Please Help! A circular tube with inner and outer diameters of 1.75 inches and 2
ID: 1862049 • Letter: P
Question
Please Help!
A circular tube with inner and outer diameters of 1.75 inches and 2.10 inches, respectively, is insulated on its outside surface. The outer diameter of the insulation is 3.75 inches, within the tube, there is a liquid flow whose bulk temperature is 240 degree F and local heat transfer coefficient h is 63 Btu/hr-ft2-degree F. The tube is made of steel having a thermal conductivity of 30.5 Btu/hr-ft-degree F, while the insulation is a foam whose conductivity is 0.021 Btu/hr-ft- degree F. Outside the insulation, there is a forced convection airflow with an h value of 9.6 Btu/ hr-ft2-degree F and a temperature of 85 degree f. What is the rate of heat loss from the liquid flow in the tube to the outside air per foot of tube length? What is the temperature at the outside surface of the insulation?Explanation / Answer
since 1 inch =0.0833 feet so 1.75 inch = 0.15 feet , 2.10 inch = 0.175 feet and 3.75 inch = 0.312 feet . since Q / L =2 (pi ) (change in temp) / [1 / (h1r1 ) + ln (r2 / r1) / k1 + ln (r3 / r2) / k2 + 1 / (h2r3) ] = 2 (pi) (240 - 85) / [ 1 / (63x0.15) + ln (0.175 / 0.15) / 30.5 + ln ( 0.312 / 0.175) / 0.021 + 1 / ( 9.6x0.312) ] = 973.89 / 27.98 = 34.80 btu / ft
2.) heat flow must be same so 34.80 = ( T - 240) / {27.98 - 1/(9.6*0.312)} means 34.80 = (T - 240) / 27.65 so T - 240 = 962.22 so wecan find T