1.A double pipe HE is constructed of a copper (k=380 W/mC) inner tube of internal diameter 1.2 cm and external diameter 1.6 cm and an outer tube of diameter 3.0. the convection heat transfer coefficient is reported to be hi = 700 W/m2 C on the inner surface of the tube and ho=1400 W/m2C on its outer surface. For a fouling factor Rfi=0.0005 m2 C/W on the tube side and Rfo = 0.0002 on the shell side, Determine (a) the thermal resistance of the HE per unit length and (b) Uo and Ui
(a) thermal resistance per unit length: R/L = [1/(2*3.1416*(0.6/100)*700)] + ln(0.8/0.6)/(2*3.1416*380) + [1/(2*3.1416*(0.8/100)*1400] + 0.0005 + 0.0002 R/L = 0.053 m-C/W (b) Uo = 1/{ [0.8/(0.6*700)] + [0.8*ln(0.8/0.6) / 380] + 1/1400 + 0.0002 } = 289.2 W/m2-C Ui = 1/{ 1/700 + 0.6*ln(0.8/0.6) / 380 + 0.6/(1400*0.8) + 0.0005 } = 342.6 W/m2-C
