Influence of transient heat pulse on heat transfer performance of vapor chamber with different filling ratios

Due to the different application for portable electronic devices, there are instantaneous changes in the thermal load of the CPU and battery in the operation. The traditional uniform structure wick can not allow for evaporation and reflow of the working fluid under complex conditions, hence reducing the heat transfer performance of the vapor chamber (VC). This paper puts forward a novel style of VC to overcome the difficulty of heat export for electronic devices with dual heat sources. The wick with gradient structure in heat source zone and reflow zone was made by the method of zonal sintering, which could effectively promote the evaporation and reflow of working fluid with multi-heating sources and complex conditions. The influence of step heating condition and pulse heating condition on the heat transfer performance of the VC with various filling ratios was analyzed. The results showed that under the step heating condition, the best heat transfer performance of the VC was achieved at a filling ratio of approximately 90%, with a minimum thermal resistance of only 0.31 oC/W at 45 W. Under the pulse heating condition, in order to significantly reduce the temperature hysteretic effect of the VC, a gradient structure core was sintered in different regions, and the maximum hysteretic temperature was 2.7 oC when the filling ratio wass 80% and 100%. The temperature lag could be effectively eliminated when the filling ratio was 90%. The results of the research supplied a theoretical basis for the design and testing of VC under complex working conditions and the development of efficient heat transfer elements.