To address the technical challenge of erosion damage caused by sand particles to cage throttle valve sleeves during natural gas extraction，this study investigates the erosion mechanism using YW3 hard alloy sleeves as the research object.Through laboratory erosion tests，an erosion model for YW3 hard alloy was established and validated via numerical analysis.This model was further applied to erosion simulation of throttle valves to analyze solid particle trajectories，erosion mechanisms，and predict the service life of cage throttle valve sleeves.The results show that with increasing erosion angle，the erosion rate of YW3 first increases and then decreases，reaching its maximum at 45°.Under an erosion angle of 90°，the velocity exponent n and particle size function C（dp） for YW3 are 2.41 and 3.684 4×10^-9，respectively.The main damaged area of the sleeve is at the outlet of the throttle hole.This research provides reference for material selection and life assessment of throttling components in cage throttle valves used in high‑sand‑content gas fields.

In view of the problems of high noise and poor acoustic performance in the fresh air system of air conditioners，this study takes the fresh air system of a centrifugal fan for air conditioners as the research object and conducts research and analysis on the layered structure of centrifugal fan blades.Adopting the method combining numerical simulation and orthogonal experiments，the effects of the blade height ratio of upper and lower layers，the offset angle of upper and lower blades，and the number of lower‑layer blades on the aerodynamic performance of the centrifugal fan were analyzed.The research results show that the main parameters affecting the flow rate of the fan system，in order of significance，are the blade height ratio，offset angle，and number of blades.By optimizing these impeller structural parameters，the flow field in the flow passages between blades near the rear plate and at the volute bottom can be effectively improved，thereby enhancing the aerodynamic performance.Specifically，when the blade height ratio，offset angle，and number of lower‑layer blades are adjusted to 4.5，3.5°，and 57 respectively，the air volume increases by 6% at the same rotational speed，while the total noise level remains comparable.Furthermore，the low‑frequency broadband noise （0~600 Hz） is reduced by 2.1 dB（A），and the cavity noise is significantly attenuated.The research results can provide a reference for the aerodynamic optimization and noise reduction design of similar fresh air products.

To investigate the internal flow field characteristics of a straight‑tube distributor in falling film evaporators，a three‑dimensional computational model was established based on industrial design criteria for liquid distributors.Following model validation，the influence mechanisms of geometric parameters and operational conditions on distributor performance were systematically studied.Results indicate that the internal flow field of straight‑tube liquid distributors is significantly affected by inflow position and wall structure：a distinct impingement zone forms in the bottom area due to fluid impact，resulting in notably higher flow velocities at outflow holes near the inlet compared to other regions；whereas areas farther from the inlet develop stable pre‑orifice flow regions，effectively reducing mechanical energy loss.Under constant unit orifice area conditions，appropriately increasing orifice diameter and spacing significantly enhances initial distribution mass，though optimization effects exhibit parameter threshold limitations.Concurrently，increasing tube diameter ratio and branch pipe cross‑sectional area helps reduce average outflow velocity while further improving initial distribution mass.Variable‑condition studies reveal that as inlet flow rate increases，outflow velocity shows monotonic growth，while initial distribution mass first rises to a peak before stabilizing.The optimal initial distribution quality is 0.758 6，corresponding to an optimal operational flow rate of 0.453 kg/s，with distributors of different structural parameters exhibiting specific optimal operational ranges.The research can provide reference for the optimization design of straight pipe distributors

To address the efficiency reduction caused by clearance backflow at the volute tongue of a double‑suction multi‑wing centrifugal fan，a clearance adjustment control structure unit is proposed.This unit is installed on the front and rear cover plates of the volute near the volute tongue to achieve clearance adjustment.By adding structural units of different thicknesses to adjust the clearance，numerical analysis methods are used to simulate the internal flow field of the fan under different clearances.The effectiveness of the clearance adjustment is verified through aerodynamic performance and noise tests of the fan.The results show that the clearance adjustment unit can effectively reduce backflow at the volute tongue，improve the static pressure recovery capability of the volute，and ameliorate the backflow state at the impeller front shroud.It also enhances the axial distribution uniformity of the annular flow rate at the impeller outlet，thereby increasing the impeller work efficiency.However，when the axial thickness of clearance adjustment unit is excessive，it aggravates impact at the volute tongue，leading to a noise increase of 4.8 dB.When the axial thicknesses of the two clearance adjustment units are equal to the axial distances between the impeller front and rear shrouds and the volute front and rear cover plates，respectively，the measured noise can be reduced by 0.7 dB，the maximum air volume increased by 0.8 m³/min，and the efficiency improved by nearly 2%.This study provides a theoretical basis and engineering practice reference for the aerodynamic performance optimization and low‑noise design of multi‑wing centrifugal fans.

To investigate the sealing performance of the auxiliary rubber O‑ring for the compensating ring in high‑pressure pump mechanical seals，a two‑dimensional axisymmetric nonlinear contact model was established.Based on the fluid pressure penetration method，the effects of parameters such as different medium pressures，compression ratios，and installation gaps on the stress and sealing performance of the O‑ring were analyzed.The accuracy of the computational model was verified through an O‑ring axial force measurement test apparatus.The results show that the various stresses of the O‑ring increase with rising medium pressure，with contact stress exhibiting the most significant increase；when the medium pressure is in the range of 9~15 MPa，the pressure dominates the influence on O‑ring stress；when the compression ratio is >10%，its effect on O‑ring stress becomes negligible；when the medium pressure is below 20 MPa and the installation gap is <0.2 mm，the installation of the backup ring has little effect on the stress and sealing performance of the O‑ring.The research results can provide theoretical guidance for the design of rubber O‑rings in related high‑pressure pump mechanical seals.

Aiming at the problem that traditional discrete particle swarm optimization algorithm is prone to getting stuck in local optima and unable to obtain the global optimal value in the aerodynamic optimization design process of centrifugal compressors，an improved discrete particle swarm algorithm is proposed by introducing chaos operators，redefining learning factors and inertia weights，and combining control parameter descent strategy，as well as optimizing position probability iteration formula and other methods.Based on expanding the optimization range，the algorithm effectively balanced the global search ability and the local search ability，solving the problem of getting stuck in local extremums.The algorithm was adopted to conduct optimization design research on a certain centrifugal compressor.The results show that compared with the traditional particle swarm optimization algorithm，the improved algorithm can achieve a better aerodynamic design and effectively control the flow field separation at the impeller outlet.Under the premise of little change in pressure ratio，the isentropic efficiency increased from 85.7% to 88.7%.The research results can provide reference for the aerodynamic optimization of centrifugal compressors，and can also be applied to the aerodynamic optimization design of axial compressors and radial and axial turbines.

Aiming to address the issue of uneven air supply in data center fan‑wall air supply systems，a numerical model was established using computational fluid dynamics （CFD） simulation technology.The model was validated using measured data.Based on this validated model，an optimization study on airflow distribution in the data center was conducted for the air supply system.The impacts of optimization schemes，such as optimizing the air supply angle and adding rack inlet deflectors，on indicators such as the maximum inlet temperature of IT equipment，the average inlet temperature rise of risk racks，and the return air temperature index were analyzed systematically.The results show that optimizing the air supply angle and adding rack inlet deflectors can enhance the uniformity of airflow distribution；among which，when a 100 mm-wide，30°-inclined rack inlet deflector is used，the average inlet temperature rise of risk racks is significantly reduced by 0.81 °C，and the temperature uniformity in the equipment room is optimal.In contrast，reconfiguring the positions of air supply outlets does not optimize the airflow distribution in the data center.This research can provide a reference for the design of fan‑wall air supply systems.

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.