In a chemical plant a solution of density 1100 kg/m3 and specific heat capacity 4.6 kJ/kg-K is to be heated from 65 to 1000C.The required flow rate of the solution is 11.8 kg/s. A tubular heat exchanger is used for this with the solution flowing at about 1.2 m/s in 25 mm bore iron tubes and being heated by wet steam at 1150C.The length of the tubes is not to exceed 3.5m. Taking inside and outside heat transfer coefficient as 5 and 10 kW/m2 K and neglecting the thermal resistance of the tube wall estimate the number of tubes and the number of tube passes required.