This application is a continuation, of application Ser. No. 07/090,512, filed Aug. 28, 1987.

FIELD OF THE INVENTION

The present invention relates to a heater which is used as a secondary heat source for heating a Stirling engine.

BACKGROUND OF THE INVENTION

A prior art technique of this kind is disclosed in Japanese Patent Laid-Open No. 93,939/1980 entitled "Heat Exchanger in External Combustion Engine." In this prior art technique, heater tubes for a Stirling engine are disposed inside the heating chamber of a heater. The space in which the heater tubes are located is filled with inert gas. The heater tubes are heated by a high-temperature heat source located outside the heating chamber via the inert gas. This technique is intended for homogeneous distribution within the heater tubes and also for protection of the tubes against heat.

This prior art technique has certain problems. For example, when the amount of heat supplied from the high-temperature heat source varies, the amount of heat supplied from the heater head of the Stirling engine and used in operating the cycle changes. This heat change varies the shaft horsepower of the engine, and, as a result, a stable output cannot be obtained.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a heater which permits a Stirling engine to deliver output in a stable manner even if the amount of heat supplied from the high-temperature heat source varies.

The above object and others are achieved by a heater comprising a burner, heater tubes disposed in the burner, a high-temperature heat source for heating the heater tubes, and a space formed around the heater tubes and filled with heat-storing material which is sealed by a seal member and through which heat produced by the high-temperature heat source is supplied to the heater tubes. The heat-storing material acts as a secondary heat source for supplying the stored heat to the heater tubes.

The above object is also achieved by a method for heating a working fluid in a Stirling engine comprising providing a high-temperature heat source having a variable output including a low output range and a high output range, transferring heat to the working fluid from the heat source through a heat-storing material, storing heat from the heat source when said source is in the material, and maintaining the heat transfer to the working fluid at a substantially steady rate through transfer of the stored heat when the heat source is in the low output range.

When the amount of heat supplied from the primary heat source, i.e., the high-temperature heat source of the aforementioned heater, is large, heat is stored in the sealed heat-storing material. At the same time, heat is supplied to the heater tubes of the Stirling engine through the heat-storing material. When the amount of heat supplied from the high-temperature heat source is small or zero, the heat stored in the secondary heat source, i.e., the heat-storing material, is supplied to the heater tubes of the Stirling engine. Therefore, if the amount of heat supplied from the primary heat source, i.e., the high-temperature heat source, varies, the amount of heat supplied to the heater tubes and then to the cycle does not vary. This relatively constant supply of heat makes the shaft horsepower of the engine stable. In this way, the novel heater is free from the foregoing problem with the prior art technique.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a cross-sectional view of a heater according to the invention, the heater being used for a Stirling engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the FIGURE, a Stirling engine 10 has a heater 1 according to the invention mounted thereon. The heater 1 comprises a burner or burner housing 2, heater tubes 3 disposed in the burner housing 2, heat-storing material 5 that fills a space 4 formed around the heater tubes 3, a seal member 6 for sealing the heat-storing material 5, and a high-temperature heat source 7. The heater tubes 3 transfer a working fluid of the engine and connect expansion spaces 8 with heat accumulators 9, respectively. Heat produced by the heat source 7 is supplied to the heater tubes 3 through the heat-storing material 5. In addition, heat stored in the heat-storing material 5 can be furnished to the heater tubes 3 and, therefore, the heat-storing material 5 acts as a secondary heat source.

The heat-storing material 5 can make use of sensible heat, latent heat, or a chemical reaction to store heat. When sensible heat is employed, Na, NaK, or LiF is used. When latent heat (i.e., heat of fusion) is utilized, Li₂ CO₃, NaCl, or MgCl₂ is used. When a chemical reaction is employed, any of the following chemical reactions can be used:

Li₂ CO₃ ⃡Li₂ O+CO₂ +53.4 Kcal/mol

SrCO₃ ⃡SrO+CO₂ +56.5 Kcal/mol

CaCO₃ ⃡CaO+CO₂ +42.6 Kcal/mol

It is also possible to combine two or more sensible heat materials, or two or more latent heat materials. Two or more chemical reaction materials can also be combined, but generally it is not feasible to combine different types of materials (e.g., a chemical reaction material with a sensible heat material or a latent heat material).

Generally, the Stirling engine is operated at a temperature of from about 700° C. to about 900° C. A sensible heat material is generally kept at subatmospheric pressures, while latent heat materials and chemical reaction materials are utilized under substantially atmospheric pressure.

In the heater 1, the heat-storing material 5 is sealed in the burner or burner housing 2. When the amount of heat supplied to the heater 1 from the high-temperature heat source 7 is large, that is the heat source has a high output, heat is stored in the inserted heat-storing material 5. When the amount of heat supplied from the high-temperature source 7 is small or zero, heat is supplied to the heater tubes 3 of the Stirling engine 10 from the heat-storing material 5 acting as a secondary heat source. Therefore, if the amount of heat supplied from the high-temperature heat source 7 varies, the quantity of heat supplied from the heater tubes 3 to the cycle will not vary. Consequently, the shaft horsepower of the engine is stable.

As described above, the use of the novel heater makes the temperature distribution uniform within the heater tubes of the heater head, and protects the tubes against excessive heat. Also, even if the amount of heat supplied from the high-temperature heat source varies, a stable shaft horsepower is obtained. Since the layer for storing heat is formed around the heater head, the changes in the temperature of the heater tubes are minute irrespective of the changes in the amount of heat applied. This eliminates the problem of thermal fatigue.

As an example, the engine is used as an engine for a generator that employs solar heat as its heat source. The engine is installed in an artificial satellite which makes one revolution around the earth in 90 minutes. In this case, when the prior art techniques are used, heating of 45 minutes alternates with non-heating of 45 minutes. In the present invention, during heating, heat is stored simultaneously with the operation of the engine and s the engine is continuously run for 90 minutes per period. Therefore, the engine can be run continuously. Hence, the novel engine generates twice as much electric power as the power generated by the existing engine of the same size. In addition, causes of troubles are avoided, because it is not necessary to repeatedly start and stop the engine.