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Condensation
heat pump |
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Condensation Heat Pump |
Sunoba Renewable Energy Systems |
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Heat pumps use work to transfer
heat energy from a cold reservoir to a hot reservoir. Common examples are refrigerators and
reverse-cycle air conditioners. It is possible to
construct a heat pump with opposite function to the evaporation engine, that is: power + moist air
→ heated dry air + water In
addition to drying the air and removing impurities, the condensation heat
pump might be useful for air heating in cool moist climates. Other applications might be as a hot water
heater, frost protection for crops, drying of goods or foodstuffs, and
de-fogging public spaces. The
condensation heat pump uses a low-pressure gas cycle, in which moist air is
expanded and undergoes condensation at reduced pressure and temperature. The condensate is collected and the
thermodynamic cycle is completed by returning the pressure to ambient. This cycle can be implemented in
continuous-flow or piston-in-cylinder configurations. The
piston-in-cylinder version is analysed in Article
[4]. As an
example of output of the piston-in-cylinder version, take saturated air at
15°C and expand it to 1.32 of its original volume. That requires expansion work of − 4,252 J/kg dry air, and will
result in condensation of 5.1 ml of water per kg of dry air. The condensate is removed from the air in
the chamber where the temperature will be just above freezing. On allowing the air to re-compress back to
atmospheric pressure, work of + 3,743 J/kg dry air can be reclaimed. The nett specific
work associated with the cycle is w
= − 509 J per kg of dry air where the minus sign denotes that work must
be supplied. For the
above example, the outlet temperature is 13.1°C warmer than the inlet and the
Coefficient of Performance of the condensation heat pump (CP*ΔT/w) is 25.9. If it could be economically manufactured,
this device would be a superb heat pump for saturated inlet air in the range
10-20°C, which corresponds to conditions when humans start to feel the need
of extra warmth. In addition to the
heat pump effect, the drying engine will dry and purify the air, which might
be important in various applications. The Coefficient of Performance of the
condensation heat pump is remarkably good, as shown theoretically in Technical Reports 2011-1 and 2012-1. An abridged version can be viewed at www.sunoba.blogspot.com (see the
post for 8 December 2011). The effect
of inevitable turbine and compressor losses in a continuous-flow version has
been studied in Technical Reports 2011-2 and 2012-2. |
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© Sunoba Pty Ltd 9 February 2012 |
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