Question 1. Fouling factor (70 marks) A brass tube of inner and outer diameters is 25 mm and 28 mm, respectively, is use

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Question 1 Fouling Factor 70 Marks A Brass Tube Of Inner And Outer Diameters Is 25 Mm And 28 Mm Respectively Is Use 1 (188.89 KiB) Viewed 21 times

Question 1. Fouling factor (70 marks) A brass tube of inner and outer diameters is 25 mm and 28 mm, respectively, is used in a crossflow heat exchanger. The inner fluid is water with inlet temperature of 70 °C and velocity of 0.5 m/s. The crossflow fluid is air at 20°C with a velocity of 15 m/s. The fouling factors, R's, for the inner and outer surfaces are 0.0004 and 0.0002 m² K/W, respectively. (a) Make a simple sketch to demonstrate the problem. Determine the overall heat transfer coefficient based on the outside area of the tube (U.) and the water outlet temperature. Compare the thermal resistances due to convection, tube wall conduction, and fouling. Assume constant thermal conductivity of the solid material. Validate the referenced temperature used for the thermal-physical properties of the fluids. (30 marks) (b) The air velocity is varied between 5 and 25 m/s: calculate and plot the corresponding heat transfer between the two fluids. (20 marks) (c) Assume the above fouling factors increase 40% every year. Air velocity is fixed at 15 m/s: calculate and plot the overall heat transfer coefficient which reduces over 5 years. If the equipment is to be serviced when the overall heat transfer coefficient is reduced by 25% from its initial value, how long after installation should the first cleaning be scheduled for continuous operation? (20 marks)