Superheated vapor is flowing at a rate of 1.08x 10^6 grams/hour inside a pipe wi

Question

Superheated vapor is flowing at a rate of 1.08x 10^6 grams/hour inside a pipe with 0.05 m in diameter and 1x10^4 cm in length. The pipe is located in a power plant at 300 K, and has a uniform pipe surface temperature of 380 K. If the temperature drop between the inlet and exit of the pipe is 30 K, and the specific heat of the vapor is 2190 J/kg.K, determine the heat transfer coefficient as a result of convection between the pipe surface and the surroundings. Discuss how the heat loss from the vapor in the pipe can be reduced.

Explanation / Answer

The probelm can be solved by equating the heat transfers Heat lost by air inside pipe = heat lost by pipe through convention

mdot *Cp(dT) = hA(Ts-Tambient), here A is circumferencail area

Tambient = 300 K

Ts = 380

dT = 30

mdot = 1.08x10^6 gm/hr = 0.3 kg/s

A = pi*D*L = pi*0.05*100    = 15.707 (converting length of pipe from cm to m)

0.3*2190*30 = h*15.707*(380-300)

=====>h = 15.68 W/(m2 -K)

This can be reduced by insulating the pipe with non conducting material so that heat if at all gets trasfered from vapour to pipe surface but cannot escape to enviroment (in short reduce 'h')

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