8.29.2 The rate of heat transfer to the surroundings from a person at rest is ab
ID: 1818066 • Letter: 8
Question
8.29.2 The rate of heat transfer to the surroundings from a person at rest is about 400 kj/h. Suppose that the ventilation system fails in an auditorium containing 100 people. How much will the internal energy of the air in the auditorium increase during the first 10 minutes after the ventilation systems falls. Considering the auditorium and all the people in it as a control mass, how much does the internal energy of this control mass changes? How do you explain the fact that the temperature of the air increases?Explanation / Answer
Given:
Heat generated by each person at rest, = 400kJ/h
Solution:
(1)
There are 100 people in the room and the ventilation system fails and the heat generated by each person is 400 kJ/h.
The heat generated by each person in ten minutes
once the ventilation system fails is = 400x(10/60)66.67 kJ/h
The heat generated by 100 hundred people is given by = 66.67 x 100 = 6666.67 kJ/h
The internal energy generated is given by E = 6666.67 kJ/h
(2)
The people and auditorium as a whole possess a definite mass and an equivalent specific heat. The energy generated by the people is assummed to be given uniformly to this control mass and so there is a finite temeratutr change for a given finite thermal energy generation
E = mcpT
T = E/mcp
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