17. Questions for Practice

An organic vapor is condensing on the outer surface of a 5 m long copper (\(k=400\) W/m.K) tube having 25 mm OD and 20 mm ID. The heat transfer coefficient of the vapor is 1500 W/m\(^2\).K. The coolant enters at 300 K and leaves at 325 K. The coolant side heat transfer coefficient is 2500 W/m\(^2\).K and the fouling coefficients on the inner and outer surfaces are 2000 W/m\(^2\).K and 4000 W/m\(^2\).K respectively. The vapor condenses at 355 K. Determine the overall heat transfer coefficient and the heat transfer rate. (AU-Nov-2007)

2: A shell and tube heat exchanger with 2-shell passes and 8-tube passes is used to heat ethyl alcohol ($C_P=2670$ J/kg.oC) in the tubes from 25oC to 70oC at a rate of 2.1 kg/s. The heating is to be done by water ($C_P=4190$ J/kg.oC) that enters the shell side at 95oC and leaves at 45oC. If the overall heat transfer coefficient is 950 W/m2,oC, determine the heat transfer and the surface area of the heat exchanger. (AU-Nov-2016)



3. A chemical plant produces 300 metric tons of sulphuric acid per day. The acid is to be cooled from 333 K to 313 K by 500 metric tons of water per day, which has a initial temperature of 288 K. A counter flow cooler consisting of concentric pipes 12.5 mm thick is to be used. The inner pipe through which the acid flow is 75 mm bore and outer one 125 mm bore. The outside diameter of the inner pipe is 100 mm. The physical properties of the fluid the mean temperature are as follows:

Acid Water
Density, kg/m\(^3\) 1800 998.2
Heat capacity, kJ/kg.K 1.465 4.187
Thermal conductivity, W/m.K 0.302 0.669
Viscosity, kg/m.s 0.0112 0.0011

Thermal conductivity of the pipe material is 46.52 W/m.K. Use Dittus-Boelter equation for the calculation of \(h\). Also calculate the length of pipe required. (AU-Nov-2014)