Chapter 1, Problem 1.39P

A household refrigerator operates with cold- and hot-temperature reservoirs of $T_c=5°\text{C}$ and $T_h=25°\text{C,}$ respectively. When new, the cold and hot side resistances are $R_{c,n}=0.05\text{K/W}$ and $R_{h,n}=0.04\text{K/W,}$ respectively. Over time, dust accumulates on the refrigerator’s condenser coil, which is located behind the refrigerator, increasing the hot side resistance to $R_{h,d}=0.1\text{K/W}\text{.}$ It is desired to have a refrigerator cooling rate of $q_{\text{in}}=750\text{W}\text{.}$ Using the results of Problem 1.38, determine the modified coefficient of performance and the required power input $\stackrel{.}{W}$ under (a) clean and (b) dusty coil conditions.