A refrigerator is thermally equivalent to a box of cork board $$90$$ mm thick and $$6$$ $$m2$$ in inner surface area, the thermal conductivity of cork being $$0.05$$ $$W/mK$$. The motor of the refrigerator runs $$15$$% of the time while the door is closed. The inside wall of the door, when it is closed, is kept, on an average, $$22$$°C below the temperature of the outside wall. The rate at which heat is taken from the interior wall while the motor is running is

Question

A refrigerator is thermally equivalent to a box of cork board $$90$$ mm thick and $$6$$ $$m2$$ in inner surface area, the thermal conductivity of cork being $$0.05$$ $$W/mK$$. The motor of the refrigerator runs $$15$$% of the time while the door is closed. The inside wall of the door, when it is closed, is kept, on an average, $$22$$°C below the temperature of the outside wall. The rate at which heat is taken from the interior wall while the motor is running is

Infinity Learn · Accepted Answer

Consider a time interval Δt while the door is closed. Then the rate of heat into the box isQ∆$$t=kA$$∆T∆$$x=(0.05)(6)220.09=73.3W$$ To remove heat at this rate, while the motor runs only for a time (0.15) Δt, it must cause heat to leave at the rate,$$H=73.30.15=500W$$

Remember concepts with our Masterclasses.

Ready to Test Your Skills?

free study material