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Thermodynamics HW Solutions 813

# Thermodynamics HW Solutions 813 - Chapter 10 Boiling and...

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Chapter 10 Boiling and Condensation 10-27E Water is boiled at a temperature of T sat = 250 ° F by a nickel-plated heating element whose surface temperature is maintained at T s = 280 ° F. The boiling heat transfer coefficient, the electric power consumed, and the rate of evaporation of water are to be determined. Assumptions 1 Steady operating conditions exist. 2 Heat losses from the boiler are negligible. 3 The boiling regime is nucleate boiling since Δ TTT s = = = ° sat F 280 250 30 which is in the nucleate boiling range of 9 to 55 ° F for water. Properties The properties of water at the saturation temperature of 250 ° F are (Tables 10-1 and A-9E) ρ σ l v l = = == = 5882 0 0723 0 003755 01208 143 . . .. . lbm / ft lbm / ft lbf / ft lbm / s Pr 3 3 2 h fg l pl = =⋅ ° lbm / h ft t u / l b m F T s =280 ° F Water 250 ° F 946 0556 1015 Btu / lbm C B μ . . Heating element Also, g = 32.2 ft/s 2 and 0.0060 and n = 1.0 for the boiling of water on a nickel plated surface (Table 10-3). Note that we expressed the properties in units that will cancel each other in boiling heat transfer relations. C sf = Analysis ( a ) Assuming nucleate boiling, the heat flux can be determined from Rohsenow relation to be
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