Development of a Closed-Loop Heat-Pipe for Heat Recovery With Mini-Channels Enhancing Evaporation

A vast number of industrial processes require the addition and removal of heat at different stages of the same process. To accomplish heat recovery there are several technological options with specific characteristics. Thermal integration has been the focus of recent industrial developments to reduce variable costs through new investments when using fossil fuels for thermal energy generation. The conventional equipment for heat recovery uses conduction and convection heat transfer mechanisms and high surface area of a metal wall (normally subjected to corrosion and fouling) for the contact of the cold and hot fluids. Heat pipes are an option for heat recovery with less metal surface area (and therefore lower tendency to corrosion and fouling) because of their higher thermal conductivity, but have been used mostly for heat removal in electronic equipment. This study develops a closed-loop heat pipe configuration for heat recovery in industrial operations starting with a configuration for desalination. The variables of the heat pipe operation that were considered include the mini-channels structures associated to the evaporator section, the effect of the inclination of condenser to evaporator, the working fluids (ethanol-water mixtures, acetone, methanol, and isopropanol), and the internal pressure of the heat pipe (atmospheric and vacuum). The highest heat flux values (3.2 W/cm²) were obtained with a single layer mini-channels structure, 90° of inclination between the condenser and the evaporator, and a mixture of 16% ethanol in water as working fluid in the loop-heat-pipe because this mixture had the highest heat transfer parameter (that describes the capacity of the fluid to perform in a heat pipe) among the fluids tested and corresponded to the highest heat transfer rate measured.