Consider the composite solid shown. Solid A is a thermally conductive material that is 0.5-cm thick and has a thermal conductivity, k_A= 50 W/m · K. The back side of solid A (x = 0) is thermally insulated. Electrical current is applied to solid A such that 20 W per cm³is generated as heat. Solid B is 0.2-cm thick and has a thermal conductivity of k_B= 20 W/m · K. The surface of solid B is exposed to air. The surface temperature, T_s, of solid B is 80°C. The bulk air temperature is constant at 30°C. The process is at steady state. 

a. What is the heat-transfer rate per unit area (flux) at x = L₂? What is the temperature T₁ at x = L₁, the boundary between solid A and solid B?

b. What is the required convective heat-transfer coefficient, h, for the flowing air?

c. What is the temperature T₀ at x = 0, the insulating side of solid A?

Heat transfer in composite solid.

solid A solid B kA = 50 W/m-K kg = 20 W/m-K : bulk gas film To gas Ts = 80C T = 30C insulated boundary x = L2 = 0.7 cm %3D 0 X = L, = 0.5 cm