Characteristics of heat storage and release of gravel layer in solar collectors by hot air natural circulation

The thermal characteristics of heat storage and release of the gravel layer used in the solar collector in winter were analyzed. Air from the solar collector was expected to circulate through the gravel layer naturally without other energy consumption. The gravel layer consisted of river gravels with diameter from 50 mm to 100 mm. The temperature of the solar collector, gravel layer and cement mortar surface were measured respectively to analyze thermal characteristics of heat storage during daytime and heat release at night in the gravel layer. The horizontal and vertical heat characteristics of the gravel layer and cement mortar surface were analyzed. Results of the thermal characteristics of the gravel layer in the solar collector can be used as basic data for the thermal analysis of gravel layer.