A shell-and-tube heat exchanger (1 shell pass, 2 tube passes) is to be used to condense 2.73 kg/s of saturated steam at 340 K. Condensation occurs on the outside tube surfaces, and the corresponding convection coefficient is 10,000 W/m ² K. The temperature of the cooling water entering the tubes is 15?C and the exit temperature is not to exceed 30?C. Thin wall tubes of 19-mm diameter are specified and the mean velocity of water flow through the tube is to be maintain at 0.5 m/s.

a. What is heat transfer rate for the heat exchanger? What is the required water flow rate? What is the minimum number of tubes that should be used and what is the corresponding tube lengths per pass?

b. To reduce 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 a factor of two, what is the required length per pass.

Sat. water (340 K): h _fg = 2.342 x 10 ⁶ J/kg: Sat. water (T? _c = 22.5?C ? 295 K): ? = 998 kg/m ³ , c _p = 4181 J/kg-K, ? = 959 x 10 ^-6 N.s/m ² , k = 0.606 W/m.K. P _r = 6.62.

ho= 10,000 W/m-K N tubes D = 0.019m Saturated steam mcond = 2.73 kg/s, Th = 340 K TC,0 30C Tc,i = 15C Um = 0.5 m/s Water