In this study,four types of spiral fins with varying parameters were mounted on an upstream cylinder,and the effects of spiral fins on the vibration response of heat exchange tubes and the vortex structure in cross fl...In this study,four types of spiral fins with varying parameters were mounted on an upstream cylinder,and the effects of spiral fins on the vibration response of heat exchange tubes and the vortex structure in cross flow were studied through experiments and numerical simulations.The results indicate a strong dependency of the cylinder's vibration response on the fin parameters.The results indicate that the vibration response and wake structure of the cylinder are significantly influenced by the parameters of the fins.The introduction of a finned cylinder affects both its own vibration amplitude and frequency,as well as the downstream cylinder.The amplitudes of finned cylinders Ⅰ and Ⅲ are reduced by 57.8% and 59.9%,respectively,compared to the bare cylinder.This reduction helps to restrain vibration and diminishes the amplitudes of the downstream cylinder.Although finned cylinder Ⅱ slightly decreases its own vibration,it increases the amplitude of the downstream cylinder by 13.7%.The mean drag coefficient and the root mean square of the lift coefficient of the finned cylinder are higher than those of the bare cylinder when the finned cylinder is positioned upstream.Smaller pitch and larger equivalent diameter will lead to increased drag,resulting in enhanced vortex shedding in the wake,which amplifies the vibrations of the cylinder in that wake.The downstream of finned cylinder Ⅱ has the widest wake and higher vortex strength,and the dynamic load and vibration of the downstream cylinder are increased.The vortex intensity decays faster in the wake of finned cylinder Ⅲ,and the vibration of the downstream cylinder is weaker.展开更多
In this paper, the standard k-ε two-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By vari...In this paper, the standard k-ε two-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By variable transformation, the original 3-D problem is converted into a 2-D problem in spiral coordinates. The algorithm of SIMPLEC is used to study the fully developed fluid flow and heat transfer in the spiral finned tube at constant periphery temperature and constant axial heat flux. The computed results agree pretty well with the experimental data obtained from the industry. Further studies on the fluid flows and temperature profiles at different Reynolds numbers within straight and spiral finned tubes are conducted and the mechanisms involved are explored. It is found that with the spiral finned tube, pressure drop increases to a great extent whereas heat transfer tends to be decreased.展开更多
Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was ...Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was shown that pathlines remain mostly circular for different geometries. Moreover, the contributions of fin periphery, fin side and bare tube to heat transfer were specified. It was shown that the heat transfer per unit area of fin periphery can be several times that of other parts. Moreover, in higher finspacing, the heat transfer from the bare tube can be more important than fin sides.展开更多
The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder.The solutal and thermal buoyancy forces are sustained by maintaining ...The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder.The solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinders at uniform temperatures and concentrations.Buoyancy effects are also considered,with the Boussinesq approximation.The forced convection effect is induced by the outer cylinder rotating with an angular velocity(ω)in an anti-clockwise direction.The studies are made for various combinations of dimensionless numbers;buoyancy ratio number(N),Lewis number(Le),Richardson number(Ri)and Grashof number(Gr).The isotherms,isoconcentrations and streamlines as well as both average and local Nusselt and Sherwood numbers were studied.A finite volume scheme is adopted to solve the transport equations for continuity,momentum,energy and mass transfer.The results indicate that the use of fins on the inner cylinder with outer cylinder rotation,significantly improves the heat and mass transfer in the annulus.展开更多
Oxidative dehydrogenation of propane with carbon dioxide(CO_(2)-ODP)characterizes the tandem dehydrogenation of propane to propylene with the reduction of the greenhouse gas of CO_(2)to valuable CO.However,the existin...Oxidative dehydrogenation of propane with carbon dioxide(CO_(2)-ODP)characterizes the tandem dehydrogenation of propane to propylene with the reduction of the greenhouse gas of CO_(2)to valuable CO.However,the existing catalyst is limited due to the poor activity and stability,which hinders its industrialization.Herein,we design the finned Zn-MFI zeolite encapsulated noble metal nanoparticles(NPs)as bifunctional catalysts(NPs@Zn-MFI)for CO_(2)-ODP.Characterization results reveal that the Zn2+species are coordinated with the MFI zeolite matrix as isolated cations and the NPs of Pt,Rh,or Rh Pt are highly dispersed in the zeolite crystals.The isolated Zn2+cations are very effective for activating the propane and the small NPs are favorable for activating the CO_(2),which synergistically promote the selective transformation of propane and CO_(2)to propylene and CO.As a result,the optimal 0.25%Rh0.50%Pt@Zn-MFI catalyst shows the best propylene yield,satisfactory CO_(2)conversion,and long-term stability.Moreover,considering the tunable synergetic effects between the isolated cations and NPs,the developed approach offers a general guideline to design more efficient CO_(2)-ODP catalysts,which is validated by the improved performance of the bifunctional catalysts via simply substituting Sn4+cations for Zn2+cations in the MFI zeolite matrix.展开更多
This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crysta...This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crystallizer has been designed, the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature. The model is developed based on the basic heat transfer equation, and by considering the solution's and the coolant's convective heat transfer coefficient(h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model. Consequently, the study found that the model helps in enhancing the PFC system.展开更多
The height, thickness and spacing of fins have an impact on the thermal characteristics of a radiator. The calculation of heat output and metal thermal intensity for cast iron finned radiator are given by using heat t...The height, thickness and spacing of fins have an impact on the thermal characteristics of a radiator. The calculation of heat output and metal thermal intensity for cast iron finned radiator are given by using heat transfer formula of vertical plate and parallel fins. Each factor having effect on the metal thermal intensity of a radiator is analyzed and the optimum structure parameters of a radiator are given in order to maximize metal thermal intensity.展开更多
With the widespread use of high-power and highly integrated insulated gate bipolar transistor(IGBT),their cooling methods have become challenging.This paper proposes a liquid cooling scheme for heavy-duty automated gu...With the widespread use of high-power and highly integrated insulated gate bipolar transistor(IGBT),their cooling methods have become challenging.This paper proposes a liquid cooling scheme for heavy-duty automated guided vehicle(AGV)motor driver in port environment,and improves heat dissipation by analyzing and optimizing the core component of finned heat sink.Firstly,the temperature distribution of the initial scheme is studied by using Fluent software,and the heat transfer characteristics of the finned heat sink are obtained through numerical analysis.Secondly,an orthogonal test is designed and combined with the response surface methodology to optimize the structural parameters of the finned heat sink,resulting in a 14.57%increase in the heat dissipation effect.Finally,the effectiveness of heat dissipation enhancement is verified.This work provides valuable insights into improving the heat dissipation of IGBT modules and heat sinks,and provides guidance for their future applications.展开更多
This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat...This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.展开更多
This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat...This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.展开更多
This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material(PCM)inside a rectangular enclosure heated by multiple discrete pulsed protruding heat source...This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material(PCM)inside a rectangular enclosure heated by multiple discrete pulsed protruding heat sources.The fin and the phase change material filling the enclosure store the thermal energy extracted from the heat sources,in sensible and latent forms.The heat sources are assumed to simulate electronic components undergoing a superheating technical issue.By extracting heat from the electronics,the PCM plays the role of a heat sink.To analyze the thermal behavior and predict the cooling performance of the proposed cooling system,we derive a nonlinear mathematical model based on mass,momentum and energy conservation laws.Several numerical investigations are conducted to quantify the influence of the fin position on the thermal behavior and the cooling performance of the heat sink.Predictions include the transient maximum temperature occurring inside the heat sources and the liquid volume.A comparison between our numerical results and experimental data selected from the literature shows a good agreement.The main conclusion is that the presence of the fin leads to a slight increase in the melting time.展开更多
This study aims to investigate the output work and temperature drop in a compressor disk cavity equipped with a Finned Vortex Reducer(FVR)to improve the performance of the secondary air system of gas turbine engines.B...This study aims to investigate the output work and temperature drop in a compressor disk cavity equipped with a Finned Vortex Reducer(FVR)to improve the performance of the secondary air system of gas turbine engines.Based on the experimentally validated simulation results,we explore the effects of the rotating speed of the disk,coolant mass flow rate and the size of the fin on the flow and energy transfer of the radial inflow in the rotating cavity.The results show that the circumferential acceleration of the flow by Coriolis force is inhibited by the radial assembled fins from the rotating coordinate system,forcing the swirl ratio into one in the finned region and resulting in the reduction of the pressure drop.Outside the finned region,the variation characteristics of the swirl ratio follows that of a free vortex,which is typically found in the radial inflow through a simple cavity,i.e.,cavity without any vortex reducer.For the output work of the FVR cavity flow,it is mainly caused by the pressure difference on the fin surfaces,while those by the viscous shear force could be neglected.We propose a simplified model to predict the output work and total temperature change in the FVR cavity,which generally matches well with the simulation result.The research findings can provide guidance for the design and optimization of secondary air system in gas turbines.展开更多
The Heat Recovery Steam Generators(HRSGs)are designed to recapture heat from gas turbine exhaust to generate electric power by a steam turbine.Finned tubes are critical heat transfer components of HRSG,whose design an...The Heat Recovery Steam Generators(HRSGs)are designed to recapture heat from gas turbine exhaust to generate electric power by a steam turbine.Finned tubes are critical heat transfer components of HRSG,whose design and optimization play an essential role in realizing effective energy utilization in power plants.In this study,an optimization method with multi-layered neural network(MNN)and tree-structured parzen estimator(TPE)is proposed for the finned tube heat exchanger with curved serration.This method has high fitting accuracy and global optimization efficiency,and is suitable for complex heat transfer design and optimization problems caused by novel irregular finned tubes.The developed thermal-fluid model is validated with existing experimental data,and a satisfactory agreement is found in terms of Nusselt number and Fanning friction factor.It is shown that increasing the curved serration angle is beneficial to destroy the thermal boundary layer and enhance turbulent kinetic energy.When the Reynolds number is between 5000 and 25000,the heat transfer factor of finned tubes with a curved serration angle of 10°is 20%higher than that of flat serrated finned tubes on average.The optimized geometric parameters are obtained from the optimization approach,and the optimal solution has achieved excellent results in comprehensive performance.Compared with the baseline design,the optimized results show a 9%higher heat transfer factor,which is better than those based on commonly used optimization methods.展开更多
Enhancing the efficiency of phase-change heat storage is vital for maximizing the utilization of renewable energy.This study examines the synergistic effect of non-uniformly shaped fins and nanoparticles on the meltin...Enhancing the efficiency of phase-change heat storage is vital for maximizing the utilization of renewable energy.This study examines the synergistic effect of non-uniformly shaped fins and nanoparticles on the melting performance of phase-change storage tanks.The problem is addressed using a finite volume framework coupled with the enthalpy–porosity method,with the numerical model rigorously validated against experimental data.The analysis explores the influence of varying fin deflection angles and nanoparticle concentrations on melting dynamics.It is shown that a downward fin deflection of 6◦reduces melting time to 570 s,representing a 20.8% improvement over uniform fins.Introducing 1% nanoparticles further accelerates melting,reducing time by 36.54% compared to the nanoparticle-free case.The combined strategy of 6◦fin deflection and 1%nanoparticle addition shows the most economic heat storage rate,achieving an exceptional 80.74% enhancement relative to a tank with uniform fins.展开更多
Direct brazing was employed to fabricate a“Cu circuit layer-Si_(3)N_(4) ceramic-Cu heat sink”structure for power electronic devices,enabling a shortened heat dissipation path and enhanced thermal management.Structur...Direct brazing was employed to fabricate a“Cu circuit layer-Si_(3)N_(4) ceramic-Cu heat sink”structure for power electronic devices,enabling a shortened heat dissipation path and enhanced thermal management.Structural components(60 mm×60 mm and 30 mm×30 mm)were brazed at 780°C for 20 min to simulate finless and finned heat sinks.The effects of composite brazing filler metal and copper underlayer stiffness on warpage and thermal resistance were systematically evaluated.The results show that composite fillers effectively suppressed warpage,reducing deformation in a 60×60 mm²-finned component from 0.95%to 0.73%,with a measured thermal resistance of 0.1936 K/W.After surface soldering of the insulated gate bipolar transistor(IGBT),the total thermal resistance from junction to ambient decreased by 10.2%compared with conventional structures.This study demonstrates a practical route to improve heat dissipation and optimize the thermal design of highpower modules,providing an industry-ready thermal management solution for high-power-density SiC/GaN devices.展开更多
Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which ca...Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which can provide different grades of thermal energy with two heat transfer fluids(oil and water),is designed to improve thermal efficiency.In this FPTR-IT,an inner tube and straight fins are employed to respectively lessen heat loss at upper and lower parts of the absorber.Based on the design,a numerical model is developed to investigate its performance.Comparisons with other PTRs indicate that the FPTR-IT can combine the advantages of PTR with inner tube and finned PTR and obtain the best performance.Moreover,performance evaluation under broad ranges of direct normal irradiances(300–1000 W/m^(2)),flow rates(50–250 L/min)and inlet temperatures(400–600 K)of oil as well as flow rates(3.6–10 L/min)and inlet temperatures(298.15–318.15 K)of water is investigated.Compared with conventional PTR,heat loss is reduced by 20.7%–63.2%and total efficiency is improved by 0.03%–4.27%.Furthermore,the proportions of heat gains for water and oil are located in 8.3%–73.9%and-12.0%–64.3%,while their temperature gains are located in 11.6–37.9 K and-1.2–19.6 K,respectively.Thus,the proposed FPTR-IT may have a promising application prospect in remote arid areas or islands to provide different grades of heat for electricity and freshwater production.展开更多
In this article,a new evaporative condenser with an annular elliptic firmed tube heat exchanger that includes a round inner tube and elliptic outer finned tube was designed and analyzed.The refrigerant flows between t...In this article,a new evaporative condenser with an annular elliptic firmed tube heat exchanger that includes a round inner tube and elliptic outer finned tube was designed and analyzed.The refrigerant flows between the round inner tube and the elliptic outer tube,and it simultaneously exchanges heat with the cooling water in the inner tube,the spray water,and the cooling air flowing past the outer tube.Using field measurement for the traditional round finned tube evaporative condenser in the Futong Metro Station of Line 14 in Beijing,China,the theoretical heat transfer performance of the annular elliptic finned tube evaporative condenser was analyzed and simulated.Compared with a round finned tube heat exchanger,the heat exchange capacity of the annular elliptic finned tube increased by 2.34%to 9.28%;the total heat transfer coefficient increased by 47.42%,and the power consumption of the fan in the air-conditioning system with an annular elliptic finned tube heat exchanger decreased by 11.18%to 14.65%.Therefore,the energy-saving performance and the heat transfer performance of the new annular elliptic finned tube heat exchanger were enhanced compared to the round finned tube heat exchanger.展开更多
Numerical solutions for fully developed laminar flow in internally finned tubes with trapezoidal and triangular fin profiles were given with Finite Element Method (FEM): The heat transfer characteristics were obtained...Numerical solutions for fully developed laminar flow in internally finned tubes with trapezoidal and triangular fin profiles were given with Finite Element Method (FEM): The heat transfer characteristics were obtained and compared under the boundary conditions of uniform heat flux, uniform wall temperature, and the third boundary condition with finite wall thermal conductivity considered. The numerical results show that boundary conditions have pronounced effects on the temperature field.Furthermore, a new mechanism on the heat transfer augmentation of internally finned tubes is proposed.展开更多
Tunneling diodes hold significant promise for future rectification in the terahertz(THz)and visible light spectra,thanks to their femtosecond-scale transit-time tunneling capabilities.In this work,TiN/ZnO/Pt fin tunne...Tunneling diodes hold significant promise for future rectification in the terahertz(THz)and visible light spectra,thanks to their femtosecond-scale transit-time tunneling capabilities.In this work,TiN/ZnO/Pt fin tunneling diodes(FTDs)with tunneling distances of 10 and 5 nm are fabricated,which demonstrate remarkable characteristics,including ultrahigh asymmetry(1.6×10^(4)for 10 nm device and 1.6×10^(3) for 5 nm device),high responsivity(25.3 V^(-1) for 10 nm device and 28.3 V^(-1) for 5 nm device)at zero bias,surpassing the thermal voltage limit of conventional Schottky diodes,and low turn-on voltage(V_(on))of approximately 100 mV for both devices,making them ideal for power conversion applications.Using technology computer-aided design(TCAD)simulations,the observed asymmetry in electronic transport is attributed to the transition between Fowler-Nordheim tunneling(FNT)and trap-assisted tunneling(TAT)under different biasing conditions,as illustrated by the corresponding energy band profiles.Furthermore,by integrating the FTDs,a rectifier bridge circuit is designed and exhibits full-wave rectification behavior,validated through SPICE simulations for THz-band operations.This advancement offers a highly efficient solution for THz-band energy conversion and effective detection applications.展开更多
基金financially supported by the National Natural Science Foundation of China(22478286)。
文摘In this study,four types of spiral fins with varying parameters were mounted on an upstream cylinder,and the effects of spiral fins on the vibration response of heat exchange tubes and the vortex structure in cross flow were studied through experiments and numerical simulations.The results indicate a strong dependency of the cylinder's vibration response on the fin parameters.The results indicate that the vibration response and wake structure of the cylinder are significantly influenced by the parameters of the fins.The introduction of a finned cylinder affects both its own vibration amplitude and frequency,as well as the downstream cylinder.The amplitudes of finned cylinders Ⅰ and Ⅲ are reduced by 57.8% and 59.9%,respectively,compared to the bare cylinder.This reduction helps to restrain vibration and diminishes the amplitudes of the downstream cylinder.Although finned cylinder Ⅱ slightly decreases its own vibration,it increases the amplitude of the downstream cylinder by 13.7%.The mean drag coefficient and the root mean square of the lift coefficient of the finned cylinder are higher than those of the bare cylinder when the finned cylinder is positioned upstream.Smaller pitch and larger equivalent diameter will lead to increased drag,resulting in enhanced vortex shedding in the wake,which amplifies the vibrations of the cylinder in that wake.The downstream of finned cylinder Ⅱ has the widest wake and higher vortex strength,and the dynamic load and vibration of the downstream cylinder are increased.The vortex intensity decays faster in the wake of finned cylinder Ⅲ,and the vibration of the downstream cylinder is weaker.
文摘In this paper, the standard k-ε two-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By variable transformation, the original 3-D problem is converted into a 2-D problem in spiral coordinates. The algorithm of SIMPLEC is used to study the fully developed fluid flow and heat transfer in the spiral finned tube at constant periphery temperature and constant axial heat flux. The computed results agree pretty well with the experimental data obtained from the industry. Further studies on the fluid flows and temperature profiles at different Reynolds numbers within straight and spiral finned tubes are conducted and the mechanisms involved are explored. It is found that with the spiral finned tube, pressure drop increases to a great extent whereas heat transfer tends to be decreased.
文摘Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was shown that pathlines remain mostly circular for different geometries. Moreover, the contributions of fin periphery, fin side and bare tube to heat transfer were specified. It was shown that the heat transfer per unit area of fin periphery can be several times that of other parts. Moreover, in higher finspacing, the heat transfer from the bare tube can be more important than fin sides.
文摘The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder.The solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinders at uniform temperatures and concentrations.Buoyancy effects are also considered,with the Boussinesq approximation.The forced convection effect is induced by the outer cylinder rotating with an angular velocity(ω)in an anti-clockwise direction.The studies are made for various combinations of dimensionless numbers;buoyancy ratio number(N),Lewis number(Le),Richardson number(Ri)and Grashof number(Gr).The isotherms,isoconcentrations and streamlines as well as both average and local Nusselt and Sherwood numbers were studied.A finite volume scheme is adopted to solve the transport equations for continuity,momentum,energy and mass transfer.The results indicate that the use of fins on the inner cylinder with outer cylinder rotation,significantly improves the heat and mass transfer in the annulus.
基金supported by the National Natural Science Foundation of China(21902097,21636006 and 21761132025)the China Postdoctoral Science Foundation(2019M653861XB)+1 种基金the Natural Science Foundation of Shaanxi Province(2020JQ-409)the Fundamental Research Funds for the Central Universities(GK201901001 and GK202003035)。
文摘Oxidative dehydrogenation of propane with carbon dioxide(CO_(2)-ODP)characterizes the tandem dehydrogenation of propane to propylene with the reduction of the greenhouse gas of CO_(2)to valuable CO.However,the existing catalyst is limited due to the poor activity and stability,which hinders its industrialization.Herein,we design the finned Zn-MFI zeolite encapsulated noble metal nanoparticles(NPs)as bifunctional catalysts(NPs@Zn-MFI)for CO_(2)-ODP.Characterization results reveal that the Zn2+species are coordinated with the MFI zeolite matrix as isolated cations and the NPs of Pt,Rh,or Rh Pt are highly dispersed in the zeolite crystals.The isolated Zn2+cations are very effective for activating the propane and the small NPs are favorable for activating the CO_(2),which synergistically promote the selective transformation of propane and CO_(2)to propylene and CO.As a result,the optimal 0.25%Rh0.50%Pt@Zn-MFI catalyst shows the best propylene yield,satisfactory CO_(2)conversion,and long-term stability.Moreover,considering the tunable synergetic effects between the isolated cations and NPs,the developed approach offers a general guideline to design more efficient CO_(2)-ODP catalysts,which is validated by the improved performance of the bifunctional catalysts via simply substituting Sn4+cations for Zn2+cations in the MFI zeolite matrix.
基金the financial support through Research University Grant and Fundamental Research Grant Scheme(Vot nos.04H46 and 4F224)Chemical Engineering Department,Universiti Teknologi PETRONAS for its support
文摘This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crystallizer has been designed, the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature. The model is developed based on the basic heat transfer equation, and by considering the solution's and the coolant's convective heat transfer coefficient(h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model. Consequently, the study found that the model helps in enhancing the PFC system.
文摘The height, thickness and spacing of fins have an impact on the thermal characteristics of a radiator. The calculation of heat output and metal thermal intensity for cast iron finned radiator are given by using heat transfer formula of vertical plate and parallel fins. Each factor having effect on the metal thermal intensity of a radiator is analyzed and the optimum structure parameters of a radiator are given in order to maximize metal thermal intensity.
基金Supported by the National Key Research and Development Plan Program(No.2022YFB4701101)National Natural Science Foundation of Chi-na(No.U1913211)Natural Science Foundation of Hebei Province of China(No.F2021202062)。
文摘With the widespread use of high-power and highly integrated insulated gate bipolar transistor(IGBT),their cooling methods have become challenging.This paper proposes a liquid cooling scheme for heavy-duty automated guided vehicle(AGV)motor driver in port environment,and improves heat dissipation by analyzing and optimizing the core component of finned heat sink.Firstly,the temperature distribution of the initial scheme is studied by using Fluent software,and the heat transfer characteristics of the finned heat sink are obtained through numerical analysis.Secondly,an orthogonal test is designed and combined with the response surface methodology to optimize the structural parameters of the finned heat sink,resulting in a 14.57%increase in the heat dissipation effect.Finally,the effectiveness of heat dissipation enhancement is verified.This work provides valuable insights into improving the heat dissipation of IGBT modules and heat sinks,and provides guidance for their future applications.
文摘This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.
文摘This work contributes to the improvement of energy-saving in air conditioning systems. The objective is to apply the thermal efficiency of heat exchangers for localized determination of the thermal performance of heat exchangers with individually finned heat pipes. The fundamental parameters used for performance analysis were the number of fins per heat pipe, the number of heat pipes, the inlet temperatures, and the flow rates of hot and cold fluids. The heat exchanger under analysis uses Freon 404A as a working fluid in an air conditioning system for cooling in the Evaporator and energy recovery in the Condenser. The theoretical model is localized and applied individually to the Evaporator, Condenser, and heat exchanger regions. The results obtained through the simulation are compared with experimental results that use a global approach for the heat exchanger. The thermal quantities obtained through the theoretical model in the mentioned regions are air velocity, Nusselt number, thermal effectiveness, heat transfer rate, and outlet temperature. The comparisons made with global experimental results are in excellent agreement, demonstrating that the localized theoretical approach developed is consistent and can be used as a comprehensive analysis tool for heat exchangers using heat pipes.
文摘This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material(PCM)inside a rectangular enclosure heated by multiple discrete pulsed protruding heat sources.The fin and the phase change material filling the enclosure store the thermal energy extracted from the heat sources,in sensible and latent forms.The heat sources are assumed to simulate electronic components undergoing a superheating technical issue.By extracting heat from the electronics,the PCM plays the role of a heat sink.To analyze the thermal behavior and predict the cooling performance of the proposed cooling system,we derive a nonlinear mathematical model based on mass,momentum and energy conservation laws.Several numerical investigations are conducted to quantify the influence of the fin position on the thermal behavior and the cooling performance of the heat sink.Predictions include the transient maximum temperature occurring inside the heat sources and the liquid volume.A comparison between our numerical results and experimental data selected from the literature shows a good agreement.The main conclusion is that the presence of the fin leads to a slight increase in the melting time.
基金the support from the National Science and Technology Major Project,China(No.2022-Ⅲ-0003-0012)。
文摘This study aims to investigate the output work and temperature drop in a compressor disk cavity equipped with a Finned Vortex Reducer(FVR)to improve the performance of the secondary air system of gas turbine engines.Based on the experimentally validated simulation results,we explore the effects of the rotating speed of the disk,coolant mass flow rate and the size of the fin on the flow and energy transfer of the radial inflow in the rotating cavity.The results show that the circumferential acceleration of the flow by Coriolis force is inhibited by the radial assembled fins from the rotating coordinate system,forcing the swirl ratio into one in the finned region and resulting in the reduction of the pressure drop.Outside the finned region,the variation characteristics of the swirl ratio follows that of a free vortex,which is typically found in the radial inflow through a simple cavity,i.e.,cavity without any vortex reducer.For the output work of the FVR cavity flow,it is mainly caused by the pressure difference on the fin surfaces,while those by the viscous shear force could be neglected.We propose a simplified model to predict the output work and total temperature change in the FVR cavity,which generally matches well with the simulation result.The research findings can provide guidance for the design and optimization of secondary air system in gas turbines.
基金funded by the National Natural Science Foundation of China(52375274)the Key R&D Project of Zhejiang Province(2023C01066,2024C01120,2024C01116)the Key R&D Project of Hangzhou(2023SZD0049,2023SZD0111,2023SZD0080)。
文摘The Heat Recovery Steam Generators(HRSGs)are designed to recapture heat from gas turbine exhaust to generate electric power by a steam turbine.Finned tubes are critical heat transfer components of HRSG,whose design and optimization play an essential role in realizing effective energy utilization in power plants.In this study,an optimization method with multi-layered neural network(MNN)and tree-structured parzen estimator(TPE)is proposed for the finned tube heat exchanger with curved serration.This method has high fitting accuracy and global optimization efficiency,and is suitable for complex heat transfer design and optimization problems caused by novel irregular finned tubes.The developed thermal-fluid model is validated with existing experimental data,and a satisfactory agreement is found in terms of Nusselt number and Fanning friction factor.It is shown that increasing the curved serration angle is beneficial to destroy the thermal boundary layer and enhance turbulent kinetic energy.When the Reynolds number is between 5000 and 25000,the heat transfer factor of finned tubes with a curved serration angle of 10°is 20%higher than that of flat serrated finned tubes on average.The optimized geometric parameters are obtained from the optimization approach,and the optimal solution has achieved excellent results in comprehensive performance.Compared with the baseline design,the optimized results show a 9%higher heat transfer factor,which is better than those based on commonly used optimization methods.
文摘Enhancing the efficiency of phase-change heat storage is vital for maximizing the utilization of renewable energy.This study examines the synergistic effect of non-uniformly shaped fins and nanoparticles on the melting performance of phase-change storage tanks.The problem is addressed using a finite volume framework coupled with the enthalpy–porosity method,with the numerical model rigorously validated against experimental data.The analysis explores the influence of varying fin deflection angles and nanoparticle concentrations on melting dynamics.It is shown that a downward fin deflection of 6◦reduces melting time to 570 s,representing a 20.8% improvement over uniform fins.Introducing 1% nanoparticles further accelerates melting,reducing time by 36.54% compared to the nanoparticle-free case.The combined strategy of 6◦fin deflection and 1%nanoparticle addition shows the most economic heat storage rate,achieving an exceptional 80.74% enhancement relative to a tank with uniform fins.
基金supported by National Science and Technology Major Project of China(Grant numbers 2024ZD06049××)State Key Laboratory of Precious Metal Functional Materials(Grant No.YPML-20240502045).
文摘Direct brazing was employed to fabricate a“Cu circuit layer-Si_(3)N_(4) ceramic-Cu heat sink”structure for power electronic devices,enabling a shortened heat dissipation path and enhanced thermal management.Structural components(60 mm×60 mm and 30 mm×30 mm)were brazed at 780°C for 20 min to simulate finless and finned heat sinks.The effects of composite brazing filler metal and copper underlayer stiffness on warpage and thermal resistance were systematically evaluated.The results show that composite fillers effectively suppressed warpage,reducing deformation in a 60×60 mm²-finned component from 0.95%to 0.73%,with a measured thermal resistance of 0.1936 K/W.After surface soldering of the insulated gate bipolar transistor(IGBT),the total thermal resistance from junction to ambient decreased by 10.2%compared with conventional structures.This study demonstrates a practical route to improve heat dissipation and optimize the thermal design of highpower modules,providing an industry-ready thermal management solution for high-power-density SiC/GaN devices.
基金supported by the China Postdoctoral Science Foundation(Grant No.2020M672344)。
文摘Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which can provide different grades of thermal energy with two heat transfer fluids(oil and water),is designed to improve thermal efficiency.In this FPTR-IT,an inner tube and straight fins are employed to respectively lessen heat loss at upper and lower parts of the absorber.Based on the design,a numerical model is developed to investigate its performance.Comparisons with other PTRs indicate that the FPTR-IT can combine the advantages of PTR with inner tube and finned PTR and obtain the best performance.Moreover,performance evaluation under broad ranges of direct normal irradiances(300–1000 W/m^(2)),flow rates(50–250 L/min)and inlet temperatures(400–600 K)of oil as well as flow rates(3.6–10 L/min)and inlet temperatures(298.15–318.15 K)of water is investigated.Compared with conventional PTR,heat loss is reduced by 20.7%–63.2%and total efficiency is improved by 0.03%–4.27%.Furthermore,the proportions of heat gains for water and oil are located in 8.3%–73.9%and-12.0%–64.3%,while their temperature gains are located in 11.6–37.9 K and-1.2–19.6 K,respectively.Thus,the proposed FPTR-IT may have a promising application prospect in remote arid areas or islands to provide different grades of heat for electricity and freshwater production.
基金The work was supported by the Natural Science Foundation of Shaanxi Province(No.2018JM5084)“the 13th Five-Year”National Science and Technology Major Project of China(No.2017YFC0702202)+1 种基金the Shaanxi Key Science and Technology Innovative Tea m Project(No.2016KCT-22)the Fundamental Research Funds for the Central Universities(CHD300102289203).
文摘In this article,a new evaporative condenser with an annular elliptic firmed tube heat exchanger that includes a round inner tube and elliptic outer finned tube was designed and analyzed.The refrigerant flows between the round inner tube and the elliptic outer tube,and it simultaneously exchanges heat with the cooling water in the inner tube,the spray water,and the cooling air flowing past the outer tube.Using field measurement for the traditional round finned tube evaporative condenser in the Futong Metro Station of Line 14 in Beijing,China,the theoretical heat transfer performance of the annular elliptic finned tube evaporative condenser was analyzed and simulated.Compared with a round finned tube heat exchanger,the heat exchange capacity of the annular elliptic finned tube increased by 2.34%to 9.28%;the total heat transfer coefficient increased by 47.42%,and the power consumption of the fan in the air-conditioning system with an annular elliptic finned tube heat exchanger decreased by 11.18%to 14.65%.Therefore,the energy-saving performance and the heat transfer performance of the new annular elliptic finned tube heat exchanger were enhanced compared to the round finned tube heat exchanger.
文摘Numerical solutions for fully developed laminar flow in internally finned tubes with trapezoidal and triangular fin profiles were given with Finite Element Method (FEM): The heat transfer characteristics were obtained and compared under the boundary conditions of uniform heat flux, uniform wall temperature, and the third boundary condition with finite wall thermal conductivity considered. The numerical results show that boundary conditions have pronounced effects on the temperature field.Furthermore, a new mechanism on the heat transfer augmentation of internally finned tubes is proposed.
基金National Key Research and Development Program of China(2024YFA1410700,2021YFA1200700)National Natural Science Foundation of China(62474065,T2222025,62174053)+3 种基金Natural Science Foundation of Chongqing(CSTB2024NSCQ-JQX0005)Shanghai Science and Technology Innovation Action Plan(24QA2702300,24YF2710400)National Postdoctoral Program(GZB20240225)Fundamental Research Funds for the Central Universities。
文摘Tunneling diodes hold significant promise for future rectification in the terahertz(THz)and visible light spectra,thanks to their femtosecond-scale transit-time tunneling capabilities.In this work,TiN/ZnO/Pt fin tunneling diodes(FTDs)with tunneling distances of 10 and 5 nm are fabricated,which demonstrate remarkable characteristics,including ultrahigh asymmetry(1.6×10^(4)for 10 nm device and 1.6×10^(3) for 5 nm device),high responsivity(25.3 V^(-1) for 10 nm device and 28.3 V^(-1) for 5 nm device)at zero bias,surpassing the thermal voltage limit of conventional Schottky diodes,and low turn-on voltage(V_(on))of approximately 100 mV for both devices,making them ideal for power conversion applications.Using technology computer-aided design(TCAD)simulations,the observed asymmetry in electronic transport is attributed to the transition between Fowler-Nordheim tunneling(FNT)and trap-assisted tunneling(TAT)under different biasing conditions,as illustrated by the corresponding energy band profiles.Furthermore,by integrating the FTDs,a rectifier bridge circuit is designed and exhibits full-wave rectification behavior,validated through SPICE simulations for THz-band operations.This advancement offers a highly efficient solution for THz-band energy conversion and effective detection applications.
