I want to know how to solve part B Problem 1: A thin walled copper tube having a

Question

I want to know how to solve part B

Problem 1:

A thin walled copper tube having an outside metal radius r= 0.008m carries steam at 383K.It is inside a room where the surrounding air temperature is 298K.It is insulated with 85% magnesia insulation having an approximate thermal conductivity of 0.071 W/m.K

a)      What is the critical thickness of insulation for an external convective coefficient h=4 W/m2K?

(Assume negligible conductive resistance due to the wall of the copper tube)

Note: Critical thickness is given by rcritical =k/h

Where k= thermal conductivity

              h = heat transfer coefficient

B)

b)      Under these conditions, determine the radial heat transfer rate per meter of tube length q

Explanation / Answer

Rate of heat transfer H = dQ/dt = KA(T2-T1)/d

A. d = KA(T2-T1)/H = 0.0071 * 3.14 * 0.008^2 * (383-298)/4

d = 30.3 um

b. dQ/dt = 0.0071 * 3.14 * 0.004*0.004 * 85/30.3*10^-6

dQ/dt = 1 W/m^2

c. 4 W.m^2K

d. dQ/dt = 0.0071 * 3.14 * 0.05*0.05 * 85/30.3*10^-6 = 1.84 Wm^2K

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