Question

Consider geothermal hot water at P1 and T1; it is throttled to P2 in a unit called a flasher and satu rated vapor is used to drive a turbine which exhausts a wet mixture at P3. The saturated liquid is returned back to the ground. As flash pressure P2 is decreased, more vapor is produced and hence, more mass of vapor is sent to turbine. However, expansion ratio in turbine is reduced with reduced work output per unit mass of vapor in turbine.

Determine the optimum work if water is discharged as liquid at pressure P2 if T1 = 250°C, P1 = 4000 kPa, and if outlet pressure P3 is fixed at 4000 kPa and at 40°C. Assume state 3 to be incompressible.

Answer 1

In this solution some basic concepts of Thermodynamics and steam table data are used. Please refer to any standard textbook for more information or drop a comment below. Don't forget to give a positive rating if solution is helpful.

The trick behind the solution is simply that, the condition given at point actually lies exactly on the saturated line, so we would use the enthalpy of water hf at this stage. Follow the steps below.

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