The Fabrication And Performance Study Of Enhanced Heat And Mass Transfer Structure On Micro Channel

Thermal management is significant in both developing new energy and saving exiting energy.The solution of enhancing heat transfer should achieve both performance target and economy efficiency.Micro-channel heat exchanger with simple structure but effective heat enhancement,is the most potential scheme to achieve high efficiency-low cost target.This study focuses on the fabrication,optimization and enhancement of micro-channel heat exchanger.Firstly,study begins with the optimal structural parameters design of the micro-channel heat exchanger.Next,inclination angle and working fluid optimization of aluminum micro-groove heat pipe will be conducted.Finally,micro-channel will be enhanced in both heat and mass transfer based on micro-nano technology.The major research contents include:The optimization of aluminum micro channel-acetone system in micro scale is absent and needed.Simulation was conducted to optimize the depth-width ratio,fin thickness and the heat enhancing rid distance of aluminum micro channel with acetone as flowing fluid.The results shown that the depth-width ratio greatly influences the thermal resistance of groove.The total groove thermal resistance decreased as the depth-width ratio increased.In addition,the optimal fin thickness is 0.36 mm,in which the corresponding Nusselt number reached the maximum.The optimal distance of heat transfer rid was found out to be 2.05 mm.The typical form of aluminum micro channel applied in heat pipe is micro grooved aluminum heat pipe array?MGA-HPA?.Theory of the optimal inclination angle and working fluid of the MGA-HPA will be conducted in this chapter.This study firstly discovered the inclination mechanism based on liquid film profile and proposed the optimal inclination theory by a balance of liquid distribution.In addition,the coupling relationship of fluid parameters and heat pipe performance was investigated.The results shown that acetone is the best working fluid of the MGA-HPA.The underlying mechanism is the small liquid-vapour shearing force and flowing viscous friction.In addition,experimental data shown a strong dependence of MGA-HPAs'thermal resistance on the inclination angle due to gravitational effect on axial liquid film distribution.Finally,a criterion was firstly proposed to predict the optimal inclination angle of the MGA-HPA.In this study,a volumetric fraction(?_a,c)of 74±7%has been proved to accurately predict the optimal inclination angle of the MGA-HPAs with various heat loads and working fluids.In order to enhance the mass transfer in micro channel,this paper presented an alkaline corrosion treatment for aluminium micro-channel wick,which greatly enhanced the capillary limit of grooved aluminium heat pipes.This study investigated the effect of corrosion parameters?both molar concentration and reaction time?on the capillary performance.Experimental results reveal that the corroded-aluminium micro-channel wicks always present higher capillary performance than non-corroded ones.In this study,the optimal corrosion parameters were 1.25mol/L NaOH for 10 min,with the best capillary performance parameter(?P_cap.K)of 8.97±0.38×10^-77 N.This data demonstrated an performance enhancement of 155%compared with the non-corroded wicks.The underlying mechanism is associated with the improved hydrophilicity and the micro-coarse-structured morphology of the corroded aluminium surface.Furthermore,a novel prediction model was proposed to calculate the capillary limit of heat pipes based on the results of IR rate-of-rise tests on wicks.In order to enchance the heat transfer coefficient of micro channel,this study proposed a novel micro-scale mesh coated with nano-porous structure.After that,it was fabricated to be multi-scale mesh-micro channel hybrid wick by sintering process.Three structures,i.e.micro channel,single scale and multi-scale porous hybrid wick,were fabricated to compare the heat transfer coefficient?HTC?.Furthermore,the optimal coverage rate of hybrid wick in heat pipe was investigated.Experimental results shown that 500?-60 seconds is the optimal parameter.The corresponding morphology has the maximum roughness in nano-scale.The mesh could greatly enhance the HTC of micro channel.Multi-scale porous structure slightly enhanced the HTC in comparison to single-scale porous hybrid wick.The enhancing mechanism is improved wettability and increased density of boiling nucleate core.Experimental results shown that the partial hybrid wick structure is the optimal pattern,in which the corresponding effective thermal conductivity was improved by over 80%than grooved one.The underlying mechanism is high efficiency thin film evaporation induced by mesh porous structure.