Question

Thermodynamics ~ The break shoe and steel drum on a car continuously absorbs 75W as the car slows down. Assume a total outside surface area of 0.10m^2 with a convective heat transfer coefficient of 10W/m^2K to the air at 20 degrees C. How hot does the outside brake surface temperature become? Assume that steady state conditions prevail.

Answer 1

The total heat absorbed by the brake shoe drum will completely transfer convectively to the surrunding air at steady state condition.

So we can use steady state Convective heat transfer Equation.

Q=hA(T_brake -T_air)

Where

Q = Heat absorbed by the brake drum = 75W.

h = heat transfer coefficient = 10W/(m²k)

A = Total outside surface area of brake drum =0.1m²

T_air= 20 degrees C

T_brake= ?.

On substituting we get  

75=10*0.1(T_brake -20)

75 = 1*(T_brake -20)

T_brake= 95 degrees C.

So final Answer, outside brake surface temperature = 95 degrees C.