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)

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.