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5. A small solar engine for desert water pumping uses steam as the working fluid. The

hardware is shown in the figure below. Water enters the pump as a saturated liquid at

50°C and is pumped up to 0.2 MPa by a small centrifugal pump. The boiler, powered

by solar collectors, evaporates water at 0.2 MPa, and saturated vapor at this pressure

enters the small turbine. The steam leaves the turbine with 6% liquid at 50°C and is

subsequently condensed. The flow rate is 140 kg/hr and the pump is driven by a 400

W motor operating at full load. Making suitable idealizations, determine the power

output of this plant (net power) and the energy conversion efficiency (net shaft-work

output to energy transfer to fluid in the boiler), and estimate the area of solar collectors

that would be required, assuming the collectors can pick up 800 W/m².

QSOLAR

Pump

We

1

1

Boiler

Condenser

Qc

Figure 1: Schematic for problem 5.

4

Turbine

Wp

Fig: 1