Temperature Stabilization System

Abstract

A system for temperature stabilization through the use of a heat pipe, that zone of the heat pipe which is remote from the heating zone having an inert gas plug whose volume varies with the vapour pressure of the heat vehicle. The plug effects variation in the heat pipe wall area actually radiating heat according to changes in the volume of the plug, and includes a secondary heat pipe which is in good thermal connection with that part of the first heat pipe where the inert gas plug is disposed.

Description

The invention relates to temperature stabilization, for example stabilization of the temperature of the caesium reservoir in a thermionic converter.

It has already been proposed to stabilize the temperature of a heated region or surface despite changes in environmental conditions by means of a heat pipe operable to extract variable amounts of heat from the region or surface. A heat pipe essentially comprises a hermetically closed vessel containing a heat carrying vehicle (e.g., a metal) which circulates by a natural cycle of evaporation and condensation between a heating zone and a cooling zone. In some arrangements of heat pipes the circulation of the vehicle is assisted by capillary action. When a heat pipe is used for the above purpose the heating zone is arranged to receive heat from the region or surface to be stabilized and within the vessel there is a plug of inert gas of which the volume varies with variations in the vapor pressure of the vehicle. If the temperature to be stabilized increases so does the temperature of the heating zone of the heat pipe and the quantity of heat absorbed thereby increases. This causes an increase in the vapor pressure of the vehicle, and the inert gas plug, which is disposed in the cooling zone of the pipe, is compressed. Consequently, since the inert gas is a much poorer heat conductor than the heat vehicle, the heat pipe wall area actually radiating heat increases as does the amount of heat radiated. It has also been proposed to provide a central displacement member in the boundary region between the heat vehicle and the inert gas plug, with the aim of improving the control characteristic by making a given change in vapor pressure produce an increased change in actual radiating surface.

A disadvantage of heat pipes when used as above described is that the temperature of the inert gas plug has considerable effect on the accuracy of control, more particularly because there is only a small temperature difference between the temperature in the environment around the heat pipe and the temperature of the plug and because the pipe walls are good heat conductors. Another consideration when systems of this kind are used in the range of radioactivity is the gamma heat evolved in the heat pipe wall. These disturbances make it difficult to provide accurate temperature stabilization of the pipe heating zone, since they also affect the position of the boundary zone between the heat vehicle vapor and the inert gas plug.

The present invention seeks to reduce or overcome these disadvantages.

This invention provides a system for temperature stabilization through the agency of a heat pipe, that zone of the heat pipe which is remote from the heating zone having an inert gas plug whose volume varies with the vapor pressure of the heat vehicle, such plug effecting variation in the heat pipe wall area actually radiating heat, according to changes in the volume of the plug, characterised in that that part of the heat pipe where the inert gas plug is disposed is in good thermal connection with the heating zone of a secondary heat pipe.

Preferably, the heating zone of the secondary heat pipe is fitted like a pot or cover over that part of the first heat pipe where the inert gas plug is disposed. Preferably, an inert gas plug is also provided in the secondary heat pipe.

To improve stability still further, a displacement member (e.g., fixed) may be provided in the primary or secondary heat pipe (or both). Alternatively or in addition a tertiary heat pipe may be connected to the secondary heat pipe in just the same way as the latter is connected to the primary heat pipe. Preferably, the displacement member is in good mechanical and thermal connection with the heat pipe end wall remote from the heating zone, since the temperature of such end wall is more stable than the temperature of the side walls contiguous with or adjacent to such wall. Advantageously, to reduce heating of the displacement members by gamma radiation in cases where they will be subject to such radiation, the displacement members are empty hollow receptacles whose wall thickness is exactly suitable for the working pressure (i.e., the minimum thickness necessary to resist the working pressure).

The present invention greatly reduces the effect of environmental factors on the temperature of the inert gas plug in the primary heat pipe, and so the position of the boundary between heat-vehicle vapor and the inert gas depends substantially only upon the quantity of heat taken up from the heating zone of the primary pipe.

Some examples of the invention will be described in greater detail hereinafter with reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic sectioned view of a first system;

FIG. 2 shows another system comprising a displacement member;

FIG. 3 shows another system, having two displacement members;

FIG. 4 shows a system comprising three heat pipes, and

FIG. 5 is a detailed sectional view showing the suspension of a displacement member.

The underlying idea of the invention will be described with reference to FIG. 1. It will be assumed that a surface 1 to be stabilized (e.g., part of the surface of a caesium reservoir) is also the heating surface of a first or primary heat pipe 2. Arrows 3 near the heating zone indicate the supply of heat. Heat pipe 2 is made of a high-temperature-resistant substance covered internally with longitudinally extending capillary grooves (not shown). The heat carrying vehicle is a metal; at normal working temperature the metal is in vapor form in the heating zone and condenses in the cooling zone remote from the heating zone. Tube 2 has as well as a metal-vapor chamber 4, an inert gas plug 5 which, since it is carried along in the heat-vehicle vapor, is disposed at the top of the tube 2 -- i.e., in the zone remote from the heating zone. A line 6 denotes the horizontal boundary layer between the heat vehicle and the plug 5, although in fact the boundary should be considered as a transitional region. Since the heat pipe wall is a good conductor of heat, the boundary is particularly fluid at the pipe wall. Since the inert gas is a much poorer heat conductor than the metal vapor, the line 6 represents a temperature jump and is a boundary of that region of the heat pipe which is actually operative for heat flow and heat radiation.

A second heat pipe 7 is fitted over the pipe 2 near the line 6 and the external wall surfaces of pipe 7 act as heat radiators. The heat is radiated in a direction indicated by arrows 8. The second or secondary pipe 7 therefore acts as a cooler of the primary pipe 2, with the result that at start-up the line 6 first rises rapidly to the position shown, then remains there substantially stationary subject substantially only to variation in the vapor pressure of the metallic heat carrier due to variations in the temperature of the heating zone. Since the inert gas plug is completely surrounded by the second heat pipe and scarcely alters its temperature, the temperature stabilization of surface 1 is likely to be much better than can be provided by earlier suggestions.

To further improve stabilization, the system shown in FIG. 2 can be used, like elements having like references. The only difference from FIG. 1 is that the system shown in FIG. 2 has a displacement member 9 near the line 6 in the primary heat pipe 2. The displacement member 9 acts in a known manner to produce an increased change in effective wall area for a given change in plug volume.

The temperature stabilization of surface 1 can be further improved by the system shown in FIG. 3, like references again denoting like elements. The difference from FIG. 2 is that in FIG. 3 the secondary pipe 7 also has an inert gas plug 10, and so the secondary pipe 7 has a boundary line 11 which varies with the heat flow. Preferably in this case too, a displacement member is used to act appropriately on the variation characteristic.

Stabilization can be improved still further by further cascaded arrangements of heat pipes, although the expense is likely to make any cascade consisting of more than three heat pipes of little practical value. FIG. 4 shows a three pipe system -- i.e., in this embodiment substantially all the heat is radiated by the third pipe 13. One way of improving stabilization relatively cheaply is for the displacement members to be in good mechanical and, more particularly thermal, connection with that region of the surrounding heat pipe which has the most stable temperature pattern. Such region is always the surface 14 remote from the heating zone. FIG. 5 is a diagrammatic view of how a connection of this kind can be provided in one heat pipe or in all the heat pipes. A metal block 15 which is a good heat conductor forms a bridge between the wall 14 and a displacement member 16. As can also be gathered from FIG. 5, the displacement member is preferably hollow and has a wall thickness which just withstands the maximum working pressure. This ensures that heating of the displacement member as a result of gamma radiation has very little effect on the temperature of the inert gas plug 17. Structural bracing or the like (not shown) can be provided to improve the mechanical stability of the displacement member.

Claims

We claim:

1. A system for temperature stabilization comprising an arrangement of at least two serially disposed heat pipes, the first heat pipe having a heating zone coupled to a space where stabilization of temperature is desired and a cooling zone, said first heat pipe enclosing a condensable-vaporizable heat vehicle and an inert gas plug which during operation is displaced in said cooling zone, there being a boundary region between the heat vehicle and the gas plug; a second heat pipe having a heating zone and a cooling zone, the heating zone of said second heat pipe being in good thermal connection with the cooling zone of the first heat pipe where the inert gas plug is disposed and a displacement member positioned in the heat pipe interior to effectively reduce its cross-sectional area in the boundary region.

2. A system as set forth in claim 1, in which the displacement member is in good mechanical and thermal connection with the heat pipe end wall remote from the heating zone.

3. A system as set forth in claim 2, in which the displacement member is a hollow empty receptacle whose wall thickness is the minimum necessary to resist the working pressure.

4. The system of claim 1 in which the second heat pipe also encloses a condensable-vaporizable heat vehicle and an inert gas plug, there being a boundary region therebetween.

5. The system of claim 4 including a displacement member positioned in the second heat pipe interior to effectively reduce its cross-sectional area in the boundary region.

6. The system of claim 4 including a tertiary heat pipe enclosing a condensable-vaporizable heat vehicle and an inert gas plug, there being a boundary region therebetween; the heating zone of the tertiary pipe being in good thermal connection with that point of the second heat pipe where its inert gas plug is disposed.

7. The system of claim 6 including a displacement member positioned in the tertiary heat pipe interior to effectively reduce its cross-sectional area in the boundary region.