Da Vinci Co., a start-up company specializing in heat control technologies in Nara Prefecture, Japan., has been developing a system that recovers low-temperature waste heat and generates electricity using a rotary heat engine (RHE). The utilization of low-temperature waste heat of 80 to 200 degrees Celsius has long been considered technologically unfeasible. The company intends to complete a 30-kilowatt system by May 2011, start production around December after an durability test, and commence sales in March 2012.
Da Vinci's RHE is an external-combustion type, Wankel-based rotary heat engine driven by the Rankine cycle. Da Vinci has developed RHEs jointly with the University of Tokyo, completing a 500-watt model in June 2009.
The RHE consists of a rotor, power generator, evaporator, condenser, and working fluid. External waste heat applied to the engine vaporizes the working fluid in the evaporator, which rotates the rotor, generating electricity with a directly-coupled generator. Gas that comes out of the rotor turns back into fluid in the condenser, from which point it returns to the evaporator.
Different working fluids including water, ethanol, and ammonia can be chosen for different waste heat temperatures. The system harnesses temperature differentials near the boiling point of the working fluid to effectively recycle low-temperature waste heat, and can be applied to generate power from waste heat recovered in factories, co-generation systems, and boilers. Read more from Japan for Sustainability