To address the heating capacity attenuation of air‑source heat pumps under low‑temperature conditions，an experimental setup with a flash tank for vapor injection was established to investigate the influence of parameters such as intermediate refrigerant pressure and superheat degree on system performance under superheated vapor injection conditions.The results show that the flow rate and state of the injected refrigerant are key factors.When the vapor injection pressure increases，the superheat degree decreases and the refrigerant dryness approaches 1.As the electronic expansion valve opening increases from 10% to 40%，the vapor injection pressure rises from 1.48 MPa to 1.79 MPa under minimum operating conditions and from 1.01 MPa to 1.71 MPa under low‑temperature operating conditions.Both the vapor injection enthalpy increment and heating coefficient of performance （COP） exhibit a trend of first increasing and then decreasing，with an overall improvement in heating capacity.When the electronic expansion valve opening is approximately 25%，the COP reaches 3.64 under minimum operating conditions and a maximum value of 2.62 under low‑temperature operating conditions.Maintaining the injected refrigerant close to saturated vapor state is an important control factor，while the theoretically optimal enthalpy‑increasing pressure is not universally applicable.This study can provide references for the design，operation，and control of low‑temperature heat pump water heaters.

To address the issue of insufficient ventilation in kitchen exhaust systems operating under high‑resistance conditions，this study proposes reducing resistance by placing a duct fan downstream of the range hood.A test platform was constructed to simulate a kitchen environment with high exhaust resistance，and the feasibility of using duct fans in series to assist exhaust in systems equipped with several types of range hoods was investigated.On this basis，the study analyzed the impact of adding a duct fan on the system's air volume and noise when the exhaust air volume fails to meet the empirical requirement of 11 m³/min due to excessively high pipeline network resistance.Experimental results showed that when the selected duct fan operates at a constant speed of 2 800 r/min，the operating air volume of all 4 selected range hood models increases by approximately 2 m³/min，meeting the 11 m³/min exhaust air volume requirement.Increasing the range hood's rotation speed to achieve a 2 m³/min increase in air volume will result in a noise increment of 5 dB~6 dB，while the series‑connected duct fan scheme has a 3 dB~7 dB advantage in comparison.Moreover，the higher the pipeline network resistance，the greater the noise difference.This research can provide a theoretical reference for the engineering application of series‑connected duct fans in assisting exhaust，and its experimental method is applicable to the study on the practical value of various systematic exhaust schemes.

To address the issue of pipeline vibration and excessive noise caused by asymmetric working processes in single‑screw compressors，a bilateral full‑process dynamic characteristic test platform was established.The impact of lubricant secondary distribution on working processes was tested，and exhaust/leakage characteristics in upper and lower working chambers were analyzed.Results show that for a 6.77 m³/min compressor at 1 800 r/min and 900 kPa discharge pressure，the pressure difference between upper and lower working processes reaches 39 kPa.Lower‑side discharge pressure exceeds upper‑side by 10~15 kPa.Asymmetry can be reduced by delaying upper‑side exhaust，decreasing lower‑side spray pipeline valve opening，or reducing lower‑side spray hole diameter.This study provides reference for pipeline vibration reduction and noise control in single‑screw compressors.

To investigate the impact of intake configuration on the performance and flow field of a centrifugal compressor，characteristic tests were conducted to measure performance，while PDA and PIV techniques were employed to characterize the inlet‑duct flow.The effects of curved‑duct intake on the compressor′s pressure ratio，efficiency and inlet uniformity were analyzed.The results reveal how a 90° elbow affects both performance and flow behavior.Compared with a straight inlet，the elbow reduces the pressure ratio（-0.8 % to -2.7 %） and efficiency（-1.4% to -9.8%） at the maximum efficiency point across the tested speed range（60 000~100 000 r/min），and the deterioration grows as rotational speed increases.Especially under high‑flow conditons，the decline in pressure ratio and efficiency is more pronounced.When the speed exceeds 70 000 r/min，the circumferential static‑pressure non‑uniformity at the compressor inlet becomes pronounced；The maximum static‑pressure ratio at the 120° location rises from 1.002 8 to 1.011 5.With a straight inlet，the flow at the maximum efficiency point is nearly uniform，whereas the bent inlet generates severe inlet distortion：two counter‑rotating vortex cores appear on the radial section.The research results provide a theoretical basis for optimizing the inlet conditions of centrifugal compressors and improving their actual operating efficiency and stability in the future.

To address the issue of the increasing trend of temperature in the key area of the chip rise caused by increasing power density in insulated‑gate bipolar transistor （IGBT） modules，a fluid-solid coupling model of the IGBT module and water‑cooling plate was established，and an optimized design method for the water‑cooling plate of the IGBT module was proposed.The effectiveness of the method was verified through finite element simulation and experiments.Based on the dimensions and heat dissipation power characteristics of the IGBT module，three water‑cooling plates with different heat dissipation areas （122 mm×61 mm×20 mm，122 mm×122 mm×20 mm，122 mm×183 mm×20 mm） were simulated，analyzed，and optimized to systematically evaluate the influence of heat dissipation area on cooling efficiency.After determining the optimal size，straight ribs were welded inside the flow channel，and an orthogonal experimental method was employed to derive the optimal structural parameters（flow channel depth，rib height，and rib thickness）.The results show that when the flow channel depth is 9 mm，the rib height is 5 mm，and the rib thickness is 1.5 mm，the optimized water‑cooling plate reduces the maximum temperature of the IGBT by 7.1 ℃，significantly improving thermal performance.Comparative experiments under different power losses and inlet water temperatures verifies the variation patterns of the maximum temperature on the chip and substrate surfaces，confirming the effectiveness of the proposed optimization scheme.This study provides a new solution for the thermal design of IGBT modules，which is of great significance for promoting their applications in renewable energy generation，smart grids，and high‑power electronic systems.

To investigate the drag reduction mechanism of a biomimetic fish scale centrifugal pump，the response surface methodology was employed to optimize the structural parameters of biomimetic fish scale pits，and the values of each structural parameter corresponding to the optimal drag reduction effect were determined.The study revealed that under different operating conditions，the biomimetic fish scale pit structure can enhance the hydraulic performance of centrifugal pumps，with the most significant improvement observed under the rated operating condition.Compared to the baseline pump，the head and efficiency increased by 0.88 m and 3.71 percentage points，respectively，with an efficiency gain rate of 5.13% and a drag reduction rate of 4.30%.On one hand，the biomimetic fish scale pits expand the contact area between the blade working surface and the internal fluid，thereby improving the shear stress distribution on the blade wall.On the other hand，they thicken the near‑wall boundary layer and reduce the Reynolds stress in the near‑wall region of the blade.Furthermore，the biomimetic fish scale pits can disrupt the vortex structure on the blade surface，reduce the vortex core inside the centrifugal pump and the vortex area at the blade outlet，and weaken the intensity of energy exchange and conversion.This delays boundary layer separation，inhibits the transition from laminar to turbulent flow during fluid movement，and makes the internal flow more uniform，ultimately reducing the resistance encountered by the centrifugal pump during operation.This research can provide a reference for the optimal design of centrifugal pumps.

In order to study the influence of geometric dimensions of floating ring on the head and efficiency of centrifugal pumps，five different sizes of floating ring were installed on the experimental pump for ZM65-40-125 centrifugal pump. When the length of the floating ring gap was the same and the width of the ring gap was changed （0.06，0.12，0.24 mm），and the width of the floating ring gap was the same but the length of the ring gap was changed（3，5，7 mm），the changes in pump flow rate and head were compared and analyzed；Calculate the theoretical leakage flow rate at the mouth ring and compare it with the test data.The results show that as the floating wear ring clearance width increases，both pump head and efficiency decrease.When clearance width increases from 0.06 mm to 0.24 mm，the maximum head reduction is 1.19 m and maximum efficiency reduction is 4.6%.As the floating wear ring clearance length shortens，both head and efficiency decrease.When clearance length decreases from 7 mm to 3 mm，the maximum head reduction is 0.38 m and maximum efficiency reduction is 1.78%，indicating insignificant decline.These trends are essentially consistent with calculated leakage flow comparisons.This study provides reference for designing centrifugal pumps with floating wear ring structures.

In order to study the thrust coupling characteristics of unsteady parallel jet flows，a numerical simulation model was established to investigate the effects of jet velocity function，central axis distance，and time phase difference on the thrust coupling characteristics.The model was verified using experimental data.The results show that when the central axis distance is 1.5D （where D is the nozzle diameter），the average thrust ratio K between the dual‑nozzle and single‑nozzle jets increases with the increase in time phase difference within one jet cycle，with a maximum thrust loss of 8.53%.At larger time phase differences，K>1 occurs，indicating that the coupled thrust exhibits an enhancement effect.However，the maximum thrust enhancement is only 0.42%，suggesting that the thrust enhancement effect generated solely by the mutual induction between vortex rings is very weak.For central axis distances of 2.5D and 2.0D，the average thrust ratio K ranges from 0.994 5 to 0.997 3 and from 0.986 6 to 0.997 5，respectively，and both exhibit a trend of first decreasing and then increasing as the time phase difference increases.The research findings can provide a reference for the design of underwater unsteady propulsors.In particular，the new insights into thrust enhancement offer new ideas for the development of high‑efficiency underwater propulsors.

A large hub to hub ratio model stage is proposed to address the issue of the existing conventional hub to hub ratio model stage for domestic compressors being unable to meet the rotor stability requirements of the seven stage two‑stage scheme and can only adopt a dual cylinder design.Based on the medium hub‑tip ratio model stage of a double‑cylinder gas storage compressor，the design and development of a high hub‑tip ratio model stage has been completed by combining the forward design method，automatic optimization method and test method.The geometry，macroscopic performance，and internal flow field characteristics of different hub‑tip ratio model stages were also compared and analyzed，and it revealed the flow characteristics of the high hub‑tip ratio model stage.The study shows that the polytropic efficiency of the 0.46 high hub‑tip ratio model stage is 4.3% lower than that of the 0.39 hub‑tip ratio model stage，and the efficiency drop of the impeller part is the largest，accounting for 67.4% of the efficiency drop of the whole model stage.Adjusting the blade profile，the number of blades，and reducing the Mach number inside the impeller and the bladeless diffuser have a greater potential to improve the efficiency of the model stage.The deviation of the efficiency between the CFD and the experimental results is all within 3%，which has strong reference value.The developed model stage hub ratio has been increased by 18%，which solves the rotor stability problem of the seven‑stage two‑section scheme and realizes the design and development of a single‑cylinder gas storage compressor with a small floor area.This study addresses the stability issues of single‑cylinder seven‑stage two‑stage rotors，and fills the research gap in the application of large wheel hub ratio compressors in China，and provides valuable reference significance for the aerodynamic design，development and application of the high hub‑tip ratio model of centrifugal compressors.

In order to enhance the gas‑liquid interface stability and cryogenic cavitation characteristics of the liquid‑sealing impeller，the effects of different groove structures on the sealing performance and cryogenic cavitation characteristics of the first‑stage liquid‑sealing impeller of the liquid oxygen turbopump were numerically analyzed.The results show that the sealing performance of the liquid‑sealing impeller is jointly influenced by the groove/blade structure，fluid flow guidance design（radial/backward‑leaning/backward‑bending），and configuration（blade‑type/flow passage‑type）.Radial blade structure demonstrates outstanding advantages in achieving low leakage and lower temperature rise，making them the preferred choice for most operating conditions.Compared to the radial flow channel structure，the radial blade structure reduces leakage by 96.3%，shaft power increases by 14.8%，and sealing power ratio reduces by 2%.Backward‑leaning/ backward‑bending structure significantly enhance gas‑liquid interface stability by optimizing flow guidance，serving as the primary option for prioritizing stability.A backflow vortex is formed in the outer clearance of the groove on the outer diameter side of backward‑leaning/ backward‑bending structure，which increases the shaft power by about 14.8% and 25.0% respectively compared to the radial flow channel structure.Flow channel structure（especially backward‑leaning） can be considered as alternative solutions under high‑speed conditions.The research results can provide a reference for the design of liquid‑sealing impeller of liquid oxygen turbopump.

To simplify the complexity of designing interference free tooth profile pairs for gear pumps，a new method is proposed to directly obtain complex interference free driven tooth profile designs from the interference free active tooth profile.A general coordinate equation for the internal conjugate tooth profile was established with conjugate distance and transmission angle as design parameters.By analyzing the interference of the tooth profile and the coordinate variation relationship at the interference point，innovative methods for zero coordinate derivative and minimum meshing angle are proposed.The application verification is carried out through involute and linear tooth profile design.The results indicate that the conjugate distance and transmission angle are functions of contact ratio，locking angle，and the number of teeth on the driving gear； the zero coordinate derivative method is equivalent to the zero curvature radius method，and the minimum locking angle is solely a function of contact ratio and the number of teeth on the driving gear，for example，when the driving and driven teeth‑number is 6 and 9，the coincidence‑degree is 1.04，the standard pressure angle （20°） and the standard addendum coefficient （1.0），the minimum engagement-angle without interference is 28.57º for involute tooth‑profile； when the driving and driven teeth‑number is 9 and 12，The zero coordinate derivative method is straightforward，and the locking angle design theory is correct and reliable，making it applicable to interference‑free designs of any internal meshing tooth‑profile pairs.

The porous medium model is widely used in the research of fluid sealing leakage rate calculation due to its high accuracy.The application of porous medium models was introduced in the research of static and dynamic sealing mechanisms，and the establishment methods of various porous medium models as well as the advantages and disadvantages of different leakage rate calculation methods was summarized，the development direction of future porous media models was elucidated.In the study of static sealing mechanism，the establishment methods of porous medium models based on percolation grid model，statistical contact model and capillary bundle model were analyzed，and the application characteristics of Darcy equation，N-S equation and Hagen-Poiseuille equation in leakage rate calculation were compared.In the research on the mechanism of dynamic sealing，the process of establishing the basic model based on the continuity equation and the N-S equation was expounded，and the method of deriving the resistance coefficient with the aid of the Ergun equation and Chew theory was discussed.Studies show that the Darcy equation is the most widely used method for calculating leakage rate，while the N-S equation and the Hagen-Poiseuille equation are subject to certain limitations due to the complexity of the geometry of the flow channel.The method based on the Ergun equation for calculating the leakage rate is simple in form and highly accurate，while the results based on the Chew theory have wider adaptability.In subsequent research，the porous medium model should focus on the rapid prediction of leakage rate based on neural networks，providing reference for design of sealing structures.

To address the excessive noise issue in reciprocating compressors，a series of vibration and noise reduction tests were conducted，including modal analysis，vibration testing，adjustments to the thickness of the outer casing，and replacement of sound‑absorbing materials.Ultimately，the noise level was successfully controlled to 58.7 dB（A）〔meeting the requirement of L_P≤60 dB（A）〕.The study indicates that low‑frequency vibrations （10~100 Hz） cause noise radiation from the compressor casing.Modifying boundary conditions can effectively reduce certain low‑frequency vibrations，and vibration transmission pathways determine the characteristics of noise radiation.When acoustic enclosures are not connected to the sound source，they can reduce noise in the mid‑to‑high frequency range （500~2 000 Hz）.Vibro‑acoustic coupling occurs in the form of solid-solid interaction，propagating outward at the first‑order excitation frequency through a single path.Boundary conditions govern both the intensity of vibro‑acoustic coupling and the magnitude of radiated sound waves.Sound‑absorbing materials can only function effectively if they fully enclose the sound‑radiating surfaces.Vibration isolators are effective for noise reduction in the high‑frequency range but fail to reduce low‑frequency noise.This research provides guidance for vibration and noise reduction in similar compressors.

To address wear issues in a catalytic cracking unit cyclone separator，a gas‑solid two‑phase erosion mathematical model was established.Numerical simulations reproduced distribution characteristics of flow parameters including velocity fields and wear rates under typical operating conditions.Combined with field failure cases，erosion mechanisms were analyzed and control solutions proposed.Results show the swirler internal flow exhibits a dual‑layer rotational structure with outer downward flow and inner upward flow.Wall thinning primarily results from combined cutting wear and deformation wear.Silica particles continuously impact the swirler top at low angles，causing severe wear with a wear rate of 6.02×10^-9 kg/（m²·s）.During spiral downward movement，particles cause cutting wear on the cylinder wall.Reduced motion radius increases centrifugal force，leading to severe impact wear at the underflow orifice with a wear rate of 5.52×10^-9 kg/（m²·s）.Numerical results show high consistency with field cases.Wear‑resistant electrode overlay welding extends equipment life by 3~6 months，while alumina ceramic lining extends life by over 10 months.The established wear analysis method and control strategy can be applied to failure assessment and life optimization of cyclone separator wall thinning.

To enhance the efficiency and accuracy of three‑dimensional finite element model updating for nuclear power valve piping systems and ensure the reliability of analysis results，a three‑dimensional finite element model updating technique based on an inverse response surface model is proposed. First，a radial basis function‑backpropagation neural network is employed to fit an inverse response surface model that directly maps the resonant frequencies，anti‑resonant frequencies，and structural parameters of the valve piping system. Then，the measured frequencies are used as inputs to solve for the correction parameters，addressing challenges such as the difficulty in modeling vibration control equations for the three‑dimensional finite element model，the uncertainty of results from intelligent optimization algorithms，and the inefficiency of iterative updating processes. The proposed method is validated using an actual valve piping system. The results demonstrate that after measuring the actual dynamic characteristics，the trained inverse response surface model can complete the three‑dimensional model updating within seconds. The maximum error between the calculated frequencies of the updated model and the measured frequencies is reduced from 15.43% to 3.53%.The proposed method can be applied in engineering practice to update the three‑dimensional finite element model of nuclear power valve piping systems using measured frequencies.