This study investigates the enhancement of convective heat transfer in a serpentine pipe using ferrofluid flow influenced by dual non-uniform magnetic sources.The primary objective is to improve thermal performance in...This study investigates the enhancement of convective heat transfer in a serpentine pipe using ferrofluid flow influenced by dual non-uniform magnetic sources.The primary objective is to improve thermal performance in compact cooling systems,such as those used in heat exchangers.A two-dimensional,steady-state Computational Fluid Dynamic(CFD)model is developed in ANSYS Fluent to simulate the behavior of an incompressible ferrofluid under applied constant heat flux and magnetic fields.The magnetic force is modeled using the Kelvin force,which acts on magnetized nanoparticles in response to spatially varying electromagnetic fields generated by two strategically positioned current-carrying wires.The effects of magnetic field strength,quantified by the magnetic number(Mn),on flow behavior and temperature distribution are thoroughly analyzed.The results indicate that increasing Mn leads to higher Nusselt numbers,demonstrating enhanced convective heat transfer.Secondary vortices induced by magnetic forcing improve fluid mixing,particularly in curved regions of the pipe.A mesh-independence study and model validation with benchmark data support the reliability of the numerical framework.This work highlights the potential of magnetic-field-assisted thermal control in energy-efficient cooling applications and provides a foundation for the further development of advanced ferrofluid-based heat transfer systems.展开更多
Regenerative catalytic oxidizers(RCO)are widely used to remove volatile organic compounds(VOCs)due to their energy-saving and stability.In this study,a multi-component catalytic reaction model was constructed to numer...Regenerative catalytic oxidizers(RCO)are widely used to remove volatile organic compounds(VOCs)due to their energy-saving and stability.In this study,a multi-component catalytic reaction model was constructed to numerically investigate the reaction process of hydrocarbon-containing VOCs in RCO using computational fluid dynamics(CFD)simulation.To obtain the conversion characteristics of multi-component hydrocarbons,the effects of intake load,equivalence ratio,and the composition of multi-component hydrocarbons on the flow,heat transfer,and conversion rate of the reactor were analyzed.A feasibility study plan targeting the hard-to-convert components was also proposed.The results indicated that as the load increases,the conversion rates of the various components decrease,while the reaction rates increase.Moreover,increasing the flow velocity intensifies turbulence and enhances the collision frequency between the gas and the wall surfaces.This,in turn,amplifies the resistance effect of the porous medium.As the equivalence ratio of VOCs to oxygen increases,the oxygen-deficient condition leads to a decrease in the molecular weight of the hydrocarbons involved in the reaction.The reaction temperature also shows a downward trend.A comparative analysis of the catalytic combustion characteristics of multi-component VOCs and single-component gases reveals that adding ethane and propane can facilitate methane oxidation.展开更多
The buoyancy-induced flow constitutes a core scientific issue for thermal management of electronic devices and thermal design of energy systems,where accurate characterization of flow and heat transfer is essential to...The buoyancy-induced flow constitutes a core scientific issue for thermal management of electronic devices and thermal design of energy systems,where accurate characterization of flow and heat transfer is essential to improve thermal efficiency.In this work,buoyancy-induced flow above two heating elements flush-mounted at the bottom of a square enclosure containing air is numerically investigated over a range of Rayleigh numbers(0<Ra≤1.5×10^(8)),with a focus on equal and unequal heat flux conditions under a constraint of constant total thermal energy input.Distinct flow transitions are observed in both cases,leading to the identification of three flow regimes:Steady,periodic unsteady,and chaotic unsteady.Two types of periodic flows are distinguished,in which the first is a periodic flow dominated by a fundamental frequency(FF)and its integer-multiple frequencies(INTMF),while the second is a more complex periodic flow featuring FF,INTMF,and their sub-harmonics.The transitions between these regimes are affected by the relative heat flux of the two heaters.When the heat flux of the two heaters is unequal,the range of Rayleigh numbers corresponding to periodic flow is suppressed.It is also found that the time-averaged maximum temperature of the strong heater increases more rapidly with Ra,while that of the weak heater increases more slowly,reflecting the interaction between buoyancy-driven flow dynamics and asymmetric heat input.Analysis of the time-averaged Nusselt number demonstrates that heat dissipation from the isothermal walls remains roughly equivalent,even when the heat flux of the two heaters differs by a factor of two.These findings highlight the critical roles of Rayleigh number,the number of heaters,and the heat flux ratio of the heaters in determining heat transfer and flow characteristics for buoyancy-driven convection systems,providing important theoretical support and design references for engineering scenarios such as electronic devices and design of new energy systems.展开更多
Van der Waals(vdW)heterostructures have attracted much attention due to their distinctive optical,electrical,and thermal properties,demonstrating promising potential in areas such as photocatalysis,ultrafast photonics...Van der Waals(vdW)heterostructures have attracted much attention due to their distinctive optical,electrical,and thermal properties,demonstrating promising potential in areas such as photocatalysis,ultrafast photonics,and free electron radiation devices.Particularly,they are promising platforms for studying thermionic emission.It is illustrated that using vdW heterostructure-based thermionic emission can enhance heat transfer in vacuum devices.As a proof of concept,the approach is demonstrated to offer a promising solution for the long-standing overheating issue in X-ray tubes.Specifically,it is shown that the saturated target temperature of a 2000 W X-ray tube can be reduced from around 1200℃ to 490℃.Additionally,it is also demonstrated that by reducing the height of the Schottky barrier formed in the vdW heterostructures,the thermionic cooling performance can be enhanced.The findings pave the way for the development of high-power X-ray tubes.展开更多
In response to the actual demands of the energy storage type organic Rankine power generation cycle,this study proposes a new type of jacketed shell and tube heat exchanger with integrated cold storage and heat exchan...In response to the actual demands of the energy storage type organic Rankine power generation cycle,this study proposes a new type of jacketed shell and tube heat exchanger with integrated cold storage and heat exchange.N-tedecane is selected as the phase change material for cold storage,low-temperature water as the cold source,and R134a as the heat source.The phase change material for cold storage is filled inside the jacket tube of the heat exchanger.Cold fluid is introduced into the inner tube to cause the phase change material to condense and store cold.After the cold storage is completed,R134a flows in from the shell side and condenses through heat exchange with the solidified phase change material for energy storage.This study discusses the influence laws of different cold water mass flow rates and temperatures on the cold storage performance of this heat exchanger,and analyzes the condensation effect of R134a.The results show that when the mass flow rate is 0.5 kg/s and the cold water temperature is between 3 and 4℃,the average power of the energy storage heat exchanger in the condensation experiment is 80W,and the average convective heat transfer coefficient is 110.73 W/(m^(2)⋅K).This research provides an experimental basis for the development of energy storage organic Rankine power generation cycles.展开更多
The growing need for enhanced heat dissipation is compelling the development of more effective heat exchangers.Innovation inspired by nature bionics,four types of leaf-shaped pin fins were proposed and four combinatio...The growing need for enhanced heat dissipation is compelling the development of more effective heat exchangers.Innovation inspired by nature bionics,four types of leaf-shaped pin fins were proposed and four combinations of them were considered.The leaf-shaped design of the cooling pin fin enhances uniformity and synergy,effectively creating an optimized flow path that boosts cooling performance.Eight three-dimensional conjugate heat transfer models in staggered arrangement were developed using ANSYS-Fluent software.Aluminum6061material was used as the heat sinkmaterial and single-phase liquid water flowed through the rectangular channel where the Reynolds(R_(e))number varies from 40 to 100.Using the same boundary conditions as the software simulations,two leaf-shaped channels were printed to validate numerical models.Velocity field and temperature differences of the eight proposed leaf-shaped pin fins configurations were discussed by comparison with cylindrical pin fins.Based on the findings of this study,at a Reynolds number of 80,the Leaf B Staggered Array(LBSA)records a maximum temperature that is 0.72 K lower than that of the cylindrical pin fins arrangement.Additionally,the LBSA exhibits a reduction in the friction factor by approximately 33.3%relative to the circular pin fins array under the same R_(e).This implies that the design of LBSA has been optimized to provide better heat dissipation performance while maintaining lower energy consumption.Furthermore,the LBSA demonstrates the most favorable thermal-hydraulic performance index(TPI),which is 1.18 times higher than that of the circular pin fins arrangement at R_(e)=80.The temperature reduction and friction factor reduction of the lobed channel is more pronounced than that of the conventional cooling channel,highlighting its potential to increase heat transfer efficiency and reduce energy consumption in practical applications.展开更多
The use of nanofluids as heat transfer media represents an innovative strategy to enhance heat transfer performances.This study investigates experimentally the turbulent convective heat transfer characteristics of wat...The use of nanofluids as heat transfer media represents an innovative strategy to enhance heat transfer performances.This study investigates experimentally the turbulent convective heat transfer characteristics of waterbased nanofluids containing TiO_(2),CuO,and graphene nanoplatelet(GNP)nanoparticles as they flow through a copper tube.Both the dynamic viscosity and thermal conductivity of these nanofluids were modeled and experimentally measured across varying nanoparticle concentrations(0.01,0.02,and 0.03 vol.%)and temperatures(25℃,35℃,and 45℃).The findings indicate that the behavior of nanofluids depends on the parameter used for comparison with the base fluid.Notably,both the friction factor and heat transfer coefficient increase with higher nanoparticle volume concentrations at a constant Reynolds number.The results further reveal that the GNP/water nanofluid,with a volume concentration of 0.03%at 45℃,exhibit the highest Nusselt number,followed by the CuO/water and TiO_(2)/water nanofluids,with respective increases of 17.8%,11.09%,and 8.11%.展开更多
The latent heat thermal energy storage system with solid-liquid phase-change material(SLPCM-LHTES)as energy storage medium provides outstanding advantages such as system simplicity,stable temperature control,and high ...The latent heat thermal energy storage system with solid-liquid phase-change material(SLPCM-LHTES)as energy storage medium provides outstanding advantages such as system simplicity,stable temperature control,and high energy storage density,showing great potential toward addressing the energy storage problems associated with decentralized,intermittent,and unstable renewable energy sources.Notably,effective heat transfer within the SLPCM-LHTES is crucial for extending its application potential.Therefore,a comprehensive understanding of the heat transfer processes in SLPCM-LHTES from a theoretical perspective is necessary.In this review,we propose a three-stage heat transfer pathway in SLPCM-LHTES,including external heating,interfacial heat transfer,and intrinsic phase transition processes.From the perspective of this three-stage pathway,the theoretical basis of heat transfer processes and typical efficiency enhancement strategies in SLPCM-LHTES are summarized.Moreover,an overview of the typical applications of SLPCM-LHTES in various fields,such as building energy efficiency,textiles and garments,and battery thermal management,is presented.Finally,the remaining challenges and possible avenues of research in this burgeoning field will also be discussed.展开更多
The overall heat transfer coefficient(OHTC)of rock fractures is a fundamental parameter for characterizing the heat transfer behavior of rock fractures in hot dry rock(HDR)geothermal mining.Although a number of practi...The overall heat transfer coefficient(OHTC)of rock fractures is a fundamental parameter for characterizing the heat transfer behavior of rock fractures in hot dry rock(HDR)geothermal mining.Although a number of practical formulae for heat transfer coefficients have been developed in the literature,there is still no widely accepted analytical solution.This paper constructs highly accurate analytical solutions for the temperatures of the inner fracture wall and the fluid.Then they are employed to develop new definition-based formulae(formula A and its simplification formula B)of the OHTC,which are well validated by the experimental and numerical simulation results.An empirical correlation formula of heat transfer coefficient is proposed based on the definition-based formulae which can be directly used in the numerical simulations of heat transfer in rock fractures.A site-scale application example of numerical simulation also demonstrates the effectiveness of the empirical correlation formula.展开更多
Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass rat...Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass ratio,has not been systematically carried out.In this paper,the heat transfer and flow characteristics of related high temperature fuels are studied by using typical engine parallel channel structure.Through numeri⁃cal simulation and systematic experimental verification,the flow and heat transfer characteristics of parallel chan⁃nels under typical working conditions are obtained,and the effectiveness of high-precision calculation method is preliminarily established.It is known that the stable time required for hot start of regenerative cooling engine is about 50 s,and the flow resistance of parallel channel structure first increases and then decreases with the in⁃crease of equivalence ratio(The following equivalence ratio is expressed byΦ),and there is a flow resistance peak in the range ofΦ=0.5~0.8.This is mainly caused by the coupling effect of high temperature physical proper⁃ties,flow rate and pressure of fuel in parallel channels.At the same time,the cooling and heat transfer character⁃istics of parallel channels under some conditions of high heat-mass ratio are obtained,and the main factors affect⁃ing the heat transfer of parallel channels such as improving surface roughness and strengthening heat transfer are mastered.In the experiment,whenΦis less than 0.9,the phenomenon of local heat transfer enhancement and deterioration can be obviously observed,and the temperature rise of local structures exceeds 200℃,which is the risk of structural damage.Therefore,the reliability of long-term parallel channel structure under the condition of high heat-mass ratio should be fully considered in structural design.展开更多
As the dominant seepage channel in rock masses,it is of great significance to study the influence of fracture roughness distribution on seepage and heat transfer in rock masses.In this paper,the fracture roughness dis...As the dominant seepage channel in rock masses,it is of great significance to study the influence of fracture roughness distribution on seepage and heat transfer in rock masses.In this paper,the fracture roughness distribution functions of the Bakhtiary dam site and Oskarshamn/Forsmark mountain were fitted using statistical methods.The COMSOL Multiphysics finite element software was utilized to analyze the effects of fracture roughness distribution types and empirical formulas for fracture hydraulic aperture on the seepage field and temperature field of rock masses.The results show that:(1)The fracture roughness at the Bakhtiary dam site and Oskarshamn/Forsmark mountain follows lognormal and normal distributions,respectively;(2)For rock masses with the same expected value and standard deviation of fracture roughness,the outflow from rock masses with lognormal distribution of fracture roughness is significantly larger than that of rock masses with normal distribution of fracture roughness;(3)The fracture hydraulic aperture,outflow,and cold front distance of the Li and Jiang model are significantly larger than those of the Barton model;(4)The outflow,hydraulic pressure distribution,and temperature distribution of the Barton model are more sensitive to the fracture roughness distribution type than those of the Li and Jiang model.展开更多
Utilizing superwettability micro/nanostructures to enhance the condensation heat transfer(CHT)performance of engineering materials has attracted great interest due to its values in basic research and technological inn...Utilizing superwettability micro/nanostructures to enhance the condensation heat transfer(CHT)performance of engineering materials has attracted great interest due to its values in basic research and technological innovations.Currently,exploring facile micro/nanofabrication approaches to create high-efficiency CHT surfaces has been one of research hotspots.In this work,we propose and demonstrate a type of new superwettability hybrid surface for high-efficiency CHT,which consists of superhydrophobic nanoneedle arrays and triangularly-patterned superhydrophilic microdots(SMDs).Such hybrid surface can be fabricated by the facile growth of densely-packed ZnO nanoneedles on the Zn-electroplated copper surface followed by fluorosilane modification and mask-assisted photodegradation.Through regulating the diameters and interspaces of SMDs,we obtain the optimized triangularly-patterned hybrid surface,which shows 42.7%higher CHT coefficient than the squarely-patterned hybrid surface and 58.5%higher CHT coefficient than the superhydrophobic surface.The key of such hybrid surface design is to considerably increase CHT coefficient brought about by SMD-triggered drop sweeping at the cost of slightly reducing heat transfer area of superhydrophobic functional zone for drop jumping.Such new strategy helps develop advanced CHT surfaces for high-efficiency electronic cooling and energy utilization.展开更多
This comprehensive research examines the dynamics of magnetohydrodynamic(MHD)flow and heat transfer within a couple stress fluid.The investigation specifically focuses on the fluid’s behavior over a vertical stretchi...This comprehensive research examines the dynamics of magnetohydrodynamic(MHD)flow and heat transfer within a couple stress fluid.The investigation specifically focuses on the fluid’s behavior over a vertical stretching sheet embedded within a porous medium,providing valuable insights into the complex interactions between fluid mechanics,thermal transport,and magnetic fields.This study accounts for the significant impact of heat generation and thermal radiation,crucial factors for enhancing heat transfer efficiency in various industrial and technological contexts.The research employs mathematical techniques to simplify complex partial differential equations(PDEs)governing fluid flow and heat transfer.Specifically,suitable similarity transformations are applied to convert the PDEs into a more manageable system of ordinary differential equations(ODEs).The homotopy perturbation method(HPM)is employed to derive approximate analytical solutions for the problem.The influences of key parameters,such as magnetic field strength,heat generation,thermal radiation,porosity,and couple stress,on velocity and temperature profiles are analyzed and discussed.Findings indicate that the mixed convection parameter positively affects flow velocity,while the magnetic field parameter significantly alters the flow dynamics,exhibiting an inverse relationship.Further,this type of flow behavior model is relevant to real-world systems like cooling of nuclear reactors and oil extraction through porous formations,where magnetic and thermal effects are significant.展开更多
We are pleased to introduce this special thematic section on Nanofluid Mechanics and Heat Transfer that is being included in Acta Mechanica Sinica(AMS).This thematic issue consists of 6 papers selected from papers tha...We are pleased to introduce this special thematic section on Nanofluid Mechanics and Heat Transfer that is being included in Acta Mechanica Sinica(AMS).This thematic issue consists of 6 papers selected from papers that were presented at the 18th International Symposium on Numer-ical Analysis of Fluid Flows,Heat and Mass Transfer-Nu-merical Fluids 2023,held in Heraklion,Crete Greece,11-17 September 2023,and invited through a general call.The symposium covers various subjects:from new numerical methods and fundamental research until engineering appli-cations,and it is a part of the International Conference of Numerical Analysis and Applied Mathematics(ICNAAM),held annually.展开更多
This study aims to elucidate the connection between the shape factor of GO(graphene oxide)nanoparticles and the behavior of blood-based non-aligned,2-dimensional,incompressible nanofluid flow near stagnation point,und...This study aims to elucidate the connection between the shape factor of GO(graphene oxide)nanoparticles and the behavior of blood-based non-aligned,2-dimensional,incompressible nanofluid flow near stagnation point,under the influence of temperature-dependent viscosity.Appropriate similarity transformations are employed to transform the non-linear partial differential equations(PDEs)into ordinary differential equations(ODEs).The governing equations are subsequently resolved by utilizing the shooting method.The modified Maxwell model is used to estimate the thermal efficiency of the nanofluid affected by different nanoparticle shapes.The impact of various shapes of GO nanoparticles on the velocity and temperature profiles,along with drag forces and heat flux at the stretching boundary,are examined with particular attention to factors such as viscosity changes.Numerical findings are based on the constant concentration of ϕ=5% with nanoparticles measuring 25 nm in size.The influence of different shapes of GO nanoparticles is analyzed for velocity,temperature distributions,as well as drag forces,and heat transfer at the stretching boundary.The velocity profile is highest for spherical-shaped nanoparticles,whereas the blade-shaped particles produced the greatest temperature distribution.Additionally,itwas observed that enhancing the nanoparticles’volume fraction from 1%to 9%significantly improved the temperature profile.Streamline trends are more inclined to the left when the stretching ratio parameter B=0.7 is applied,and a similar pattern is noted for the variable viscosity case with m=0.5.Furthermore,the blade-shaped nanoparticles exhibit the highest thermal conductivity,while the spherical-shaped nanoparticles display the lowest.展开更多
This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,...This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.展开更多
A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the in...A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the increasing number of droplet ejection experiments,the peak heat fluxes between droplet and substrate decreased firstly(1rd–5th ejection),then increased(5th–7th ejection),and finally decreased again(>7th ejection).In the first five experiments,the interfacial thermal resistance between the droplet and the substrate improved with increasing film thickness.However,at the onset of the 6th droplet ejection experiment,the deposited film initiated its melting process due to the accumulated thermal resistance,which has the potential to eradicate the cavity or air space existing between the droplet and the substrate.Consequently,the interfacial contact condition was improved gradually with the increasing melting area from 5th to 7th droplet ejection experiments,leading to an increase in heat fluxes.Increased SiO_(2) content in deposited films for 3.5 wt.%Si steel led to lower peak heat fluxes than for 2.5 wt.%Si steel.The solidification structure of the 2.5 wt.%Si steel droplet sample comprised a fine grain zone at the base,a columnar grain zone in the center,and an equiaxed grain zone at the top.However,the solidification structure of the 3.5 wt.%Si steel droplet only contained columnar grains and equiaxed grains,with a larger average grain size due to the lower interfacial heat flux.展开更多
Plate heat exchangers suffer from significant energy losses,which adversely affect the overall efficiency of thermal systems.To address this challenge,various heat transfer enhancement techniques have been investigate...Plate heat exchangers suffer from significant energy losses,which adversely affect the overall efficiency of thermal systems.To address this challenge,various heat transfer enhancement techniques have been investigated.Notably,the incorporation of surface corrugations is widely recognized as both effective and practical.Chevron corrugation is the most employed design.However,there remains a need to investigate alternative geometries that may offer superior performance.This study aims to find a novel corrugation design by conducting a comparative CFD analysis of flat,square,chevron,and cylindrical corrugated surfaces,assessing their impact on heat transfer enhancement within a plate heat exchanger.ANSYS Fluent software was used for simulation at four distinct Reynolds numbers(10,000,18,000,26,000,and 28,000),with a heat flux of 12,000 W/m^(2).A structured mesh was generated using Pointwise software.The material of the solid plates was modelled as aluminum,the fluid was modelled as water,and the flow was turbulent.To obtain a fully developed turbulent flow,a separate inlet duct was modelled,and the output velocity profile of the inlet duct was input into the plate heat exchanger.The Nusselt number(Nu)and heattransfer coefficient(h)were calculated to evaluate the performance of all surfaces.The results indicate that cylindrical corrugated surfaces exhibit higher Nusselt numbers than chevron,square,and flat plates.This higher performance is because of the generation of vortices in the middle of the cylindrical texture.Consequently,flow recirculation occurs,leading to reattachment to the mainstreamflow.This phenomenon induces increased turbulence,thereby enhancing the heat transfer efficiency.To validate the results,a grid-convergence independence test was performed for three different mesh sizes.In addition,empirical calculations were performed using the Dittus-Boelter and the Genilaski equations to validate the results of the flat-plate heat exchanger.It was concluded that the cylinder was the best corrugated surface and had a maximum heat transfer 35%higher than that of a flat plate.展开更多
The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,s...The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,surface wettability modification was found to be highly effective owing to its significant influence on boiling dynamics and heat transfer mechanisms.In this study,we modified surface wettability using a nanocomposite coating composed of graphene nano plate(GNPs)and multi-walled carbon nanotubes(MWCNT)and then examined how the modification affected the transfer of boiling heat in microchannels.The resultant heat transfer coefficients for hydrophilic and hydrophilic composite(GNPs+MWCNT)microchannels were,respectively,42.8%and 33.95%higher compared with that of the uncoated surface.These results verify that hydrophilic GNP-based coating significantly improves boiling heat transfer performance.It was observed that a minor increase in contact angle,θfrom 73.142°to 75.73°,resulted in a noticeable decrease in thermal performance.This is attributed to diminished liquid film stability,reduced nucleation site activity,and weakened capillary-driven liquid replenishment.These findings underscore the crucial role of optimized surface wettability in maintaining efficient microchannel boiling.At high mass flux,the GNPS microchannels exhibited maximum pressure drop values,with a pressure drop ratio as high as 36%compared to 29%for the GNPs+MWCNT composite samples.Nevertheless,when a composite hydrophilic–hydrophobic coating was deposited through electrodeposition,the enhancement in heat transfer was less significant.This was probably due to decreased surface uniformity,diminished liquid film stability,and the disruption of effective nucleation behavior,all associated with the slight increase in surface contact angle.The obtained results can be used as guidance for designing advanced cooling surfaces in high-performance microelectronic and energy systems,where precise control of surface characteristics is critical.展开更多
In exploring hypersonic propulsion,precooler combined engines require the development of lightweight,efficient,and compact heat exchangers(HX).As additive manufacturing technology continues to progress,triply periodic...In exploring hypersonic propulsion,precooler combined engines require the development of lightweight,efficient,and compact heat exchangers(HX).As additive manufacturing technology continues to progress,triply periodic minimal surface(TPMS)structures,characterized by exceptionally high surface area to volume ratios and intricate geometric structures,have demonstrated superior heat transfer performance.This research examines the thermal-hydraulic(TH)behavior of FKS and Diamond as heat transfer structures under different Reynolds numbers through numerical simulations.The Nusselt number for FKS is 13.2%–17.6%higher than Diamond,while the friction factor for FKS is approximately 18.8%–29.3%higher.A detailed analysis of the internal flow mechanisms reveals that the flow pattern within TPMS can be summarized as cyclic convergence-separation-convergence.The fluid experiences constant disturbances from the structure in all spatial directions,generating strong turbulent mixing and large wall shear stresses,which significantly enhance heat transfer performance.展开更多
文摘This study investigates the enhancement of convective heat transfer in a serpentine pipe using ferrofluid flow influenced by dual non-uniform magnetic sources.The primary objective is to improve thermal performance in compact cooling systems,such as those used in heat exchangers.A two-dimensional,steady-state Computational Fluid Dynamic(CFD)model is developed in ANSYS Fluent to simulate the behavior of an incompressible ferrofluid under applied constant heat flux and magnetic fields.The magnetic force is modeled using the Kelvin force,which acts on magnetized nanoparticles in response to spatially varying electromagnetic fields generated by two strategically positioned current-carrying wires.The effects of magnetic field strength,quantified by the magnetic number(Mn),on flow behavior and temperature distribution are thoroughly analyzed.The results indicate that increasing Mn leads to higher Nusselt numbers,demonstrating enhanced convective heat transfer.Secondary vortices induced by magnetic forcing improve fluid mixing,particularly in curved regions of the pipe.A mesh-independence study and model validation with benchmark data support the reliability of the numerical framework.This work highlights the potential of magnetic-field-assisted thermal control in energy-efficient cooling applications and provides a foundation for the further development of advanced ferrofluid-based heat transfer systems.
基金supported by National Key Research&Development Program of China(2022YFB4101500).
文摘Regenerative catalytic oxidizers(RCO)are widely used to remove volatile organic compounds(VOCs)due to their energy-saving and stability.In this study,a multi-component catalytic reaction model was constructed to numerically investigate the reaction process of hydrocarbon-containing VOCs in RCO using computational fluid dynamics(CFD)simulation.To obtain the conversion characteristics of multi-component hydrocarbons,the effects of intake load,equivalence ratio,and the composition of multi-component hydrocarbons on the flow,heat transfer,and conversion rate of the reactor were analyzed.A feasibility study plan targeting the hard-to-convert components was also proposed.The results indicated that as the load increases,the conversion rates of the various components decrease,while the reaction rates increase.Moreover,increasing the flow velocity intensifies turbulence and enhances the collision frequency between the gas and the wall surfaces.This,in turn,amplifies the resistance effect of the porous medium.As the equivalence ratio of VOCs to oxygen increases,the oxygen-deficient condition leads to a decrease in the molecular weight of the hydrocarbons involved in the reaction.The reaction temperature also shows a downward trend.A comparative analysis of the catalytic combustion characteristics of multi-component VOCs and single-component gases reveals that adding ethane and propane can facilitate methane oxidation.
基金supported by the Tianjin Education Commission Research Program Project(No.2024KJ105)。
文摘The buoyancy-induced flow constitutes a core scientific issue for thermal management of electronic devices and thermal design of energy systems,where accurate characterization of flow and heat transfer is essential to improve thermal efficiency.In this work,buoyancy-induced flow above two heating elements flush-mounted at the bottom of a square enclosure containing air is numerically investigated over a range of Rayleigh numbers(0<Ra≤1.5×10^(8)),with a focus on equal and unequal heat flux conditions under a constraint of constant total thermal energy input.Distinct flow transitions are observed in both cases,leading to the identification of three flow regimes:Steady,periodic unsteady,and chaotic unsteady.Two types of periodic flows are distinguished,in which the first is a periodic flow dominated by a fundamental frequency(FF)and its integer-multiple frequencies(INTMF),while the second is a more complex periodic flow featuring FF,INTMF,and their sub-harmonics.The transitions between these regimes are affected by the relative heat flux of the two heaters.When the heat flux of the two heaters is unequal,the range of Rayleigh numbers corresponding to periodic flow is suppressed.It is also found that the time-averaged maximum temperature of the strong heater increases more rapidly with Ra,while that of the weak heater increases more slowly,reflecting the interaction between buoyancy-driven flow dynamics and asymmetric heat input.Analysis of the time-averaged Nusselt number demonstrates that heat dissipation from the isothermal walls remains roughly equivalent,even when the heat flux of the two heaters differs by a factor of two.These findings highlight the critical roles of Rayleigh number,the number of heaters,and the heat flux ratio of the heaters in determining heat transfer and flow characteristics for buoyancy-driven convection systems,providing important theoretical support and design references for engineering scenarios such as electronic devices and design of new energy systems.
基金supported by National Natural Science Foundation of China(61921002 and 92163204)。
文摘Van der Waals(vdW)heterostructures have attracted much attention due to their distinctive optical,electrical,and thermal properties,demonstrating promising potential in areas such as photocatalysis,ultrafast photonics,and free electron radiation devices.Particularly,they are promising platforms for studying thermionic emission.It is illustrated that using vdW heterostructure-based thermionic emission can enhance heat transfer in vacuum devices.As a proof of concept,the approach is demonstrated to offer a promising solution for the long-standing overheating issue in X-ray tubes.Specifically,it is shown that the saturated target temperature of a 2000 W X-ray tube can be reduced from around 1200℃ to 490℃.Additionally,it is also demonstrated that by reducing the height of the Schottky barrier formed in the vdW heterostructures,the thermionic cooling performance can be enhanced.The findings pave the way for the development of high-power X-ray tubes.
基金the the basic scientific research Funds project of Heilongjiang Universities[grant numbers 2024-KYYWF-0554].
文摘In response to the actual demands of the energy storage type organic Rankine power generation cycle,this study proposes a new type of jacketed shell and tube heat exchanger with integrated cold storage and heat exchange.N-tedecane is selected as the phase change material for cold storage,low-temperature water as the cold source,and R134a as the heat source.The phase change material for cold storage is filled inside the jacket tube of the heat exchanger.Cold fluid is introduced into the inner tube to cause the phase change material to condense and store cold.After the cold storage is completed,R134a flows in from the shell side and condenses through heat exchange with the solidified phase change material for energy storage.This study discusses the influence laws of different cold water mass flow rates and temperatures on the cold storage performance of this heat exchanger,and analyzes the condensation effect of R134a.The results show that when the mass flow rate is 0.5 kg/s and the cold water temperature is between 3 and 4℃,the average power of the energy storage heat exchanger in the condensation experiment is 80W,and the average convective heat transfer coefficient is 110.73 W/(m^(2)⋅K).This research provides an experimental basis for the development of energy storage organic Rankine power generation cycles.
基金supported by the Shandong Provincial Natural Science Foundation,China(Grant ZR2024ME136).
文摘The growing need for enhanced heat dissipation is compelling the development of more effective heat exchangers.Innovation inspired by nature bionics,four types of leaf-shaped pin fins were proposed and four combinations of them were considered.The leaf-shaped design of the cooling pin fin enhances uniformity and synergy,effectively creating an optimized flow path that boosts cooling performance.Eight three-dimensional conjugate heat transfer models in staggered arrangement were developed using ANSYS-Fluent software.Aluminum6061material was used as the heat sinkmaterial and single-phase liquid water flowed through the rectangular channel where the Reynolds(R_(e))number varies from 40 to 100.Using the same boundary conditions as the software simulations,two leaf-shaped channels were printed to validate numerical models.Velocity field and temperature differences of the eight proposed leaf-shaped pin fins configurations were discussed by comparison with cylindrical pin fins.Based on the findings of this study,at a Reynolds number of 80,the Leaf B Staggered Array(LBSA)records a maximum temperature that is 0.72 K lower than that of the cylindrical pin fins arrangement.Additionally,the LBSA exhibits a reduction in the friction factor by approximately 33.3%relative to the circular pin fins array under the same R_(e).This implies that the design of LBSA has been optimized to provide better heat dissipation performance while maintaining lower energy consumption.Furthermore,the LBSA demonstrates the most favorable thermal-hydraulic performance index(TPI),which is 1.18 times higher than that of the circular pin fins arrangement at R_(e)=80.The temperature reduction and friction factor reduction of the lobed channel is more pronounced than that of the conventional cooling channel,highlighting its potential to increase heat transfer efficiency and reduce energy consumption in practical applications.
文摘The use of nanofluids as heat transfer media represents an innovative strategy to enhance heat transfer performances.This study investigates experimentally the turbulent convective heat transfer characteristics of waterbased nanofluids containing TiO_(2),CuO,and graphene nanoplatelet(GNP)nanoparticles as they flow through a copper tube.Both the dynamic viscosity and thermal conductivity of these nanofluids were modeled and experimentally measured across varying nanoparticle concentrations(0.01,0.02,and 0.03 vol.%)and temperatures(25℃,35℃,and 45℃).The findings indicate that the behavior of nanofluids depends on the parameter used for comparison with the base fluid.Notably,both the friction factor and heat transfer coefficient increase with higher nanoparticle volume concentrations at a constant Reynolds number.The results further reveal that the GNP/water nanofluid,with a volume concentration of 0.03%at 45℃,exhibit the highest Nusselt number,followed by the CuO/water and TiO_(2)/water nanofluids,with respective increases of 17.8%,11.09%,and 8.11%.
基金financial support was provided by the National Natural Science Foundation of China(Nos.52476146,52006008,and 52471219)the Guangdong Basic and Applied Basic Research Foundation(2023A1515140059 and 2025A1515011255)+2 种基金the Peking University Third Hospital Haidian transformation project(HDCXZHKC2023210)the National Foreign Expert Individual Human Project(Category H,No.H20240116)the State Key Laboratory of New Ceramic Materials Tsinghua University(No.KFZD202402).
文摘The latent heat thermal energy storage system with solid-liquid phase-change material(SLPCM-LHTES)as energy storage medium provides outstanding advantages such as system simplicity,stable temperature control,and high energy storage density,showing great potential toward addressing the energy storage problems associated with decentralized,intermittent,and unstable renewable energy sources.Notably,effective heat transfer within the SLPCM-LHTES is crucial for extending its application potential.Therefore,a comprehensive understanding of the heat transfer processes in SLPCM-LHTES from a theoretical perspective is necessary.In this review,we propose a three-stage heat transfer pathway in SLPCM-LHTES,including external heating,interfacial heat transfer,and intrinsic phase transition processes.From the perspective of this three-stage pathway,the theoretical basis of heat transfer processes and typical efficiency enhancement strategies in SLPCM-LHTES are summarized.Moreover,an overview of the typical applications of SLPCM-LHTES in various fields,such as building energy efficiency,textiles and garments,and battery thermal management,is presented.Finally,the remaining challenges and possible avenues of research in this burgeoning field will also be discussed.
基金support of this work by the National Natural Science Foundation of China (Grant Nos.41972316 and 41672252).
文摘The overall heat transfer coefficient(OHTC)of rock fractures is a fundamental parameter for characterizing the heat transfer behavior of rock fractures in hot dry rock(HDR)geothermal mining.Although a number of practical formulae for heat transfer coefficients have been developed in the literature,there is still no widely accepted analytical solution.This paper constructs highly accurate analytical solutions for the temperatures of the inner fracture wall and the fluid.Then they are employed to develop new definition-based formulae(formula A and its simplification formula B)of the OHTC,which are well validated by the experimental and numerical simulation results.An empirical correlation formula of heat transfer coefficient is proposed based on the definition-based formulae which can be directly used in the numerical simulations of heat transfer in rock fractures.A site-scale application example of numerical simulation also demonstrates the effectiveness of the empirical correlation formula.
文摘Due to the complex high-temperature characteristics of hydrocarbon fuel,the research on the long-term working process of parallel channel structure under variable working conditions,especially under high heat-mass ratio,has not been systematically carried out.In this paper,the heat transfer and flow characteristics of related high temperature fuels are studied by using typical engine parallel channel structure.Through numeri⁃cal simulation and systematic experimental verification,the flow and heat transfer characteristics of parallel chan⁃nels under typical working conditions are obtained,and the effectiveness of high-precision calculation method is preliminarily established.It is known that the stable time required for hot start of regenerative cooling engine is about 50 s,and the flow resistance of parallel channel structure first increases and then decreases with the in⁃crease of equivalence ratio(The following equivalence ratio is expressed byΦ),and there is a flow resistance peak in the range ofΦ=0.5~0.8.This is mainly caused by the coupling effect of high temperature physical proper⁃ties,flow rate and pressure of fuel in parallel channels.At the same time,the cooling and heat transfer character⁃istics of parallel channels under some conditions of high heat-mass ratio are obtained,and the main factors affect⁃ing the heat transfer of parallel channels such as improving surface roughness and strengthening heat transfer are mastered.In the experiment,whenΦis less than 0.9,the phenomenon of local heat transfer enhancement and deterioration can be obviously observed,and the temperature rise of local structures exceeds 200℃,which is the risk of structural damage.Therefore,the reliability of long-term parallel channel structure under the condition of high heat-mass ratio should be fully considered in structural design.
基金College Students Innovation and Entrepreneurship Project of Guangzhou Railway Polytechnic(2025CXCY015)。
文摘As the dominant seepage channel in rock masses,it is of great significance to study the influence of fracture roughness distribution on seepage and heat transfer in rock masses.In this paper,the fracture roughness distribution functions of the Bakhtiary dam site and Oskarshamn/Forsmark mountain were fitted using statistical methods.The COMSOL Multiphysics finite element software was utilized to analyze the effects of fracture roughness distribution types and empirical formulas for fracture hydraulic aperture on the seepage field and temperature field of rock masses.The results show that:(1)The fracture roughness at the Bakhtiary dam site and Oskarshamn/Forsmark mountain follows lognormal and normal distributions,respectively;(2)For rock masses with the same expected value and standard deviation of fracture roughness,the outflow from rock masses with lognormal distribution of fracture roughness is significantly larger than that of rock masses with normal distribution of fracture roughness;(3)The fracture hydraulic aperture,outflow,and cold front distance of the Li and Jiang model are significantly larger than those of the Barton model;(4)The outflow,hydraulic pressure distribution,and temperature distribution of the Barton model are more sensitive to the fracture roughness distribution type than those of the Li and Jiang model.
基金supported by National Natural Science Foundation of China(No.21573276)Natural Science Foundation of Jiangsu Province(No.BK20170007)Jiangsu Funding Program for Excellent Postdoctoral Talent(No.2022ZB846).
文摘Utilizing superwettability micro/nanostructures to enhance the condensation heat transfer(CHT)performance of engineering materials has attracted great interest due to its values in basic research and technological innovations.Currently,exploring facile micro/nanofabrication approaches to create high-efficiency CHT surfaces has been one of research hotspots.In this work,we propose and demonstrate a type of new superwettability hybrid surface for high-efficiency CHT,which consists of superhydrophobic nanoneedle arrays and triangularly-patterned superhydrophilic microdots(SMDs).Such hybrid surface can be fabricated by the facile growth of densely-packed ZnO nanoneedles on the Zn-electroplated copper surface followed by fluorosilane modification and mask-assisted photodegradation.Through regulating the diameters and interspaces of SMDs,we obtain the optimized triangularly-patterned hybrid surface,which shows 42.7%higher CHT coefficient than the squarely-patterned hybrid surface and 58.5%higher CHT coefficient than the superhydrophobic surface.The key of such hybrid surface design is to considerably increase CHT coefficient brought about by SMD-triggered drop sweeping at the cost of slightly reducing heat transfer area of superhydrophobic functional zone for drop jumping.Such new strategy helps develop advanced CHT surfaces for high-efficiency electronic cooling and energy utilization.
文摘This comprehensive research examines the dynamics of magnetohydrodynamic(MHD)flow and heat transfer within a couple stress fluid.The investigation specifically focuses on the fluid’s behavior over a vertical stretching sheet embedded within a porous medium,providing valuable insights into the complex interactions between fluid mechanics,thermal transport,and magnetic fields.This study accounts for the significant impact of heat generation and thermal radiation,crucial factors for enhancing heat transfer efficiency in various industrial and technological contexts.The research employs mathematical techniques to simplify complex partial differential equations(PDEs)governing fluid flow and heat transfer.Specifically,suitable similarity transformations are applied to convert the PDEs into a more manageable system of ordinary differential equations(ODEs).The homotopy perturbation method(HPM)is employed to derive approximate analytical solutions for the problem.The influences of key parameters,such as magnetic field strength,heat generation,thermal radiation,porosity,and couple stress,on velocity and temperature profiles are analyzed and discussed.Findings indicate that the mixed convection parameter positively affects flow velocity,while the magnetic field parameter significantly alters the flow dynamics,exhibiting an inverse relationship.Further,this type of flow behavior model is relevant to real-world systems like cooling of nuclear reactors and oil extraction through porous formations,where magnetic and thermal effects are significant.
文摘We are pleased to introduce this special thematic section on Nanofluid Mechanics and Heat Transfer that is being included in Acta Mechanica Sinica(AMS).This thematic issue consists of 6 papers selected from papers that were presented at the 18th International Symposium on Numer-ical Analysis of Fluid Flows,Heat and Mass Transfer-Nu-merical Fluids 2023,held in Heraklion,Crete Greece,11-17 September 2023,and invited through a general call.The symposium covers various subjects:from new numerical methods and fundamental research until engineering appli-cations,and it is a part of the International Conference of Numerical Analysis and Applied Mathematics(ICNAAM),held annually.
文摘This study aims to elucidate the connection between the shape factor of GO(graphene oxide)nanoparticles and the behavior of blood-based non-aligned,2-dimensional,incompressible nanofluid flow near stagnation point,under the influence of temperature-dependent viscosity.Appropriate similarity transformations are employed to transform the non-linear partial differential equations(PDEs)into ordinary differential equations(ODEs).The governing equations are subsequently resolved by utilizing the shooting method.The modified Maxwell model is used to estimate the thermal efficiency of the nanofluid affected by different nanoparticle shapes.The impact of various shapes of GO nanoparticles on the velocity and temperature profiles,along with drag forces and heat flux at the stretching boundary,are examined with particular attention to factors such as viscosity changes.Numerical findings are based on the constant concentration of ϕ=5% with nanoparticles measuring 25 nm in size.The influence of different shapes of GO nanoparticles is analyzed for velocity,temperature distributions,as well as drag forces,and heat transfer at the stretching boundary.The velocity profile is highest for spherical-shaped nanoparticles,whereas the blade-shaped particles produced the greatest temperature distribution.Additionally,itwas observed that enhancing the nanoparticles’volume fraction from 1%to 9%significantly improved the temperature profile.Streamline trends are more inclined to the left when the stretching ratio parameter B=0.7 is applied,and a similar pattern is noted for the variable viscosity case with m=0.5.Furthermore,the blade-shaped nanoparticles exhibit the highest thermal conductivity,while the spherical-shaped nanoparticles display the lowest.
基金supported by the National Natural Science Foundation of China(Grant No.52306026)the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01)The APC was covered by the Special Innovation Project Fund of the the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01).
文摘This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.
基金supports from National Natural Science Foundation of China(Nos.52304361 and 52130408)Natural Science Foundation of Hunan Province(2023JJ40737)are great acknowledged.
文摘A novel droplet solidification technique was developed to emulate sub-rapid solidification and facilitate the formation of deposited films during the strip casting of silicon steels(w(Si):2.5 and 3.5 wt.%).With the increasing number of droplet ejection experiments,the peak heat fluxes between droplet and substrate decreased firstly(1rd–5th ejection),then increased(5th–7th ejection),and finally decreased again(>7th ejection).In the first five experiments,the interfacial thermal resistance between the droplet and the substrate improved with increasing film thickness.However,at the onset of the 6th droplet ejection experiment,the deposited film initiated its melting process due to the accumulated thermal resistance,which has the potential to eradicate the cavity or air space existing between the droplet and the substrate.Consequently,the interfacial contact condition was improved gradually with the increasing melting area from 5th to 7th droplet ejection experiments,leading to an increase in heat fluxes.Increased SiO_(2) content in deposited films for 3.5 wt.%Si steel led to lower peak heat fluxes than for 2.5 wt.%Si steel.The solidification structure of the 2.5 wt.%Si steel droplet sample comprised a fine grain zone at the base,a columnar grain zone in the center,and an equiaxed grain zone at the top.However,the solidification structure of the 3.5 wt.%Si steel droplet only contained columnar grains and equiaxed grains,with a larger average grain size due to the lower interfacial heat flux.
文摘Plate heat exchangers suffer from significant energy losses,which adversely affect the overall efficiency of thermal systems.To address this challenge,various heat transfer enhancement techniques have been investigated.Notably,the incorporation of surface corrugations is widely recognized as both effective and practical.Chevron corrugation is the most employed design.However,there remains a need to investigate alternative geometries that may offer superior performance.This study aims to find a novel corrugation design by conducting a comparative CFD analysis of flat,square,chevron,and cylindrical corrugated surfaces,assessing their impact on heat transfer enhancement within a plate heat exchanger.ANSYS Fluent software was used for simulation at four distinct Reynolds numbers(10,000,18,000,26,000,and 28,000),with a heat flux of 12,000 W/m^(2).A structured mesh was generated using Pointwise software.The material of the solid plates was modelled as aluminum,the fluid was modelled as water,and the flow was turbulent.To obtain a fully developed turbulent flow,a separate inlet duct was modelled,and the output velocity profile of the inlet duct was input into the plate heat exchanger.The Nusselt number(Nu)and heattransfer coefficient(h)were calculated to evaluate the performance of all surfaces.The results indicate that cylindrical corrugated surfaces exhibit higher Nusselt numbers than chevron,square,and flat plates.This higher performance is because of the generation of vortices in the middle of the cylindrical texture.Consequently,flow recirculation occurs,leading to reattachment to the mainstreamflow.This phenomenon induces increased turbulence,thereby enhancing the heat transfer efficiency.To validate the results,a grid-convergence independence test was performed for three different mesh sizes.In addition,empirical calculations were performed using the Dittus-Boelter and the Genilaski equations to validate the results of the flat-plate heat exchanger.It was concluded that the cylinder was the best corrugated surface and had a maximum heat transfer 35%higher than that of a flat plate.
文摘The pivotal role microchannels play in the thermal management of electronic components has,in recent decades,prompted extensive research into methods for enhancing their heat transfer performance.Among these methods,surface wettability modification was found to be highly effective owing to its significant influence on boiling dynamics and heat transfer mechanisms.In this study,we modified surface wettability using a nanocomposite coating composed of graphene nano plate(GNPs)and multi-walled carbon nanotubes(MWCNT)and then examined how the modification affected the transfer of boiling heat in microchannels.The resultant heat transfer coefficients for hydrophilic and hydrophilic composite(GNPs+MWCNT)microchannels were,respectively,42.8%and 33.95%higher compared with that of the uncoated surface.These results verify that hydrophilic GNP-based coating significantly improves boiling heat transfer performance.It was observed that a minor increase in contact angle,θfrom 73.142°to 75.73°,resulted in a noticeable decrease in thermal performance.This is attributed to diminished liquid film stability,reduced nucleation site activity,and weakened capillary-driven liquid replenishment.These findings underscore the crucial role of optimized surface wettability in maintaining efficient microchannel boiling.At high mass flux,the GNPS microchannels exhibited maximum pressure drop values,with a pressure drop ratio as high as 36%compared to 29%for the GNPs+MWCNT composite samples.Nevertheless,when a composite hydrophilic–hydrophobic coating was deposited through electrodeposition,the enhancement in heat transfer was less significant.This was probably due to decreased surface uniformity,diminished liquid film stability,and the disruption of effective nucleation behavior,all associated with the slight increase in surface contact angle.The obtained results can be used as guidance for designing advanced cooling surfaces in high-performance microelectronic and energy systems,where precise control of surface characteristics is critical.
基金supported by the Natural Science Basic Research Program of Shaanxi(Program No.2024JC-YBMS-449)Project ZR2022QE233 supported by Shandong Provincial Natural Science Foundation.
文摘In exploring hypersonic propulsion,precooler combined engines require the development of lightweight,efficient,and compact heat exchangers(HX).As additive manufacturing technology continues to progress,triply periodic minimal surface(TPMS)structures,characterized by exceptionally high surface area to volume ratios and intricate geometric structures,have demonstrated superior heat transfer performance.This research examines the thermal-hydraulic(TH)behavior of FKS and Diamond as heat transfer structures under different Reynolds numbers through numerical simulations.The Nusselt number for FKS is 13.2%–17.6%higher than Diamond,while the friction factor for FKS is approximately 18.8%–29.3%higher.A detailed analysis of the internal flow mechanisms reveals that the flow pattern within TPMS can be summarized as cyclic convergence-separation-convergence.The fluid experiences constant disturbances from the structure in all spatial directions,generating strong turbulent mixing and large wall shear stresses,which significantly enhance heat transfer performance.
