2.25 Find the critical insulation radius for wool-felt insulation surrounding a
ID: 700928 • Letter: 2
Question
2.25 Find the critical insulation radius for wool-felt insulation surrounding a tube exposed to room air at 20°C with h 8 w/m2.K. what is the heat loss per meter of length for a 1-in. type K copper tube with and without a 2.0-cm-thick layer of this insulation if the temperature of the copper tube wall is 65°C? length inside radius of tube outside radius of tube 12.635 14.29 34.29 401 045 rl r2 r3 mmoutside radius of insulation KIWm K W/m K thermal conductivity, copper thermal conductivity, wool felt k2
Explanation / Answer
Critical radius of insulation = k/h
= 0.045/8 = 0.005625 m = 5.625 mm
Heat loss with insulation
Q = (T1 - T2) / [ln (r2/r1) *(1/2*3.14*k1*L) + ln (r3/r2) *(1/2*3.14*k2*L) + (1/h*2*3.14*r3*L)]
Q = (65 - 20) / [ln (14.29/12.635) *(1/2*3.14*401*1) + ln (34.29/14.29) *(1/2*3.14*0.045*1) + (1/8*2*3.14*34.29*10^-3*1)]
= 45/ [(4.887 x 10^-5) + (3.097) + (0.58047)]
Q = 12.24 W/m
Heat loss without insulation
Q = (T1 - T2) / [ln (r2/r1) *(1/2*3.14*k1*L) + (1/h*2*3.14*r2*L)]
Q = (65 - 20) / [ln (14.29/12.635) *(1/2*3.14*401*1) + (1/8*2*3.14*14.29*10^-3*1)]
= 45/ [(4.887 x 10^-5) + (1.392)]
Q = 32.31 W/m
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