Question

A heat exchanger is being investigated as a waste heat recovery device. A heat exchanger is common device for using a hot fluid to heat a cold fluid without the fluids mixing. The cold fluid stream of liquid A enters at 294.2 K and leaves the device at a temperature of 330.91 K. Liquid A flows at a rate of 0.006 Kg/s and has a specific heat of 4180 J/(Kg K) and a specific volume of 0.00102 m³/Kg. Liquid B enters the device at a temperature of 350.2 K and flows at a rate of 0.005 Kg/s and has a specific heat of 3900 J/(Kg K) and a specific volume of 0.00133 m³/Kg. The dead state is at 293.2 K and 1 bar. The device is adiabatic and the pressure loss for fluid A is 0.001 bars and for fluid B it is 0.002 bars. Both liquids can be considered to be incompressible materials.

1. Using the first law determine the exit temperature of fluid B.
2. Calculate the heat transfer rate between the fluids.
3. Calculate the rate of exergy destroyed in the heat exchanger
4. Calculate the second law efficiency for this device. The exergy product is the exergy increase in liquid A and the exergy input is the exergy change in liquid B.
5. If the exiting liquid B is not used for any useful purpose, calculate the exergy destroyed associated with it.

Answer 1

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