Awell-sealed room contains 60 kg of air at 200 kpa and 40°c. now solar energy enters the room at an average rate of 0.8 kj/s while a 120-w fan is turned on to circulate the air in the room. if heat transfer through the walls is negligible, the air temperature in the room in 30 min will be °c.

The air temperature in the room in 30 min will be 78.4 °C

Explanation:

The process is done at constant volume (Cv of air: 0.718 kJ/(kg*degC)), so the relation of the heat flow with the temperature of the air is:

The heat flow is the sum of the heat coming from the sun and the heat of the fan:

In 30 minutes the total amount of heat that enters into the room is

The variation of temperature in the air can be calculated as

As the initial temperature of the air was 40 deg C, the final temperature will be (40+38.4)=78.4 deg C