GB1583857A

GB1583857A - Two phase thermo-syphon apparatus

Info

Publication number: GB1583857A
Application number: GB2418176A
Authority: GB
Original assignee: NOLAN DESIGN Ltd J
Current assignee: NOLAN DESIGN Ltd J
Priority date: 1977-06-09
Filing date: 1977-06-09
Publication date: 1981-02-04

Description

(54) TWO PHASE, THERMO-SYPHON APPARATUS (71) We, JOHN NOLAN DESIGN LIMITED, a British Company of 41 Welbeck Street, London WIM 7HF, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to two phase, thermo-syphon apparatus which is a modification of the so-called Perkins tube.

Perkins tubes transmit heat by vaporising fluid in one region and condensing it in another. They are thereby very efficient conductors of heat. However, such devices also have certain disadvantages which are described below.

Thermal performance is reduced by the presence of undesirable contaminants in the fluid which is vaporised. These contaminants may be present at the time of manufacture, or they may build up during the life of the device for a variety of reasons. With devices which are intended to be sealed for life, strict precautions may be necessary, during manufacture, for reducing to acceptable levels such contamination and its likely build-up. These precautions can be costly when advanced techniques and equipment are required.

The object of the invention is to improve the design and operation of the Perkins tube. As more than one vaporiser and/or condenser can be employed in embodiments of the invention, the invention will be defined in terms of apparatus comprising at least one vaporiser and condenser.

According to the invention, two phase, thermo-syphon apparatus is provided which can be constructed and used with a minimum of advanced techniques and/or equipment and which can be overhauled at intervals, for example, by the user, to improve its thermal performance. More particularly, the apparatus of the invention comprises enclosing means which defines at least one vaporiser and condenser, a fluid which is contained, during normal operation, within the interior of the enclosing means and which transmits heat by intercommunication between said vaporiser and said condenser, the enclosing means being such that the fluid condensate is free to return to said vaporiser unimpeded by wicks or capillary means, the enclosing means communicating with openable sealing means having at least a joint, or removable cap or plug, or a valve, and a liquid trap containing a liquid compatible with the fluid in the enclosmg means, said trap being arranged such that the liquid therein will enter the enclosing means in the event of a leak in said sealing means.

The invention, enables a number of advantages to be achieved. For example, the device can be disassembled by the user to facilitate and to reduce the cost of maintenance. Access can be gained easily to the interior to exchange the fluid or to remove some of the fluid depending on the circumstances. Safety is thereby improved because an excess amount of fluid can be removed to prevent an excess pressure build up. The sealing means may include a pressure relief valve in the latter respect. The liquid trap is provided so that, in the event of a leak in the sealing means, the atmosphere acts on the liquid and only said liquid enters the enclosing means. A reduction in liquid level in the trap makes leak detection possible.

Some known devices have no means for varying the heat transfer characteristics. To provide such means creates technical problems to which a preferred embodiment of the invention is directed. One of such problems is that some known devices have a vaporising section which defines a liquid reservoir holding a comparatively large mass of liquid which requires to be heated before vapour begins to flow towards the condenser and hence the device is not as efficient with small bursts of thermal energy as it is when the liquid in the vaporising reservoir has reached a working temperature.

The preferred embodiment of the invention seeks to provide variable heat transfer characteristics at least for the following reasons which are largely inter-related: (i) to be able to operate at different temperatures, (ii) to be able to transfer both small and large amounts of heat with acceptable efficiency, (iii) to have one or more vaporisers which may be made active or inactive as required, (iv) to be able to vary the amount of heat delivered to a condenser.

These four aims may be achieved by controlling the manner in which the working fluid condensate is released to a vaporiser or vaporisers. More particularly, the apparatus includes control means for controlling the amount of condensate returned to said vaporiser.

In the case of temperature control, the greater the rate of release of condensate to the vaporiser the greater can be the rate of vaporisation and hence vapour pressure, temperature of operation and the rate of heat delivered to said condenser. Where a vaporiser is required to be inactive, for example, where heat is not required from the heat source associated with the vaporiser, the condensate supplied to that vaporiser may be cut off. In the case of small amounts of heat, undesirable absorption of heat can be reduced to a minimum. For example, the amount of condensate can be reduced in contact with said vaporiser, which amount must be heated before heat transfer to the condenser takes place.Also, the materials of the apparatus should be such that its thermal properties, including thermal capacity (specific heat) and thermal conductivity, reduce undesirable heat absorption to a minimum. On the other hand, for high heat transfer rates, additional condensate is allowed to circulate.

The means for controlling the amount of condensate returned to said vaporiser may include temperature and/or pressure responsive means. For example, temperature responsive means may respond to the temperature of, or at said vaporiser, said condenser, or bodies associated with the same whereby the amount of condensate returned is regulated. Similarly, pressure responsive means may detect changes in vapour pressure within the enclosing means or bodies associated with the vaporiser and/or condenser for regulating the condensate return. The control means may be such as to adjust the flow rate of condensate returned to said vaporiser. Alternatively, the amount of condensate returned to said vaporiser may be regulated with the aid of an auxiliary reservoir. The condensate control may be either continuous or discontinuous.

When the control means includes a reservoir, there may be provided means for altering the volume of condensate stored in the reservoir, or the flow of condensate through the reservoir, or both. The reservoir may include a valve or weir to control the amount of condensate in, or flowing through, the reservoir, as required. Said valve or weir is controlled by an element responsive to pressure, or preferably temperature, and which is located at or adjacent said vaporiser. For example, such a thermally responsive element may cause an expansion which is taken up by elastic or resilient means in the intermediate reservoir to release condensate to said vaporiser.

The preferred embodiment of the invention enables the realisation of a heat transfer control which is most advantageous for applications such as solar heating, or controlled cooling. In the first case, small bursts or amounts of thermal energy may be experienced wherein the sun acts on a vaporiser for brief intervals during cloudy weather. In the second case, apparatus according to the preferred embodiment of the invention could be used to control the cooling of a shut down furnace at a more accelerated rate than under natural conditions. The apparatus may also be adapted so as to exercise control over the temperature of the condenser or of elements to which the condenser transfers heat.

In the case of using a plurality of vaporisers and condensers, separate condensate regulating means are provided to effect the desired control either manually or automatically. For example, a plurality of vaporisers may supply vapour to a common condenser, each vaporiser being heated by a separate heat source and controlled by regulating means for returning condensate in accordance with the heat supplied.

A further disadvantage of known devices is that they often incorporate only a single tube wherein a counterflow of vapour and condensate takes place. In certain circumstances, the operation of the device can be seriously impaired by entrainment of condensate in vapour due to such counterflow and little or no account may be taken of the different flow requirements of vapour and condensate, often in counterflowing directions, with regard to the required heat transfer characteristics. A further embodiment of the invention is directed to overcoming these problems. This is generally achieved, by having a separate condensate return with regard to the path of vapour flow. More particularly condensate return means are provided wherein the path of vapour flow between said vaporiser and said condenser is substantially different from the path of condensate returned from said condenser to said vaporiser.

This avoids the entrainment of condensate in vapour due to counterflow conditions and reduces the chance of condensate or vapour locks and also improves thermal efficiency. The enclosing means may be in the form of a tube which is configured in a closed and continuous loop. This may be a simple loop or it may include sections which are wound as a coil, spiral, or helix to improve thermal efficiency. Other embodiments may include a tube having sections which lie inside or outside the main body of the enclosing means and having ends which lie either inside said main body or join with said main body in the form of a closed loop.

According to one arrangement, said enclosing means defines a tube having at least one re-entrant section for isolating the vapour of the fluid from the fluid condensate at least along a part of said re-entrant section. A re-entrant section may have an inlet adjacent or within said condenser for collecting the condensate. Alternatively, the outlet of a re-entrant may be adjacent said vaporiser.

Preferably, the vapour and the condensate are conducted through passageways which, at least in one section, are dimensioned with respect to the different flow requirements of vapour and condensate. For example, a condensate tube may be provided having a smaller cross sectional area than a vapour tube.

In the case of using a single tube, providing communication between said vaporiser and said condenser, the tube may contain a series of scoops or baffles which are preferably arranged gradually to reduce the cross sectional area of the passageway which conducts vapour from said vaporiser to said condenser.

A further disadvantage of some known devices is that no precautions are taken to prevent or to relieve an excess pressure. The devices may also be of a shape which do not withstand pressures which are much greater than atmospheric pressure. Besides the problems of safety, other problems exist with regard to purging the devices during maintenance, servicing or filling with a working fluid. Another embodiment of the invention is directed to overcoming these problems by providing isolating means by which one or more vaporizers or condensers can be isolated from one another.

Said vaporisers or said condensers may be in the form of flat panels. The intercommunicating sections may be defined by a tube including an auxiliary reservoir and a pressure relief valve, said tube being isolated from the respective vaporiser and the respective condenser by respective valves.

The isolating means may be temperature responsive and provided for preventing vapour flow. Alternatively, the isolating means may be operative to prevent an excess build up of pressure or temperature within any part of the enclosing means.

The different embodiments of the invention described above may be adopted in combination as will be apparent from the following description of preferred embodiments of the invention. Referring to the accompanying schematic drawings: Fig. 1 is a cross-section in elevation of apparatus comprising a tube with a removable plug, the Figure being included to show a stage in the development of the invention, Fig. 2 is a partly sectioned elevation of two phase, thermo-syphon apparatus according to one embodiment of the invention, Fig. 3 is a section through a spring loaded ball valve with vents, Fig. 4 is a section through a liquid trap, Fig. 5 is a broken away elevation of another two phase, thermo-syphon apparatus according to another embodiment of the invention.

Fig. 6 is a broken away elevation of apparatus similar to that of Fig. 2 but which has been adapted to heat a liquid in a tank, Figs. 7 and 8 are broken away sections in elevation showing liquid trap sealing means, Fig. 9 is an elevation in perspective, partly broken away, showing a two phase, thermo-syphon apparatus according to a further embodiment of the invention Fig. 10 is a broken away section in elevation of a detail of an embodiment similar to that of Fig. 9, Figs. 11 and 12 show further embodiments of the invention employing a conical coil, Fig. 13 shows a simplified arrangement with a closed loop, the Figure being included to show a stage in the development of a feature used in some embodiments of the invention, Figs. 14, 15 and 16 are broken away sectioned elevations of heat transfer control arrangements which are used in some embodiments of the invention, Fig. 17 shows a modification of Fig. 2.

Figs. 18-21 show further embodiments of the invention in which part of the enclosing means is in the form of a conventional radiator, Fig. 22 is an elevation in section of part of another embodiment of the invention with a heat transfer control, and Fig. 23 is a schematic diagram of a multivaporiser system.

Referring to Fig. 1, a tube 1 encloses a fluid 2 which is in liquid and vapour states.

The tube is sealed by a removable plug 3.

Liquid 2 collects in the lower part A of the tube and heat applied to part A causes some vaporisation. The vapour travels to a cooler upper part B of the tube, where it condenses and releases the heat of vaporisation. The condensed liquid flows back to part A under gravity or under any other accelerational field if the device is correctly orientated with respect to that field. This cycle of vaporisation and condensation will continue whilst there remains a suitable temperature difference between parts A and B.

The apparatus shown in Fig. 1 differs from a heat pipe wherein a wick is used to return condensate to the vaporiser A by capillary action. An advantage of a heat pipe over a Perkins tube is that the positioning of parts A and B, relative to an acceleration field, is less restricted. However, pumps can be used with a Perkins tube or the tube 1 to return or recirculate the condensate.

The sealing means or plug 3 is used in the following method of charging the tube 1 with fluid 2. First, the tube is filled with the fluid in its liquid state as completely as possible with the plug 3 loosened. Plug 3 is designed to seal the tube 1 but when loosened, the end of the tube 1 provides a connection between the interior of tube 1 and a suction pump (not shown) positioned with 3 at the lowest point, or preferably at the level at which the liquid/vapour interface of fluid 2 is to lie. As liquid 2 is removed by suction, a vapour space is left above the liquid. When sufficient vapour space has been created, defined either by the positioning of plug 3 or otherwise, plug 3 is used to seal off tube 1.Plug 3 which may include a liquid seal as described later, enables contaminants to be removed or kept to an acceptable level and recharging to be carried out during the lifetime of the tube.

Therefore, contamination is not so critical and thus simpler and cheaper techniques and equipment can be used in the manufacture and charging of the device. The suction method can be carried out whilst the tube 1 is heated in order to raise the temperature and vapour pressure of fluid 2 to reduce the suction required.

The device of Fig. 1 may be unsuitable if it is overheated, when dangerous temperatures and pressures can occur, because the tube could burst. To prevent this, the tube 1 may include a bursting disc, designed to rupture at a predetermined pressure. Since the pressure and temperature in tube 1 are related, a bursting disc could also be used to limit temperature. The bursting disc should be set to rupture at the pressure dictated by maximum pressure or maximum temperature, whichever give the lower pressure. If maximum temperature is the governing criterion the bursting disc could, in some cases, be replaced by a fusible plug. Such devices must, of course, be placed in suitable positions. Basic disadvantages of the above sealing devices are that they have to be replaced and therefore do not reseal automatically when critical conditions have passed.As pressures and temperatures in tube 1 fall, contaminants may well enter the device. Other monitoring means could be fitted to control the heat supply before such failures occur, but they may be costly.

A sealing means in accordance with one embodiment of this invention, which can be made simple, effective, and automatic in operation, is a one-way relief valve. If pressures in tube 1 get too high a limit is set by the valve. In order to relieve as much energy as possible whilst losing the minimum of fluid 2 the valve is best positioned in the vapour region of the tube 1. The valve will reseal when pressures drop below a level set by the valve. However, if there is slight leakage in the valve, some ambient fluid may still enter tube 1 and cause undesirable contamination. The embodiment of the invention shown in Fig. 2 overcomes this problem.

With reference to Fig. 2, the tube 1 is fitted at its upper end with a sealing means consisting of a one-way relief valve 4. The valve is immersed in a liquid 5 here contained in a small vessel 6. In some cases the liquid 5 might be replaced with a semi-solid material. Where necessary, means could also be provided for topping up the level of liquid 5, automatically or otherwise. Means could also be provided to indicate if the level of liquid 5 drops too low. The purpose of liquid 3 is to ensure that, in the event of a leak in the relief valve 4, a minimum of ambient fluid e.g. air enters the tube 1. Such a device will be necessary where the ambient fluid would act as an undesirable contaminant. Liquid 5 might, however, contain a small amount of ambient fluid in solution or otherwise.A desirable characteristic of liquid 5 is that it should not easily dissolve the ambient fluid. Some very important characteristics of liquid 5 are that it should be compatible with the substances with which it comes into contact, its presence in tube 1 should not act as an undesirable contaminant impairing the performance of the device. If the device is overheated inten tionallyto urge contaminants, or otherwise, fluid 2 in vapour form will be blown off through valve 4, but only liquid 5 can re-enter. Such a feature is useful where outgassing may occur within tube 1 impairing the performance. Various details can be added depending upon the application. For example, the vessel 6 can be left open as illustrated, or it can be sealed with a dust cap 7 or a liquid trap. Alternatively, it can be sealed with a further one-way relief valve. This last design and its function will now be described.

Referring to Fig. 5, the sealing arrangement of Fig. 2 is shown with the addition of a second relief valve 9. Preferably, both valves 4 and 9 are preloaded by any suitable known means, such as the spring loaded ball 70, 71 of Fig. 3. If valve 4 is set to a pressure so that, during normal running, substantial vaporisation or boiling of liquid 5 can occur, then liquid 5 must also be pressurised. This is the purpose of fitting valve 9. Since the maximum absolute pressure within the tube 1 will now be ambient plus the sum of the pressure settings of valves 4 and 9, the design must take this into account.

Previously a method has been described in which the embodiment of Fig. 1 could be charged with the right amount of fluid 2 using a suction device. The method used to purge the tube 1 of contaminants was to fill it initially with liquid 2, surplus liquid then being sucked out to leave a vapour space.

Where a one-way relief valve is fitted as in the case of the embodiment of Fig. 2, purging can be carried out simply by supplying enough heat to the device. The vapour pressure of fluid 2 will rise to ambient plus the relief valve setting and the escaping vapour 2 will take with it much of the gaseous contaminants previously within the tube. Gaseous contaminants are often the most serious, since their pressures, which can be high by comparison with the working vapour pressure of fluid 2, suppress vaporisation of fluid 2. The presence of gas can thus raise the lower threshold temperature at which the device will start to transmit heat effectively.

This can be very undesirable. The upper temperature of operation will be governed mainly by the pressure settings of the relief valves, the effect of any contaminants should be comparatively small.

Referring to Fig. 6, an embodiment is shown in which a device of the type of Fig.

2, preferably with an extended surface 10, is fitted into a tank 11, which contains a liquid 12 or other suitable material, to be heated.

In this case materials 12, 5 and 2 are basically the same, e.g. water. Fluid 2 might be distilled water and 5 and 12 be ordinary water. In the embodiment of Fig. 6, liquid 5 is not shown because it can be identical to liquid 12. In normal operation the one-way relief valve 4 and the vessel 6, if present, are covered by liquid 12. After the device has been constructed, it may be filled with fluid 2 and then purged of undesirable contaminants by methods already described. Vessel 6 is only required if the method of purging by heating requires the tank 11 to be empty in order to reduce heat losses. Other ways of reducing heat losses with the tank full or empty are to shroud surface 10 thus impeding convection, or to reduce the preloading in valve 4, thus reducing the temperature at which purging will take place.

With reference to Figs. 4, 7 and 8, the principle of liquid or semi-solid sealing may be applied to any joints where it is required.

Fig. 4 shows a liquid trap 8 sealing a screwed joint. In Fig. 7, the seal covers a joint 14 between two vertical parts of the tube 1. A container 15 holds liquid 5 which covers the joint 14. In Fig. 8, the joint 16, is between two parts of tube 1 which are close to the horizontal. A container 17 holds liquid 5.

Where the sealing material would otherwise boil or evaporate too rapidly, containers 15 and 17 may also be provided with sealing means to serve the function of valve 9 in the embodiment of Fig. 3. By providing sight glasses or other indicating or monitoring means of known types, liquid sealing means can also act as detectors for leaks into the enclosing means.

In the previous arrangements, the condensate of fluid 2 flows in the opposite direction to the vapour of fluid 2. At high heat transmission rates, the condensate can become entrained in the vapour impairing the heat transmission performance. In the embodiment of Fig. 9, a smaller tube 18 is placed inside tube 1. Holes in the upper end 19 of tube 18 communicate with the interior of tube 1. Associated scoops 21 and 22 catch the liquid condensate which can enter tube 19 via the holes. Since the volume of condensate is very small compared with the same weight of vapour, the tube 18 can be very small, its internal diameter being determined by factors that include the flow rate versus pressure drop of condensate in tube 18. The condensate returns to the vaporiser tube 13 where heat is applied.Preferably, tube 13 increases in cross section either continuously or in steps along the length of the vaporising coil (to accommodate increasing quantities of vapour) before merging with the tube 1. In the parts of the vaporising coil where there is little liquid, it may be desirable to have a wick lining the tube to spread the liquid by capillary action so that vaporisation can take place in a way that will reduce hot spots on the tube wall.

Such a lining is not essential to returning the condensate to the vaporiser as in known heat pipes. In normal operation, the flow of condensate of fluid 2 into tube 18 will be spontaneous due to the pressure head of gravity or some other acceleration field acting on the mass of liquid collecting at scoops 21 and 22. Furthermore the design is such that, in the vaporiser, the flow of liquid and vapour of fluid 2 will be wholly or substantially in the same direction. Other designs could feature a tube 18 wholly enclosed in tube 1, the designs of Figs. 1, 2, 5 and 6 could be improved in this way. The tube 18 would simply terminate within tube 1 at some point preferably in the vaporiser (not shown on all Figures) where heat is applied.

Such designs would have an advantage of simplicity in shape and construction.

Fig. 10 illustrates a preferred scoop design. Together with the rate at which con densate can recirculate through tube 18, heat transmission can be limited by the sonic velocity of the vapour. As scoops reduce the area for vapour flow they could also reduce performance. However, multiple scoops may be advantageous as shown in Fig. 10. A first scoop 23 is large enough to catch the condensate formed by the vapour flowing past it at sonic velocity. This establishes the size and position of scoop 23. Subsequent scoops 24, 25 , will be sized and positioned according to similar principles.

The minimum scoop size is determined by the amount of condensate formed between it and the preceding scoop. Scoop 24 is smaller than scoop 25 and so on. Whilst scoops have the advantage of providing a device with a simple or smooth exterior, they have some degree of complexity and restrict the tube 1 and cause some counterflow between the liquid and vapour of fluid 2. Such counterflow occurs between the scoops and also between the vapour of fluid 2 and any condensate which has escaped the scoops and is flowing back down tube 1, but outside tube 18. To reduce such problems, the outflow from each scoop should pass into a tube, which tube passes a sufficient distance down inside outflow tube for the following scoop.

Sufficient distance is that which allows sufficient gravity head within the outflow tube of the following scoop to carry away condensate with minimum or negligible outflow of the scoop. Preferably, the design principles used for the vaporiser in Fig. 9 can also be used for the condenser.

With reference to Fig. 11, the condenser 27 is shaped as an inverted cone. Vapour of fluid 2 passes up through the vertical part of tube 1, to reduce condensation in this section, the walls of the tube could be insulated. A relief valve 28 is also shown. Condensation takes place in the descending spirals of the cone, as the vapour flow decreases, the tube size decreases until tube 1 finally merges with tube 18. Although the condenser is shown here as an inverted cone, it could also be a cylindrical spiral or other known configurations. Each configuration has its own advantages regarding heat transfer and manufacturing methods.

The coils may be formed of a tube which has an external extended surface.

In Fig. 12, the inverted cone of tube 27 has been flattened, a chimney 28 has been added to improve the natural convection, and louvres or suitable ducts 29 are fitted to improve the flow by acting as diffusers and/or guides.

Fig. 13 shows an arrangement wherein tube 30 is separate from tube 1 with respect to vaporiser 31 and condenser 32. However, regarding the tube design in the embodiments of Figs. 9, 11 and 12, there are advantages in putting the intermediate section 18 of tubes 23 and 27 inside tube 1 with regard to installation, reduced heat loss and the use of cheaper materials for tube 18 which is thus protected by tube 1.

In combining the condenser of Figs. 11 and 12 with the vaporiser of Fig. 9, there may be negligible counterflow of condensate and vapour. Furthermore, any pressure recovery resulting from condensing vapour should aid re-circulation of condensate.

If a thermal system is required to work over a wide range of temperature and heat transfer, heat may be wasted. Saucepans are often removed from the rings of electric cookers when the rings are at red heat and all this heat is wasted. Modified tubes as discussed above could be adapted to transmit a lot of this heat to, for example, a hot water tank. In a larger industrial application, the heat in a shut down furnace could be saved or recovered along with the advantage of controlled and accelerated cooling.

For the efficient transfer of small quantities of heat, only a small amount of working fluid will be required. A larger amount would absorb more heat in simply warming up the condensate with less heat transfer. In this connection it is necessary to consider optimum relationships of thermal capacity and conductivity of various parts of the device. On the other hand, a large amount of waste heat requires a larger amount of fluid 2 to avoid hot spots which occur if all the fluid 2 is either in vapour form or is in the process of recirculating to the vaporiser but has not yet reached it. The vaporiser will then be starved of liquid 2 and thermal performance will be impaired even if the heat source is of low temperature. It would thus be advantageous to have means automatically to vary the amount of fluid 2 which is effectively in circulation.

Fig. 14 shows means for controlling the flow rate of the condensate. A tube 34 leads into a reservoir 35 which feeds the continuation 36 of tube 34. The flow of condensate 2 out of reservoir 35 is controlled by a valve 37. Valve 37 is operated by a control rod 38, which in turn is actuated by a temperature sensing/actuating element (not shown) which may be of known design. The temperature sensing element may be located at a part where hot spots are most likely to occur. When the temperature at the sensing/actuating element rises above some predetermined threshold value, valve 37 opens and allows liquid condensate to flow to the vaporiser (not shown). When the temperature at the sensing element falls below the threshold level, valve 37 closes and the returning condensate tops up the reservoir 35. Whilst basic advantages of this system are simplicity and the comparatively small movements required by valve 37, it has a disadvantage. A slight leak in valve 37 may lead to too much condensate in the vaporiser so that small amounts of heat are not effectively transferred. Such a disadvantage could be important in a solar heating application, for example, where the sun appears for short intervals from behind cloud. A further disadvantage is that all the liquid in the reservoir 35 must be heated up over a longer period of operation. An embodiment to reduce this latter disadvantage will now be described.

With reference to Fig. 15, a cylindrical tube 39 contains a valve 41 similar to valve 37. Operation is in two stages. First, valve 41 opens as before at the threshold temperature and allows condensate to recirculate via tube 34, tube 39 and valve 41, to by-pass the reservoir 40. During this stage, condensate is prevented from recirculating from the reservoir. Thus, only a limited amount of condensate is recirculated, the remainder being held in the reservoir 40. If required, the tube 39 may be made of an insulating material to reduce heat losses. If the sensed temperature continues to rise, then an actuator 42 on rod 38 lifts the cylindrical tube 39 to release the stored condensate for recirculation. When the temperature falls, actuator 42 lowers tube 39 and subsequently valve 41 closes at the threshold temperature.Condensate from tube 34 first fills a small reservoir in the body of tube 39 and then overflows into the reservoir 40.

This embodiment may have a disadvantage associated with a leaking valve and the next embodiment overcomes this.

The embodiment of Fig. 16 has some features similar to that of the embodiment of Fig. 15. A cylindrical tube 44 is sealed to the bottom of a reservoir 45 and incorporates a flexible element 46, here shown as a spring bellows but which could include rolling diaphragms and other types of positive sealing devices. The top of tube 44 can thus move up and down, trapping a greater or lesser amount of condensate 2 in the reservoir 45. A valve 47 is positioned to seat in an extension and modification 48 of the incoming tube 34. The embodiment works in two stages. First, valve 47 opens and, due to the design of the seating, condensate passes through tube 44. If the sensed temperature continues to rise, an actuator 49, fitted to rod 38 moves the top of tube 44 down allowing condensate to spill over into the recirculating system from the reservoir 45.

When the sensed temperature falls, first of all the top of tube 44 rises so that no more condensate enters the recirculating system.

Valve 47 then closes, when the sensed temperature falls below the threshold, and condensate recirculating through tube 34 spills through holes 50 and back into the reservoir 45. Due to the positive sealing of tube 44, condensate cannot leak back into the system from the reservoir. The variation of the amount of fluid 2 in circulation may be less than that of Figs. 14 and 15 and this could be a disadvantage. In the above embodiments, the actuating rod 38 could be replaced by other known means of control.

Moreover, the action of the controller need not be limited to one or two stages as described. Furthermore, a pressure sensor/actuator could be used in some cases in place of the said temperature sensor/actuator. For optimum operation, differential, integral and proportional control capabilities may be desired in any combination.

Fig. 17, represents the embodiment of Fig. 2 with a second sealing means 51 of a type which may be identical to Fig. 1. To facilitate the correct charging of the device with the fluid 2, means 51 is placed at a suitable height. A tube (not shown) may also be incorporated in means 51 which extends upwards or downwards into tube 1 in order to provide an adjustment in the condensate height. Purging may be carried out by either of the methods described above. In the heating method where vapour 2 is blown off through valve 4 (Fig. 2), initial filling is done via means 51 which is then sealed up before purging starts. In the sucking off method, a suction device is attached to means 51, the plug fitted to means 51 is removed and the device is filled with liquid 2. The plug is then refitted. The liquid is then sucked off through means 51 until vapour begins to appear in quantity.Means 51 is then sealed up and the suction device is removed.

Where a device is normally operated at temperatures such that internal pressures do not exceed ambient pressure, it may be uneconomic or undesirable in other ways to adopt constructional methods for some parts of the enclosing means such that they can withstand even the slight excess pressure or elevated temperature associated with the heating method of purging described above. On the other hand, this may be desirable for simplicity, so that suction apparatus is not required. In the embodiment of Fig. 18, it is supposed that the vaporising region 52 of the enclosing means consists of flat plates 53 and a wick structure adapted to cool the hot elements of a freezer. The plates 53 are sealed round their edge and cannot, effectively, take excess pressure. The condensing region 54 of the enclosing means uses plates 55 and is of similar construction to region 52.Both regions 52 and 54 are connected by tube 1 which can take some excess pressure and temperature. Fitted to tube 1 are one way relief valve 56 and auxiliary reservoir 57.

Regions 52 and 54 can be sealed off internally by valves operated magnetically or by other known means, which valves are positioned at 58 and 59. Reservoir 57 is designed to take some excess pressure and temperature, so that heat can be applied.

Regions 52 and 54 are constructed so that they can be filled and emptied as required.

To set up and purge the embodiment, the procedure is as follows.

Valves 58 and 59 are closed. Regions 52 and 54 and auxiliary reservoir 57 are filled with working fluid 2 in liquid form and are sealed. Heat is applied to reservoir 57 so that vapour 2 blows off through valve 56 taking with it undesirable contaminants.

The heat is removed from reservoir 57, the valves 58 and 59 are opened at a suitable moment and the device is put into operation. The device is designed so that, in operation, the required amount of working fluid 2 is in circulation. In further embodiments (not shown) other valves, which are internal to the enclosing means, can be provided to control the transfer of pressure or heat or both from one part of the enclosing means to another as is desired. For example, if several heat sources are provided of which the cooling coils of a freezer are one, these coils could become overheated by a heat source at higher temperature. In yet another application e.g., in connection with the electric cooker already described, it may be desirable not to transmit heat from a heat source until required.In this case, valves can be used to prevent return of condensate to a vaporising region, which region will have to be constructed to withstand any temperatures that might result.

With reference to Figs. 19, 20 and 21, flat panels are used as part of the enclosing means of two phase, thermo-syphon apparatus according to the invention. The arrangements are fitted with openable sealing means having a liquid trap (not shown).

The panels themselves may be operated at reduced pressure and they could be very light weight in construction. In the embodiments to be described attention is paid to new aspects of design. In actual designs items according to the features already described would be included as necessary.

With reference to Fig. 19, the condensing region 60 is formed by a flat panel 61. It is connected to the vaporising region 62 by the tube 1 which may have some flexible sections. Tubes 34, 36 of Figs. 14-16 may also be fitted. Preferably, panel 61 has a slight tilt to encourage recirculation of condensate 2. Region 62 may be heated by any suitable means. Water could be used as the fluid 2 and the device could be used as an overhead low temperature radiant heater. The design should be such that liquid looks do not occur to prevent the free flow of vapour.

Fig. 20 shows an adaptation of the system of Fig. 19. A hot water, steam or other hot pipe 63, passes through a jacket 64. The working fluid 2 is contained by jacket 64, tube 1 and panel 65, and is heated by contact with pipe 63. Although the small heating area of pipe 63 and the large radiant area of panel 65 might appear to be illmatched, the heat transmission from the surface of panel 65, due to the radiant heat and heat lost by convection to a gas, is comparatively low. On the other hand, heat transmission rates from the surface of pipe 63, due to the evaporation or boiling of the fluid 2, can be comparatively high. The flow conditions inside the pipe 63 must be such that the heat transfer coefficient inside the pipe is sufficiently high.This embodiment could be adapted to known applications the tube 1 passing through the floor indicated by 66, and the panel 65 being used to heat rooms, offices and other spaces.

With reference to Fig. 21, an embodiment is shown in which the pipe 63 runs through the bottom of the panel 65 and, tube 1 is dispensed with. Water or other suitable substance is in contact with pipe 63. The water boils, is condensed on the panel 65 and flows back to pipe 63. The means already described for controlling the amount of fluid in circulation can be adapted as a temperature control for the surroundings. In a system working on the principle of the embodiment of Fig. 14, the reservoir could be built as a gutter running along one wall of the panel 65. Valve 37 is operated by the temperature at the condenser or of some object or the surroundings to be heated. If the surroundings are too hot then valve 37 is closed, the reverse of the previous case.

Water accumulates in the reservoir and eventually none runs back into contact with the pipe. This does not matter in the present case, because with this form of heating, hot spots will not develop. When the temperature of the surroundings drops sufficiently the valve 37 opens and water comes into contact with the pipe 63. Any other suitable known forms of heat source can be used. In some cases special controls will be needed.

In the case of electrical heating a control will be required to prevent the electrical element from overheating.

Fig. 22 shows an alternative and simple means of heat transfer control. In the embodiment of Fig. 16, bellows were used to enable the top of tube 44 to be adjusted.

In the embodiment of Fig. 22, the amount of the condensate 66 returned is adjusted by raising or lowering the free end of a yielding or flexible tube 67 with respect to the condensate level in reservoir 68. This concept can be embodied as a heat transfer control as was the case with the intermediate reservoirs 35, 40, 45 of Figs. 14, 15 and 16 respectively.

Many of the above devices can incorporate pumps for recirculation of the condensate. An advantage of using coiled tube for heating and cooling is that the distance bet ween coils can be readily adjusted for maximum heat transmission. A sealing means that can be used to drain the devices would be useful. Useful accessories would be temperature and pressure gauges to check the conditions inside the device against those that should prevail for the physical properties of the particular working fluid. In the embodiments described above, not all features are given that may be desirable in a real piece of equipment. Features may be combined in any compatible way.

Just as sealing means can be adapted, in known ways, so that quantities of fluid 2 can be sucked out of the enclosing means, so similar or identical adaptation can be used for passing controlled quantities of fluid 2 into the enclosing means whilst undesirable contaminants are substantially excluded.

Internal valves, can be conveniently operated electromagnetically or by any other suitable known means, e.g., through movable, sealed diaphragms. Such methods will possess known advantages related particularly to good sealing.

Fig. 23 schematically represents a apparatus including a plurality of vaporisers 75, 76, 77 connected by vapour flow tubes to a common condenser 78. The condensate return 79, 80, 81 to each vaporiser is reu- lated by a respective valve or weir 82 83 84. Each valve or weir is controlled, for example, with respect to the temperatures of the heat source H1, Ha, H3 in contact with the respective vaporiser 75, 76, 77. Other arrangements are possible such as a plurality of condensers connected to a common reservoir for selective condensate return, or a plurality of vaporisers and condensers connected to provide a desired heat exchange with respect to temperature and/or pressure.The apparatus of Fig. 23 is fitted with openable sealing means having a liquid trap (not shown).

WHAT WE CLAIM IS: 1. Two phase, thermo-syphon apparatus comprising enclosing means which defines at least one vaporiser and condenser, a fluid which is contained, during normal operation, within the interior of the enclosing means and which transmits heat by intercommunication between said vaporiser and said condenser, the enclosing means being such that the fluid condensate is free to return to said vaporiser unimpeded by wicks or capillary means, the enclosing means communicating with openable sealing means having at least a joint, or a removable cap or plug, or a valve, and a liquid trap containing a liquid compatible with the fluid in the enclosing means, said trap being arranged such that the liquid therein will enter the enclosing means in the event of a leak in said sealing means.

2. Apparatus according to claim 1 wherein the sealing means comprises at least one non-return valve.

3. Apparatus according to claim 1 in which said valve responds to a predetermined pressure.

4. Apparatus according to claim 1 wherein said enclosing means is in two or more sections and respective liquid traps surround the joints between adjacent sections.

5. Apparatus according to claim 1 wherein said sealing means is temperature responsive in order to relieve excess pressure in said enclosing means.

6. Apparatus according to claim 3 or 4 wherein said sealing means is pressure responsive in order to relieve excess pressure in said enclosing means.

7. Apparatus according to claim 1 wherein a plurality of valves are provided for sequential operation at different pressures.

8. Apparatus according to claim 1 or 7 wherein said valve or valves are provided at said condenser.

9. Apparatus according to any one of the preceding claims wherein the liquid trap contains fluid similar to that in said enclosing means.

10. Apparatus according to any one of the preceding claims wherein the enclosing means and the liquid trap both contain water.

11. Apparatus according to any one of the preceding claims wherein the liquid trap has a transparent section for inspecting liquid level.

12. Apparatus according to any one of the preceding claims including control means to control the amount of condensate returned to said vaporiser.

13. Apparatus according to claim 12 wherein said control means includes a temperature responsive actuating means for returning condensate to said vaporiser.

14. Apparatus according to claim 12 wherein said control means includes pressure responsive actuating means for returning condensate to the condenser.

15. Apparatus according to claim 12 wherein said control means comprises means for adjusting the flow rate of the condensate returned to said vaporiser.

16. Apparatus according to claim 12 including condensate reservoir means and wherein said control means is provided for regulating the amount of condensate stored in said reservoir means.

17. Apparatus according to any one of claims 12, 13 or 16 wherein said control means includes a weir for returning condensate to said vaporiser and reservoir means for storing said condensate for return by said weir.

18. Apparatus according to claim 17

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ween coils can be readily adjusted for maximum heat transmission. A sealing means that can be used to drain the devices would be useful. Useful accessories would be temperature and pressure gauges to check the conditions inside the device against those that should prevail for the physical properties of the particular working fluid. In the embodiments described above, not all features are given that may be desirable in a real piece of equipment. Features may be combined in any compatible way. Just as sealing means can be adapted, in known ways, so that quantities of fluid 2 can be sucked out of the enclosing means, so similar or identical adaptation can be used for passing controlled quantities of fluid 2 into the enclosing means whilst undesirable contaminants are substantially excluded. Internal valves, can be conveniently operated electromagnetically or by any other suitable known means, e.g., through movable, sealed diaphragms. Such methods will possess known advantages related particularly to good sealing. Fig. 23 schematically represents a apparatus including a plurality of vaporisers 75, 76, 77 connected by vapour flow tubes to a common condenser 78. The condensate return 79, 80, 81 to each vaporiser is reu- lated by a respective valve or weir 82 83 84. Each valve or weir is controlled, for example, with respect to the temperatures of the heat source H1, Ha, H3 in contact with the respective vaporiser 75, 76, 77. Other arrangements are possible such as a plurality of condensers connected to a common reservoir for selective condensate return, or a plurality of vaporisers and condensers connected to provide a desired heat exchange with respect to temperature and/or pressure.The apparatus of Fig. 23 is fitted with openable sealing means having a liquid trap (not shown). WHAT WE CLAIM IS:

1. Two phase, thermo-syphon apparatus comprising enclosing means which defines at least one vaporiser and condenser, a fluid which is contained, during normal operation, within the interior of the enclosing means and which transmits heat by intercommunication between said vaporiser and said condenser, the enclosing means being such that the fluid condensate is free to return to said vaporiser unimpeded by wicks or capillary means, the enclosing means communicating with openable sealing means having at least a joint, or a removable cap or plug, or a valve, and a liquid trap containing a liquid compatible with the fluid in the enclosing means, said trap being arranged such that the liquid therein will enter the enclosing means in the event of a leak in said sealing means.

18. Apparatus according to claim 17

wherein said weir co-operates with a valve controlled by a thermally responsive element located at or adjacent said vaporiser.

19. Apparatus according to claim 18 wherein said thermally responsive element causes expansion which is taken up by yieldable or resilient means in the reservoir means to release condensate to said vaporiser.

20. Apparatus according to any one of the preceding claims wherein the path of vapour flow between said vaporiser and said condenser is substantially different from the path of condensate returned from said condenser to said vaporiser.

21. Apparatus according to claim 20 wherein the enclosing means is in the form of a tube which is configured in a closed and continuous loop.

22. Apparatus according to claim 21 wherein the tube has straight sections.

23. Apparatus according to claim 21 wherein a section of the tube is wound in a coil.

24. Apparatus according to claim 21 wherein a section of the tube is wound in a spiral.

25. Apparatus according to claim 21 wherein a section of the tube is wound in a helix.

26. Apparatus according to claim 25 wherein the helix is wound in a conical form.

27. Apparatus according to any one of claims 21-26 where in the tube has a section or sections which lie inside the main body of the enclosing means.

28. Apparatus according to claim 27 wherein the ends of the or each section lie either inside said main body or join with said main body in the form of a closed loop.

29. Apparatus according to claim 20 or 21 wherein the enclosing means defines a tube having a re-entrant section for isolating the vapour of the fluid from the fluid condensate at least along a part of said section.

30. Apparatus according to claim 29 wherein the inlet of the re-entrant section is adjacent or within said condenser for collecting the condensate.

31. Apparatus according to claim 29 wherein the outlet of the re-entrant section is adjacent said vaporiser.

32. Apparatus according to claim 20 wherein said vaporiser is in the form of a coil having an upper end forming a reentrant tube section projecting inwardly of the enclosing means.

33. Apparatus according to claim 32 wherein the vapour flows in a substantially straight section between the coil and said condenser.

34. Apparatus according to any one of claims 20-33 wherein the cross sectional area of the condensate return means is reduced with respect to the path of vapour flow.

35. Apparatus according to any one of claims 20-34 herein the vapour and condensate are conducted through passageways which, at least in one section, are dimensioned with respect to the relative flow of vapour and condensate.

36. Apparatus according to claim 35 wherein a single tube contains a series of scoops or baffles arranged gradually to reduce the cross sectional area of the passageway which conducts vapour from said vaporiser to said condenser.

37. Apparatus according to any one of the preceding claims including isolating means by which one or more vaporisers or condensers can be isolated from one another.

38. Apparatus according to claim 37 wherein said isolating means is temperature responsive and is provided for preventing vapour flow.

39. Apparatus according to claim 37 or 38 wherein said isolating means is operative to prevent an excess build-up of pressure within any part of the enclosing means.

40. Apparatus according to claim 37 wherein said isolating means is operative to prevent an excess build-up of temperature within any part of the enclosing means.

41. Apparatus according to any one of claims 37-40 wherein said vaporiser and/or said condenser are in the form of flat panels.

42. Apparatus according to claim 41 wherein a section of the enclosing means is defined by a tube including a pressure relief valve, the tube being isolated from said vaporiser and said condenser by respective valves.

43. Apparatus according to claim 41 wherein said section is defined by a tube including an auxiliary reservoir and a pressure relief valve, the tube being isolated from said vaporiser and said condenser by respective valves.

44. Apparatus according to claim 1 and substantially as herein described with reference to Figure 2 of the accompanying drawings.

45. Apparatus according to claim 1 and substantially as herein described with reference to Figure 5 of the accompanying drawings.

46. Apparatus according to claim 1 and substantially as herein described with reference to Figure 6 of the accompanying drawings.

47. Apparatus according to claim 1 and substantially as herein described with reference to Figure 7 of the accompanying drawings.

48. Apparatus according to claim 1 and substantially as herein described with reference to Figure 8 of the accompanying drawings.

49. Apparatus according to claim 1 and substantially as herein described with reference to Figure 9 of the accompanying drawings.

50. Apparatus according to claim 1 and substantially as herein described with reference to Figure 10 of the accompanying drawings.

51. Apparatus according to claim 1 and substantially as herein described with reference to Figure 11 of the accompanying drawings.

52. Apparatus according to claim 1 and substantially as herein described with reference to Figure 12 of the accompanying drawings.

53. Apparatus according to claim 1 and substantially as herein described with reference to Figure 13 of the accompanying drawings.

54. Apparatus according to claim 1 and substantially as herein described with reference to Figure 14 of the accompanying drawings.

55. Apparatus according to claim 1 and substantially as herein described with reference to Figure 15 of the accompanying drawings.

56. Apparatus according to claim 1 and substantially as herein described with reference to Figure 16 of the accompanying drawings.

57. Apparatus according to claim 1 and substantially as herein described with reference to Figure 17 of the accompanying drawings.

58. Apparatus according to claim 1 and substantially as herein described with reference to Figure 18 of the accompanying drawings.

59. Apparatus according to claim 1 and substantially as herein described with reference to Figure 19 of the accompanying drawings.

60. Apparatus according to claim 1 and substantially as herein described with reference to Figure 20 of the accompanying drawings.

61. Apparatus according to claim 1 and substantially as herein described with reference to Figure 21 of the accompanying drawings.

62. Apparatus according to claim 1 and substantially as herein described with reference to Figure 22 of the accompanying drawings.

63. Apparatus according to claim 1 and substantially as herein described with reference to Fig. 23 of the accompanying drawings.