Heat exchange – Regenerator – Heat collector
Patent
1990-12-07
1992-02-18
Davis, Jr., Albert W.
Heat exchange
Regenerator
Heat collector
165917, F28D 2000
Patent
active
050885480
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a heat accumulator comprising a storage container with a wall region provided for the introduction of heat and a storage medium arranged in this storage container.
On account of their high melting heat, alkali fluorides or alkaline-earth fluorides or their eutectics are, for example, very well suited for storing heat at high temperatures. High-alloy steels or high-purity nickel are used to encapsulate this storage medium in order to reduce the corrosion and ensure sufficient stability of the storage container at the high temperatures.
The encapsulation of the storage medium in such storage containers is very problematic as this storage medium undergoes great changes in volume of the order of magnitude of 20 to 30% during the melting or solidifying process, with the completely molten storage medium exhibiting a volume which is 20 to 30% larger than that of the solidified storage medium. The volume contraction during the solidification of the storage medium results in the formation of cavities (contraction cavities) in the interior of the storage medium.
These changes in volume cause problems during the melting process as the storage medium starts to melt in its region facing the walls of the storage container during the heating of the heat accumulator and the molten storage medium then exhibits a volume which is approximately 30% larger. However, so long as still solidified storage medium remains firm in the storage container, the molten storage medium must be provided with additional volume if it is not to deform the storage container because the contraction cavities are initially unable to compensate the increase in volume. In the hitherto known storage containers, it was not possible to provide the molten storage medium with additional volume. The storage container had to be so stable that the molten storage medium was able to displace the still solidified storage medium in order to create the necessary volume for itself. Attempts were made to remedy the situation by heat conducting plates being inserted in the interior of the storage container. However, owing to the changes in volume of the storage medium, these became deformed in a uncontrolled manner.
In addition, the mechanical stability of the storage container was impaired by the occurrence of corrosion problems, in particular, at the weld seams.
The object underlying the invention is, therefore, to so improve a heat accumulator of the generic kind that it has as long a service life as possible and, in particular, withstands a plurality of melting and solidifying processes.
This object is accomplished in accordance with the invention in that the wall region is provided with recesses which are open towards the storage medium, in that a wall surface of the wall region facing the storage medium is made of a material which is not wettable by the storage medium, and in that facing wall surfaces in the recesses exhibit such a spacing from one another that the storage medium does not penetrate into these to any substantial degree in the completely liquid state owing to the capillary forces.
The advantage of the inventive solution is to be seen in that all kinds of corrosion damage are prevented by the wall surface being made of a material which is not wettable by the storage medium and, in addition, the recesses create additional volume which the storage medium does not penetrate to any considerable degree in the completely liquid state and hence does also not penetrate in the solidified state, but it can penetrate into these against the action of the capillary forces when in the course of the melting process, the molten portion of the storage medium is under increased pressure owing to the increase in volume, and so the storage container is not subjected to increased pressure forces. Once a sufficiently large portion of the storage medium has then melted, it will have the possibility of penetrating into the cavities created during the solidification process owing to the volume contraction in the interior of the storage medium, an
REFERENCES:
patent: 4509590 (1985-04-01), Svetlila
patent: 4693338 (1987-09-01), Jensen et al.
patent: 4993481 (1991-02-01), Kamimoto et al.
Patent Abstracts of Japan, vol. 13, No. 526 (M-897) (3874), Nov. 22, 1989; & JP A 1212983 (Agency of Ind. Science & Technol.) Aug. 25, 1989.
Lindner Friedrich
Staehle Hans-Joerg
Tattermusch Peter
Davis Jr. Albert W.
Deutsche Forschungsanstalt fuer Luft - und Raumfahrt e.V.
Lipsitz Barry R.
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