Barton evaporation engine

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Thermodynamics
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The Barton evaporation engine (BEE) is a heat engine developed by Sunoba Pty Ltd.

Principle

The principle of the BEE is based on: (1) adiabatic expansion of unsaturated air; (2) evaporative cooling at reduced pressure; and (3) re-compression back to atmospheric pressure with further evaporation. By this means, the engine produces power and cooled moist air from water and hot dry air:

hot dry air + water → power + cooled moist air

With a modest amount of passive solar pre-heating, the engine theoretically is able to produce power in hot arid climates. As well as being a heat engine, the BEE can also be used as an evaporative cooler.

Moreover, the BEE has broadly comparable theoretical efficiency to simple Rankine steam turbines, without need for high-pressure boiler or condenser. The BEE can function well on industrial waste heat, particularly the exhaust gas of open cycle gas turbines.

Performance

It is claimed ^[1] that under suitable weather conditions, and assuming evaporation to saturation at constant volume in the low-pressure section and no further evaporation, a BEE engine would convert approximately 4-5% of energy collected at 30-40C above ambient into electrical or mechanical power (further evaporation during the re-compression step (3) would more than double this estimate). Whilst this efficiency is not high, the inputs will be inexpensive since the requisite pre-heating can be accomplished by passive solar methods, and hot air is both the heat transfer medium and the working gas. The engine does not require heat exchangers or condensers as with Rankine cycle engines.

In general, the efficiency of the BEE increases with the inlet temperature and the expansion ratio. A full thermodynamic analysis is available ^[2]. If the inlet air is sourced from an Open-Cycle Gas Turbine exhaust at 500 degrees Celsius, the theoretical work output is approximately 150 kJ per kg of dry air throughput.

The thermodynamic cycles for the BEE and the Brayton gas engine can be combined in an engine consisting of a single device which would have remarkably high efficiency.

See also

• Drinking bird - a toy that works on similar principles.

References

External links

• About Sunoba Pty Ltd