Chapter 10 Boiling and Condensation10-27EWater is boiled at a temperature of Tsat= 250°F by a nickel-plated heating element whose surface temperature is maintained at Ts= 280°F. The boiling heat transfer coefficient, the electric power consumed, and the rate of evaporation of water are to be determined. Assumptions1Steady operating conditions exist. 2Heat losses from the boiler are negligible. 3The boiling regime is nucleate boiling since ΔTTTs=−=−=°satF280 25030which is in the nucleate boiling range of 9 to 55°F for water. PropertiesThe properties of water at the saturation temperature of 250°F are (Tables 10-1 and A-9E) ρσlvl=====58820 07230 00375501208143.....lbm / ftlbm / ftlbf / ftlbm / sPr332hfglpl==⋅°lbm/ h fttu/lbmFTs=280°FWater 250°F94605561015Btu /lbmC Bμ..Heating elementAlso, g = 32.2 ft/s2and 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. Csf=Analysis(a)Assuming nucleate boiling, the heat flux can be determined from Rohsenow relation to be
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