Thermal conductivity enhancement in a latent heat storage system

Latent heat storage systems especially those employing organic materials have been reported to exhibit a rather slow thermal response. This is mainly due to the relatively low thermal conductivity of organic latent heat materials. In this study, experiments were carried out to investigate a method of enhancing the thermal conductivity of paraffin wax by embedding aluminum powder in it. The size of the aluminum powder particles was 80 pm. The tested mass fractions in the PCM-aluminum composite material were 0.1, 0.3, 0.4, and 0.5 of aluminum. The used mass fraction in the experimental work was 0.5. The experiments were conducted by using a compact PCM solar collector. In this collector, the absorber-container unit performed the function of absorbing the solar energy and storing the phase change material (PCM). The solar energy was stored in the PCM and was discharaed to cold water flowing in pipes located inside the PCM. Charging and discharging processes were carried out. The propagation of the melting and freezing fronts was studied during the charging and the discharging processes. The time wise temperatures of the PCM were recorded during the processes of charging and discharging. The solar intensity was recorded for the charging process. It was found that the charging time was reduced by approximately 60% by adding aluminum powder in the wax. In the discharging process, experiments were conducted for different water flow rates of 9-20.4 kg/h. It was found that the useful heat gained increased when adding aluminum powder in the wax as compared to the case of pure paraffin wax. The heat transfer characteristics were studied. (c) 2006 Elsevier Ltd. All rights reserved.