530.231_HW6 - 530.231 Fall 2009 HOMEWORK NO.6 1. In a steam...

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530.231 Fall 2009 HOMEWORK NO.6 1. In a steam power plant 1.5 MW is added in the boiler, 0.86 MW is taken out in the condenser and the pump work is 0.05 MW. Find the plant thermal efficiency. If everything could be reversed find the coefficient of performance as a refrigerator. 2. Refrigerant-12 at 80°C, x = 0.3 flowing at 1.5 kg/s is brought to saturated vapor in a constant-pressure heat exchanger. The energy is supplied by a heat pump with a coefficient of performance of β′ = 3.0. Find the required power to drive the heat pump. 3. A temperature of about 0.01 K can be achieved by magnetic cooling. In this process a strong magnetic field is imposed on a paramagnetic salt, maintained at 1 K by transfer of energy to liquid helium boiling at low pressure. The salt is then thermally isolated from the helium, the magnetic field is removed, and the salt temperature drops. Assume that 1.5 mJ is removed at an average temperature of 0.2 K to the helium by a Carnot-cycle heat pump. Find the work input to the heat
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530.231_HW6 - 530.231 Fall 2009 HOMEWORK NO.6 1. In a steam...

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