Question

Find the heat flow rate through the composite wall as shown in  Assume one dimensional flow. 

k_A = 150 W/m°C, 

k_B = 30 W/m°C, 

k_C = 65 W/m°C and 

k_D = 50 W/m°C.

Answer 1

The thermal circuit for heat flow in the given composite system (shown in has been illustrated in Thickness : 

L_A = 3 cm = 0.03 m ; L_B = L_C = 8 cm = 0.08 m ; L_D = 5 cm = 0.05 m 

Areas : 

A_A = 0.1 × 0.1 = 0.01 m² ; 

A_B = 0.1 × 0.03 = 0.003 m² 

A_C = 0.1 × 0.07 = 0.007 m² ; 

A_D = 0.1 × 0.1 = 0.01 m2 

Heat flow rate, Q : 

The thermal resistances are given by

The equivalent thermal resistance for the parallel thermal resistances R_th–B and R_th–C is given by :

Now, the total thermal resistance is given by 

(R_th) _total = R_th–A + (R_th)_eq. + R_th–D 

= 0.02 + 0.147 + 0.1 = 0.267