Performance limits of flat plate heat pipes

The heat pipe is a device capable of transferring high rates of heatunder isothermal conditions. Recently, the thermal load of electronicdevices are increasing, so an improvement of their heat radiationcharacteristics is longed for. A solution for this will be contacting theelectronic device with a heat sink; a flat shaped heat pipe, therebyeffectively diffusing the heat from the electronic device. It is effective as aheat radiation means for electronic devices employed in an artificialsatellite or under other space environments. The procedure to design sucha heat pipe for this specific application requires the consideration ofoperation limits. Therefore, the present study concentrates on studying theperformance limits of flat plate heat pipe. The heat pipe consists of acircular container, whose interior wall is lined with wrapped screens wickstructure saturated with the working fluid. Heat transfer from theevaporator plate (constant heat flux) causes the liquid in the wick toevaporate and flow to the condensing plate where it is condensed. In thistype of heat pipes (flat plate), there is no adiabatic section. The return ofliquid from the condenser to the evaporator occurs due to the capillaryforces in the wick that create a surface tension pressure differential toovercome the vapor and liquid pressure DROPs, including that due togravity.As in conventional cylindrical heat pipe, the heat transfer capabilityof the flat plate heat pipe can be limited by sonic flow of vapor, viscous,entrainment, capillary (wicking) and boiling limits. These limits arestrongly depend on the geometry of the pipe, wick structure, vapor channel