Chapter 11, Problem 11.67P

Humid air at 40 psia, 50oF, and 90 percent relative humidity is heated in a pipe at constant pressure to 120oF. Calculate the relative humidity at the pipe outlet and the amount of heat, in Btu/lbm dry air, required.

Determine the relative humidity and dew point temperature of moist air at 95 F dry bulb temperature, 80 F thermodynamic wet bulb temperature, and 13.2 psia pressure.

A 1.5-m-diameter, 4-m-long cylindrical propane tank is initially filled with liquid propane, whose density is 581 kg/m3. The tank is exposed to the ambient air at 25°C in calm weather. The outer surface of the tank is polished so that the radiation heat transfer is negligible. Now a crack develops at the top of the tank, and the pressure inside drops to 1 atm while the temperature drops to -42°C, which is the boiling temperature of propane at 1 atm. The heat of vaporization of propane at 1 atm is 425 kJ/kg. The propane is slowly vaporized as a result of the heat transfer from the ambient air into the tank, and the propane vapor escapes the tank at -42°C through the crack. Assuming the propane tank to be at about the same temperature as the propane inside at all times, determine how long it will take for the tank to empty if it is not insulated.