Water flowing at 5000 kg/hr is to be heated from 20 C to 35 C by using hot water from another source at 100C. If the temperature drop of the hot water is not to exceed 15 C, how much tube length is needed in a parallel flow arrangement if a nominal 3 inch outer pipe and nominal 2 inch inner pipe are used. Assume the inner pipe wall thickness is 1/8 inch carbon steel with thermal conductivity k = 54 W/mK.

1. If the heat exchanger is to be composed of 1.25 m U-tubes connected in series, how many will be required. Also, determine the pressure drop for each fluid stream.

2. The heat exchanger is insulated to prevent losses, and the hot water flows in the annulus while the cold water which is to be heated flows in the inner pipe