Power plants – Motor operated by expansion and/or contraction of a unit of... – Unit of mass is a gas which is heated or cooled in one of a...
Patent
1998-10-05
2000-03-28
Nguyen, Hoang
Power plants
Motor operated by expansion and/or contraction of a unit of...
Unit of mass is a gas which is heated or cooled in one of a...
60513, 60515, F01B 2910
Patent
active
060415991
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a thermal power machine of the type which is mentioned in the preamble of claim 1 and 9, is disclosed in DE-A1-41 09 289 and has a moving regenerator. The invention relates in particular to a thermal power machine for obtaining mechanical energy from solar energy.
One specific form of a thermal power machine having a regenerator is represented, for example, by the Stirling engine, also called a hot-gas engine, which embodies the oldest thermal power machine as well as the steam machine. The thermodynamic process of the Stirling engine comprises, in an idealized manner, four state changes: compression at low temperature (isothermal with heat extraction); heat supply at constant volume (isochoric); expansion at high temperature (isothermal with heat supply) and heat extraction at constant volume (isochoric). As a rule, Stirling engines have a stationary regenerator. Exceptions to this are low-temperature Stirling engines and cryocoolers.
In the case of Stirling engines of the type explained above, an auxiliary device is normally provided by means of which the regenerator is moved backward and forward between the heat sink and the heat source. This auxiliary device may be a mechanical coupling between the operating piston and the regenerator, with the interposition of an inertia mass. The disadvantage of this arrangement is its relatively complicated structure.
As an alternative to this, it is known for the regenerator of a Stirling engine to be moved backward and forward by a separate variable-volume component in the form of a small auxiliary piston which draws its power from the pressure fluctuations of the operating medium in the housing of the Stirling engine. As in the case of the solution using mechanical feedback from the operating piston to the regenerator, quoted above, the concept also has the disadvantage that an additional device, namely the auxiliary piston, is required. In addition, the force produced by the auxiliary piston is transmitted to the regenerator via a relatively small area. The forces to be overcome by the regenerator, namely its inertia and its flow resistance are, however, distributed homogeneously over the entire regenerator volume. For this reason, the physical difference between the force available from the auxiliary piston and the force required by the generator must be covered by said regenerator itself. However, because of its highly porous structure, the regenerator is not suitable for relatively large mechanical loads. For this reason, the use of an auxiliary piston is suitable for only very low Stirling engine frequencies at which no significant inertia forces occur, and thus only for low power densities. If, on the other hand, the power density is predetermined, as is the case, for example, with solar-powered flat collector engines, this concept is linked to large movement amplitudes of the regenerator and of the operating piston, as well, because of the low frequency. In addition, since a relatively high piston mass is required, the production costs of this thermal power machine type are correspondingly high. Furthermore, JP-3-78554A discloses a thermal power machine which has a large displacement cylinder and, coaxially with respect to it, a small piston cylinder, which cylinders are connected by a helical spring.
The invention is based on the object of providing a thermal power machine of the type mentioned initially and having a moving regenerator, with which higher operating frequencies and power densities can be achieved than with the conventional Stirling engine.
This object is achieved by the subject matter of claims 1 and 9. Advantageous developments of the invention are specified in the subclaims.
In the context of the present invention, operating piston should be understood as meaning any device which is suitable for varying the operating volume, for example a membrane, a bellows which is closed at one end, a liquid column or a gas column.
In other words, the thermal power machine designed according to the invention operates without an
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patent: 4367625 (1983-01-01), Vitale
patent: 5417066 (1995-05-01), Kawano et al.
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