Stirling Cooler and Stirling Engine

The Stirling cycle machine, which can operate as either an engine or a heat pump, has aroused much interest because of its many favorable characteristics. These include:

Minimal pollution. In the case of an engine, the exhaust gases are comparatively clean and cool.
Silent and practically vibrationless operation in some configurations.
Potential for low fuel or energy consumption. The maximum attainable efficiency or COP for any heat engine operating between the same temperature differential.
Multi-fuel capability. The energy source may be almost of any form whatever, so long as it is available at a sufficiently high temperature. Stirling engines have been run on solar energy and a variety of liquid and solid fuels. This applies to heat pumping as well by the use of the duplex configuration.
In many instances, it is possible to hermetically seal the machine thus eliminating problems arising from dirt ingress. Some of these configurations have demonstrated operating lives exceeding 10 years.
Reversible operation allowing the same device to be used as an environmentally friendly wide temperature range refrigerator or heat pump. This feature also introduces the possibilities of regenerative braking.
Reasonable specific power (currently between 0.067 kW(e)/kg for higher power engines down to 0.033 kW(e)/kg for lower power engines). As a low capacity heat pump (up to a few hundred Watts), the specific lift is considerably better than other heat pump technologies (30 to 40 W/kg).
Favorable torque characteristics for transportation applications. This leads to simpler transmission designs.
Mechanical simplicity. In some configurations gas bearings are easily implemented thus avoiding the need for oil lubrication.