To address the challenge of the unclear coupling mechanism between cross‑flow and counter‑flow heat transfer in printed circuit heat exchanger（PCHE） operation，a key issue hindering equipment design，a numerical model was developed to simulate conjugate flow and heat transfer processes within PCHEs.The SLENDER BLOCK+ structured meshing method was introduced for discretizing the PCHE core，enabling quality mesh generation and numerical simulation for industrial‑scale units.The industrialized test data were used to verify the model's accuracy.The error in heat transfer load was less than 10%，and the pressure drop error was less than 5%.The results revealed two critical phenomena：Significant natural gas channel temperature non‑uniformity，characterized by an enhanced heat transfer zone near the seawater inlet and an impaired zone near the outlet；a calculated overdesign margin of 40.5%，indicating considerable potential for flow‑path optimization.This method establishes a robust framework for PCHE performance prediction and engineered optimization design in domestic engineering applications.

To enhance the recovery and utilization efficiency of high‑temperature flue gas waste heat in natural gas heat treatment furnaces，an efficient bionic‑honeycomb twisted tube waste heat recovery unit is proposed to deeply recover waste heat from flue gas.The study designed a waste heat recovery unit consisting of nine bionic‑honeycomb twisted tubes and conducted numerical simulations of its condensation‑coupled heat transfer process using the CFD software Fluent.By varying the volume flow rates of combustion air and flue gas，the heat transfer and resistance characteristics of the bionic‑honeycomb twisted tubes were systematically analyzed.The results show that when the flue gas and combustion air volume flow rates are 0.889，0.978 m³/s，respectively，the system achieves optimal performance，cooling the 950 ℃ flue gas to 135 ℃ while heating the combustion air to 588 ℃.Under the operating condition with a Re of 6 860 and a water vapor content of 10%，the comprehensive heat transfer and economic performance of the recovery unit are optimal，with its performance evaluation index significantly improved by approximately 25% compared to conventional circular tube heat exchangers.Due to its unique structure，the bionic‑honeycomb twisted tube waste heat recovery unit achieves efficient energy recovery through enhanced heat transfer and can be universally applied to industrial furnace flue gas waste heat recovery，providing a reliable solution for industrial energy‑saving technological transformation.

Addressing the issue that existing research lacks quantitative analysis of the relative contributions of each heat transfer process in plate‑type evaporative condensers，which restricts precise performance optimization，this study investigates the relative contributions of air‑wall convective heat transfer，spray water convective heat transfer，and evaporative heat transfer in a novel plate‑type evaporative condenser through theoretical analysis and quantitative comparison.It systematically analyzes the influence of different air velocities and spray water flow rates on heat transfer performance and pressure drop characteristics.Numerical simulation models for the novel high‑efficiency plate‑type evaporative condenser were established under dry and wet operating conditions，respectively，and its heat transfer performance was compared with that of a traditional tubular structure.The results show that convective heat transfer from the spray water and the evaporation process together contribute over 80% to the total heat transfer in the plate‑type evaporative condenser.Compared to the traditional tubular structure，under the same air velocity，the total heat transfer of the novel plate‑type evaporative condenser can be increased by up to 6.19%，while the flow resistance is significantly reduced.Under the condition of a spray water flow rate of 20 m³/h，the pressure drop is only about 70.8% of that of the tubular structure，demonstrating its comprehensive advantages in enhanced heat transfer and reduced power consumption.Additionally，appropriately increasing air velocity and spray water flow rate can both enhance heat transfer.This research provides important theoretical basis and data support for the optimal design of plate‑type evaporative condensers.

To address the erosion wear problem of U‑shaped heat exchange tubes by particle‑containing cooling water，a solid‑liquid two‑phase flow erosion model was established based on ANSYS Fluent.Through orthogonal experiments and single‑factor analysis，the effects of inlet velocity，particle diameter，particle concentration，and tube diameter on tube wall erosion characteristics were systematically studied.The results show that inlet velocity has the most significant influence，with the maximum erosion rate increasing quadratically with velocity.When velocity increases from 1 m/s to 5 m/s，the maximum erosion position migrates from θ_u=30° to near θ_u=180°，with a service life of only 3.08 years at 5 m/s；when particle diameter increases from 0.1 mm to 0.5 mm，the erosion rate increases by 321%，and service life decreases to 17.18 years；when particle concentration increases from 0.01% to 0.03%，the erosion rate rises by 246%；increasing tube diameter can disperse the erosion area，reduce erosion rate，and extend heat exchanger life；by controlling velocity and optimizing tube diameter，the service life of U‑shaped heat exchange tubes can be significantly extended.The research provides references for optimal design of heat exchangers.

To improve the design accuracy of microchannel oil coolers，numerical calculations and experimental studies on flow and heat transfer of oil in airfoil‑channel printed circuit heat exchangers （PCHE） were conducted，focusing on the impact of oil inlet temperature and flow velocity on the flow resistance and heat transfer performance of the heat exchanger.Empirical correlations for Nu and f of oil in airfoil channels were fitted.The results show that the maximum error between numerical calculations and experimental results is within 20%，indicating the reliability of the numerical model.Flow velocity is a key factor affecting the thermal‑side Nu_h，while temperature has a weaker influence.Within the studied operating range，increasing the flow velocity from 0.2 m/s to 1 m/s raises Nu_h by approximately 78%，whereas a temperature increase of 10 K only changes Nu_h by 0.1~0.2.Both temperature and flow velocity significantly affect pressure drop.Thermal‑side pressure drop is positively correlated with oil inlet flow velocity，increasing by 270%~300% as flow velocity rises from 0.2 m/s to 1 m/s.When the thermal‑side inlet flow velocity is constant，pressure drop decreases with rising oil temperature.A temperature increase of 10 K reduces pressure drop by 8 460~48 800 Pa.The maximum errors of the fitted empirical correlations for Nu and f are 6.23% and 11.68%，respectively.The research results provide a theoretical basis for the accurate design of microchannel oil coolers.

To address the performance failure of conventional centrifugal pumps under high gas content multiphase transportation conditions，a high‑speed gas‑liquid multiphase booster pump covering conventional centrifugal pump performance parameters was designed.Maintaining bubbly inflow and through visualization testing，its performance and internal flow characteristics under variable conditions were analyzed.The results show that the pump can transport mixed medium with inlet gas volume fraction of 55% under rated conditions；as inlet gas volume fraction increases，the pump head coefficient shows a nonlinear decreasing trend，and the inlet flow pattern gradually transitions from bubbly flow Ⅰ to bubbly flow Ⅱ，Ⅲ，Ⅳ.When the flow pattern develops to bubbly flow Ⅲ，the pump performance loss and inlet flow pattern transition delay reach their maximum；increasing rotational speed can achieve up to 6.65% maximum inlet flow pattern transition delay rate and enhance the pump's gas mixing resistance capability；small liquid flow rate helps slow down performance degradation under high inlet gas volume fraction conditions，while increasing liquid flow rate intensifies gas‑liquid separation inside the pump；reducing liquid flow rate can achieve up to 7.04% maximum inlet flow pattern transition delay rate.This research provides theoretical support for the optimal design and efficient operation of gas‑liquid multiphase booster pumps.

To address the issue of excessive ventilation energy consumption caused by the assumption of uniform pollutant distribution in industrial ventilation methods，an intelligent ventilation control method based on flow field prediction and traversal optimization is proposed.This method can dynamically regulate the ventilation system according to the needs of target control points.First，proper orthogonal decomposition （POD） is used to reduce the dimensionality and reconstruct the pollutant concentration field，obtaining low‑dimensional basis functions and their coefficients；then，basis coefficient interpolation technology is employed to predict dynamic pollutant concentration distributions under different air supply parameters；finally，a traversal optimization algorithm is adopted to search and determine the optimal combination of air supply parameters，which is verified in a two‑dimensional air supply parameter space.The results show that the pollutant concentration distribution predicted by this method has a small relative error compared with numerical simulation values，and can accurately predict the concentration field；the optimization algorithm can precisely locate the optimal air supply parameters that meet the requirements，achieving an optimal control error of 0.1%；the running time of the control program in the two‑dimensional parameter space is only 78 s，demonstrating the potential of this method for real‑time ventilation control.The intelligent ventilation control method proposed in this study provides a new intelligent solution for industrial ventilation，with good applicability and application prospects.

To address the issue of uncertain pressure pulsation characteristics during the cyclic downward movement of particles in a standpipe-valve system and the lack of quantitative characterization，an experimental study on pressure pulsation characteristics was conducted.By varying the particle mass flow rate，the dynamic pressure of the gas-solid two‑phase flow before and after the valve （at measuring points P1 and P2） was measured.Through analytical methods including dynamic pressure，static pressure，standard deviation，and power spectral density，the pressure fluctuation characteristics within the standpipe-valve system were thoroughly investigated.The results indicate that as the particle mass flow rate G_s increases from 0 to 117.72 kg/（m²⋅s），significant low‑frequency，high‑amplitude pressure fluctuations occur in the system，primarily due to particle clustering，gas‑solid interactions，and bubble disturbances.The standard deviation of the dynamic pressure at point P2 shows a linear relationship with the particle mass flow rate，suggesting that the standard deviation can be used for real‑time monitoring of the particle mass flow rate in circulating fluidized beds.When the particle mass flow rate G_s=0，both points P1 and P2 on the standpipe exhibit a single dominant frequency with relatively low power spectral density.As the particle mass flow rate increases to 6.28 kg/（m²⋅s），both P1 and P2 display dual‑frequency characteristics，comprising a primary frequency and a secondary frequency.The power spectral density at P1 initially increases and then decreases with increasing particle mass flow rate，while at P2，it increases with increasing particle mass flow rate.The pressure pulsations within the standpipe are all low‑frequency （<0.41 Hz） and act as the excitation force causing standpipe vibration.This study provides a theoretical basis and experimental support for the optimal design and safe operation of particle circulation systems in circulating fluidized beds.

To investigate the causes and characteristics of asymmetric pressure distribution in scroll chambers，mathematical models for geometric analysis and thermodynamic processes were established based on asymmetric features.Dynamic pressure measurement tests inside the scroll chamber of an electric vehicle scroll compressor were conducted，validating model rationality.Under pressure ratios of 2 and 5 and rotational speeds of 3 000 r/min and 8 000 r/min，pressure variations in scroll chambers，valve rear chambers，exhaust ports，and pressure relief ports versus orbiting scroll angle were calculated.Results show that with a 50° difference in end angles between fixed and orbiting scrolls，a pressure difference of approximately 0.02 MPa exists in bilateral scroll chambers during early‑mid compression.At pressure ratio 5，asymmetric pressure distributions remain similar across speeds，with maximum discharge pressure reaching 2.1 MPa at high speeds indicating severe over‑compression.At 3 000 r/min，asymmetric pressure characteristics differ with increasing pressure ratios due to changes in the relative magnitude of designed internal versus operational external pressure ratios.Under low pressure ratios，implementing pressure relief structures reduces indicated power by 1.4% at 3 000 r/min but increases it by 0.65% at 8 000 r/min compared to non‑relief configurations.This study provides guidance for scroll profile design and optimization.

In order to explore the energy conversion characteristics of the vacuum cleaner fan，the full‑flow field numerical simulation of the fan flow field under different working conditions was carried out to analyze the flow characteristics.After verification by performance tests，the distribution of the local entropy production rate of the impeller was analyzed based on the entropy production theory.The results indicate that there is an obvious flow impingement at the blade inlet.At the impeller outlet，the mixing of wake and jet increases the velocity gradient and forms a jet wake structure.As the flow rate decreases，large‑scale backflow occurs inside the impeller.Local entropy production is the main factor affecting the energy consumption of the fan.Under the design conditions，the proportion of local entropy production is 59.06%，and the high entropy production area is mainly concentrated at the blade inlet，the suction surface of the blade leading edge and the blade outlet trailing edge.By analyzing the distribution of secondary flow in different annular sections of the impeller，it is found that the secondary flow at the impeller inlet becomes more obvious as the flow rate increases，and the high entropy production areas mostly appear in the regions where secondary flow is generated，indicating that secondary flow is an important factor causing energy loss.