducer was designed，and the effects of wrap angles （ranging from 100° to 200°） on the performance of the inducer and the entire pump were systematically studied.The results show that the inducer wrap angle has a significant impact on the head and efficiency of both the inducer itself and the entire pump.When the wrap angle is 140°，the inducer achieves the optimal efficiency and provides a head of 11.86 m，which can meet the anti‑cavitation requirements.After assembling this inducer，the head of the optimized entire pump is increased to 71.29 m，and the efficiency reaches 81.76%，which are 4.47% and 5.44% higher than those before optimization，respectively.In addition，the critical cavitation point shifts leftward after optimization，and the available net positive suction head （NPSH_a） increases to 21.37 m，with an increase of about 1.25 times，indicating that the anti‑cavitation capacity of the system is significantly enhanced，and both the head and efficiency meet the design requirements.This study can provide a theoretical basis and engineering reference for the high‑performance design of high‑speed centrifugal pumps under lightweight constraints.

In order to optimize the elicitation performance of the elicitor of the hydrogen recirculation system of a proton exchange membrane fuel cell in the low‑power region，structural parameters of the elicitor of a 40 kW‑class fuel cell were simulated.Univariate influence tests were carried out at a given power to investigate the influence of nozzle throat diameter，mixing chamber diameter，mixing chamber length and the distance between the outlet of nozzle and the inlet of the mixing chamber on the performance of the ejector.The orthogonal tests were carried out by selecting the better three parameters from each of the four factors mentioned above，and the extreme deviation of the test results was analyzed to get the optimal combinations of the parameters mentioned above and the sequence of the degree of influence on the ejection performance of the ejector.Finally，the optimized ejector was simulated.The results show the maximum hydrogen reflux ratio of 2.315 is obtained when the nozzle throat diameter，mixing diameter，mixing chamber length，and the distance between the outlet of nozzle and the inlet of the mixing chamber are taken as 0.8，3.0，18，2.5 mm，respectively，under the working condition of 60 A.The results of the study show that among the four parameters mentioned above，low power condition has a significant effect on the ejection coefficient，while low power condition has a significant effect on the ejection coefficient，and low power condition has a significant effect on the ejection coefficient.Among the four parameters mentioned above，the parameter that has the greatest influence on the ejection coefficient under low power condition is the nozzle throat diameter，and the parameter that has the least influence on the ejection coefficient is the distance between the outlet of nozzle and the inlet of the mixing chamber.The results of the study provide a reference for the optimization of the structural parameters of the ejector under low‑power working conditions.

To address the issues of cumbersome design procedures and long design cycles for the throttling profile of straight‑through single‑seat control valves，a high‑efficiency design method for the valve plug profile based on an orifice throttling model combined with variations in flow resistance coefficient is proposed.By establishing a calculation model for the effective flow area of the control valve at arbitrary openings，the analytical expression for the equal‑area curve is derived，and subsequently the mathematical expression for the valve plug profile coordinates is obtained.Based on this valve plug throttling profile design method，a preliminary DN50 straight‑through single‑seat control valve model with equal percentage flow characteristic is established.Simulation conditions are set according to the test requirements of GB/T 30832—2014，numerical simulation analysis is carried out，and flow coefficient tests are conducted on the control valve.The results show that the initial design exhibits flow coefficient simulation deviations beyond the allowable range specified in IEC 60534-2-4：2009 for openings below 60%.After optimizing the valve plug profile using an iterative method that mutually maps the structural characteristics and inherent flow characteristics，the simulation deviations across the full opening range are reduced to 0.30%~10.78%，meeting the standard requirements.The measured deviations of the optimized control valve under the main operating range and full‑open conditions are 2.24%~9.66%，meeting the accuracy requirements of the IEC 60534-2-4：2009 standard，and its flow characteristic approaches the equal percentage inherent flow characteristic.This study provides a reference for simplifying the design process of valve plug profiles and improving design efficiency.

Addressing the current issues of low accuracy in calculation methods for gas pulsation in high‑pressure pipelines and insufficient research on gas pulsation in hydrogen storage and transportation compressor pipelines，a study on the calculation and testing of gas pulsation in a 90 MPa hydrogen diaphragm compressor pipeline was conducted.An algorithm for 1D unsteady flow in pipelines based on real gas properties was proposed to solve the physical quantities of pulsating gas flow at various points in the pipeline in the time domain.Experimental tests for gas pulsation were performed on the second‑stage exhaust pipeline system of a hydrogen diaphragm compressor under three pressure conditions：90，63.5，46 MPa，with analysis conducted using a self‑developed numerical program.The results show that the calculated pressure pulsation at the measurement points agrees well with the measured data，with larger amplitudes for low‑order harmonics below 100 Hz.The pressure pulsation level is highest at the cylinder outlet （peak‑to‑peak value of 13.4 MPa） and decreases to a lower level downstream at the buffer tank （peak‑to‑peak value of 2.5 MPa）.The variation of pressure pulsation with rotational speed differs across pipeline locations.The changes in pressure pulsation at the cylinder outlet and measurement points exceed 2% of the local average pressure，while the variation with rotational speed is smaller in the pipeline sections near the buffer tank.The buffer tank reduces the maximum pressure pulsation in the pipeline by more than 25%.From the perspective of suppressing maximum pressure pulsation，there exists an optimal value for the buffer tank's inner diameter.The research findings can provide technical support for the design and modification of pipelines in high‑pressure hydrogen storage and transportation compressors.

To improve the atomization effect of multiple nozzles in snowmaking machines，a 3D transient multiphase flow model was constructed using the discrete phase model （DPM） and the Taylor analogy breakup （TAB） model.Combined with experimental validation，the variation laws of atomization characteristics under linear，circular，right triangular，and equilateral triangular nozzle arrangements were systematically analyzed.Meanwhile，the regulatory effects of installation height and spacing differences on atomization characteristics were investigated.The results indicate that on the same plane，the equilateral triangular and circular arrangements exhibit good and similar distribution uniformity.Among them，the equilateral triangular arrangement has a larger sauter mean diameter SMD （94.31 μm） and better atomization effect.For the right triangular arrangement，the proportion of large‑sized droplets in the far‑field region reaches 72%，showing a stronger droplet coalescence effect.The linear arrangement has the smallest SMD （92.8 μm），achieving the best droplet breakup effect.Meanwhile，differences in nozzle installation height and spacing have a limited impact on the overall atomization characteristics but can effectively regulate atomization interference behavior.The research results reveal the influence mechanism of nozzle geometric layout on the synergistic atomization characteristics of multiple nozzles，providing a reference for the layout design of snowmaking machine nozzles.

To meet the demand for fast response in the range of 5%~15% small opening by the rubber‑lined centerline‑typebutterfly valve under specific working conditions in the post‑rolling cooling system，the design principle of the conventional type was analyzed，especially in terms of structural sides，sealing modes，opening and closing strokes of the sealing pair.Based on the process requirements and the advantages and disadvantages of the conventional structure，the valve seat design was improved by leveraging the good plasticity of the rubber‑lined valve seat.The design ideas and corresponding advantages were elaborated.Finally，a simulation combined with flow test verification was conducted to compare and analyze the flow rate between the improved structure and the conventional structure.The results indicate that the Cv value of the improved structure at 5% opening is comparable to that of the conventional structure at 15% opening.The improved valve can produce flow at 5% opening，and within the range of 15% opening，the Cv value of the improved structure is 100%~250% higher than that of the conventional structure.Within the range of 20%~50% opening，the Cv values of the two structures tend to be the same，while in the range of 50%~100% opening，the Cv value of the improved structure is 10%~25% lower than that of the conventional structure.Additionally，by comparing actual flow test data with simulation results，the flow trend is consistent，particularly in the small‑opening range，confirming the credibility of the improved design.The findings of this study provide a reference for optimizing the small‑opening and flow rate performance of centerline‑type rubber‑lined butterfly valves.

To investigate the reliability of electric gate valves and challenges in minor fault identification，reliability enhancement testing （RET） technology was applied to simulate valve faults under non‑destructive conditions. Response data from two typical failure modes were collected and analyzed using three machine learning methods （decision tree，random forest，gradient boosting） combined with two optimization approaches （grid search，actor‑critic reinforcement learning）. Results indicate that RET effectively simulates valve sticking and jamming faults without physical damage，achieving cost‑efficient fault replication. The integration of current and vibration features significantly enhances fault recognition accuracy： normal data identification accuracy reaches 98% with random forest and gradient boosting，while fault data identification peaks at 82% using random forest and decision tree. Multi‑feature fusion improves model performance by leveraging data characteristics. Reinforcement learning boosts random forest accuracy by 21% （vibration features），15% （vibration‑current features），and 6% （current features），but degrades gradient boosting performance. Decision Tree excels in processing multi‑feature data with superior fault recognition，while random forest maintains robust performance across single and combined features. Gradient boosting exhibits instability requiring feature‑specific optimization. For industrial applications，random forest and decision tree with multi‑feature fusion are recommended to enhance classification performance. This study provides technical references for electric gate valve fault diagnosis.

In order to improve the heat transfer performance of the evaporator in the cold storage refrigeration system，a new type of plate evaporator was designed.The influence of refrigerant mass flow rate and air side velocity on the heat transfer characteristics of the plate evaporator was discussed by using the method of simulation combined with experiments，and an optimized structure with an intermediate channel was proposed.The heat transfer characteristics of the plate evaporator were studied when the inlet dryness of refrigerant R22 was 0.27，the temperature was -5 ℃，the saturation pressure at this temperature was 0.421 8 MPa，the mass flow rate was 0.017 kg/s，the air inlet temperature was 6 ℃，the relative humidity was 80%，and the flow rate was 3 m/s.The results show that in the design conditions，the cooling capacity in this design condition is 2.86 kW，the refrigerant side pressure drop is 1 150 Pa，and the air side pressure drop is 412 Pa.As the mass flow rate of refrigerant increases，the cooling capacity increases，but the growth rate slows down significantly after reaching 0.017 kg/s.The pressure drop on the refrigerant side also increases，and the growth rate gradually increases.As the inlet flow rate on the air side increases，the cooling capacity increases，but the growth rate slows down significantly after reaching 3 m/s.The pressure drop on the air side also increases，and the growth rate gradually increases.The refrigerant mass flow rate should match the air inlet conditions.Compared with the original structure，the plate evaporator with a middle connected structure has increased cooling capacity by more than 9.4%，increased refrigerant side pressure drop by 18.3%，and increased air side pressure drop by 20.2%.The intermediate connected structure can improve the heat transfer performance of the evaporator.The research results can provide reference for the study and design of evaporators in cold storage refrigeration systems.

To address the cylinder fracture issue in 90 MPa diaphragm compressors for hydrogen refueling stations，a thermo‑mechanical coupling model of the high‑pressure stage membrane head was established using Ansys Workbench finite element analysis software. The cylinder strength was analyzed，and an improved through‑hole bolt cylinder connection structure was proposed and verified. Results show that when the cylinder bottom fillet radius is 0.5 mm，the local stress reaches 1 665 MPa，exceeding the material yield strength and causing stress concentration，leading to fatigue failure under cyclic alternating loads. Increasing the fillet radius to 3 mm reduces the maximum stress to 793 MPa，meeting strength requirements. The improved through‑hole bolt structure reduces the maximum stress by 17% for cylinders with the same fillet radius. At a 3 mm fillet radius，the optimized structure achieves a maximum stress of 649 MPa，satisfying design specifications. This study provides reference for structural design of 90 MPa diaphragm compressor cylinders.