Thermodynamics HW Solutions 969

Thermodynamics HW Solutions 969 - Chapter 12 Radiation Heat...

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Chapter 12 Radiation Heat Transfer 12-86 The average mean radiation temperature during a cold day drops to 12 ° C. The required rise in the indoor air temperature to maintain the same level of comfort in the same clothing is to be determined. Assumptions 1 Air motion in the room is negligible. 2 The average clothing and exposed skin temperature remains the same. 3 The latent heat loss from the body remains constant. 4 Heat transfer through the lungs remain constant. Properties The emissivity of the person is 0.95 (from Appendix tables). The convection heat transfer coefficient from the body in still air or air moving with a velocity under 0.2 m/s is h conv = 3.1 W/m 2 ⋅° C (Table 12-3). Analysis The total rate of heat transfer from the body is the sum of the rates of heat loss by convection, radiation, and evaporation, && & & ( & ) QQ Q Q Q Q Q Q body, total sensible latent lungs conv rad latent lungs =+ + = + + + Noting that heat transfer from the skin by evaporation and from the lungs remains constant, the sum of the
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