To address the issue that the Perry correlation does not account for the coupled effect of orifice scale and gas temperature，leading to significant design deviations under complex operating conditions and failing to meet the detailed design requirements of modern aircraft anti‑icing systems，a variable‑temperature piccolo tube flow test platform was established，and a full‑process one‑dimensional simulation model for the piccolo tube was constructed.Systematic investigations were conducted on the discharge coefficient and pressure drop characteristics under different orifice diameters and pressure ratios within the temperature range of 20 ℃ to 260 ℃.The results indicate that the Perry formula exhibits notable deviations under both normal temperature （20 ℃） and high temperature （260 ℃） conditions，with maximum relative errors in mass flow prediction reaching 12% and 10%，respectively，failing to accurately describe the flow variation law over a wide temperature range.The discharge coefficient increases monotonically with the pressure ratio.The macroscopic variation is essentially the result of the competition between the microscale effect and the high‑temperature viscous effect.At normal temperature，the orifice scale effect dominates：the smaller the orifice diameter，the larger the discharge coefficient.At high temperatures，the gas viscous effect is significantly enhanced，forming a complex interaction with the scale effect.Based on multi‑condition experimental data，a new empirical correlation for the discharge coefficient was fitted，comprehensively considering the pressure ratio，temperature，and geometric dimensions.The prediction accuracy of the new correlation is better than 4% within the experimental range，reducing the error level by more than 60% compared with traditional correlations.The new correlation meets the high‑precision design requirements of aircraft hot‑air anti‑icing systems.

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.

In order to improve the comprehensive performance of the CO₂ transcritical heat pump water heater system，thermodynamic models of single‑stage and two‑stage cycles adopting pure CO₂ and CO₂/R41 azeotropic mixture as working fluids are established.Based on energy and exergy analysis methods，the comprehensive performance of the four cycle systems is calculated and comparatively analyzed.The results show that the two‑stage cycle can effectively reduce the compressor discharge temperature （a maximum reduction of 61.79 ℃） and power consumption，accompanied by a partial decline in exergy efficiency.The CO₂/R41 mixed working fluid dramatically decreases the optimal high pressure （a maximum reduction of 20.96%） and increases the specific heating capacity （a maximum increment of 19.68%），while raising the specific power consumption of the compressor.The addition of R41 exerts a slight influence on the irreversible loss ratio of each component in the CO₂ transcritical cycle.Among the four cycle systems，the capillary tube presents relatively high irreversible loss.The CO₂/R41 two‑stage cycle system achieves the highest COP and superior specific heating capacity，as well as a relatively low discharge temperature and operating pressure.This study can provide theoretical support for the engineering application and performance optimization of CO₂/R41 mixed working fluids in two‑stage transcritical heat pump systems.

To address the issue of insufficient cooling capacity of current air‑cooled units under high‑temperature conditions in summer，a performance analysis of a 3D vertical tube parallel‑flow composite evaporative cooling condenser was conducted from the perspectives of entropy and exergy.The thermal performance of the device was simulated and calculated in conjunction with engineering application conditions，and the influence of different ambient air conditions on the cooling performance of the device was studied.The results show that when the wet‑bulb temperature varies within the range of 25~35 ℃ and other control parameters remain unchanged，the condensing pressure of the 3D vertical tube parallel‑flow composite evaporative cooling condenser increases by 7.87%.When the condensing pressure is kept constant，as the wet‑bulb temperature rises from 25 ℃ to 35 ℃，the condensing capacity decreases by 10.09%.Meanwhile，the pressure loss during the condensation process remains at a low level.The simulation results were verified and validated under the design operating point，showing good agreement with the design parameters.The influence of ambient temperature changes on this condensing device is significantly smaller than that on air‑cooled condensers，which is beneficial for improving the "peak load shifting in summer" capability of air‑cooled units.This device can be considered as a preferred auxiliary cooling device for peak shaving cooling of air‑cooled units in summer.The research provides a theoretical reference for the design optimization of evaporative cooling condensers.

To address the significant potential of oval tube evaporative condensers in reducing air‑side pressure drop and enhancing overall performance，yet the underlying mechanism of its influence remains unclear，a numerical simulation method was employed to systematically investigate the effects of operating parameters and structural parameters on the performance of oval tube evaporative condensers.The analysis focused on the influences of air velocity and spray water flow rate on heat transfer and pressure drop characteristics，and the performance differences between oval tube and round tube structures were compared to determine the optimal structural parameters.The results indicate that air velocity has a significant impact on heat transfer rate and pressure drop.A critical spray water flow rate of 20 m³/h is identified，beyond which the increase in heat transfer rate diminishes considerably.Under identical operating conditions，the oval tube structure demonstrates a clear performance advantage over the round tube structure，achieving an 11.1% increase in total heat exchange capacity and a 35.7% reduction in pressure drop. Through parameter optimization，the optimal aspect ratio for the oval tube evaporative condenser was determined to be 1.74. This study elucidates the mechanism by which structural parameters influence performance，providing theoretical guidance and data support for the engineering design and performance optimization of evaporative condensers..

To investigate the effect of the distance between tandem valves on the flow and noise within the pipeline，based on the IDDES turbulence model and Lighthill's acoustic analogy theory，combined with computational fluid dynamics and acoustic finite element methods，the internal flow field and its induced acoustic field within the valve pipeline under three different spacing conditions were solved.The influence of varying valve spacing on the flow‑induced noise within the valve pipeline was analyzed.The results show that as the spacing increases，the low‑pressure region between the valves decreases，while the area of the low‑pressure region at the downstream valve increases.The continuity of the high‑velocity regions on both sides of the downstream valve weakens，and the shedding position of the high‑velocity wake occurs earlier.The influence of the upstream valve's trailing vortex between the valves diminishes，while the downstream vortex system develops more fully，with increased vortex velocity and vorticity.The intensity of pressure pulsation between the valves is significantly weakened （maximum reduction of 10.38%），while the total level of pulsating pressure behind the valve shows an increasing trend （maximum increase of 2.09%）.Regarding acoustic characteristics，the flow‑passing components such as the valve shaft and the edge of the valve disc are the main sound sources.As the spacing increases，the area of high sound source intensity between the valves and behind the valve decreases，with sound pressure energy concentrated within 80 Hz.With increasing valve spacing，the total sound pressure level at the measurement point between the valves at a spacing of 2.5D decreases by 8.52% and 4.96% compared to spacings of 1.5D and 2.0D，respectively.At the measurement point behind the valve，the total level at a spacing of 2.5D increases by 2.13% and 1.2% compared to spacings of 1.5D and 2.0D，respectively.The high sound pressure level area is concentrated at the edge of the valve disc and on both the upper and lower sides of the pipeline behind the valve shaft.As the spacing increases，the area and proportion of high sound pressure between the valves decrease，the energy weakens，while the area of high sound pressure behind the valve increases.This study provides a theoretical basis for the low‑noise design of ships and similar industrial pipeline systems.

To improve the accuracy of the heat and mass transfer mathematical model for indirect evaporative cooling （IEC），a set of heat and mass transfer equations considering the coupled convection and conduction processes of the spray water liquid film was established.Based on the variation of spray water flow rate，the relationship between liquid film velocity and thickness was derived，and the influence of liquid film velocity and thickness on IEC performance was simulated.The accuracy of the model was validated using experimental results.The results indicate that compared with the original model，the proposed modified model improves the prediction accuracy of the air state parameters on the secondary side by up to 5.57%.When the spray water liquid film velocity increases from 0.1 m/s to 0.4 m/s，the wet‑bulb efficiency and enthalpy efficiency increase significantly from 51% and 50% to 54% and 53%，respectively.When the velocity continues to increase to 0.9 m/s，the growth of wet‑bulb efficiency and enthalpy efficiency slows down，eventually reaching 56% and 55%，respectively.When the liquid film thickness increases from 0.1 mm to 0.4 mm，the wet‑bulb efficiency and enthalpy efficiency drop sharply from 0.81 and 0.90 to 0.59 and 0.52，respectively.As the spray water liquid film velocity increases，both the system enthalpy efficiency and wet‑bulb efficiency increase.As the spray water liquid film thickness increases，the thermal conduction resistance increases，and the heat transfer effect is weakened.This study can provide data support for the optimal design of spray water systems in indirect evaporative coolers.

To address the challenge of predicting leakage between grid plates of ceramic grid seal structures for hypersonic aircraft，a numerical analysis method integrating similarity principle and flow factor was proposed.A 3D rough surface model was constructed using Abaqus/RufGen and scaled up proportionally.Subsequently，smooth and rough leakage region models at the same scale were established.The flow factor was obtained through simulation calculations.Finally，by combining the leakage rate of a smooth channel at the actual size，the leakage of the rough surface contact seal was predicted.The results indicate that the similarity principle effectively correlates the leakage characteristics of models at different scales.The leakage rate is synergistically regulated by temperature，pressure ratio，and gap height.Under the extreme condition of a pressure ratio of 7 and an operating temperature of 1 200 K，the leakage rate between grid plates with a roughness of 1.2 μm is approximately 1.3 mm³/s.The flow factor decreases with increasing roughness and decreases with increasing temperature.The "gap narrowing+resistance enhancement" dual effect between grid plates with small roughness significantly reduces the leakage rate.This study provides a reference for the design of contact seals under extreme environments.

To address the conflicting characteristics between labyrinth seal leakage and friction power consumption，a collaborative optimization study of key parameters was carried out to improve the efficiency of aviation fuel centrifugal pumps.Through theoretical analysis and numerical simulation，the influence mechanisms of key variables such as seal length，number of teeth，and surface roughness on leakage characteristics and power consumption characteristics were revealed.The results show that changing a single parameter leads to a trade‑off between leakage flow rate and friction power consumption，so finding the optimal balance point is necessary.Accordingly，an orthogonal experimental design was adopted to quantify the sensitivity of the coupled effects of key parameters on both leakage and power consumption，and a collaborative optimization method aiming for optimal overall efficiency was established.The obtained optimal seal parameter combination is a seal ring length of 12 mm，a wear ring length of 14 mm，and a roughness Ra of 3.2 μm for both.Experimental verification shows that this optimization scheme effectively improves centrifugal pump performance.In the high‑efficiency operating range （0.8Q_d~1.2Q_d），the relative efficiency is increased by an average of 5.5%，and overall the relative efficiency improvement exceeds 5%.This study provides theoretical support for the design of high‑performance，low‑power aviation fuel centrifugal pumps，and offers a reference for the application of labyrinth seals in other high‑performance fluid machinery.

Aiming at the discomfort of the human body caused by “direct cold air blowing” under the refrigeration condition of household air conditioners，a double‑layer air deflector soft air structure is proposed and verified.Based on the principles of airflow softening and human thermal comfort，the classification of comfortable wind speed is proposed.Fluent was used to carry out parametric simulation of the double‑layer air guide plate，and the effects of nozzle width，nozzle bias，number of outer round holes and layout on the axial wind speed，≤0.3 m/s coverage and air volume at 1 m，2 m and 2.5 m in front of the air outlet were investigated.The wind speed distribution and air volume comparison test are carried out on the prototype.The results show that compared with the existing single‑layer microporous air deflector，the airflow softening rate of the double‑layer air deflector has been improved，the axial wind speed is softened by at least 42%，the soft wind range is increased by at least 25%，and the soft air volume is increased by at least 43%，and the overall soft wind effect meets the comfort standard of soft wind above grade A.The research results can provide a reference for the design of air conditioning soft air structure.