查看更多>>摘要：Augmentation of the quenching heat transfer at higher temperature regimes is an issue of greater importance in nuclear reactors, avionics, material science, electronic cooling, and solar thermal power plants. The occurrence of film boiling and dependency of bubble behavior on cooling surface orientation are the pressing problems associated with the two-phase cooling process. The present work aims to enhance the cooling efficiency by averting the film boiling and surface orientation effect. In this work, we performed the quenching of Al6061 in de-ionised (DI) water with various additives like tri-sodium phosphate (TSP), Na2SO4, MgSO4, and surfactants like dodecyltrimethylammonium bromide (DTAB) at vertical and horizontal orientations under standard atmospheric conditions. The influence of added additives on overall cooling performance, film boiling time, vapor layer behavior, and bubble dynamics was investigated via cooling curves and visualization techniques. At higher temperature regimes aside from surfactant, other added salt additives exhibited enhanced cooling performance than pure DI-water for all the considered orientations. Among the considered salts, TSP almost nullified the effect of surface orientation and showed an appreciable reduction in cooling time by up to 27.2% compared to de-ionized water. Visualization studies revealed that micro explosion of vapor bubbles and the absence of bubble coalescence are the significant physical mechanisms governing the enhancement in cooling performance.
查看更多>>摘要：The effects of porosity, pore diameter and heating direction on the heat transfer performance of copper foam under natural convection were experimentally investigated. The open cell copper foam with highly controllable porosity ranging from 65% to 85% and mean pore diameters of 330 μm, 560 μm, 850 μm and 1200 μm were manufactured using a space holder method. The natural convective heat transfer coefficient of the copper foam was measured using a purpose-designed device. The influence mechanism of porosity, pore diameter and heating direction on heat transfer was analysed and discussed. The results showed that when the porosity is less than 75%, the effect of porosity on heat transfer is not significant, but as the porosity increases further, the heat transfer performance decreases significantly. The optimal pore size was found to be 850 μm, while the heat transfer performance of other pore sizes depends on the porosity. It was also found that the samples heated from the side generally showed better heat transfer performance than the samples heated from the bottom. The influence of porosity and pore size on natural convective heat transfer performance is mainly caused by changes in thermal conductivity and permeability. This research provides important guidance for the design of future heat sinks.
NSTL
Elsevier