Home	Investors	Key people
BEE introduction	BEE cycle	Brayton-BEE cycle
BDE introduction	References	Contact

The Barton Evaporation Engine* * patent pending	Sunoba Renewable Energy Systems
The BEE is a heat engine which 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 will produce useful power in hot arid climates. As well as being a heat engine, the BEE can also be used as an evaporative cooler. How does this fit with the 2nd Law of Thermodynamics? You might think that the concept hot dry air + water → power + cooled moist air violates the 2^nd law of thermodynamics (2LT). How is it possible to convert the heat energy in the vibrations of air molecules into power, and yet not decrease the entropy in the overall system (which would violate 2LT)? The answer lies in the fact that entropy increases as water evaporates into vapour; the entropy gain in the vapour offsets the entropy loss in the air as it is cooled. There is no violation of 2LT. The BEE cycle The BEE uses a low-pressure gas cycle in which hot dry air is expanded and then evaporatively cooled at reduced pressure. Evaporative cooling continues as the air is allowed to re-compress back to atmospheric pressure. The moistened air is released to the atmosphere. Surplus work is available during the thermodynamic cycle, which can be implemented in continuous-flow and piston-in-cylinder configurations. In its piston-in-cylinder form, the BEE will be quiet, large but unobtrusive, and slow-revving. In general, the BEE will have comparable theoretical efficiency to simple Rankine steam turbines, without need for high-pressure boiler or condenser. As an example of the output of the BEE, air at 30°C and 47% relative humidity pre-heated to 85°C theoretically delivers 4.9 kJ work output per kg of dry air by evaporation of 19 ml of water per kg of air at an expansion ratio of 1.64. If the cycle time is 1 second, the theoretical average power output would be 4.9 kW/kg of air. (At 30°C, 1 kg of air occupies a little less than 1 cubic metre.) If the same ambient air is heated to 400°C and an expansion ratio of 4.3 is used, the theoretical work output is 105.6 kJ/kg of air from evaporation of 98.5 ml water.
Some headline theoretical results are: ► specific water consumption is approximately 20 litres water per kWhr at 65°C inlet temperature, but much less at high inlet temperatures (approximately 4 litres per kWhr at 400°C) ► the efficiency increases with the amount of pre-heating: for the examples above, the efficiency is 8.7% at 85°C and 27.7% at 400°C ► the exhaust gas from the BEE is saturated and much cooler than the inlet; evaporative coolers can deliver useful power! ► in common with all gas cycle engines, the BEE has a high back-work ratio (here, the work required to expand the gas divided by the work received on re-compression); the design for the experimental BEE was developed to cope with losses that arise from such a high ratio	The headline results at left do not take account of losses, which are the subject of research such as the leakage-friction tests shown above. Reference: Technical Report 2007-2.
An experimental BEE has been constructed and successfully tested. Shown below is a concept sketch for the design that was used. This design incorporates an inertial dual-acting piston, which was introduced to help control back-work losses in the engine. The experimental engine has two chambers, with inlet and outlet valves at each end. Each stroke delivers power. This mechanical concept will be radically modified in the prototype that is under consideration.
	© Sunoba Pty Ltd 21 April 2010