Phase change driving mechanism and modeling for heat pipe with porous wick

Abstract

According to heat pipe theory, capillary force is the only driving force for the circle of working fluid in heat pipe with porous wick. By developing a simulating circuit of liquid and vapor flow in heat pipe with porous wick, this paper presents a new driving mechanism which is from phase change of fluid. Furthermore, by analyzing transport process of working fluid between evaporation and condensation interfaces, a mathematical model is developed to describe this driving mechanism. Besides, calculating examples are given for heat pipe with water as working fluid to predict its driving force and flow resistance. By applying the model presented in the paper, thermal design and calculation for heat pipe with porous wick, especially for miniature heat pipe, can be made correctly, and phase change driving mechanism of working fluid can be explained, which thereby leads to a better understanding of heat transfer limitation of heat pipe with porous wick.Heat pipe, porous wick; phase change; driving mechanism; modeling Heat pipe is a kind of heat transfer device and its operating principle is based on evaporation and condensation of working fluid [1][2][3][4][5][6][7] . Heat pipe with porous wick is a kind of heat pipe which utilizes capillary pumping forces to ensure fluid circulation [8] . Heat pipe with porous wick has obvious advantages, for example, it is capable of passively transporting more heat over long distance with small temperature difference, and there are no moving parts for pumping working fluid. Therefore, heat pipe with porous wick is widely used in the field of cooling for equipment both in space and ground. Figure 1 shows the structure of a typical heat pipe with porous wick. It is made up of evaporation section, adiabatic section and condensation section, and its inner wall is covered by porous wick. The working process of a heat pipe with porous wick is that liquid evaporates in the evaporation section, vapor comes to the condensation section via vapor line and condenses to liquid, then liquid flows back to the evaporation section driving by capillary force of the porous wick.