Water at a flow rate of 20,000 kg/h will be heated from 20°C to 35°C by...

Water at a flow rate of 20,000 kg/h will be heated from 20°C to 35°C by hot water at 140°C. A 15°C hot water temperature drop is allowed. A number of 3.5 m hairpins of 3 in. (ID = 0.0779 m) by 2 in. (ID = 0.0525 m, OD = 0.0603 m) counter flow double-pipe heat exchangers with annuli and pipes, each connected in series, will be used. Hot water flows through the inner tube. Fouling factors are: Rf i = 0.000176 m² ? K/W, Rfo = 0.000352 m² ? K/W. Assume that the pipe is made of carbon steel (k = 54 W/m ? K). The heat exchanger is insulated against heat losses. Assume that the allowable pressure drop in the annulus is 10 kPa. The velocity of cold water through the annulus will be around 3 m/s, which would require a large pressure drop to drive the cold fluid through the inner tube. The pressure drop could be reduced by using several units with cold water flowing in four parallel units and hot water flowing through the inner tube in series. Calculate: a. The overall heat transfer coefficient b. Pressure drop in the annulus c. The appropriate mean temperature difference.

Expert Solution

samet mamat answered 2 years ago

Water flowing at a rate of 0.03 kg/s is heated from 20 to 40°C in a...

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