The boiling temperature of nitrogen at atmosphericpressure at sea level (1 atm) is -196°C. Therefore, nitrogenis commonly used in low-temperature scientific studies sincethe temperature of liquid nitrogen in a tank open to the atmosphereremains constant at -196°C until the liquid nitrogen inthe tank is depleted. Any heat transfer to the tank results inthe evaporation of some liquid nitrogen, which has a heatof vaporization of 198 kJ/kg and a density of 810 kg/m3 at1 atm.Consider a 4-m-diameter spherical tank initially filledwith liquid nitrogen at 1 atm and -196°C. The tank isexposed to 20°C ambient air with a heat transfer coefficientof 25 W/m2·K. The temperature of the thin-shelled sphericaltank is observed to be almost the same as the temperatureof the nitrogen inside. Disregarding any radiation heatexchange, determine the rate of evaporation of the liquidnitrogen in the tank as a result of the heat transfer from theambient air.
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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