Theorical and experimental evaluation of heat transfer limits in heat pipes

Abstract

This research proposal for Scientific Initiation is part of a series of projects involving heat transfer with phase change in compact heat exchangers currently being developed by the Heat and Mass Transfer Group of the Mechanical Engineering Department at EESC-USP. A technique of broad application developed in this group is the technique of convective boiling in microchannels, which enables the development of compact heat exchangers that can transfer heat flux over 100 MW/m². However, in this technique, it is necessary the use pumps or compressors in the system for its operation, which generates additional costs. Heat pipes are passive devices that transport heat from a heat source (evaporator) to a heat sink (condenser), using the latent heat of vaporization of the working fluid. The great advantage over convective boiling is that by its passive nature, it does not require pump or compressor to function and thus has simple operation, high durability and low maintenance. Among the major limitations of heat pipes are the lowest rates of heat transfer, limitations related to operational distances between the evaporator and condenser and greater sensitivity to gravitational effects. In this sense, this research proposal aims to evaluate heat pipes under similar experimental conditions that have already been evaluated with the technique of convective boiling in microchannels and thus determine limits of operation and application of the techniques of heat pipes and convective boiling. Two configurations of heat pipes will be evaluated with hydraulic diameters reaching the lower limit of 0.40 mm and operating with fluids acetone, water, ethanol and R245fa. It is expected by the end of this project that a broader map of application potentials for each of these two new techniques be indicated.