The boiling temp of nitrogen at 1 atm is -196°C. If the temperature of liquid nitrogen in a tank open to the atmosphere at sea level will remain constant until it is depleted, then 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 3.5-m-diameter spherical tank that is initially N; vapor filled with liquid nitrogen at 1 atm and -196°C. The tank is exposed to ambient air at 16°C, with a convection heat transfer coefficient of 32 W/m2- °C. 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 (in kg/s) as a result of I atm Liquid N3 -196°C" heat transfer from the ambient air if the tank is (a) not insulated, (b) insulated with 6-cm thick fiberglass insulation (k=0.035 W/m-°C) and (c) insulated with 2-cm thick super-insulation which has an effective thermal conductivity of 0.00045 W/m-°C. Insulation

The boiling temp of nitrogen at 1 atm is -196°C. If the temperature of liquid nitrogen in a tank open to the atmosphere at sea level will remain constant until it is depleted, then 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 3.5-m-diameter spherical tank that is initially N; vapor filled with liquid nitrogen at 1 atm and -196°C. The tank is exposed to ambient air at 16°C, with a convection heat transfer coefficient of 32 W/m2- °C. 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 (in kg/s) as a result of I atm Liquid N3 -196°C" heat transfer from the ambient air if the tank is (a) not insulated, (b) insulated with 6-cm thick fiberglass insulation (k=0.035 W/m-°C) and (c) insulated with 2-cm thick super-insulation which has an effective thermal conductivity of 0.00045 W/m-°C. Insulation

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.34P

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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.
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