At steady state, a reversible heat pump cycle discharges energy at the rate q˙h to a hot reservoir at temperature th, while receiving energy at the rate q˙c from a cold reservoir at temperature tc. (a) if th = 13°c and tc = 2°c, determine the coefficient of performance. (b) if q˙h= 15 kw, q˙c= 8.75 kw, and tc = 0°c, determine th, in °c. (c) if the coefficient of performance is 20 and th = 27°c, determine tc, in °c.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?