Repeat Problem 1.23 but assume that the surface of the storage vessel has an absorptance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at ???183°C is 213.3 kJ/kg.

From Problem 1.23: A spherical vessel of 0.3 m in diameter is located in a large room whose walls are at 27°C (see sketch). If the vessel is used to store liquid oxygen at ???183°C and the surface of the storage vessel as well as the walls of the room are black, calculate the rate of heat transfer by radiation to the liquid oxygen in watts and in Btu/h.

GIVEN

A spherical vessel of liquid oxygen in a large black room

Emittance of vessel surface (ε) = 0.1

Liquid oxygen temperature (To) = ???183°C = 90 K

Sphere diameter (D) = 0.3 m

Room wall temperature (Tw) = 27°C = 300 K

Heat of vaporization of oxygen (hfg) = 213.3 kJ/kg

ASSUMPTIONS

Steady state prevails

The temperature of the vessel wall is equal to the temperature of the oxygen

Convective heat transfer isnegligible

-Tw- 300 K Lig. OX -183C To-90 K