Experimental analysis, modeling and simulation of a solar energy accumulator with paraffin wax as PCM

Abstract

Soft drink cans filled with paraffin wax mixed with 7.5% aluminum stripes, obtained from disposable cans, doubled the thermal conductivity of cans filled only with paraffin wax. Promising results obtained in a prototype heat exchanger encouraged the construction of this unit 6 times bigger. We experimentally evaluated and model a heat exchanger for solar energy accumulation, composed by 300 disposable soft drink cans filled with a total of 59.25kg of paraffin wax mixed with 7.5% aluminum stripes. The effect of adding 2.75kg of aluminum fins for enhancing heat transfer from the outer surface of the cans to the circulant air was experimentally analyzed. In sunny days, the wax melted completely in about 4h. The accumulated energy in form of latent heat (about 13,000kJ) allowed to increase the temperature of 0.040kg/s of circulant air in at least 20°C during a period of 2.5h. For an air mass rate of 0.018kg/s the period was extended practically to 5h. The accumulator thermal analysis was presented and a subsequent numerical simulation with Matlab was performed to compare with the experimental results obtaining good agreement specially for higher air mass flow rates. The low cost accumulator presented is of simple construction and will allow extended use of solar energy for applications such as drying processes or household calefaction system.