# Question: 3 as the example we did in class a stainless...

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3. As the example we did in class, A stainless steel pipe (k=17 W/mK) containing hot condensate at 100 ˚C is insulated by a 1 cm thick layer of insulation (k=0.015 W/mK). The pipe has di = 0.03561 m and do = 0.0381 m. Air on the outside of the pipe at 25 ˚C resulted in a ho=6.8 W/m2K. For air at 25 ˚C, β=3.55x10-3/K, ρ=1.205 kg/m3, cp=1.005 kJ/kg·K, k=0.0263 W/m·K, η= 15.54x10-6m2/s. Now, the condensate flows at an average velocity of 1.5 m/s, and with a viscosity of 1.33x10-3Pa.s, a density of 1,032 kg/m3. A layer of scale developed inside the pipe over time, with a negligible thickness, but a fouling coefficient of hf = 100. W/m2K. (note: Rf = 1/Ahf) , and cp = 4117 J/kg.K, k = 0.622 W/m.K Find the overall heat transfer coefficient, U, and the rate of heat transfer per unit length of pipe, and the temperature at the outside surface of the insulation. You may use Nu = 0.023*Re0.8Pr1/3 for turbulent flow inside the pipe, if Re>10,000.