Impact of ultrasound on the melting process and heat transfer of phase change material

Abstract

Latent heat storage (LHS) in a phase change material (PCM) has gained a growing interest in the building sector, due to its higher energy storage density and smaller temperature swing compared to sensible heat storage. However, low thermal conductivity of PCMs, particularly paraffin, presents a major obstacle to their successful applications in building products. In response to this issue, various heat transfer enhancement technologies through adding high conductivity materials such as metal foam and carbon fiber, have been proposed in previous studies. Although these technologies have received positive results, most of them suffers from the fact that the storage density will be reduced. To overcome this limitation, a heat transfer enhancement method using ultrasound was proposed in this study, and a series of experiments were conducted based on an experimental platform able to simulate the working condition of a domestic hot water system. The aim is to evaluate the impact of ultrasound on the charging/melting process of PCMs. Results show that, compared to the case without ultrasound, the charging time of the LHS unit reduced 60.69% and the average heat transfer coefficient increased 250.97% as the inlet temperature and flow rate of hot water were set at 60℃ and 3L/min, respectively. Moreover, much more bubbles were generated during the charging process, thereby improving both the natural convection of PCM and heat transfer between PCM and hot water.