Question

A tent is pitched on a mountain in an exposed location in the Swiss Alps. The tent walls are opaque to thermal radiation. On a clear night, the outside air temperature, T∞ is -1°C, and the effective temperature of the sky, Tsky, as a black radiation sink is -60°C. The convective heat transfer coefficient, hc,t, between the tent and the ambient air can be taken as 8 W/m2.K. If the temperature Ts of the outer surface of a sleeping bag on the tent floor is measured to be 10°C, estimate the rate of heat loss from the bag in W/m2,

a) if the emissivity of the tent material is 0.7, and

b) if the outer surface of the tent is aluminised to give an emissivity of 0.2

Discuss the effect of aluminising the outer surface of the tent on the rate of heat loss from the sleeping bag. What would be the rate of radiation heat loss from the sleeping bag if a powerful wind gust were to blow the tent away?

For the sleeping bag, take an emissivity of 0.8 and a convective heat transfer coefficient, hc,b, of 4 W/m2.K. Assume that the ambient air circulates through the tent such that the air in the tent is also at -1°C

Answer 1