Chapter 1, Problem 1.63P

A $50\text{mm}\text{×}\text{45}\text{mm}\text{×}\text{20}\text{mm}$ cell phone charger has a surface temperature of $T_s=33°\text{C}$ when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity $\epsilon =0.92$ and is subject to a free convection heat transfer coefficient of $h=4.5{\text{W/m}}^{\text{2}}\cdot \text{K}\text{.}$ The room air and wall temperatures are $T_{\infty }=22°\text{C}$ and $T_{\text{sur}}=20°\text{C,}$ respectively. If electricity costs $C=\$0.18\text{/kW}\cdot \text{h,}$ determine the daily cost of leaving the charger plugged in when not in use.