Experimental Study On The Effects Of Suspensions Of Nanoparticles And Microcapsules For LED Heat Dissipation

Light emitting diodes（LEDs）,with many advantages over traditional lighting,is a high-performance lighting device and have been widely applied.However,the light emitting efficiency of LEDs is less than 30%,and the remaining energy is dissipated as heat,possibly resulting in a significant reduction in lifetime or performance of the device.Therefore,thermal management is crucial to ensure and improve the efficiency of LED.Nanofluid and microencapsulated phase change material suspension（MPCMS）are new functional fluids,which have shown excellent thermophysical properties and improved heat transfer capacity.As a functional fluid or coolant,although there are studies showing their suitability for thermal management,there are little experimental research on the field of electronic heat dissipation especially on LED heat dissipation,and the way of effective application of them on LED thermal management still need to be studied.In this thesis,the thermal performance of different suspensions and the heat dissipation performance under different conditions of use are investigated by applying different coolant to an LED thermal management system which integrates thermoelectric cooler（TEC）with microchannel heat sink（MHS）and comparing their cooling effects.The main work of the thesis is as follows:（1）The performance of LED thermal management system using Ti O₂nanofluid as coolant was studied.By orthogonal test and variance analysis,various influence factors were studied,including the power of thermoelectric cooler,the nanofluid concentration,the inlet temperature of coolant and the LED ambient temperature.The significance of the four factors from high to low on LED heat dissipation were studied.It was found that the cooling performance of nanofluid was better than that of water.The concentration of nanofluid was found to be the dominant factor,and the optimal concentration was obtained.The influence of LED ambient temperature and nanofluid temperature on cooling performance was investigated.The influence of dispersion stability of nanofluid on cooling performance was analyzed.（2）The microencapsulated phase change suspension（MPCMS）was applied as a coolant;the morphology,phase change and thermophysical properties of the microencapsulated phase change material（MPCM）were observed and their influence on the cooling performance of the LED thermal management system were studied.found to improve the cooling performance of LED thermal management systems.It was found that MPCMS as a coolant can be applied to higher TEC power and exhibited enhanced cooling capacity compared to water.The significance of the MPCMS compared to water was more remarkable at higher ambient temperatures of fluid radiator.The effects of flow rate and mass concentration of the MPCMS on performance were also investigated and optimal values were obtained.The effects of specific heat,thermal conductivity and viscosity on the cooling performance were investigated by a dimensionless thermophysical factor,and it was found that the highest value of thermophysical factor was obtained at the optimum MPCMS concentration.（3）Hybrid suspensions which composed of the mixtures of nanoparticles and MPCM were prepared.The influence of different nanoparticles on dispersion stability and thermophysical properties of the MPCMS was studied.The MPCM/Al₂O₃hybrid suspension was found to have the best comprehensive performance and used as the coolant for the LED thermal management.It was found that the cooling performance with the hybrid suspension coolant was significantly improved compared with the mono nanofluid or MPCMS.The influence of factors of such as concentration and inlet temperature were further studied.