Stone mix concrete slabs are used to absorb thermal energy from flowing air that is carried from a large concentrating solar collector. The slabs are heated during the day and release their heat to cooler air at night. If the daytime airflow is characterized by a temperature and convection heat transfer coefficient of T_∞  = 200°C and h = 35 W/m² · K, respectively, determine the slab thickness 2L required to transfer a total amount of energy such that Q/Q_o = 0.90 over a t = 8-h period. The initial concrete temperature is T_i = 40°C.

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From solar collector 5.39. T_, h Th Th Th 2L 124 Concrete slabs