A cylindrical pure aluminum tube has liquid nitrogen flowing through it. It ente

Question

A cylindrical pure aluminum tube has liquid nitrogen flowing through it. It enters the tube at 77K as saturated liquid. The outer surface is exposed to air at 25 degree celcius with a heat transfer coefficient of 35 W/m^2.K. The inner surface heat transfer coefficient is 120 W/m^2.K. The inner diameter is 2 cm and the tubing is 0.2 cm thick. If the tube is 5 meters long and the mass flow rate is 0.2 kg/s, will the liquid nitrogen coming out of the tube be 100% vapor ? The heat of vaporization for liquid nitrogen is 125 KJ/kg.

A cylindrical pure aluminum tube has liquid nitrogen flowing through it. It enters the tube at 77K as saturated liquid. The outer surface is exposed to air at 25 degree celcius with a heat transfer coefficient of 35 W/m^2.K. The inner surface heat transfer coefficient is 120 W/m^2.K. The inner diameter is 2 cm and the tubing is 0.2 cm thick. If the tube is 5 meters long and the mass flow rate is 0.2 kg/s, will the liquid nitrogen coming out of the tube be 100% vapor ? The heat of vaporization for liquid nitrogen is 125 KJ/kg.

Explanation / Answer

heat of vaporization for liquid nitrogen is 125 KJ/kg

Now heat Gain by liquid nitrogen

=(T2-T1)/Rth Rth=thermal resistance

Now Rth=1/h1A1+ln(r2/r1)/(2*pi*k*l)+1/h2A2

K for aluminium=237 W

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