Calculate the net thermal resistance and the net heat transfer for a composite

wall comprising of three walls of lengths L. L_{2} La and thermal

conductivities K 1, K_{2} K_{3} respectively in series. Area of cross-section is the

same for all three walls and is given as A

1 answer

The net thermal resistance for the composite wall can be calculated using the formula:

R_net = R_1 + R_2 + R_3

where R_1, R_2, and R_3 are the thermal resistances of each individual wall, calculated as:

R_1 = L/K_1A
R_2 = L_2/K_2A
R_3 = La/K_3A

Substituting the values, we get:

R_net = L/K_1A + L_2/K_2A + La/K_3A

Simplifying, we get:

R_net = (L/K_1 + L_2/K_2 + La/K_3) / A

The net heat transfer through the composite wall can be calculated using the formula:

Q = (T1 - T2) / R_net

where T1 and T2 are the temperatures on either side of the wall.

Therefore, the net thermal resistance of the composite wall is (L/K1 + L2/K2 + La/K3)/A and the net heat transfer is (T1 - T2)/(L/K1 + L2/K2 + La/K3)/A.