GB2037977A

GB2037977A - Thermal storage device

Info

Publication number: GB2037977A
Application number: GB7942360A
Authority: GB
Original assignee: Stichting Bouwcentrum
Current assignee: Stichting Bouwcentrum
Priority date: 1978-12-22
Filing date: 1979-12-07
Publication date: 1980-07-16
Also published as: DE2949209A1; BE880786A; FR2444919A1; NL169640B; DE2949209C2; NL169640C; NL7812510A

Abstract

A medium for the storage of heat comprises a substantially homogeneous mixture of gravel (1) (defined as being stone, pebbles or sand) and aluminium particles (2) including chippings, grains and/or powder. <IMAGE>

Description

SPECIFICATION A medium for the storage of heat, and apparatus comprising such a medium.

This invention relates to a medium for the storage of heat, and to an apparatus for the storage of heat, comprising such a heat storage medium, and including means for supplying heat to the apparatus and means for removing heat from the apparatus.

Apparatus for the storage of heat and the heat storage mediums used therein are generally known. Such apparatus is used, for example, in combination with collectors for collecting heat from solar radiation. The mediums for the storage of heat which are commonly used can be divided into solid mediums and non-solid mediums. For reasons of operating safety, solid mediums are preferred in many cases. For the use of a non-solid medium involves the risk that leakage occurs in the apparatus, with all the undesirable consequences of that. With a solid medium there is no such danger. As a solid medium for the storage of heat, concrete has already found acceptance on a wide scale.

It is an object of the present invention to provide a medium for the storage of heat, which, like prior mediums, has good heat storage properties, but can be processed and utilized more economically than known mediums, for example concrete.

This object is attained according to the present invention with a medium consisting essentially of a substantially homogeneous mixture of gravel and aluminium chippings, aluminium grains and/or aluminium powder. In this connection, homogeneous mixture means a mixture which exhibits everywhere a virtually constant ratio between the percentage by volume of gravel and the percentage by volume of aluminium particles, and further exhibits as few hollow spaces between the components as possible. In this connection gravel means a mixture of stone and pebbles possibly of different sizes. There is no lower limit for these dimensions according to the present invention, so that gravel includes coarse sand.

Aluminium particles means aluminium grains, aluminium chippings or aluminium powder, possibly in admixture with each other.

In a preferred embodiment of the medium according to the invention, it consists as to 60 to 70 % by volume of gravel and as to 40 to 30 % by volume of aluminium particles. Furthermore, the medium according to the invention preferably consists of gravel having dimensions of 1-3 cm and of aluminium particles having dimensions not exceeding 5 mm. It will be clear that the ideal ratio between the proportion of gravel and the proportion of aluminium in the medium according to the invention is such that all cavities between the gravel particles are substantially entirely filled with aluminium particles.

The advantage of using the medium according to the invention, as compared with non-solid mediums, is that it has a virtually unlimited service life, is not susceptible to the effects of corrosion, and does not cause these in the apparatus in which it is used. As far as the medium is concerned, no maintenance is required of the apparatus in which it is used. The advantage of the medium according to the invention as compared with a solid medium, such as concrete, is that it can be more easily processed. At the present time the cost of the medium according to the invention and of concrete, with equal volumes, are comparable.The heat capacity of the medium according to the invention is slightly less than that of concrete, and is in the order of 400-420 kcal/m3/0C, as against approximately 525 kcal/m3/0C. On the other hand, the medium according to the invention has a considerably higher heat conductivity than concrete. As a consequence of all this, when the medium according to the invention is used, the apparatus may be of smaller volume than in the case of concrete, without this leading to any appreciable deterioration of the operation of the apparatus. A smaller apparatus occupies less room, and is therefore more economic.

The medium according to the invention essentially consists of gravel and aluminium. If desired, other materials may be admixed in not unduly large proportions. Thus, on the ground of cost price calculations, it may be desirable to replace a small quantity of the aluminium particles by a cheaper material, for example, fine sand.

Naturally, it will not be possible to admix too much sand instead of aluminium, as this adversely affects the characteristics of the medium according to the invention. For in fact replacement of a portion of the aluminium by sand will change the ratio of gravel to aluminium, since, as stated before, according to the present invention, sand can in essence be regarded as coming under the term gravel.

The invention will be described in more detail with reference to the accompanying drawings, in which Fig. 1 is a cross-section view of a quantity of the storage medium according to the present invention; Fig. 2 is a cross-sectional view of an embodiment of a heat storage apparatus employing the medium according to the invention; and Fig. 3 is a cross-sectional view, taken on the line Ill--Ill of Fig. 2.

Fig. 1 shows a cross-sectional view of a quantity of the heat storage medium according to the present invention. As shown in the figure, the medium consists of gravel pieces 1, with the spaces between the pieces 1 being filled with aluminium particles 2. The dimensions of the gravel pieces 1 are preferably 1-3cm, although larger pieces may be used, and smaller particles, down to sand are not excluded. The aluminium particles 2 comprise both grains and powder. It is also possible to use aluminium chippings, if desired in admixture with grains and/or powder.

Suitable chippings are, for example, strips having dimensions of 5-15 mm long, 1-2 mm wide and 0.1-0.2 mm thick. Maximum dimensions of the aluminium grains of 5 mm turned out to be highly suitable. If desired, other materials may be admixed. Thus, on the basis of cost price considerations, it may be recommendable to mix a quantity of sand with the aluminium. The storage medium is in essence homogeneous, which means that the ratio between the percentage by volume of gravel and the percentage by volume of aluminium is virtually constant throughout the medium, while the aluminium virtually fully fills the spaces between the gravel pieces, so that there are as few spaces as possible in the medium which are filled with air, these having an adverse effect on the heat storage capacity and heating conductivity.

Figs. 2 and 3 show an apparatus for the storage of heat, comprising the medium according to the invention. The apparatus comprises a housing 3 of rectangular cross-sectional configuration. The cross-sectional form is not essential, and may also be, for example, circular or oval. A rectangular cross-section, however, is very suitable when the apparatus is used as an integral storage unit, as described in British patent application No.

8640/78. Housing 3 is secured to an insulated bottom plate 4 and provided with a cover 5.

Through the centre of housing 3 extends a central tube 6 passed through cover 5. In operation, a heat transporting medium, e.g. air, is supplied through tube 6. For this purpose tube 6 may be connected in a suitable manner to a piping system that can be connected to an apparatus for supplying heat to the transporting medium, e.g. to a collector for collecting heat from solar radiation.

For particulars, reference may had to the above prior patent application.

At the bottom of housing 3, tube 6 terminates in a reversing space or distributing chamber 7. The transporting medium supplied through the tube is reversed in flow direction in chamber 7 as indicated by the arrows and subsequently flows upwards through a number of conduits 8 to a header 9. Conduits 8 are located more outwardly relative to central tube 6, as ciearly shown in Fig.

3. From header 9, the transporting medium can be discharged from the apparatus through one or more tubes 10. It will be clear that, if desired, more headers 9 may be provided, spaced one above the other. Such a construction is shown in the above prior applications, see e.g. Fig. 2, and is very suitable for use with systems in which tubes 10 terminate direct in rooms to be heated.

Disposed within housing 3 and around tubes 6, 8 and 10 and headers 7 and 9 is the storage medium 11 according to the present invention, consisting of an essentially homogeneous mixture of gravel and aluminium particles.

An apparatus of the type as described with reference to Figs. 2 and 3 can be made in a suitable manner as follows. At the place where the apparatus is desired, the housing, which may consist of a suitable metal or of wood, is erected.

The housing may be secured direct to the bottom plate, but instead of the bottom plate a grid provided with small apertures may be used. If the ultimate bottom plate is already mounted at the beginning of the construction, temporary or permanent apertures in the bottom of the housing should preferably be covered with a fine gauze for the removal of water, for reasons to be explained hereinafter.

The required headers, tubes and conduits are arranged and mounted in the housing, possibly by means of suitable supports and brackets.

Subsequently, gravel is poured into the housing from the top around the parts mounted in it. When the apparatus is filled with gravel up to the upper rim of the housing, a mixture of water and aluminium particles is poured into the gravel. The aluminium particles for this mixture will fill all cavities between the gravel pieces, while the water drains from the bottom of the apparatus through the grid or through the above temporary apertures. To ensure that the aluminium particles fill up all spaces between the gravel pieces and that as homogeneous a mass is formed as possible, vibration rods or like means may be used during the introduction of the aluminium particles in order that the mixture being formed is properly packed. According as the packing density is higher, the heat storage properties and heat conductivity of the medium according to the invention will be better.

After the housing has been filled with the medium according to the invention in the manner described above, the cover is mounted. If initially a grid was used as the bottom plate, this grid should yet be replaced by a fixed bottom plate.

Claims

1. A medium for the storage of heat, characterized in that the medium consists essentially of a substantially homogenous mixture of gravel and aluminium chippings, aluminium grains and/or aluminium powder.

2. A medium as claimed in claim 1, characterized in that the medium consists as to 60-70 % by volume of gravel and as to 40-30 % by volume of aluminium particles.

3. A medium as claimed in claims 1-2, wherein the gravel has dimensions of 1-3 cm and the aluminium particles have dimensions not exceeding 5 mm.

4. Apparatus for the storage of heat, comprising a heat storage medium and means for supplying heat to the apparatus and means for discharging heat from the apparatus, characterized in that the heat storage medium is a medium as claimed in any of claims 1-3.

5. A medium for the storage of heat substantially as herein described with reference to the accompanying drawing.

6. Apparatus for the storage of heat substantially as herein described with reference to the accompanying drawing.