Physical Characterization of Solar Thermal Energy Storage (TES) Materials for Solar Dryers: Case of Volcanic Stone (Pozzolan) in Chad

Abstract

Many sensible heat storage materials are regularly used as thermal energy storage (TES) systems to improve the efficiency of solar dryers. The present work focuses on the effects of the volume and particle sizes of a volcanic stone (pozzolan) for the same purpose. Samples soaked in matt black and without soaking were also considered. Heat charge and discharge tests were carried out by exposing the pozzolan contained in a solar collector of the direct solar dryer (DSD) and indirect solar dryer (ISD) to the sun. Charge and discharge heat transfer models of the pozzolan enable determining the time constant . The results show that during the charge phase, the non-soaked sample for volumes of 25 l and 20 l in the ISD and the DSD stores heat more than the soaked sample. The half-filled solar collector for ISD with a pozzolan bed depth of 5 cm gives high time-constant values compared to other studied samples. Thus, the pozzolan charges for a longer time for this volume. Soaked samples discharge more slowly than non-soaked samples for particle sizes of 8 to 12 mm and 12 to 16 mm in the ISD and 4 to 8 mm and 8 to 12 mm in the DSD.