Repeat Prob. 3–94 for liquid oxygen, which has a boiling temperature of 2183°C, a heat of vaporization of 213 kJ/kg, and a density of 1140 kg/m³ at 1 atm pressure.

Data From problem 94

The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm pressure) is 2196°C. Therefore,  nitrogen is commonly used in low-temperature scientific studies  since the temperature of liquid nitrogen in a tank open to the  atmosphere will remain constant at 2196°C until it is depleted.  Any heat transfer to the tank will result in the evaporation  of some liquid nitrogen, which has a heat of vaporization of  198 kJ/kg and a density of 810 kg/m³ at 1 atm.  Consider a 3-m-diameter spherical tank that is initially filled  with liquid nitrogen at 1 atm and 2196°C. The tank is exposed  to ambient air at 15°C, with a combined convection and radiation  heat transfer coefficient of 35 W/m² · K. The temperature of the

thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air if the tank is

(a) Not insulated,

(b) Insulated with 5-cm-thick fiberglass insulation (k = 0.035 W/m · K),

(c) Insulated with 2-cm-thick superinsulation which has an effective thermal conductivity of 0.00005 W/m·K.

Transcribed Image Text:

Tair = 15°C N₂ vapor 1 atm Liquid N₂ -196°C - Insulation