Repeat Prob. 9–42 for a pan whose outer surface is polished and has an emissivity of 0.1.

Data from problem 42

Water is boiling in a 12-cm-deep pan with an outer diameter of 25 cm that is placed on top of a stove. The ambient air and the surrounding surfaces are at a temperature of 25°C, and the emissivity of the outer surface of the pan is 0.80. Assuming the entire pan to be at an average temperature of 98°C, determine the rate of heat loss from the cylindrical side surface of the pan to the surroundings by

(a) Natural convection

(b) Radiation.

(c) If water is boiling at a rate of 1.5 kg/h at 100°C, determine the ratio of the heat lost from the side surfaces of the pan to that by the evaporation of water. The enthalpy of vaporization of water at 100°C is 2257 kJ/kg.

Transcribed Image Text:

Vapor 1.5 kg/h Water 100°C 25°C 98°C e = 0.80