$3-57$

A composite cylindrical heater involves two materials which have $k_a$ and $k_b.$ Between them is a thin electrical resistance

heater. Liquid at $T_{,i}$ is pumped through the center of the heater with an accompanying $h_i.$ The outer surface of the heater is

exposed to air at $T_{,0}$ with $h_0.$ Under steady conditions, $q_h^{\text{'}\text{'}}$ is dissipated by the heater.

Draw and label a thermal circuit for this physical situation. Write a relationship for $q_h^{\text{'}\text{'}}$ in terms of the

given parameters, including a known heater temperature, $T_h.$ Th $>T$ Infinity, & Th $>$ T infinity, $0$