Such an apparatus is known from EP-A-0 822 139 and is used, for example, in the space travel-related industry.

The apparatus proposed in accordance with the invention is characterised in that it has two work areas, namely a first work area wherein the container holds the main portion of the fluid and the heat emission to the environment is determined substantially by the thermal conduction coefficient of the radiator, and a second work area wherein at least a portion of the fluid expands or is expanded to the expansion space and the heat emission to the environment is increased with respect to the first work situation and that the apparatus changes from the first work situation to the second work situation and vice versa, depending on its temperature.

The second work area of the apparatus corresponds to an elevated temperature causing the fluid to expand to the gas phase, generating movement of the fluid all through the container, which results in a corresponding intensive heat exchange between the fluid-gas mixture in the container and the radiator. This increases the heat emission to the environment. In practice a heat emission ratio between the two work situations of 1: 10 could be realised.

Depending on the circumstances therefore, the apparatus has a work situation in which a substantial heat flow can be emitted to the environment as well as a work situation in which the heat emission to the environment is significantly limited. This is of importance in connection with the electronics applied in space crafts, which, when in operation, produce heat that needs to be dissipated to the environment, whereas in the switched-off condition this heat emission needs to be strongly reduced in order to avoid

extensive loss of energy and temperature reduction in the space craft.

The apparatus according to the invention can conveniently be realised such that the container is a tube system mounted in or on the radiator, containing the fluid in plug form.

The function of the container and the expansion space for the fluid may suitably be realised by taking up the fluid as individual plugs that are separated from each other by vapour-filled spaces. The vapour in these spaces is fluid that is already (partly) expanded. In practice, the ratio between the space occupied by the fluid and the expansion space appears to depend on the type of fluid and varies between 1: 4 and 4: 1.

Desirably the fluid is selected from the group comprising acetone, benzene, tetrachloromethane, chloroform, cyclohexane, dowtherm A, dowtherm J, ethanol, ether, FC-87, methanol, n-pentane, R-134 A and water. Of these fluids in particular acetone, dowtherm A, dowtherm J, ethanol, ether, propane, ethane, FC-87, methanol, R-134 A and water provide very good results.

The radiator is preferably made from a carbon fibre- reinforced epoxy material. Such a material offers the sought low thermal conduction coefficient.

With respect to the container, this is preferably made from stainless steel or another metal. These materials are good conductors, with which it is possible to realise an extensive heat exchanging contact with the radiator (and the electronics).

When the container is mounted on the radiator, it is preferred for the contact between the same and the radiator to be realised by means of an adhesive. A suitable adhesive to use is, for example, polymethylacrylate, polyamide or polytetrafluoredene.

Below the invention will be further elucidated by way of a non-limiting example and with reference to the drawing.

In the drawing:

- Fig. 1A schematically shows the working principle of the apparatus according to the invention in a first working point; and - Fig. 1B shows the working of the apparatus according to the invention in a second working point ; and -Fig. 2 shows a schematic side view of the apparatus according to the invention; and - Fig. 3 shows a cross-section of a container for fluid such as is part of the apparatus according to the invention.

Similar parts in the figures are identified by identical reference numbers.

Referring first to Fig. 1, Fig. 1A schematically shows a first working point of the apparatus in accordance with the invention, wherein the same has a high heat emission, whereas Fig. 1B shows the apparatus in accordance with the invention in a second working point, wherein the heat emission to the environment is low. The apparatus 1 comprises a thermal radiator 2 on which a heat source may be mounted, for example, electronics 3. When the electronics 3 are active and the temperature is high (25°C or higher), the radiator 2 has to realise a high heat emission to the environment as visualised by means of the arrows 4. In Fig.

1B the electronics 3 are switched off and the temperature is low (10°C or lower) and the heat emission to the environment has to be correspondingly low, as visualised by means of the arrows 5.

Fig. 2 again shows the apparatus 1 according to the invention, but now in a schematic side view. The radiator 2 is part of this apparatus 1. In or on this radiator a container 6 is provided for fluid. This container 6 is preferably a folded tube system wherein the fluid is taken up in the form of plugs. A portion of this tube system is shown in Fig. 3. The plug-like fluid is indicated with reference number 7. Expansion spaces 8 are provided between the plugs 7 of the fluid to allow the fluid 7 to expand to the gas phase and thereby to cause fluid movement all through the container. This fluid 7 is selected from the group comprising

acetone, benzene, tetrachloromethane, chloroform, cyclohexane, dowtherm A, dowtherm J, ethanol, ether, propane, ethane, FC-87, methanol, n-pentane, R-134 A and water.

The material of the radiator 2 is preferably a carbon fibre-reinforced epoxy material with which the desired low thermal conduction coefficient of this radiator 2 is realised. As already mentioned, the container 6 preferably takes the form of a tube system. This tube system 6 may be realised, for example, by making channels in the material of the radiator. The container 6 may also be made from a stainless steel or another metal and this container 6 may be mounted on and in contact with the radiator or may be imbedded therein. If the container 6 is imbedded in the radiator 2, the close contact is preferably realised using an adhesive selected from the group of thermoplasts, cyanide esters, epoxy and aramide.

To the person skilled in the art it is obvious that within the scope of the invention several variants on the above example are conceivable without departing from the idea of the invention.

The above given elucidation merely serves to remove possible ambiguities in the appended claims without, however, limiting these in any way.