Acounterflow double-pipe heat exchanger is used to heat water from 20°c to 80°c at a rate of 1.2 kg/s. the heating is to be completed by geothermal water available at 160°c at a mass flow rate of 2 kg/s. the inner tube is thin-walled and has a diameter of 1.5 cm. if the overall heat transfer coefficient of the heat exchanger is 640 w/m2k, determine the length of the heat exchanger required to achieve the required heating.

L=109.16 m

Explanation:

Given

initial temperature

Final Temperature

mass flow rate of cold fluid

Initial Geothermal water temperature

Let final Temperature be T

mass flow rate of geothermal water

diameter of inner wall

specific heat of water

balancing energy

Heat lost by hot fluid=heat gained by cold Fluid

As heat exchanger is counter flow therefore

heat lost or gain by Fluid is equal to heat transfer in the heat exchanger

(LMTD)

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