A concentric tube heat exchanger is comprised of a thin wall inner tube of 25.4 mm diameter and an outer tube of 47 mm diameter. The heat exchanger is used for cooling lubricating oil. The exchanger operates in counterflow, the inner tube carrying water and the outer tube carrying the oil with an overall heat transfer coefficient of 65 W/m²K. The following figure illustrates the heat exchanger. Properties of water are in Table A.6, oil properties in Table A.5.

a)  If the oil outlet temperature is 55^oC, determine the total heat transfer and the water outlet temperature.

b)  Determine the length required for the tube heat exchanger.

A concentric tube heat exchanger, counterflow arrangement was designed to heat water from 20^oC to 80^oC using hot oil that is supplied to the annulus at 160^oC and discharged at 140^oC. The thin-walled inner tube has a 20 mm diameter. The overall heat transfer coefficient if 527 W/m² K. The designed condition requested a total heat transfer rate of 3700 W.

 a) What  is the length of this heat exchanger?

 b) After 3 years of operation, the heat exchanger performance is degradated by fouling on the water side, and the water outlet temperature is 57^oC for the same flow rate and inlet temperatures. What are the corresponding values of the heat transfer rate, the oil outlet temperature, the overall heat transfer coefficient, and the water side fouling factor, R^"_f,c?

A Shell-and-tube Heat Exchanger (1 shell pass, 2 tube passes) is to be used to condensate 3.21 kg/s of saturated steam at 350K. Condensation occurs on the outer tube surfaces, and the corresponding convection coefficient is 10,215 W/m²K. The temperature of the cooling water entering the tubes is 15^oC. Thin-walled tubes of 20mm diameter are specified, and the mean velocity of water flow through the tubes is to be maintained at 0.45 m/s.

a) What  is the minimum number of tubes that should be used?

b) What  is the corresponding tube length per pass?

c) To reduced the size of the heat exchanger, it is proposed to increase the water side convection coefficient by inserting a wire mesh in the tubes. If the mesh increases the convection coefficient by 2, what is the required tube length per pass?