GB2103782A

GB2103782A - Device for passive heat transport

Info

Publication number: GB2103782A
Application number: GB08124363A
Authority: GB
Inventors: Hans Thoma; Rodolfo Veneroni; Rudolf Friesen; Beni Gianfranco De
Original assignee: European Atomic Energy Community Euratom
Current assignee: European Atomic Energy Community Euratom
Priority date: 1981-08-10
Filing date: 1981-08-10
Publication date: 1983-02-23
Also published as: IT1149342B; FR2511140B1; IT8248952A0; ES281692Y; DE3229933A1; GB2103782B; ES281692U; FR2511140A1; GR78009B

Abstract

A device for the passive transport of heat, particularly downwardly, comprises an evaporator (1), condenser (3), a reservoir (6) and at least one non-return valve (4), all for a working fluid. The reservoir is at a level higher than the evaporator, and a tube (8) is provided for returning the liquid from the reservoir to the boiler. <IMAGE>

Description

SPECIFICATION Device for passive heat transport The present invention relates to devices for the passive transport of heat in any direction, particularly downward, without the use of an energy input other than heat energy.

Devices of this type have been discussed in United Kingdom Patent Application No.

8025792. Besides this previous proposal, a device is also described in the Belgian Patent: Brevet de Perfectionnement No. 867468 (15.5.1978). This device is similar to our previous proposal, but requires a substantial high AT between the heat source and the heat utilisation.

A device similar to that which is described here is disclosed in U.S. Patent No. 4.160.444 (Jul.10, 1979), in which, however, a pair of heat pipes is arranged together, having the boiler and the reservoir for the condensed fluid at the same level, with an external switching mechanism for alternately heating one only of the two boiler/reservoir.

In the device of the present invention the heat is transported as heat of evaporation/ condensation of a suitable fluid, and the device consists of a boiler, a condenser, and a reservoir for the condensed fluid placed at a level higher than the boiler. The tubes and self-actuated nonreturn valves connect the three main components.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which six embodiments are shown schematically in Figures 1 to 6.

Referring to the scheme of Figure 1, we have the boiler 1, a tube 2 bringing liquid vapours to the condenser 3, a non-return valve 4, a tube 5 conveying the condensed liquid to the reservoir 6, a non-return valve 7 and a tube 8 bringing the liquid back to the boiler 1. The heat is fed to the boiler 1 and the vapours so obtained release the heat in the condenser 3. At the same time the liquid has to be pushed up into the reservoir 6, and this resuit is obtained when the relative temperatures of the boiler and condenser are such that the difference of the vapour pressure of the working fluid at those temperatures is equal to the pressure produced by the column of the liquid between the reservoir and the condenser (the reservoir is supposed to be at the same temperature of the condenser).

The device contains the working fluid (having e.g. a few bars of vapour pressure in the wanted range of temperature) in the form of a liquid and its vapour. The pressure over the free surface of the liquid in the reservoir 6 equals the vapour pressure of the working fluid at the temperature of the reservoir. During the phase of downward heat transport the pressure in the reservoir 6 is lower than the pressure in the boiler 1 by an amount corresponding to the height of the column of liquid between 6 and 3, increased by the possible dynamic pressure drop (in this case very low and negligible). The liquid will not flow spontaneously from 6 to 1, and the flow of vapour from 1 to 6 is prevented by the non-return valve 7.In order to obtain the passage of the liquid from 6 to 1, necessary for a semi-continuous operation one has to make practically equal the pressure in6andin 1.

This situation can be reached by reducing the pressure of 1 down to the pressure of 6, or by increasing the pressure of 6 up to the pressure of 1. At either moment the liquid contained in 6 will flow into 1, and for a semi-continuous device this equilibration of pressures has to be obtained without discontinuing the heat supply to the boiler 1.

Both solutions are possible, and are described in the following 1 -- Equilibration of the pressures by reducing the pressure of the boiler 1.

This result is achieved as in the device described in United Kingdom Patent Application No. -- the boiler is run until it dries out (to avoid excessive overheating it shouid have a flat heating bottom and sufficient thermal inertia). At that moment, the pressure in the boiler is reduced by the condenser to the vapour pressure of the fluid at the temperature of the condenser itself. If the temperature of the fluid contained in the reservoir is not lower than the temperature of the condenser, also the pressure over the liquid in the reservoir has at least the same value now existing in the boiler-condenser side, so the liquid in the reservoir 6 can now flow freely towards the boiler 1 through tube 8 and non-return valve 7.As in the device described in our previous patent, it is necessary to prevent the liquid reaching the boiler 1 from coming directly into contact with the (hot) heating surface, so a two-step charging system (e.g. siphon as in the previous patent) has to be installed inside the boiler.

For a proper functioning of the device, the temperature of the reservoir 6 must be at least as high as that of the condenser 3. This will usually be obtained in an automatic way because it is just the liquid coming from the condenser 3 that accummulates in the reservoir 6. It can happen, however, particularly when the temperature around 6 is very low, or when the temperature of the condenser is relatively high, that the temperature of 6 is too low - compared with 3 - for obtaining a smooth passage of liquid from 6 to 1. In order to avoid this situation a simple conventional heat pipe will provide a thermal link between the condenser 3 and the reservoir 6, assuring that the reservoir will never have a temperature lower than the condenser 3.

Figure 2 represents a device as here described, in which the equilibration of the pressures is obtained through the reduction of the pressure existing in the boiler.

To help the passage of liquid from 6 to 1, the reservoir 6 will be at a level sufficiently higher than 1.

2 -- Equilibration of the pressures by increasing the pressure of the reservoir 6.

This condition can easily be obtained feeding the vapour from the boiler 1 directly into the reservoir 6 through a second tube connecting the boiler to the reservoir; this tube being usually closed by a valve that will open only at the suitable moment. When this last valve is open, the vapour from the boiler 1 goes and condenses in the upper part of the reservoir 6, so increasing its temperature up to the temperature of the boiler. The pressure in the reservoir 6 at that moment will be high enough for transferring the liquid from 6 to 1.

The valve controlling the flow of vapour through this new tube is actuated by the variation of level whether of the fluid collected in the reservoir or of the fluid still contained in the boiler; in the first case an increase of level, in the last case a decrease. In order to allow a sufficient recharge of liquid from reservoir 6 to boiler 1 a certain hysteresis will be introduced between opening and closing of this valve.

Examples of both solutions are given in the following: a.) Valve actuated by an increase of level of the condensate in the reservoir 6.

Example 1 With reference to Figure 3, the reservoir is now equipped with a float 10, that keeps closed the valve 1 3 with its weight when the container 12 is empty. During the operation the condensed liquid accummulates in the reservoir 6, but the liquid will go into the container 12 only after that its level has reached the bend of the siphon 11. Then the float 10 opens the valve 13, the pressures of 1 and 6 become equal and the liquid of the reservoir 6 flows into 1. The siphon 11 now will reverse the flow, the container 12 is emptied and the float 10 will close the valve 13; restoring the initial situation.

Example 2 With reference to Figure 4, the reservoir 6 is now equipped with a float 10, that keeps closed the valve 1 3 with its weight when the reservoir 6 is empty. During operation the liquid accummulates in reservoir 6 and its level increases. The float 10 however is kept in the lower position not only by its weight but also by the magnetic force between anchor and magnet 14 and 1 5. When the level of the liquid in the reservoir 6 is increased enough, the force of the float 10 will be sufficient for opening the valve 13. The equilibration of pressures take place and the liquid will flow from 6 to 1. The fact that the magnetic force is now strongly reduced will allow a substantial level variation of the liquid in the reservoir 6 before the valve 13 is closed; again restoring the initial situation.

b.) Valve actuated by a decrease of level of the liquid in the boiler 1.

Example.

With reference to Figure 5 the boiler is now equipped with a float 1 6 closing the valve 1 3 when the boiler is full of the working fluid. During operation the valve 1 3 is kept closed also by the difference of pressure existing between 1 and 6.

When the level of the fluid in the boiler is low enough, the weight of the float 16 is sufficient to overcome the force produced by the difference of pressure between 1 and 6, and the valve opens.

The equilibration of pressures will take place and the valve 13 will remain open until the level of the liquid in the boiler 1 is sufficient to lift the float and again close the valve 13; restoring the initial situation.

Besides the examples here given, other systems can be conceived; e.g. the float can act on the valve through a lever, or the float can have a magnetic part acting on a magnetic valve, etc.

The key point is the fact that the opening and closing of the valve is triggered by the variation of level either in the reservoir or in the boiler.

An advantage of the system with tube 9 and valve 1 3 is that the boiler will never dry out, so there is no risk of overheating. On the contrary during the initial phase of equilibration of the pressures, the temperature of the boiler will be reduced because its working pressure will be temporarily reduced. As in the prior patent application, the system for the heat transfer can be integrated into a solar collector. The version described under 2 is particularly suitable because it does not require the drying out of the collector, leaving more flexibility in its design. An example of an integrated system is given in Figure 6.

Claims

1. A device for the passive transport of heat comprising an evaporator, a condenser, a reservoir, and at least one self-actuated nonreturn valve, all for a working fluid, wherein the reservoir is at a level higher then the boiler, and means are provided for returning the liquid from the reservoir to the boiler.

2. A device as claimed in claim 1 wherein the return of the liquid is obtained by reducing the pressure of the boiler with respect to the pressure of the reservoir.

3. A device as claimed in claim 1 wherein the return of the liquid is obtained by increasing the pressure of the reservoir up to the pressure of the boiler through valves actuated by the variation of level of the liquid inside the reservoir and/or inside the boiler.

4. A device for the passive transport of heat substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.

5. A solar heat collector incorporating a passive heat transport device as claimed in any one of the preceding claims.