Chapter 5, Problem 5.53P

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 $T_{\infty }=200°\text{C}$ and $h=35{\text{W/m}}^{\text{2}}\cdot \text{K,}$ respectively, determine the slabthickness 2L required to transfer a total amount of energy such that $Q/Q_o=0.90$ over a $t=8\text{-h}$ period. The initial concrete temperature is $T_i=40°\text{C}\text{.}$