The thermal diodes consist of two metal bodies thermally coupled to the external surfaces of the diode conductive wall and interconnected by a thermally insulating central body.

Prior art There are known in the prior art of the cooling devices means (called "heat pipes") used for carrying heat from points that are otherwise hard to reach and consisting of tubular metal bodies containing a heat transferring fluid. "Heat pipes" working and characteristics of the fluid inside them will not be described herein because they are already known and in any case do not regard the purpose of the present invention.

Likewise known are panels that enable the transfer of heat (preferably) in a single direction.

These panels are described, for example, in the article by R.K. Prudhoe and L.

Dukas entitled "Thermal control of equipment enclosures - Design strategies for enhanced reliability" - INTELEC '93 - Procedures of the 15th Conference on Energy in Telecommunications - Paris, September 27-30, 1993, Volume II, pages 305-312.

Subject of the present invention is a wall, called "diode conductive wall", which comprises at least one tubular body (or "thermal diode") of new type, containing a heat transferring fluid, which improves heat transfer through the wall itself in (practically) one direction.

Summarv of the invention

The subject of the present invention is a diode conductive wall, comprising a wall made of thermally insulating material, delimited by two thermally conductive external surfaces, connected together by one or more thermal diodes which transversely cross the wall made of thermally insulating material.

A thermal diode transfers the heat in basically one direction from one external surface of the diode conductive wall to the other and consists of a tubular body, at least partially filled with a heat transferring fluid, comprising two metal bodies (each of which is thermally coupled to one of the external surfaces of the diode conductive wall) interconnected by means of a thermally insulating central body.

List of figures The invention will now be better described with reference to a non-limiting embodiment illustrated in the attached figures, where, - Figure 1 shows a sectional view of a diode conductive wall comprising two thermal diodes according to the invention; - Figure 2 shows one of the thermal diodes of Fig. 1; - Figure 3 is a schematic representation of the container used in Example No. 1; - Figure 4 presents a sectional view and a plan view of a possible application of diode conductive walls made according to the invention.

In the attached figures, the corresponding elements will be identified by means of the same numerical references.

Detailed description Figure 1 presents a sectional view of a diode conductive wall (1), which consists of a wall (2) made of thermally insulating material (e.g., polyurethane foam), delimited by two external surfaces (3, 4), which are thermally conductive and connected together by a pair of thermal diodes (5) which transversely cross the wall (2) made of thermally insulating material, enabling the heat to flow through the diode conductive wall (1) in (at least theoretically) a single direction.

In Fig. 1 may be seen the external surfaces (3, 4) consisting preferably of two sheets of metallic material, which delimit the diode conductive wall (1), the wall (2) made of thermally insulating material which thermally insulates the two external surfaces (3, 4) of the diode conductive wall (1) from one another, and a pair of

thermal diodes (5), thermally connected to the aforesaid external surfaces (3, 4), with respect to which they are inclined.

Thermal diodes made up of a tubular metal body (at least partially filled with a heat transferring fluid), the ends of which are thermally coupled to the external surfaces of a diode conductive wall are already known.

This tubular metal body constitutes (or may constitute) a "thermal bridge" across which the heat passes (or may pass) in two directions, which adversely affects the reliability and efficiency of both said thermal diode and a diode conductive wall built by means of thermal diodes (5) of known type.

A diode conductive wall (1) made according to the invention comprises at least one thermal diode (5), whose tubular body consists of two metal bodies (6) connected together by a thermally insulating body (7) as shown in Figure 2. In this way, the aforesaid "thermal bridge" is avoided.

In Fig. 1 the ends of the thermal diodes (5) thermally coupled to the external surface (3) are located lower down than the ones thermally coupled to the external surface (4). The thermal diodes (5) are therefore suitable to transfer heat from the external surface (3) to the external surface (4), whereas they are not (practically) suitable to transfer heat in the opposite direction, i.e., from the external surface (4) to the external surface (3).

There now follows a brief description of the working of the thermal diodes (5) for transferring heat from the external surface (3) to the external surface (4), should the temperature of the external surface (3) be higher than that of the external surface (4).

In contact with the external surface (3) the fluid contained in the thermal diode (5) heats up subtracting heat from the external surface (3), and comes into contact with the external surface (4), to which it transfers the heat drawn from the external surface (3), and comes back towards the external surface (3). The external surface (4) dissipates the heat transferred to it by the fluid into the environment (or in another way already known).

The fact that the thermal diode (5) is mounted inclined as illustrated in Fig. 1 favours proper circulation of the fluid in the diode itself (the heated fluid tends to rise, whilst the colder fluid tends to drop), whereas it opposes the circulation of the

fluid in the (undesired) event of the temperature of the external surface (3) becoming for any reason lower than that of the external surface (4).

The angle of inclination of the thermal diode (5) with respect to the external surfaces (3, 4) may be approximately 45" and, in any case, between 10° and 80".

In the herein described embodiment , to allow the fluid to circulate in the thermal diode (5) the following conditions are necessary: i) in contact with the external surface (3), which is hotter, the fluid must increase in volume (with or without change of state); ii) in contact with the external surface (4), which is colder, the fluid must decrease in volume (with or without change of state); iii) the difference in temperature between the external surfaces (3) and (4) must be sufficient to "sustain" the circulation of the fluid; iv) the temperature of the external surface (4), which is colder, cannot be less than a limit value, below which the fluid becomes too viscous to circulate inside the thermal diode (5) or does not change its state.

This latter condition constitutes an important feature of the invention: when the temperature of the colder external surface of the diode conductive wall (1) drops below the aforesaid limit value, which is different according to the fluid used, the thermal diode (5) is "interdicted", thus preventing further heat being subtracted from the hotter external surface of the diode conductive wall (1) even if the difference in temperature between the two external surfaces would be sufficient to "sustain" fluid circulation inside the thermal diode (5).

This feature is advantageous, for example, if the diode conductive wall (1) constitutes one of the walls of a container, the internal temperature of which (i.e., the temperature of the external surface (3)) will not drop any further whenever and for the entire period in which the temperature of the external environment (i.e., the temperature of the external wall (4)) drops below the aforesaid limit value, which is preset by suitably choosing the fluid to be used inside the thermal diodes (5).

Merely as an example, if this heat transferring fluid is water, the corresponding limit value is 4"C; if this fluid is 12% glycolated water, the corresponding limit value is -5°C; if this fluid is fluorocarbon, the corresponding limit value is 30"C.

Figure 2 shows one of the thermal diodes (5) of Fig. 1 made according to the invention. In Fig. 2 it is possible to see the metal bodies (6) thermally coupled to the external surfaces (3, 4) of the diode conductive wall (1); the central body (7), which is thermally insulating and connects together the metal bodies (6) and the metal plates (8), set between the external surfaces (3, 4) of the diode conductive wall (1) and the end of the corresponding metal body (6) to increase the contact surface between the external surfaces (3, 4) of the diode conductive wall (1) and the corresponding metal body (6) and to improve the thermal coupling thereof.

Preferably (but not necessarily) the central body (7), which is thermally insulating, is made of rubber or another deformable material. This is advantageous because it allows to fiil (almost) completely the thermal diode (5), improving the latter's efficiency, with a fluid (e.g., a gas) which dilates notably when heated, or else with a fluid (e.g., water) which changes in volume when it changes state, thus preventing any risk of breakage and/or of damage of the thermal diode (5) due to said dilation or else to said change of state.

If a thermal diode (5) does not include a central body (7) and/or if such body (7) is not made of deformable material, to prevent any risk of breakage and/or of damage of the thermal diode (5) due to a dilation or else to a change of state of the fluid contained in the thermal diode, it is not possible to fill (almost) completely the diode itself with fluid, reducing therefore its efficiency, assuming all the other conditions equal.

The characteristics of a thermal diode (5) made according to the invention and the advantages obtainable by using diode conductive walls (1), and in particular diode conductive walls (1) comprising thermal diodes (5) according to the invention, instead of walls made of insulating material of a traditional type will be evident from the following example, which in no way limits the possibilities, and from the following applications.

Example No. 1 Five cubic containers C have been built (Fig. 3), inside which a constant-heat 15- Watt source W has been set.

The first container comprises five 500x500 mm walls consisting of diode conductive walls (external surfaces made of 3-mm thick aluminium; insulating wall

made of 60 mm of polyurethane foam), each of which including four thermal diodes (comprising a thermally insulating central body) containing water, whereas the sixth wall (floor) consists of an insulating wall made of polyurethane foam.

The second container differs from the first only in that it does not include the thermal diodes.

The third container differs from the first only in that the thermal diodes consist of a single metal body.

The fourth container differs from the first only in that the thermal diodes (comprising a thermally insulating central body) are mounted "inverted" with respect to those of container 1.

The fifth container, comprising five 380x380 mm walls made of 3-mm thick aluminium sheet, corresponds to the internal envelope of the first container without the insulating walls and without the external surfaces of the diode conductive walls (the floor consists of an insulating wall made of polyurethane foam).

Maintaining the ambient temperature Ta at preset values, the temperatures (Ti, T2, T3, T4, and T5) inside the five containers were measured in degrees centigrade. The results of the set of measurements are gathered together in the following table: 1 2 3 4 5 6789 10 I Ta T1 T2 T3 T4 T5 T1- T2- T3- T4- T5- Ta T a Ta Ta Ta 25 33.5 57 31 51 29 8.5 326 26 4 0 14 33 6.5 27 4.5 14 33 6.5 27 4.5 -13 12.5 20.5 -5.5 15.5 -8 25.5 33.5 7.5 28.5 5 From the above table it may be noted that: - the thermal diodes comprising a thermally insulating central body limit the internal temperature of the container (column 1) and the difference in temperature

compared to the environment (column 6) if Ta >> 0°C; they limit the variation in internal temperature of the container if Ta < 0°C; - if the thermal diodes are absent, are made of a single metal body or are mounted "inverted", or else if the container (container 5) does not include the diode conductive walls nor the insulating walls, the difference in temperature with respect to the environment (columns 7, 8, 9 and 10, respectively) remains practically constant: the temperature variation inside the container (columns 2, 3, 4, and 5, respectively) follows the ambient temperature Ta; - the thermal diodes consisting of a single metal body are able to limit the <BR> <BR> <BR> <BR> temperature inside the container (column 3) if Ta >> 0°C, but (on account of the "thermal bridge" due to their totally metal body) they are not able to limit the temperature variation inside the container if Ta < 0°C; - the advantages that may be obtained by using thermal diodes comprising a thermally insulating central body instead of thermal diodes consisting of a single metal body may be verified comparing columns 1 and 3, and columns 6 and 8, respectively; - if the thermal diodes are mounted "inverted", similar effects are obtained to those that are obtained when the thermal diodes are absent, as may be verified by comparing column 2 to column 4, and column 7 to column 9; - if the container does not include diode conductive walls or insulating walls (container 5), the difference in temperature with respect to ambient temperature (column 10) is very low and the variation in temperature inside the container (column 5) follows the variation in ambient temperature Ta.

Figure 4 shows a sectional view and a plan view of a possible application of diode conductive walls (1) made according to the invention.

In Figure 4 a tank of water S may be seen positioned in such a way as to be exposed to rays of sunlight all day long, in which three walls are made with diode conductive walls (1) (protected by panels made of transparent material), whilst the fourth wall N (in the northern hemisphere, that exposed to the north) is made using an insulating panel of traditional type.

In the course of the day, the walls (1) are in turn exposed to the rays of sunlight, and their thermal diodes (5) (only one of which is labelled in Fig. 4 for reasons of

simplicity of graphical representation) allow the heat of the sun to penetrate inside the tank S, thus heating the water contained therein, whilst they prevent the heat stored in the tank S from escaping at night.

Applying to the tank S the diode conductive walls (1), an efficient solar collector is obtained in a simple and economical way, which is able to store heat during the entire day, thus avoiding costs deriving from purchasing and setting-up a solar panel, corresponding water connections and the non-return valves that are indispensable for preventing heat losses during the night.

Diode conductive walls according to the invention may moreover be advantageously used in active environmental conditioning systems (which include an air conditioner), or else in passive environmental conditioning systems (without air conditioner), not illustrated in the figures.

The diode conductive walls (1) behave like thermal insulators for external temperatures higher than the internal ones and, in any case, at low temperatures, and as heat conductors for external temperatures lower than internal ones. In an active environmental conditioning system, when the air conditioner has brought the ambient temperature up to the desired value, the diode conductive walls contribute to maintain this temperature value, thus reducing the operating time of the motor of the air conditioner, and consequently the corresponding running costs.

In prefabricated buildings, the walls exposed to sunlight repel solar radiation, whilst those in the shade emit the heat present inside the prefabricated building when the temperature outside the wall so permits (i.e., when the external temperature is lower than the internal one), thus reducing the overtemperature inside the prefabricated building due to solar radiation and, consequently, the need for an air conditioner and/or its operating time.

Without departing from the scope of the invention, it is possible for a skilled man to make to the diode conductive wall, which is the subject of the present description, all the modifications and improvements suggested by normal experience and by the natural evolution of techniques.