| With the development of vapor chambers tend to be ultra-thin,the limitation of thickness brings the limitation of heat transfer performance of vapor chambers.Therefore,how to increase the maximum heat transfer capacity of vapor chambers with a limited thickness is a very meaningful subject.The composite wick structure of the vapor chamber studied in this paper is composed of 4 spiral woven mesh wicks(SWM: spiral woven mesh)and a layer of copper mesh wick.In this paper,the heat transfer characteristics of the ultra-thin vapor chamber with composite wick is investigated by numerical simulation and theoretical derivation,and it is optimized.The main contents are as follows:1.A three-dimensional numerical model is established to predict heat transfer characteristics of a multi-vapor channel vapor chamber(VC)with novel composite wick.In order to validate the numerical model,the surface temperature of VC and the pressure drop of vapor are calculated and compared with the experimental results and theoretical results respectively.The mass flow rate distribution of working fluid in the wick is obtained.And the effects of the height of the vapor channel on the velocity,pressure drop of the vapor and total thermal resistance are investigated at different heating powers.The velocity,pressure drop of the vapor and total thermal resistance have the same variation trend,which all are inversely correlated to the height of the vapor channel respectively.However,the reduction of the thermal resistance of the vapor decreases as the height of the vapor channel increase.2.Currently,the maximum heat transfer capacity of the VC with composite wick is still unpredictable.In this study,the theoretical model for calculating the maximum heat transfer capacity of the VC is established.The calculated results agree well with the experimental ones.The result indicates that the maximum heat transfer capacity rises first and the decreases with the width of vapor channel increasing.Furthermore,the effects of the vapor channel and wick structure(composite structure(CW-S),layered structure(L-S)and spaced structure(S-S))on the thermal performance of VCs were analyzed.Besides,the impact of the number of SWMs can be ignored while more vapor channels will reduce slightly the heat transfer performance of the VC.For CW-S and S-S two different wick structures,the design of double vapor channel makes the VC have greater maximum heat transfer capacity,which can reach 9.45 W and10.51 W respectively under the appropriate channel width.3.In thermal management applications based on vapor chamber,the maximum temperature,temperature difference and the total thermal resistance of the vapor chamber are often concerned.The solving process of the liquid-vapor phase change and fluid flow inside the vapor chamber in numerical simulation is time-consuming.Therefore,the conduction-based model of the vapor chamber as a thermal conductor has been also developed and applied.The conduction-based model for the vapor chamber is put forward and the effective thermal conductivity of the vapor channel is derived.The maximum relative error between the surface temperature prediction based on the conduction model and the experimental data is less than5%.4.Refer to the conduction-based model for the vapor chamber,two conduction-based model for partially flattened heat pipes: the segmented anisotropic model and the layered segmentation model are put forward in the present study.The results show that the segmented anisotropy model has higher accuracy in the case of low heat pipe operating temperature(28～38°C).The maximum relative error of heat pipe simulation temperature is 5.90%.The layered and segmented model has higher accuracy in the heat pipe operating temperature range of 28～50°C.The maximum relative error of heat pipe simulation temperature is 6.51%.And the effect of the effective thermal conductivity of the wick on the accuracy of the thermal conduction-based model is also investigated. |
