Enhancing heat transfer in phase change materials

Phase change materials (PCM) are attracting a significant amount of attention these days, as they might be used in such diverse applications as thermal energy storage, thermal management electronics and energy efficient buildings. The number of research works in the field of PCM is growing very fast, and, as in many other fields of heat transfer, things are sometimes re-discovered or re-invented. This lecture's first aim is to give an historical perspective of heat transfer research in this rich and important field. It is shown that, in fact, the true interest in it arose first about half a century ago, in connection with the space exploration. In fact, many prominent heat transfer researchers contributed to this field, and it is demonstrated in the lecture how their insightful work remains more than relevant today. The second aim of this lecture is to present state-of-the-art of heat transfer enhancement in PCM, because these materials are notorious for their low thermal conductivity. Various enhancement methods are outlined and their merits are evaluated. Among those methods, we discuss extended surfaces, conductive additions, porous matrices, nanoparticles and PCM-based slurries. The presentation is based, to a very large extent, on the author's personal knowledge and experience in PCM systems, partially reflected in a number of very recent publications of our laboratory. Although “the big picture” is important, our attention is dedicated also to numerous essential details and subtleties, which can affect the processes significantly but are frequently overlooked.