Chapter 9 Natural ConvectionHeat loss by both natural convection and radiation heat can be expressed as ])K27320()273)[(1067.5)(m03.0)(8.0(C)20)(m03.0)(C.W/m696.6(W8)()(44822244+−+×+°−°=−+−=−∞sssurrssssTTTTATThAQσε&Its solution is Ts=°42.6 Cwhich is sufficiently close to the assumed value of 45°C in the evaluation of the properties and h. (c) Horizontal, hot surface facing down This time we expect the surface temperature to be higher, and assume the surface temperature to be 50. We will check this assumption after obtaining result and repeat calculations with a better assumption, if necessary. The properties of air at the film temperature of °CC35220502°=+=+=∞TTTsfare (Table A-15) 1-25K003247.0K)27335(117268.0Pr/sm10655.1CW/m.02625.0=+===×=°=−fTkβυThe characteristic length in this case is, from part (b), Lc= 0.0429 m. Then, 379,166)7268
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