Assume the water for a boiler is preheated using flue gases fromthe boiler stack. The flue gases are available at a rate of 0.25kg/s at 150°C, with a specific heat of 1000 J/kg · K. The waterentering the exchanger at 15°C at the rate of 0.05 kg/s is to beheated to 90°C. The heat exchanger is to be of the type with oneshell pass and four tube passes. The water flows inside the tubes,which are made of copper (2.5 cm ID, 3.0 cm OD). The heat transfercoefficient on the gas side is 115 W/m2 · K, while theheat transfer coefficient on the water side is 1150 W/m2· K. A scale on the water side and gas side offer an additionaltotal thermal resistance of 0.000176 m2 · K/W. a.Determine the overall heat transfer coefficient based on the outertube diameter. b. Determine the appropriate mean temperaturedifference for the heat exchanger. c. Estimate the required totaltube length. d. Calculate the percent over surface design and thecleanliness factor.
