The boiling temperature of nitrogen at atmospheric pressure at sea level (1?atm) is ??196°C. Therefore, nitrogen is commonly used in low-temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere remains constant at ??196°C until the liquid nitrogen in the tank is depleted. Any heat transfer to the tank results 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 4-m-diameter spherical tank initially filled with liquid nitrogen at 1 atm and ??196°C. The tank is exposed to 20°C ambient air with a heat transfer coefficient of 25?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. Disregarding any radiation heat exchange, determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air.
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A 4-m diameter spherical tank filled with liquid nitrogen at 1 atm and -196*C is exposed to convection with ambient air. The rate of evaporation of liquid nitrogen in the tank as a result of the heat transfer from the ambient air is to be determined.
Assumptions 1 Steady operating conditions exist. 2 Heat transfer by radiation is disregarded. 3 The convection heat transfer coefficient is constant and uniform over the surface. 4 The temperature of the thin-shelled spherical tank is nearly equal to the temperature of the nitrogen inside.
Properties The heat of vaporization and density of liquid nitrogen at 1 atm are given to be 198 kJ/kg and 810 kg/m3, respectively.
Analysis The rate of heat transfer to the nitrogen tank is
Then the rate of evaporation of liquid nitrogen in the tank is determined to be
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Fill in the blank(s) with correct word