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.

To address the issues of high energy consumption and low efficiency associated with electric heating defrosting in air‑cooled refrigerator evaporators，a dynamic CFD defrosting model was established.This model was used to investigate the melting characteristics of various tube rows operating under a constant power mode.Using the mass of melted frost as a quantitative indicator，the defrosting process was divided into six sub‑stages.Based on the principle of dynamic matching between frost load and heat supply，five stepped power reduction strategies were designed to explore the effects of variable power on defrosting energy consumption，efficiency，and the improvement of heat distribution.The results indicate that all variable power strategies achieve varying degrees of improvement compared to the constant power mode.Among them，the power step reduction strategy 1 based on the entire defrosting process performs the best.It reduces defrosting energy consumption by 14.49%，increases defrosting efficiency by 5.72%，reduces average defrosting power by 35.27%，and reduces defrosting residual heat by 19.09 kJ.This study can provide a reference for the design of variable power control strategy for electric heating defrosting systems in air‑cooled refrigerator evaporators.

To address the issue of abnormal noise at 5 200 Hz occurring in variable refrigerant flow （VRF） indoor units under heating operation，a dedicated test bench for the electronic expansion valve （EEV） was constructed to identify the excitation conditions responsible for this high‑frequency noise.Large eddy simulation （LES），coupled with the Schnerr‑Sauer cavitation model，was employed to compute the temporal evolution of the vapor volume fraction inside the EEV and the corresponding pressure fluctuation spectrum.Additionally，the acoustic finite element method was applied to determine the acoustic cavity modes within the valve chamber.The results indicate that after the refrigerant passes through the throttling region of the EEV，pronounced localized vortices are generated.The pressure at the vortex core drops below the local saturation vapor pressure，triggering localized flash cavitation.The pressure fluctuation frequency induced by cavitation couples with the acoustic cavity mode of the valve chamber at 5 237 Hz，thereby amplifying pressure pulsations near that frequency and radiating audible noise.To mitigate this issue，a chamfered flow‑guiding design on the valve seat and the addition of a buffer chamber were implemented.These modifications effectively suppress cavitation and eliminate the high‑frequency noise during heating operation.

To address the issues in traditional data‑driven fault diagnosis methods for five‑cylinder pumps，such as difficulty in obtaining fault data，insufficient diagnostic capability during the early stage of equipment operation，and poor model generalization，a multi‑domain digital twin model of the five‑cylinder pump was established.The motor system，control system，mechanical system，and hydraulic system of the five‑cylinder pump were modeled，the mathematical models and parameter transfer relationships of each subsystem were clarified，and the overall model was consequently constructed.Based on fault mechanism analysis，the injection and response quantitative analysis of four typical faults，namely piston leakage，inlet blockage，bearing damage，and motor open circuit，were realized.A multi‑domain simulation model coupled with electromechanical‑hydraulic‑control was built using MATLAB/Simscape to obtain simulation data after fault injection.The consistency of the digital twin model was verified using experimental data from the XZQ2200 drilling pump.To demonstrate the application of the model，a drilling rig circulation system model was constructed using the five‑cylinder pump digital twin model，and a TimesNet‑based fault diagnosis method was proposed.The results show that the root mean square error between the twin data and the measured data is 0.039 2.The fault diagnosis model achieves a fault location classification accuracy of 98.33% and a fault classification accuracy of 89.44% on the twin dataset.The established five‑cylinder pump digital twin model has high fidelity and can effectively support typical fault mechanism analysis and fault diagnosis model construction.This study provides a new technical approach for predictive maintenance of complex equipment.

To address the issue of seal failure in drilling pump piston‑cylinder liner sealing pairs caused by excessive friction resistance and severe temperature rise under high‑speed and high‑pressure operating conditions，surface microstructure specimens with varying diameters，depths，area ratios，and arrangements were designed and fabricated using nitrile rubber （NBR） pistons and high‑chromium cast iron cylinder liners.A sealing pair simulation test platform was established using a friction and wear tester to systematically investigate the influence of microstructure geometric parameters on the friction coefficient，surface temperature rise，and wear amount of the sealing pair.The friction reduction and temperature reduction mechanisms were revealed by analyzing the microscopic wear morphology.The results indicate that when the microstructure parameters are a diameter of 100 μm，a depth of 40 μm，and an area ratio of 4% to 5%，the comprehensive performance of the sealing pair is optimal.Compared with the non‑textured specimen，the average friction coefficient is reduced by approximately 50%，the surface temperature rise is reduced by 62.5%，and the piston wear amount is reduced by 40.7%.Under these parameters，the microstructure can achieve continuous lubrication and wear debris storage by forming a "micro‑oil reservoir"，thereby reducing abrasive wear，dispersing contact stress，and avoiding local overheating，synergistically enhancing the friction reduction，temperature reduction，and wear resistance performance of the sealing pair.This study can provide a reference for the surface structure optimization of drilling pump piston‑cylinder liner sealing pairs.

In order to improve the heat transfer performance of the heat recovery device in the closed system of heat pump dryer，a heat recovery device with a convex structure （truncated cone‑shaped and cylindrical） was proposed.The influence of the shape and arrangement of the convex structure on the heat transfer performance was analyzed by the method of experiment and numerical simulation.The results show that when Re=542~1 692，the heat transfer enhancement multiples of Nu_{truncated cone}/Nu_plate and Nu_cylinder/Nu_plate are 1.29~1.42 and 1.22~1.26，respectively，which are larger than those of smooth plate.The comprehensive thermal performance evaluation factor PEC of the truncated cone‑shaped convex heat recoverer is 1.09~1.15，which is better than that of the cylindrical convex structure with the same Re.The PEC of the staggered arrangement of the cone‑shaped convex heat collectors is 1.09~1.15.Among them，the PEC of Re=542~1 490 staggered arrangement is larger than that of grouping arrangement，and the comprehensive heat transfer performance of staggered arrangement is better.The research results provide a theoretical basis for the structural optimization of the heat recovery device of the heat pump dryer.

To investigate the hydraulic characteristics of centrifugal pumps during rapid transient processes and optimize their startup strategies，transient tests under various startup conditions were carried out on a marine centrifugal pump with a specific speed of 102.Based on a transient hydraulic performance test platform with a synchronous data acquisition system，the effects of five rotational speed variation curves and four startup times on the transient characteristics of pump startup were compared and analyzed under the conditions of rated speed of 1 450 r/min and design flow rate of 25 m³/h.The results show that under a fixed startup mode，the impact head decreases with increasing startup time.The startup acceleration has a significant effect on the impact head.Under the same startup time，the exponential startup curve produces the smallest impact head due to its lower acceleration in the final stage，with corresponding values of 6.923，6.872，6.865 and 6.836 m for the four startup times.The head overshoot rate is proposed as an indicator for evaluating the transient response of centrifugal pumps during startup.This parameter gradually decreases with time，and its variation trend exhibits an obvious concave curve characteristic.The head overshoot rate for the exponential startup mode is always the lowest，with values of 1.011 8，1.004 7，1.002 7，and 1.001 3，respectively.The exponential startup mode can effectively suppress head impact and is an ideal startup scheme for centrifugal pumps.This study can provide experimental basis and reference for the evaluation of startup status and optimization of operating performance of centrifugal pumps.

To explore the unsteady flow characteristics and evolution mechanisms of the stern jet of a pump‑jet propulsor，based on the numerical simulation results of the DES model，the dynamic mode decomposition method was used to decompose and reconstruct the stern jet flow field of the pump‑jet under different cruising conditions.By comparing the numerical simulation with experimental data，it was found that the average error of thrust performance was 6.6%，verifying the effectiveness of the model.The results indicate that the stern jet flow field of the pump‑jet can be decomposed into flow features with different energies and frequencies.The first five modes account for more than 99.9% of the total energy.The fundamental mode with zero frequency represents the steady‑state structure of the unsteady flow field，reflecting the steady‑state flow field characteristics of the pump‑jet wake under different speeds and rotor rotations.Other major modes reveal the influence of the development process of high‑energy fluid masses in the wake on the wake flow bundle.Through the dynamic mode decomposition method，a low‑dimensional approximation of the high‑dimensional multi‑scale flow field can be effectively achieved，with reconstruction errors of 4.5% （low speed），5.3% （medium speed），and 4.4% （high speed），reflecting the unsteady characteristics of the complex flow field.As the speed increases，the energy becomes more concentrated in a few dominant modes.The proportion of the first‑order mode in the total energy gradually increases，approximately 95.2% at low speed，97.6% at medium speed，and 98.9% at high speed.The period of the modal coefficients increases，the flow field stability is enhanced，the wake flow bundle fluctuation of the first‑order mode decreases，and the velocity variation becomes more uniform.This study can provide a theoretical basis for the structural optimization design of pump‑jet propulsors and wake field stability control.

Aiming at the challenge of efficient treatment and utilization of oil‑contaminated sludge generated during petroleum exploitation，processing and gathering-transportation，the distribution characteristics of turbulent flow field as well as the movement and distribution behavior of oil‑contaminated sludge particles were conducted.A DN50 axial‑flow hydrocyclone model was established and verified by experimental tests.The Eulerian multiphase flow model and RSM turbulence model was adopted to explore the turbulent desorption mechanism of oil‑contaminated sludge under rotating flow field.The results show that within the research range （flow rate of 2~6 m³/h，overflow ratio of 2%~20%），the optimal operating conditions are flow rate of 4.5 m³/h and overflow ratio of 10%，under which the crude oil recovery rate and sludge reduction rate reach 96.72% and 99.27% respectively.During the treatment of oil‑contaminated sludge，variation of flow rate affects both the rotating separation process and the desorption process of oil‑contaminated sludge simultaneously.The influence of overflow ratio on the rotating separation process is significantly greater than that on the desorption process of oil‑contaminated sludge.The turbulent effect of the rotating flow field enables efficient desorption of oil‑contaminated sludge.This study provides a reference for the industrial application of a two‑stage rotating process integrating "intensive turbulent desorption" and "enhanced cyclonic separation".

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.