Patent Publication Number: US-2015077938-A1

Title: Variable conductance thermosiphon

Description:
FIELD OF THE INVENTION 
     The present invention relates cooling system comprising at least one thermo siphon, which thermo siphon comprises at least one indoor evaporator which indoor evaporator is heat conductive connected to indoor cooling fins, in which indoor evaporator liquid refrigerant is evaporated, which indoor evaporator is by first tubing connected to at least one outdoor condenser which first tubing conduct evaporated refrigerant from the evaporator to the outdoor condenser, which outdoor condenser is heat conductive connected to outdoor cooling fins for cooling the condenser, which condenser is place en a defined vertical distance to use the gravity to generate a flow of liquid refrigerant from the condenser through a second tubing back to the evaporator. 
     BACKGROUND OF THE INVENTION 
     US2011048676A discloses A cooling system applying a thermo siphon therein, being superior in energy saving and/or ecology, with an effective cooling, and also an electronic apparatus applying that therein, in particular, for cooling a CPU mounted on a printed circuit board within a housing thereof, comprises a heat-receiving jacket, being thermally connected with a surface of the CPU generating heats therein, and for evaporating liquid refrigerant stored in a pressure-reduced inner space with heat generation thereof, a condenser for receiving refrigerant vapour from the heat-receiving jacket within a pressure-reduced inner space thereof and for condensing the refrigerant vapour into a liquid by transferring the heats into an outside of the apparatus, a vapour tube, and a liquid return tube, with applying the thermo siphon for circulating the refrigerant due to phase change thereof, wherein the condenser forms fine grooves on an inner wall surface thereof along a direction of flow of the refrigerant, and is also formed flat in a cross-section thereof, for cooling the refrigerant vapour from the heat-receiving jacket on the inner wall surface thereof, efficiently. 
     OBJECT OF THE INVENTION 
     It is the object of the present application to achieve effective automatic cooling of electronic systems placed inside a housing. A further object of the present application is to stop the cooling system in situations with low outdoor temperature and avoid cooling of the electronic system inside the housing when temperature is low and there is limited or no need for cooling. 
     DESCRIPTION OF THE INVENTION 
     The object can be fulfilled by a system as disclosed in the opening paragraph an further modified in that the second tubing comprises a valve, which valve comprises a valve seat and a moveable valve piston, which valve piston is moved by a valve actuator, which valve piston is by decreasing temperature by the actuator moving towards the valve seat for closing the valve. 
     Hereby a highly efficient cooling system can be achieved which can operate automatically without any energy supply from the outside, due to the use of the thermo siphon principle. The energy supply necessary for operation is the heating that is used for evaporating the refrigerant in the evaporator. Because the thermo siphon is an open circuit with very limited flow restriction, a highly efficient cooling can be achieved. As long as the temperature inside a housing is higher than the outside temperature, the thermo siphon will operate very efficiently. In situations where the outdoor temperature is decreasing to a low level which could occur in situations where the outdoor condensers in winter periods is cooled to a low temperature, which have the unwanted effect that the inside of the housing is cooled to an undesirable low temperature level. In such situations there is a risk that very cold liquid refrigerant will be led through the tubing towards the evaporator which evaporator in this situation will start cooling inside the housing to a temperature level near the outside temperature. By the invention according to the present application this is avoided because there is a valve in the line that transmits condensate and liquid refrigerant backwards to the evaporator. If an automatic valve is formed that is heat-sensitive, then the valve will be close and the circulation stop as soon as the temperature in the liquid refrigerant is decreasing to a certain level. Of course with the valve closed, the thermo siphon is no longer in operation, but the outdoor temperature is so low that there is less cooling demand. Depending on the cooling demand the valve could fully close or partly close. In situations where the valve is designed to start closing, the thermo siphon is typically operating at temperature differentials higher than normal because the fan speeds is reduced in these operating situations. This have an undesirable effect on the thermodynamics processes driving the coolant circulation inside the thermo siphon, which in turn facilitates that the liquid is collected in the cold condenser disagreeing gravity. This effect is known as dry boiling the evaporator. As this thermodynamic state is metastable, the liquid will eventually return to the evaporator almost momentarily separated by certain time intervals producing a very undesirable shock cooling effect—as this collapsing process tends to happen very quickly. The valve inhibits or reduces this undesirable behaviour, as it blocks or limits the liquid return flow. If the valve is designed carefully it can prohibit dry boiling occurring because the thermal resistance of the thermo siphon is increased at low temperatures, which in turn prohibit the thermodynamic state necessary to effect dry boiling, from occurring. 
     The valve seat and the front of the valve piston can be conical. By the invention according to the present patent application it is possible to use different valve seats and different valve closure elements, but to achieve an efficient thermo siphon there must be an almost unrestricted flow refrigerant through the valve when the valve is in an open position. One possible way of achieving a high degree of opening is to use a conical valve seat and also a conical valve piston. In this way the refrigerant can flow around the conical valve piston and in this way it can be achieved that the flow restriction as such is very low for the liquid refrigerant flowing through the valve. In a closed position of the valve, there will be an efficient closure between the conical valve seat and the conical valve piston. Between the two conical elements a relatively long closure distance can be achieved. If further closure has to be achieved, there is no doubt that the conical piston or the conical seat could comprise one or more recesses in which O-rings could be placed, and in this way an even more efficient closure could be achieved. 
     In an alternative embodiment the valve can comprise a shaft, which shaft connects the valve piston through a valve seat. The valve actuator can be placed in thermal contact with the liquid refrigerant flowing in the second tubing, which valve actuator comprises a wax, which wax has a decreasing volume by decreasing temperature. One possible embodiment of the present invention is to use wax or maybe some other lubricant in an actuator because this actuator then maybe could comprise a movable piston that is moved by decreasing volume of the wax or lubricant contained in the volume. In a thermo siphon it should be possible to use a relatively long cylinder filled with wax or lubricant and in this way obtain a piston that can comprise the valve closure placed on the piston so that the valve will close automatically on decreasing temperature. 
     The valve actuator comprises at least one spring, which spring makes the valve piston acting towards the valve set for closing the valve. Hereby it can be achieved that a spring can press the valve piston against the valve seat and operate against the liquid pressure that occurs because a higher level of liquid is placed in the tubing above the valve. The spring has to be adjusted very precisely according to the force that is necessary for opening the valve. Different springs or different lengths of springs can be used in order to achieve different opening characteristics of the valve. In order to protect the valve, it could be possible to let the spring operate inside a housing which housing could also support the back-end of the spring and let the valve piston be placed at the front of the spring. 
     The valve actuator can be a bellow, which bellow comprises a gas, which is non-condensable in the operation temperature level for which the system is designed. In a preferred embodiment of the invention, a bellow is used because a bellow is a highly efficient component widely used in thermostats also for automatic opening and closing in relation to decreasing temperatures. The bellow will be filled with a non-condensable gas r which probably has a pressure near the boiling temperature/pressure of the operating refrigerant in the thermo siphon system, at which the valve has to operate. Thus it is only a question of selecting the pressure to define the operating temperature of the bellow valve that is to be used inside the bellow. Alternatively refrigerants or a mixture of several refrigerants could be used instead of a gas. By using a mixture is should be possible to adjust the boiling point rather precisely in a way so that boiling will occur over a temperature range. The internal pressure and bellow should make it possible also to use springs, maybe a spring that operates against the opening direction of the bellow, so that, as soon as the pressure in the bellow is reduced, the spring contributes to opening the valve and vice versa. The operating refrigerant is outside the bellow and the pressure of this is acting on the bellow. When the temperature/pressure of the saturated operating refrigerant is higher than the non-condensable gas inside the bellow the valve is open. When the saturation temperature/pressure inside the thermo siphon falls below the non-condensable pressure inside the bellow plus the force from the bellow spring times the area, the bellow begins to close The operation band of the bellow is then defined by the pressure differentials times the area on the one hand and the spring characteristics on the other hand. 
     It should also be possible to use a bimetal spring which bimetal spring automatically changes its length independently of the temperature. The valve piston could be fixed through one end of the bimetal spring, and the other end could be fixed in relation to the tubing. 
     A conical valve seat can be formed inside a first section of the tube, which first section comprises a first small diameter and a second section which second section has a second larger diameter, which conical valve seat connect the first section small section with the lager section. Hereby a highly efficient valve seat generation inside the tube can be achieved because the tube diameter is increased. By increasing the diameter of the tube just after the valve seat, it can be achieved that the flow can pass the actuator and valve piston in a rather undisturbed way because the flow can go just around the conical valve piston and the flow is automatically divided in a circular direction around the centrally placed actuating means. 
     In a preferred embodiment for the invention can the valve be formed as a valve unit, which valve unit comprises a valve seat formed in a clips, which clips comprises one or more legs, which legs comprises fastening means for a reference plate, which reference plate caries a first end of a bellow, which bellow at a second end comprises a valve piston. In this way the valve can operate as a spring by itself, but a spring that comprises a gas such as a refrigerant which gas at the operating temperatures, is supposed to be in the gaseous phase. Using the so-called clips just for supporting the reference plate and also at the same component comprises the valve seat it is possible to achieve a highly efficient valve based on a bellow where the clips defines both the level of the reference plate and also by itself comprises the valve seat. Therefore no further adjustment of the distance between the bellow and the valve seat are necessary. Because the clips is pressed into contact with the reference plate and fastened with a second clips, the distance is very precise and achieved for the whole life of the valve unit. Hereby a very efficient valve unite is achieved by which the actual operating pressure and operating temperature can partly be adjusted by the selection of the gas that is inside the bellow. Temperature and thereby actual force of the bellow can easily be adjusted by the selection of the gas or by the pressure of the gas that is filled into the bellow. There will be a relation between temperature and gas pressure inside the bellow and the pressure and temperature of the refrigerant that is circulated outside the bellow. Because of the thermal conductivity of the bellow, the temperature inside the valve will be very close to the temperature outside the bellow, so far, no rapid temperature changes will take place. Therefore, a more or less automatic relation can be achieved, depending on the temperature of the refrigerant flowing around the valve. 
     In the preferred embodiment can the bellow comprise an inner support, which inner support comprises a tube placed inside the bellow, which inner support comprise a collar, which collar is fastened to the first end of the bellow. Hereby a highly efficient stabilization of the bellow is achieved so that the bellow at the outside is stabilized by the legs of the clips, and inside, the bellow is stabilized by the inner cylinder. The inner cylinder also defines how deep the valve piston can be pressed down because at a certain level, the inner side of the valve piston will be in touch with the top of the cylinder, and thereby an end stop is achieved. By fastening the collar toward the end plate, a very stable bellow construction is achieved. A further possibility is obtained by the inner support because the tube is hollow; inside the tube one additional spring can be placed that is pressing the valve piston towards contact with the valve seat. 
     The clips combined with the bellow and the inner support forms the valve unit, which valve unit is placed inside a section of a tube. Hereby it can be achieved that a valve unit ready to be placed in a cooling system can be prefabricated. In this way, traditional soldering operation of placing the valve unit in a new thermo siphon system or any other system where a pressure has to be controlled, the valve unit can be used. 
     In a preferred embodiment for the invention the valve comprises a cylinder, in which cylinder a hollow piston is operating, which hollow cylinder is mechanical connected to the first bellow, which hollow piston comprises a plurality of bleed openings, which bleed openings by movement of the piston in relation to the cylinder performs gradual opening of the valve. Hereby it can be achieved that the valve will start to open gradually so that by increasing pressure at the valve, only a small number of bleed holes, which number could be as few as two holes, because it is a good idea to achieve a symmetrical flow in order to avoid unbalanced in-flow forces that are achieved by the circulation of refrigerant. By increasing pressure, more bleed openings will be free from the cylinder and therefore an increasing flow is achieved. The number of bleed openings can be high, or instead it could be any other symmetrical openings that are used. Every form of opening could be used, the only technical arguments for forming bleed openings in the cylinder is that they must be designed to perform a mostly symmetrical flow of refrigerant. By a valve in which the opening is gradually increasing by further movement by a pressure difference, a variable valve can be achieved which is not an on/off valve. Probably, a position will be stable with a degree of opening that depends on the pressure. A slight change in pressure will immediately result in a slight change of the flow opening in the valve. Therefore, it can be achieved that the valve will automatically reach a position that is mostly correct to the actual cooling demand. By this variable valve, any hunting in the system should be prevented. 
     In a further preferred embodiment for the invention can the system comprises at least one second bellow, which second bellow is by at least one tube connected to at least one bulb, which second bellow and the bulb contain a second refrigerant, which second refrigerant is partly liquid in normal operation of the system, which second bellow opens the valve by increasing temperature. In order to solve a problem which can occur in situations where the actual pressure in the system is low, probably because the condenser is placed in a very cold position, the valve could be closed, but if the temperature in the housing is increasing, this could be a rather bad situation, and maybe the system is so cold that the valve will never open. Therefore the second bellow is used and activated by increasing indoor temperature in order to force the valve to open. In situations where the bulb is measuring a high indoor temperature, there will be an automatic opening of the valve independently of the actual pressure over the valve. Therefore, a cooling demand can be achieved in situations where otherwise temperature would increase to a high level before the system will start operating. By adjusting the refrigerant that is contained in the second bellow and in the bulb so that this refrigerant is both liquid and gas at the same time, it is possible, by the amount that is filled in, to adjust the temperature, so only in extreme situations, will the second bellow will activate the valve. Further, in atypical operation where the necessary cooling capacity varies, caused by varying heat dissipation of the system that needs to be cooled, the second bellow can be used to obtain a high level of temperature control for the system being cooled in situations where the low temperature primary bellow is closed due to low ambient temperatures. 
     The first bulb can be placed inside a housing, in which bulb the pressure depends of the indoor temperature, which increasing indoor temperature result in increasing pressure in both bulb and the second bellow, which second bellow forces the valve to open. Especially if the cooling system is used as a passive air conditioning system in buildings, which could be housing for electronic equipment, or any other housing where the temperature inside the housing is higher than the outside temperature. In order to avoid the disadvantages of passive cooling systems in situations where there is low condensation pressure where the valve automatically closes, it is necessary to avoid an increasing indoor temperature by measuring the indoor temperature and force the valve to open. This is achieved if the bulb is placed inside the housing, for example in the circulating air that circulates around the evaporator, then the valve will automatically be opened by the increasing temperature of the bulb, thereby increasing the pressure which pressure will automatically increase the pressure in the second bellow which will lead to opening of the valve. By rapid temperature increase, the delay of the system can be avoided as the valve opens very fast so that cooling is affected as soon as the temperature starts to increase. 
     In a further preferred embodiment for the invention the system can comprise at least a first circuit, which first circuit is operating continuously, which first circuit comprises a design gas, which design gas comprises a first refrigerant or refrigerant mixture, which deign gas further comprises a inactive gas, which inactive gas is in gas form in all operative condition, which circuit comprises a separator, which separator is connected to a at least one inactive gas cartridge. 
     Hereby can be achieved, that the gas mixture of the refrigerant and the inactive gas loses cooling efficiency at low temperatures and increases its efficiency at higher temperatures. This can be achieved because the refrigerant operates in this way of different boiling curves in a phase diagram. At very low temperatures, the refrigerant boiling process will mostly be prohibited, and the thermo syphon operation nearly ceases. Hereby it is achieved that the thermo syphon is dependent on actual power dissipation at the evaporator. In this way the first circuit can be self-adjusting without any manipulation of any valves. The efficiency is increasing by increasing temperatures up to a maximum. Probably this system operating with the design gas is operating in parallel with other systems which systems are operating by a closing valve so that these systems are prevented from any shock cooling effect. By having one circuit automatically adjusting the cooling effect, further circuits operating more primitively can work in parallel. These systems can then be adjusted so they are starting to operate by increasing temperatures. The number of parallel circuits are not limited to three as indicated in the figures, but a higher number is possible. Working with a high number of parallel operating systems makes it possible to remove heat from buildings for quite other purposes than for cooling electronic circuits. 
     In a further preferred embodiment for the invention can the separator be formed as a tank, which tank comprises a refrigeration inlet and outlet, which tank further comprises a inactive gas in and outlet, which tank comprises a lower volume for liquid refrigerant and a volume for a mixture of evaporated refrigerant and inactive gas. In the tank gravity will automatically separate liquid refrigerant from gaseous refrigerant. And the added gas will of course be mixed with the refrigerant gas. A connection to a cartridge at the top of a tank will lead to a situation where this cartridge comprises a mixture of gas and gaseous refrigerant. In the system there will exist equilibrium between gas that is carried in the liquid refrigerant and gas that is placed in the upper part of the tank and in the gas cartridge, provided quasi static isothermal conditions exists 
     It is preferred that the tank comprises a diaphragm or a membrane permeable only to the non-condensable gas for separating refrigerant and inactive gas. Placing a diaphragm over the surface of the refrigerant can isolate refrigerant totally for getting into the volume for the inactive gas. It is possible to design a diaphragm so that refrigerant molecules will be stopped by the diaphragm but the inactive gas, which probably has much smaller molecules, will penetrate the diaphragm with very little resistance. By the correct design of the diaphragm there will be an almost 100 per cent separation between refrigerant and inactive gas over the diaphragm. Hereby it is possible to adjust the fill ratio of the system more precisely thereby obtaining better performance and at the same time limit the amount of necessary refrigerant to operate the system. The inactive gas is always present below the membrane, but the molar fraction decrease with power increment and temperature increment. Nevertheless, the boiling temperature of the mixture is permanently altered prohibiting the boiling process below the specified minimum temperature of the system. By correct selection of inactive gas and refrigerant where also the actual volume could be rather important, as well as the pressure of the system, it should be possible to make a system more or less automatically working where the cooling effect is automatically adjusted. Such a system with no moving components could be very important for long-living cooling systems that should be able to operate automatically without any kind of service for several years. 
     In a preferred embodiment can the temperature of the inactive gas cartridge be regulated. By changing temperature of the gas cartridge it is also possible to change the actual volume and pressure of the inactive gas that is carried into the refrigerant. It is possible to place the heating elements outside the gas cartridge so that by electric connection the cartridge could be heated. Further it is possible that the gas cartridge is placed outside the building or housing so that outdoor temperature always is present at the gas cartridge. By then using the heating elements it is possible to change the contents of inactive gas in nearly all situations, simply by switching an electric switch on and off which could be performed by a computer control system. In many situations, the outdoor placement of the gas cartridge will be all that is necessary to establish an automatic system. The outdoor temperature will automatically have influence on the pressure inside the gas cartridge and therefore have influence on the amount of gas that is added to the refrigerant. Therefore it is simply a question of selecting the correct inactive gas in combination with the correct refrigerant. Inactive gases could for example be helium or argon. Also carbon dioxide is possible if carbon dioxide is inactive in relation to the refrigerant. Also so-called gasses with ideal gas characteristics could in fact be used. In one possible embodiment of the invention it is possible to reduce the cooling effect of the thermo syphon system simply by increasing the contents of inactive gas in the refrigerant. If the heating demand is decreasing, maybe in situations of low outdoor temperature, it is possible by correct concentration of inactive gas simply to heat the gas cartridge and in that way increase the pressure in the gas cartridge and increase the amount of gas in the refrigerant. Hereby the efficiency of the thermo syphon system can be decreased so that the cooling system as such is adjusted automatically to the actual cooling demand. In a situation where the outside temperature is relatively high, it is possible not to heat the gas cartridge and in that way reduce the contents of inactive gas in the refrigerant and in that way increase the efficiency of the cooling system. Hereby it can be achieved that a simple temperature control of a gas cartridge gives the possibility of controlling the efficiency of the entire cooling system. 
     The present patent application further concerns use of a system as disclosed in one of the claims  1 - 16  for cooling electronic systems, where electronic systems are placed inside a housing, which electronic systems generate heat, whereby the inner of the housing need cooling, which cooling is performed with at least on thermo siphon, which evaporator of the thermo siphon is placed inside the housing for the electronic system, which condenser of the thermo siphon is placed outside the housing. 
     Hereby it can be achieved effective cooling especially for electronic devices such as transmitter receiving system for mobile communication placed in small housings in relation to the communication or transformer housings placed near consumers. In all of these housing there is a climatic shield that is protecting the electro- or electronic devices inside but the devices inside the housing are producing heat which has to be removed. A plurality of thermo siphons can therefore be used because they perform the cooling of the housings rather efficiently but with very low energy consumption. The number of thermo siphons can be relatively high because when the thermo siphons has been installed there will be almost no service or operation costs. Therefore the evaporator can be placed inside the housing and the condenser can be placed outside the housing. In some situations circulating air will be used inside the housing so that air blowing means will blow air around the evaporators inside the housing and air blowing means could also be used for circulating outdoor air through the condensers. By the invention according to the present patent application it is achieved that if a situation occurs in which the outside temperature is decreasing, for example in winter cooling of the condensers can take place, the temperature of condenser is lower than the temperature of the evaporator inside the housing. In such a situation a rather unrestricted flow will occur from the condenser down to the evaporator, and the evaporator will be cooled near to the outdoor temperature. To avoid such a situation when the outdoor temperature is low, the valve is placed in the liquid line between the condenser and evaporator. As soon as the temperature decreases to a certain level, this valve will close full or partly and the thermo siphon as such will stop or reduce its operation until the temperature is increasing in the condenser, thereby increasing the temperature and pressure in the entire thermo siphon. 
     The present invention further concerns a method for operating a cooling system as disclosed in one of the claims  1 - 13  in a sequence of steps: 
     a. perform evaporation of refrigerant in a evaporator for generation a refrigerant gas,
 
b. let the gas flow in a piping towards a condenser placed a gravity level higher than the evaporator,
 
c. perform condensation in the condenser for generation of liquid refrigerant,
 
d. let the liquid refrigerant flow in a tubing towards a normal closet valve,
 
e. open the valve depending of the pressure of liquid refrigerant above the valve,
 
f. force by gravity the liquid refrigerant to flow in a piping back towards the evaporator.
 
     By this method a thermo siphon system can be achieved which automatically stops or reduces the flow of refrigerant in a situation where the temperature is so low that less cooling capacity in Watt/Kelvin is needed. In such a situation, there will probably be decreased or no cooling demand. Therefore the closing of the valve will give as result that no or reduced further refrigerant is delivered to the evaporator. Thereby it is avoided that the evaporator is further cooled by sending very cold refrigerant down to the evaporator. In an indoor environment, for example a housing for electronic circuits, it will be possible to reduce the air flow for short periods of time thereby letting the temperature in the housing increase. The increasing temperature will relatively quickly lead to a low degree of evaporation in the evaporator. Evaporated gas will continue flowing in the piping towards the condenser. If the temperature around the condenser is very low, condensation takes place immediately. However, only if there is a certain pressure of refrigerant placed above the valve, there will be circulation back to the evaporator. If the valve is correctly adjusted, a defined temperature and thereby the pressure must be achieved to start a very limited circulation, and therefore an automatic adjustment of the amount of circulating refrigerant can be achieved. Increasing temperature at the evaporator will lead to a higher degree of evaporation which then automatically increase the pressure in the condenser and an increasing pressure in the liquid refrigerant will be achieved above the valve, which valve will then open more to t increase the flow of liquid refrigerant through the valve. This will probably relate to situations in the winter period. In the summer period, with high indoor and outdoor temperatures, the valve will probably be open most of the time so that full circulation can take place. 
    
    
     
       DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a cooling system comprising a plurality of thermo siphons operating in parallel. 
         FIG. 2  shows a detailed disclosure of a thermo siphon according to the present invention. 
         FIG. 3  shows a valve and valve housing. 
         FIG. 4  shows an alternative embodiment for the valve. 
         FIG. 5  shows a possible embodiment of valve unit. 
         FIG. 6  shows the various valve components before they are assembled. 
         FIG. 7  shows the valve unit seen in  FIG. 5 , now placed inside a tubing. 
         FIG. 8  shows a sectional view of a further embodiment for the invention. 
         FIG. 9  shows a preferred embodiment of a thermo syphon cooling system. 
         FIG. 10  shows one possible embodiment of a separator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a cooling system  2  which cooling system  2  comprises evaporators  4   a ,  4   b ,  4   c . By tubing  8   a ,  8   b ,  8   c  the evaporators  4   a ,  4   b ,  4   c  are connected to condensers  10   a ,  10   b ,  10   c . By tubing  16   a ,  16   b ,  16   c  the condensers are further connected through valves  18   a ,  18   b ,  18   c  back to the evaporators  4   a ,  4   b ,  4   c.    
     In operation the evaporators  4   a ,  4   b ,  4   c  will all be placed inside a housing where for example air by an air blowing means will be blown along the evaporators. This flow of air will therefore be cooled. This leads to heating of the refrigerant that inside the evaporators  4   a ,  4   b ,  4   c , and therefore boiling takes place in the evaporators. Heated and evaporated refrigerant is now flowing as a gas steam through the tubes  8   a ,  8   b ,  8   c  into the condensers  10   a ,  10   b ,  10   c.    
     The condensers are placed outside the housing and cooled air is circulating along the condensers. Thereby heat is removed and condensation of the refrigerant will take place. Therefore liquid refrigerant will circulate through the valves  18   a ,  18   b ,  18   c  through the lines  16   a ,  16   b ,  16   c.    
     By decreasing the outside temperature, cold liquid refrigerant will flow through the line  16   a ,  16   b ,  16   c  into the evaporator. Hereby is cooling to near the outdoor level performed inside of the housing. Therefore the valves  18   a ,  18   b ,  18   c  are placed in the return line  16   a ,  16   b ,  16   c . By decreasing temperature, the valves  18   a ,  18   b ,  18   c  will automatically close and then stop circulation in the three thermo siphons. Hereby it is achieved that in situation with extremely low outdoor temperature, there will be reduced or no cooling effect in the circuits where the valve is in its operating temperature range. The valves can have different operating ranges in order for the valves to regulate at different temperatures facilitating a stepwise process at the outside temperature decreases. 
       FIG. 2  shows a thermo siphon  3  according to the present invention. This thermo siphon comprises a first evaporator  4  which evaporator  4  has cooling fins connected to the outside of the evaporator  4  and from the evaporator  4  there is a tubing  8  connecting the evaporator  6  to an outdoor condenser  10 . This outdoor condenser  10  is further connected to heating fins  12 . The condenser  10  is further connected by the tubing  16  to a valve  18 . This valve  18  comprises a valve seat  20  and a valve piston  22  and an actuator  24 . The valve  20  is shown with an open position where liquid refrigerant flows in the line  16  back to the evaporator  4 . 
     If the evaporator  4  is placed inside a housing for an electronic circuit, blowing means can perform cooling by the cooling fins  6  and the circulating air. Inside the evaporator a refrigerant will boil and thereby perform cooling. Evaporated refrigerant then circulates through piping  8  to the outside condenser where condensation is performed because the outdoor condenser is placed outside where the temperature is lower. Therefore condensation takes place inside the condenser, and liquid refrigerant is generated and will flow through the piping  16  down to the valve, and back into the evaporator. 
     In a situation where the temperature is decreasing, relatively cold refrigerant will flow in the tubing  16  towards the evaporator  4  and cooling the inside of the housing, cooling will be performed to a temperature neat the outside temperature. Therefore the valve  18  is placed in the return flow  16  of the refrigerant. By decreasing temperature in the flowing refrigerant, the valve  18  closes and the flow is interrupted or reduced. The decreasing temperature inside the housing can lead to reduced or no evaporation. In that situation will the pressure from the refrigerant acting at the valve piston  22  be reduced and the bellow and the gas inside the bellow is acting mostly like a spring against the refrigerant pressure and by reduced pressure at the valve piston  22  the valve  18  is closed. 
       FIG. 3  shows a detailed view of the valve and the valve housing.  FIG. 3  shows an inlet tube  26  which come from the condenser (not shown). The tube  26  ends in the conical valve seat  20 . The conical valve seat  20  changes the diameter of the tubing into the tube  30  which forms housing for the valve  18 . This valve  18  comprises the valve piston  22  and a bellow  24 . This bellow  24  is supported by a support disc  32  which is placed below the bellow  24 . Below the bellow  24  a tube  36  is further shown which is welded or soldered by the welding or soldering  34 . 
       FIG. 4  shows a valve seat  120  which cooperates with a valve piston  122  placed inside a tube  126  which tube is the same as the one shown as  26  in  FIG. 3 . A valve actuator  124  is formed as a bellow which bellow  124  comprises a wax or lubricant or grease. The bellow  124  is supported by a support  132 , and the bellow ends in the mechanical structure  138  to which a shaft  140  is connected. At its other end, this shaft  140  is connected to the valve piston  122 . 
     In normal operation, the valve indicated in  FIG. 4  will be in open position. Relatively warm condensed refrigerant is flowing around the bellow and in this way it keeps the temperature of the wax or lubricant or grease inside the bellow at a relatively high temperature. If the outside temperature is reduced, for example in the winter period, the volume of the bellow  124  is reduced, and the valve piston  122  is moving downwards towards contact with the valve seat  120 , and in this way, the flow of refrigerant is closed. 
       FIG. 5  shows a valve unit  218  which valve unit comprises a bellow  238  and a clips  228  which clips comprises three legs,  230 . These legs  230  comprise fastening means,  232  for fastening a support  234 . The clip  228  comprises a valve seat  226  which cooperates with valve piston  242 . The reference plate  234  is thereby fastened towards the legs  230  by the fastening means  232 . Thereby the reference plate  234  for the bellow  238  is achieved. The bellow  238  will act as a spring so a normally closed valve is achieved. The legs  230  are flexibly formed so the reduced distance between the legs is easily achieved by slide bending so that the legs can snap into a fixed locked position for the support plate  234 . 
       FIG. 6  shows an exploded view of a valve unit as indicated in  FIG. 5  but now separated into various components. At first the clips  228  is shown which at its top comprises the valve seat  216 . This valve seat is downwards oriented and, not directly indicated, formed with a conical surface. The clips  228  further comprises the flexible legs  230  which legs comprise cut-outs indicated as  232  for connection to the reference plate  236 . 
     The bellow  238  has a first end  236  pointing towards the reference plate  234 . The bellow  238  has its second upper end  240  which is connected to the valve piston  242 . This valve piston comprises a conical surface  243  for interacting with the conical surface at valve seat  216 . 
     The reference plate  234  comprises protrusions  235  for interacting with the cut-outs in the clips forming the fixation of the legs towards the reference plate. 
     Further an inner support  244  is indicated, which inner support comprises a collar  246  which collar  246  is intended for fastening towards the first end of the bellow  236 . The inner support  244  can contain a spring inside which, when assembled, will exert a spring force towards the top of the bellow  238  and therefore further press the valve piston in a closing direction. Hereby one further possibility of adjusting the valve characteristics is achieved. 
       FIG. 7  shows the valve unit  218  placed in a tube  250 . Inside the tube the clips  228  is indicated. The legs of the clips  230  and the reference plate  234  where the clips is fastened to the reference plate  234  by the fastening means  232 . At the top, the valve seat  226  and partly the valve piston  242  are indicated. Just below the bellow the inner support and its collar  246  are indicated. 
     In operation, the valve unit  218  as placed in the tube  250  will be fastened inside the tube  250  by exerting an external pressure upon the tube  250  and in this way it will fix the tube. The tube has a further function in relation to the clips because the flexible legs of the clips will be totally locked when mounted in the tube thereby locking the reference plate  234  in correct position. There is, so to say, no possibility for the legs  230  to be bent even if they are flexible because they are surrounded by the tube  250 . Hereby a valve unit in the tube  250  is achieved which can easily be used in cooling system, for example, because the tube  250  can be soldered into a fluid-tight connection with traditional piping of cooling systems. Hereby a valve can be achieved that is very easy to mount in a cooling system, and which valve is fully automatic and there is no need for any energy supply from the outside. This valve expected to have an extremely long service life because the valve as such with the bellow is well protected inside the tube and also protected by the circulating refrigerant that is circulating around the bellow. 
       FIG. 8  shows one further possible embodiment of a clip  328  which clip  328  comprises a possible embodiment of a valve  318 . Inside the clip  328  is indicated a first bellow,  338  which bellow contains a gas. Further is indicated a second bellow  339  which by a tube  340  is connected to a bulb  342 . The bulb  342  and the bellow  339  contain a second refrigerant which probably is a refrigerant that is partly liquid and partly in gaseous form. The second refrigerant or maybe a mixture of refrigerants is selected together with the amount filled into the bellow  339  and the bulb  342  for achieving an efficient and quick response to temperature changes. The actual response temperature can efficiently be adjusted by one of the above-mentioned parameters so that the refrigerant or a mixture of refrigerants could be selected, and also the amounts of liquid and gaseous refrigerant filled into the volume of the bellow  339  and the bulb  342  could be selected to achieve correct temperature response. The valve  318  comprises a hollow piston  350  which is mechanically fastened to the top of the bellow  338 . This piston  350  is moving in a cylinder  351 . The piston comprises bleed holes  352  or maybe another kind of opening such as the slits  354  so the degree of opening will increase if the piston  350  is moved further downwards in the cylinder  351 . Much different geometry for bleed holes could be used but only if a more or less symmetrical outflow of liquid refrigerant is achieved. Otherwise the result could be forces that act upon the cylinder  350  so it is pressed against the cylinder  351 . Further a shaft  356  is indicated at the bellow  359  which shaft  356  ends inside the piston  350 . It is to be understood that by increasing pressure in the bellow  339 , the shaft  356  will be pressed further downwards which will lead to an opening of the valve  318 , simply because the increasing pressure in the second bellow  339  will increase at a much higher rate than will the temperature in the bellow  338  which only comprises a gas and in this way operates as a spring. 
     In operation, the pressure above the valve will automatically act inside the piston  350 , and if the pressure in the piston is higher than the pressure in the first bellow  338 , the valve will start to open. Increasing pressure in the refrigerant in the valve will lead to a higher degree of opening. Therefore, in actual life, this will probably end up in a situation where the valve is placed at some point between closed and totally open position because the valve position will more or less automatically adjust its position to the actual cooling demand. In situations where the pressure in the valve is low, which could occur if condensing takes place in an outdoor environment, the pressure can be relatively low, but if a certain degree of cooling is demanded inside a housing, then if the bulb  342  is placed inside the housing, this increasing temperature will automatically lead to opening of the valve, so that a circulation starts. This could be very important if the valve is used in a thermo syphon. 
     As such this valve could be used not only in thermo siphon refrigeration systems, but also many other applications are possible. The use of this valve is also possible for other systems than refrigeration systems. 
       FIG. 9 . discloses an alternative embodiment of the invention as shown in the previous figure.  FIG. 9 . shows a system  402  which system comprises three different and independent thermo syphon circuits. Each of the circuits comprises indoor evaporators  404   a - c  in which liquid refrigerant is evaporated. Gas lines  408   a - c  transmit gaseous refrigerant into condensers  410   a - c . Line  410  is connected to a separator  419  which separator is further connected to a gas cartridge  421 . The separator is further connected by line  416  back to the evaporator  404   a . Further the condenser  410   b  and  410   c  connected by lines  416   b  and  416   c  to valves  418   b  and  418   c . Further tubing  415   b  and  415   c  are connected to the evaporators  404   b  and  404   c.    
     It is understood that in operation the first circuit probably operates in all temperature situations. However, the circuits  2  and  3  will start operating at increasing temperatures independently of the actual adjustment of the valves  418   b  and  418   c . Therefore, in case of very low cooling demand, only the first circuit operating with the inactive gas added to the refrigerant will be in operation. By the correct selection of pressure of the inactive gas together with the correct design of refrigerant, it is possible to perform an automatic adjustment of the cooling effect. By decreasing system temperatures, increasing amounts of inactive gas can be mixed with the refrigerant and in that way change the evaporation profile of the refrigerant. 
     In order to explain the applied hybrid principle we use a 3 circuit thermo syphon, but the number of circuits are arbitrary since this would work with any number of circuits and/or combinations. The valves are extremely efficient as a device that will decrease or totally stop the Thermo syphon operation depending on the internal saturation state of the system which in many Thermo syphon has a very strong causality to the external ambient environment. Therefore, in many applications, it is a reasonable approximation to argue that the valve will operate in accordance to the external temperature and wind condition only. In some design that is exactly what is intended. However, in other design, where power dissipation varies heavily this can be inappropriate since the valves do not react to power dissipation. To solve this paradox, one additional circuit is implemented into the Thermo syphon system. In the attached drawing, this circuit is shown as circuit  1 . This circuit contains a design gas, which is a mixture of at least two constituent&#39;s species. The idea is to facilitate the gas be designed in such a way that it loose efficiency at low temperatures and increase efficiency at higher temperatures. One of the key drivers to this is that at least one gas, the working gas, operates on the saturation curve in the phase diagram, while at least one of the gasses does not. At the high temperature limit the molar fraction of the working gas is very high. At decreasing temperatures the molar fraction of the working gas, continuously decrease. At the low temperature limit, the working gas bulk boiling process is prohibited and the Thermo syphon operation nearly ceases. In this limit, the Thermo syphon is highly dependent to power dissipation. To explain this: consider increased power dissipation. Once inside the temperature limit, Le Chatelier&#39;s principle will keep the temperature constant while boiling occur. The boiling is promotional to the power input which makes the system self-regulating. Now, the system is reacting heavily to power input. The principle of mixing one inert and one working gas is known from Variable Conductance Heat Pipes (VCHP). However, implementing this principle into a thermo syphon is very different. There are a few essential key components. A well designed separator. Such a device is not used in VCHP&#39;s. Also, one needs to facilitate that the separator is placed in an area where the condensable working fluid and the non-condensable gas is present. This is shown in the drawing. Also, the separator should be placed where the gas and liquid velocities are small. This way the huge density difference will separate the working fluid from the non-condensable gas, allowing the non-condensable gas flow to the inert gas cartridge. The cartridge could be advantageously divided into more cartridges. The first cartridge should ideally be placed above the liquid level of the condenser, while the following cartridges do not. Finally, circuits could contain both design gas, cartridge, separator and valves to obtain any number of the above described effect. 
       FIG. 10  shows a gas cartridge  521  connected to a separator  519 . The gas cartridge  521  is connected to the separator  519  by tubing  520 . This separator  519  is connected to a condenser by an inlet  516  so that the separator  519  receives mostly liquid refrigerant through the line  516 . Further a line  515  is connected to the separator  519  which line  515  is connected to an evaporator. The separator  519  comprises a diaphragm  522  separating the volume inside the separator into a lower liquid volume and an upper gas volume. The diaphragm is designed so that it has a structure where only the small gas molecules can pass through and where the relatively large molecules of refrigerant are fully prevented from passing through the structure. Thereby is achieved that the gas cartridge  521  can be filled only with gas, and refrigerant is kept below. 
     Around the gas cartridge  521   a  heating element  524  is indicated. 
     In operation, by changing the temperature of the gas cartridge  521 , it is possible to change the pressure of the inactive gas and in that way control the amount of gas contained in the refrigerant. 
     In one situation it is possible to reduce the cooling effect of a thermo syphon simply by increasing the amount of inactive gas carried in the refrigerant. By high cooling effect it is possible to operate the system with the refrigerant with low contents of inactive gas, and if the cooling demand is decreasing, maybe the temperature of the gas cartridge  521  is increased by connecting electric power to the wire  524 , it is possible to reduce the cooling effect simply by adding more of the inactive gas to the refrigerant. Hereby it is possible to achieve a thermo syphon cooling system where no mechanical parts are moving inside the system. Hereby can a system be obtained that can be controlled simply by switching on and off the heating element whereby it is possible to fully control the efficiency of the cooling system. Consequently, this cooling system is highly efficient cooling for example electronic systems for mobile communication placed at locations far away from normal service activities. 
     In some countries these radio stations are placed on mountains in order to achieve the best communication signal. Service on such systems can only be performed from helicopters. Therefore it is highly efficient to have a cooling system that can operate for very long periods of time with no need for service.