摘要

As reported in the literature, many investigations have been performed to provide a better understanding of two-phase heat transfer at the microscale, which is very important in electronics and optoelectronic components cooling by micro heat exchangers. However, these studies have not yet led to a general conclusion. Recently in the Porous Media Laboratory (Minsk, Belarus) some experiments have been carried out in investigation of mini/microscale heat transfer of two-phase fluids (propane) at heat flux ranges 10²−10⁵ W/m². Experimental investigation of pool boiling and evaporation heat transfer in mini channels on a single horizontal tube (smooth and with porous coating) has been performed for analysis of its cooling efficiency. The data obtained in the liquid pool and in confined space (from 0.1 to 2 mm) on a flooded and partially flooded horizontal tube with porous coating illustrate the phenomena of a micro heat pipe inside a porous structure. Propane, as the long-term alternative refrigerant, will be important in the future for compact heat exchangers, heat pipes, and heat pump applications due to its performance, its lack of impact on the environment (zero ODP and <3 GWP), and its physical properties, which are close to those of R-22. In the flat and annular mini channels with micro/nano coated walls investigated in this study, a microscale heat transfer effect took place inside the porous coating of the heat-loaded wall and a heat transfer miniscale effect occurred in the mini channel. The cylindrical heat-loaded tube with porous coating was disposed inside the transparent coaxial glass tube. Visual analysis and experimental data show that such a combination of plates or tubes provides evaporation and two-phase convection heat transfer enhancement. The availability of annular mini channels significantly promotes intense heat transfer (up to 2.5−3 times as high) at heat fluxes <50 kW/m², as compared with processes in the liquid pool.