Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
  • F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
  • F28D15/06—Control arrangements therefor

Definitions

• the invention relates to heat transfer devices by phase transition of a fluid, including heat pipes.
• a heat pipe is a heat transfer device which comprises a sealed enclosure, that is to say not letting pass liquids or gases, conventionally made in the form of a tube or several coaxial tubes, which contains a fluid called "coolant”, whose liquid phase is in equilibrium with the vapor phase, also called “diphasic system”.
• the enclosure consists of an evaporator, located at one end thereof and intended to be heated by a hot source, a condenser located at the other end of the enclosure and intended to be cooled by a cold source , and an intermediate zone called “adiabatic”, located between the evaporator and the condenser.
• the liquid contained in the evaporator vaporizes and the vapor thus produced migrates to the condenser in which it condenses by transferring heat to the cold source.
• the condensed liquid then returns to the evaporator for a new evaporation cycle.
• heat pipes are conventional and can take different names depending on the mechanism used to return the condensed liquid to the evaporator.
• heat pipe heat pipe
• heat pipe is used as a generic term regardless of the liquid return mechanism used.
• Heat pipes find many applications.
• the heat pipe has the function of heating a cold source by transferring heat supplied by a hot source.
• heat pipes are intended to heat water for domestic use of a building using solar radiation.
• a solar collector or "solar water heater” comprises a heat pipe, a so-called “primary” circuit in which circulates a coolant and a storage tank of the water to be heated.
• a first portion of the primary circuit is in heat exchange with the heat pipe condenser, and thus forms the cold source for the latter, and a second portion of the primary circuit is in heat exchange with the storage tank.
• the heat transfer fluid of the primary circuit flowing between these two parts thus transfers heat from the heat pipe to the water of the flask.
• Heat pipes are also conventionally used to transfer heat from a hot source to Peltier effect modules.
• the heat pipe has the function of cooling a hot source by taking heat and transferring the heat taken to a cold source. This is the case, for example, with applications for cooling electronic components. The components transfer their heat to the heat pipe, which in turn transmits it to the cooling fluid (water, air, etc.). This type of cooling is widely used in the railway field or for cooling laptops.
• heat pipes are often designed to capture and store as much heat as possible from the hot source.
• the evaporator of a heat pipe is enclosed in several layers of transparent materials to solar radiation between which vacuum is formed.
• the solar radiation is thus trapped in the heat pipe and the heat carried by the incident solar radiation is transferred substantially completely to the liquid present in the evaporator.
• Temperatures above 250 ° C can thus be reached in the evaporator, even for low temperatures.
• This fluid of the primary circuit is generally made of propylene glycol.
• the heat transfer fluids usually used for heat pipes, as well as the heat transfer fluids of the primary circuits withstand high temperatures with difficulty for a long time without degrading.
• the primary circuit fluid oxidizes and loses its heat transport capabilities. Without special precautions, there is thus a decrease in the efficiency of the heat pipes and / or the efficiency of the primary circuit, and therefore of the solar collector as a whole, sometimes at after a few months, while the solar collectors are usually intended to operate over a period of 20 years.
• the oxidation of the primary circuit fluid can also lead to chemical attack of the pipes and pipes.
• a heat pipe is associated with a device forming the cold source may be damaged by excessive heating, or it includes and / or it is in contact with materials that can degrade due to such heating .
• a reservoir accessible to the heat transfer fluid for temperatures above a threshold temperature makes it possible to obtain such a result. Indeed, as the heat transfer fluid accumulates in the tank, the heat transfer efficiency of the heat pipe decreases to be substantially zero when no liquid phase remains in the evaporator.
• the reservoir and the mechanism for opening and closing the passage between the condenser and the reservoir thus implement a function of cutting the heat pipe.
• the operation thereof is stopped.
• the problem arises in any device provided with a sealed enclosure enclosing a two-phase system whose liquid phase is to be stored partially or entirely in a tank located outside the functional portion of the enclosure for temperatures greater than a predetermined threshold temperature.
• GB 1 542 277 describes in its embodiment of Figure 2 a two-phase heat pipe, used in a vertical position, comprising a hermetic enclosure whose condenser is extended by a reservoir with which it is in communication through a reduced diameter pipe.
• a non-condensable gas immiscible with the heat transfer fluid is introduced into the heat pipe in the high position and allows or prevents the access of the tank to the vapor of the heat transfer fluid depending on the temperature. Beyond a given temperature, the non-condensable gas releases the passage to the tank where vapor of the coolant condenses to be stored.
• a passage is further provided for the return of the coolant fluid to the condenser, this passage being chosen so that the mass flow of the liquid coolant escaping from the reservoir to the condenser is equal to the mass flow rate of the fluid vapor coolant entering the tank from the condenser.
• the combination of the non-condensable gas, the reservoir and the liquid return passageway thus regulates the heat transfer rate which is set to a constant value independent of the temperature of the heat source.
• Document JP 2001-153575 describes a heat pipe comprising a hermetic enclosure including the condenser and in communication with a tank.
• a gas that is non-condensable and immiscible with the heat-transfer fluid is introduced into the heat pipe in the high position and makes it possible to control the rate of heat transfer of the heat pipe as a function of its position in the condenser to reach a maximum transfer rate when the gas: non-condensable is fully stored in its tank.
• the tank has the sole function of storing the non-condensable gas, nothing being provided for storing in the tank the coolant in its liquid phase.
• the purpose of this document is to prevent heat transfer fluid from entering the tank and thus avoid cutting the heat pipe for high temperatures.
• the passage between the reservoir and the condenser is bent and opens on a side wall of the condenser, and parallel walls are housed in the tank.
• the object of the present invention is to solve the above-mentioned reliability problem by proposing a device equipped with a liquid storage tank, whose access is controlled as a function of temperature without using a mechanical part, and implementing a device shutdown function for high temperatures.
• the invention relates to a device comprising a sealed enclosure containing a fluid whose liquid phase is in equilibrium with the vapor phase in a predetermined range of temperatures, the chamber being divided into a first and a second volume communicating through a first fluid flow passage, allowing the vapor phase of the coolant to enter the second volume by ascension the second volume comprising a reservoir in communication with said flow passage, and adapted to contain fluid in liquid phase when the device is in a predetermined position with respect to the direction of gravity.
• the second volume contains a non-condensable gas within the predetermined range of temperatures and insoluble in the fluid of the liquid phase
• the reservoir is adapted to contain all of the fluid in its liquid phase to a second predetermined temperature (7 ° ⁇ "p) of the temperature range, greater than the first temperature ();
• the device comprises a second passage allowing the passage of the liquid phase of heat transfer fluid from the reservoir to the first volume by gravity with a pressure drop, leading to a mass flow is strictly lower liquid phase to the mass flow of the defined vapor by the circulation passage of the fluid, so as to induce storage of the liquid phase of the coolant in the tank for a temperature greater than the second predetermined temperature max) ⁇
• the chamber is divided into two volumes, the first volume defining the useful volume of the device where the evaporation / condensation cycles take place in the presence of hot and cold sources, the second volume defining a fluid storage space for subtracting the fluid from the first volume.
• the device comprises at least one position allowing such storage, for example defined with respect to the direction of gravity, the device being usually designed to operate in certain positions.
• the reservoir which corresponds to part or all of the second volume, is accessible through a passage whose opening is controlled by a gaseous plug, that is to say a volume of gas whose function is to form a plug “mobile” depending on the temperature by occupying a variable portion of the tank, and therefore by a mechanism that has no mechanical part.
• a gaseous plug that is to say a volume of gas whose function is to form a plug “mobile” depending on the temperature by occupying a variable portion of the tank, and therefore by a mechanism that has no mechanical part.
• the gas forming the plug Being non-condensable in a range of operating temperatures of the device, and not so much in the liquid phase of the fluid, the gas forming the plug remains located mainly at the second volume and maintains a substantially constant mass.
• the gas and the vapor phase of the fluid are immiscible, that is to say that the vapor and the gas substantially do not mix, thus essentially defining two distinct volumes, apart from a small transition zone between the vapor and the gas in which there may be a mixture thereof.
• the fluid and the gas are respectively polar and apolar, or vice versa.
• liquid phase of the fluid is saturated with non-condensable gas so that it can not absorb additional amount of it.
• the pressure of the vapor phase of the fluid becomes more and more important. Since the mass of non-condensable gas is constant, the increase in fluid pressure will result in a reduction in the volume occupied by the non-condensable gas. The non-condensable gas is thus pushed back into the second volume, thus freeing the passage towards the latter. The vapor then enters the second volume where it condenses, the condensed vapor being stored in the reservoir provided in the second volume.
• the reservoir is designed to accommodate all of the liquid phase of the fluid, and the second passage has a low flow rate so that the liquid escaping therefrom is immediately vaporized, and thus goes up to the reservoir.
• the release of the passage to the second volume is performed for a single threshold temperature of the fluid and gas, depending on the characteristics of the gas, the fluid and the enclosure, this temperature can be estimated using laws simple thermodynamics.
• the first and second volumes are separated by at least one solid plug through which an opening in said first passage passes, in particular an opening opening on an inner tube to the second volume.
• the reservoir is thus delimited in a simple manner by the walls of the enclosure, the solid stopper and the tube.
• the plug is formed of a material capable of allowing the liquid phase of the fluid to pass from the second volume to the first volume with a high pressure drop which leads to a mass flow rate lower than the mass flow rate defined by the passage of fluid circulation.
• the plug may be a porous material and / or comprise at least one capillary capable of allowing the liquid phase of the fluid to pass from the second volume to the first volume with a mass flow rate lower than the mass flow rate defined by the fluid circulation passage.
• the flow rate via the pores or the capillaries of the stopper is less than 10% of the flow rate defined by the fluid flow passage, for example equal to 5%
• the device comprises a plurality of plugs disposed between the first and second volumes and each traversed by an opening, the openings of the plugs being angularly offset relative to one another, in particular three plugs respectively comprising three openings. angularly separated by 120 °. In this way, the positioning errors of the device during its installation are minimized or even eliminated.
• the non-condensable gas is neutral with respect to the materials with which it is in contact in the enclosure, which makes it possible to extend the life of the device.
• a more efficient gas in terms of controlling access to the tank and / or in terms of non-dissolution or miscibility, but reacting with the materials with which it is present, can be used if the application requires it, for example as part of a shorter life device.
• the non-condensable gas is immiscible with the fluid.
• the coolant is water or an alkane, especially butane, pentane or hexane
• the non-condensable gas is air, nitrogen, carbon dioxide or a rare gas , especially argon.
• the first volume is divided between a condenser, in communication with the first fluid circulation passage, and an evaporator, in communication with the condenser, and, when the device is in the predetermined position, the gas non-condensable at least partially occupies the condenser when the temperature of the gas is lower than a third predetermined temperature of the predetermined range of fluid temperatures, said third temperature being lower than the first predetermined temperature.
• the non-condensable gas occupies the entire condenser when the temperature thereof is lower than a fourth temperature of the predetermined temperature range, said fourth temperature being lower than the third predetermined temperature.
• the non-condensable gas also makes it possible to protect the heat transfer fluid for low temperatures deemed to be harmful for the device.
• the quantity of non-condensable gas is chosen so that the latter completely occupies the volume of the condenser, advantageously for negative temperatures in the field of the solar collectors, thus forcing the coolant to remain in the evaporator, and thus to occupy the the coldest part of the device.
• This also makes it possible to protect the elements with which the heat pipe is in contact with temperatures considered too low. In particular, in the context of solar collectors with a primary circuit, this also limits the risks of freezing the fluid of the primary circuit.
• the device In operation, the device is thus positioned in the predetermined position, a hot source is applied to the evaporator, and a cold source is applied at least to the condenser, and preferably also to the second volume.
• the gaseous plug according to the invention thus makes it possible to effectively define a range of operating temperatures for the device, namely a high temperature of the fluid beyond which the latter is stored in the reservoir, and a low limit of the fluid. below which the latter is stored in the evaporator, the device being disabled for any temperature of the fluid outside this range.
• FIG. 1 is a schematic sectional view of a device according to a first embodiment of the invention.
• FIGS. 2A, 2B and 2C are schematic sectional views of the first embodiment according to the invention illustrating a nominal operating thereof;
• Figures 3A, 3B and 3C are schematic sectional views of the first embodiment according to the invention illustrating the cut-off of the device when the temperature exceeds a high threshold temperature;
• Figures 4A, 4B and 4C are schematic sectional views of the first embodiment according to the invention illustrating the cutting of the first embodiment when the temperature is below a low threshold temperature;
• FIG. 5 is a schematic sectional view of a tank cap with a restart mechanism according to a first variant according to the invention
• FIG. 6 is a schematic sectional view of a tank cap with a restart mechanism according to a second variant of the invention
• Figures 7A and 7B are schematic sectional views of the first embodiment provided with a tank cap with a restart mechanism illustrating restarting of the device
• FIG. 8 is a schematic sectional view of a device according to a second embodiment
• FIG. 9A is a schematic sectional view of a device according to a third embodiment.
• FIG. 9B is a schematic view illustrating the angular distribution of openings in the plugs of the third embodiment.
• FIG. 10 is a graph showing the effectiveness of the heat transfer device according to the invention when the temperature exceeds the temperature high limit.
• a heat pipe 10 or thermosiphon, comprises a sealed chamber 12 formed of a low tubular portion 14 and a tubular portion 16 high coaxial and in communication, the upper part being for example of larger diameter than the lower part.
• the lower tubular portion 14 comprises at least in its lower part an evaporator 18 intended to receive heat from a hot source 20, for example solar radiation, and an adiabatic portion 22 disposed between the evaporator 18 and the high tubular portion 16.
• the high tubular portion 16 is for its part to be cooled by a cold source 24, for example a piping system in which circulates a coolant, or primary circuit, carrying the heat collected to a balloon of storage of cold water to be heated.
• the adiabatic portion is optional, or of very short length, the low tubular portion 14 being for example exposed along its length to the hot source 20.
• the upper portion 16 is divided between a condenser 26, disposed in the extension of the lower tubular portion 14, and a retention volume 28, positioned at the top, the condenser and the retention volume being separated by a solid plug 30.
• the plug 30 is sealingly sealed around the inner wall of the upper tubular portion 16, and is traversed, for example in its center, by an opening 32 extending through an inner tube 34, preferably straight, for example cylindrical.
• the part tubular low 14 and the lower portion 26 of the high tubular portion 16 thus form the useful part of the heat pipe in which is implemented the heat transfer by evaporation / condensation cycles.
• the reservoir 36 is capable of storing the entire liquid phase of the coolant, thus allowing a cut-off function of the heat pipe 10, as will be explained in more detail below.
• a coolant 38 for example water, or an alkane, in particular butane, pentane or hexane, is also present in the heat pipe 10 and forms a two-phase system in which the liquid phase and the vapor phase fluid are in equilibrium at least within a predetermined range of fluid temperatures [T m i n ; T max ].
• a gas 40 that is non-condensable and insoluble in the liquid phase of the coolant 38 in said temperature range is also provided above the fluid 38.
• the gas 40 is, for example, air, nitrogen, nitrogen, carbon dioxide, or a rare gas, in particular argon.
• the gas 40 is immiscible in the fluid 38, the fluid and the gas being, for example, respectively polar and apolar fluids, or the liquid phase of the fluid is saturated with gas 40 so that it can not absorb any additional quantity of said fluid. gas. Being non-condensable and not soluble in the fluid 38, the mass of gas 40 is therefore substantially constant and remains permanently located above the fluid 38.
• the non-condensable gas 40 in particular its mass, as well as the position of the plug 30, and therefore the retention volume 28, are chosen so as to define different temperature operating ranges for the heat pipe 10.
• the different operating ranges in the range [T m i n ; T max ] are in particular: a temperature range of the fluid 38; 7 ⁇ ], wherein the heat pipe 10 has a nominal operation, in particular a variable thermal efficiency.
• the non-condensable gas 40 occupies at most a limited or zero volume in the condenser 26 at the lower temperature of the range ⁇ ⁇ ⁇ ' while obstructing the passage formed by the opening 32 and the tube 34 ( Figure 2A).
• the condenser 26 thus has a minimal condensing surface and therefore the heat pipe 10 has a minimum thermal efficiency.
• the coolant 38 contained in the evaporator 18 vaporizes under the effect of the heat supplied by the hot source 20, and the vapor rises in the condenser 26 where it condenses on the wall portion of the condenser 26 free gas 40 by conductive transfer of heat to the cold source 24 through said wall.
• the condensed liquid then returns by gravity in the evaporator following mainly the wall of the heat pipe 10.
• the non-condensable gas 40 is pushed back to the retention volume 28, thereby releasing a larger surface of the condenser 26, while continuing to obstruct the passage 32, 34 to the volume. 28 ( Figure 2B).
• the heat pipe 10 then has an increasing thermal efficiency until it becomes maximum at the upper temperature of the range T ⁇ x when the entire condenser is released from the gas 40.
• the non-condensable gas 40 is entirely contained in the retention volume 28 and is flush with the outlet of the inner tube 34, and thus still opposes the passage of the steam towards the volume of retention 28 (Figure 2C).
• the length of the passage formed by the opening 32 and the inner tube 34 is chosen to adjust the temperature range of the fluid in which the heat efficiency of the heat pipe 10 is constant. Indeed, once the gas 40 removed from the condenser 26, the gas 40 occupies the passage 32, 34 over a predetermined temperature range depending in particular on the length of the passage 32, 34, and the heat pipe 10 therefore has a constant and maximum efficiency on this temperature range.
• ⁇ a temperature range of the fluid ⁇ £ TM ⁇ ; ⁇ ⁇ ⁇ ⁇ ⁇ of reduction of thermal efficiency of the heat pipe 10.
• the pressure of the vapor phase of the coolant is sufficient to push the non-condensable gas 40 out of the passage 32, 34, thus allowing the vapor of the heat transfer fluid contained in the condenser 26 of ascending into the retention volume 28.
• the retention volume 28 being in contact with the cold source and / or the condenser 26, the vapor condenses on the wall of the retention volume 28 and the liquid then accumulates by gravity in the reservoir 36.
• the evaporation / condensation cycle continues to be exercised in the heat pipe with degraded efficiency (FIG. 3A). Indeed, as the temperature of the fluid increases, the vapor pressure of the coolant increases and expels an increasing amount of the non-condensable gas 40 in the reservoir 36. The volume that can occupy the condensed liquid in the retention volume 28 thus increases as a function of temperature, so that an increasing amount of liquid is stored in the reservoir 36 ( Figure 3B). The amount of fluid in the evaporator decreasing in proportion, the effective length of the heat pipe, that is to say the length of the evaporator portion whose wall is covered with fluid in its liquid phase, decreases, and therefore the thermal efficiency of the heat pipe decreases.
• the pressure of the vapor of the coolant is sufficient to release a volume of the reservoir 36 corresponding to the total amount of liquid phase of the coolant, which is then stored entirely in the reservoir 36 and only the vapor of the fluid is contained in the evaporator 18, the adiabatic zone 22 and the condenser 26 (FIG 3C), the heat transfer between the hot source 20 and the cold source 24 is thus interrupted by the disappearance of the The heat pipe 10 is thus cut off and the fluid is stored at the cold source where it is protected from overheating.
• the mass of gas 40 is advantageously chosen so that at a temperature ⁇ TM ⁇ , the gas occupies the entire volume of the condenser 26 ( Figure 4C).
• the condensation surface being zero, the evaporation / condensation cycle is then stopped, the heat pipe 10 is consequently cut off.
• the coolant is further stored in the evaporator 18 and the adiabatic zone 22, which protects in particular the fluid of the primary circuit from excessive cooling.
• the invention allows using a single non-moving element, for example in the form of the solid plug 30, and a constant non-condensable gas mass, to effectively adjust the operation of the heat pipe 10, and this for several temperature ranges.
• the temperature ranges are chosen according to the intended application, including the nature of the coolant and / or hot and cold sources.
• the maximum temperature 7 ⁇ ° " p at which the heat pipe is cut is between 100 ° C. and 200 ° C., and preferably 150 ° C., which makes it possible to protect in particular the fluid of the primary circuit from excessive heating, and the minimum temperature ⁇ TM ⁇ at which the heat pipe is also cut is between 0 and 10 ° C, which protects in particular the fluid of the primary circuit of the gel.
• the heat pipe 10 is provided with an automatic restart mechanism from the cut-off state, for which the fluid is stored in the tank 36 when the temperature of the fluid falls below a predetermined temperature.
• the heat pipe 10 comprises a mechanism which implements a leakage of the liquid stored in the tank 36 with a low flow rate, preferably controlled by a circulation through a medium with a high pressure drop, in particular a porous medium, or having wicks. Due to the low leakage rate, the mechanism does not preclude the total storage of the liquid phase of the heat transfer fluid in the tank.
• the plug 30 is made of a porous material defining fluid passages, then in the liquid phase, from the tank 36 to the condenser 26. In particular, the plug 30 is made into a sintered metal powder.
• the plug 30 is made of a sealed material and is traversed, in addition to the opening 32, at least one capillary 50 preferably formed closest to the wall of the heat pipe 10, in particular between the plug 30 and the wall of the heat pipe 10.
• a capillary is a passage whose chosen diameter is very small so as to cause high pressure losses in order to limit the flow rate of liquid.
• the medium or high pressure loss media are, for example, through holes of small diameter, porous media or metal webs woven very finely.
• Such fabrics also known as "locks", consist of a fabric of metal wires with a diameter of less than 100 micrometers, for example 40 micrometers.
• the leakage paths in the plug 30 are advantageously chosen to define a mass flow rate strictly less than the mass flow rate through the passage 32 through which the heat transfer fluid vapor ascends into the retention volume 28, in a very small manner with respect to the mass flow rate at the through the opening 32 of the plug 30, namely a flow rate of less than 10% of the flow rate through the opening 32, and preferably a flow rate equal to 5%.
• FIGS. 7A and 7B which illustrate, for example, the variant based on capillaries, in operation, when the temperature of the heat transfer fluid is greater than or equal to 7 ° C. , and that consequently the liquid phase of the coolant is stored in the reservoir 36 (FIG. 7A), liquid flows through the stopper 30.
• the quantity of liquid that has leaked from the reservoir 36 is instantly vaporized, the quantity of additional vapor thus produced being the retention volume 28 to be condensed, in this way all of the coolant in its liquid phase remains stored in the reservoir 36, the heat transfer rate remaining zero for the temperatures above
• the liquid stored in the reservoir 36 leaks through the stopper 30 and flows along the heat pipe wall to join the evaporator 18. After a predetermined duration depending on the leakage flow, the heat pipe 10 is thus again fully operational.
• the duration of restarting of the heat pipe can be high, of the order of a few minutes, without that following damaging in view of the significant inertia found in the field of solar collectors and more generally in the field of heat transfer.
• the invention applies to heat pipes intended to be used in a horizontal or near horizontal position, for example in a position inclined with respect to the direction of gravity with an angle greater than 60 °, as illustrated. to the schematic sectional view of Figure 8 wherein a heat pipe 60 is positioned perpendicular to the gravity g.
• the inner tube 34 may also be omitted.
• the plug 30 differs by the position of the opening 32 which is off-center, the opening 32 being made in an upper portion of the plug 30, above the axis A of the tubular portions 12, 14, when the heat pipe 60 is correctly positioned. Decentering the opening 32 makes it possible to store a larger quantity of liquid in the reservoir 62 formed by the wall of the retention volume 28 and the stopper 30.
• the positioning of the opening 32 is important for implementing the gaseous plug mechanism described above.
• several solid plugs are provided with openings angularly offset relative to one another. Referring, for example, to FIGS. 9A and 9B, the stopper 30 previously described is replaced by three plugs 70, 72, 74, each provided with a through opening 76, 78, 80 formed at the periphery of the plug, and preferably formed on the edge of the cap.
• the openings are angularly separated by an angle of 120 °, so that for any position of the heat pipe, there is always an opening positioned above the axis A of the heat pipe, whose access is controlled by the condensable gas.
• a larger number of plugs may also be envisaged, for example four plugs whose openings are angularly spaced 90 °, five plugs whose openings are angularly spaced 72 °, etc ...
• the liquid phase of the coolant is contained entirely in the tank for temperatures above a high threshold temperature.
• only a part of the liquid phase can be stored, for example to define a minimum effective length of the evaporator and / or to allow the use of two different upper and lower hot springs and that we want to draw profit only from the upper source.
• the tank volume is designed to contain only part of the liquid phase of the coolant.
• heat pipes having a shutdown mechanism for temperatures below a low threshold temperature.
• the mass of non-condensable gas introduced into the heat pipe is not sufficient to occupy the entire volume of the condenser, but only for example a minority portion thereof.
• the process is then continued by the choice of the non-condensable gas.
• This choice is for example made according to its non-condensable nature at operating temperatures of the heat pipe, as well as its immiscibility properties with the heat transfer fluid, or the toxicity or dangerousness of this gas.
• the gas may also be selected as being neutral with respect to the materials with which it is in contact in the heat pipe so as to obtain a cutoff mechanism which is stable over a long period of time. period.
• the retention volume is chosen as low as possible so as to limit the size of the heat pipe.
• the non-condensable gases having the lowest possible pressure ratio between the cut-off temperatures ⁇ TM ⁇ and Tmax are selected, and therefore gases that are used far from their critical point for the temperature range and temperature. range of operating pressures of the heat pipe.
• the mass of the latter and the retention volume are chosen as a function of the particular geometry of the heat pipe and the properties of the coolant.
• the mass of the non-condensable gas and the volume of retention satisfy the following relationships:
• M g is the mass of the non-condensable gas, this mass being constant since the gas is immiscible in the coolant;
• p g (T, P) is the volume density of the non-condensable gas as a function of temperature and pressure
• V ret is the retention volume
• Vcond is I and volume of the condenser
• Vcaio I e is the volume of the functional part of the heat pipe (evaporator and condenser section adiabatic);
• Mfiuide is a mass of heat transfer fluid in the heat pipe
• Psat, vap (T) is the volume density of the vapor phase of the coolant as a function of temperature
• Psat, Uq (T) is the volume density of the liquid phase of the coolant as a function of temperature
• P S at (T) is the pressure of the vapor phase of the coolant. Since the heat transfer fluid is a two-phase system in which the liquid phase is in equilibrium with the vapor phase, the saturation pressure is therefore dependent solely on the temperature. In addition, the gas being in equilibrium with the coolant, the pressure of the gas is therefore also that of the vapor of the coolant. In addition, it is stated that the temperature of the non-condensable gas is equal to that of the vapor of the coolant. Indeed, a large retention volume 28 may possibly induce temperature differences of the order of a few degrees, but the inventors have found that such variations have little influence on the results of the calculations.
• the relation (1) expresses that, at the temperature ⁇ TM ⁇ , the non-condensable gas is confined in the volume of retention that it occupies in totality.
• the relation (2) expresses that, at the temperature ⁇ TM ⁇ , the non-condensable gas occupies exactly the retention volume and the condenser.
• Relation (3) expresses the fact that at the temperature 70 ° p the retention volume divides substantially between the volume of the non-condensable gas and the volume corresponding to the total quantity of the liquid phase of the coolant. that during the phase of accumulation of the coolant in the tank, the amount of vapor present in the retention volume is minimal, this volume being in fact substantially filled with the liquid and the non-condensable gas.
• the density of the non-condensable gas is, for example, approximated by a model of perfect fluids, in particular gases ideal for gases, the inventors having noted that this type of model makes it possible to design a heat pipe with sufficient precision. Obviously, for a more important precision sought, it is possible to choose more complex models. On the other hand, the properties of the liquid and vapor phases of the coolant are taken under saturation conditions.
• the relations (1) and (2) form a system of two equations with two unknowns, namely the mass M g of non-condensable gas, and the retention volume V ret , and are easily solvable.
• the temperature ⁇ ⁇ ⁇ ⁇ of total cutoff of the heat pipe is then given by the relation (3).
• the user imposes the temperatures ⁇ TM ⁇ and 7 ⁇ ° p as predetermined temperatures, the values M g and V ret are then determined using the relations (1) and (3), and the temperature 7 ⁇ from which coolant begins to be stored in the retention volume is then given by relation (2).
• the user imposes the retention volume and one of the temperatures ⁇ TM ⁇ , 7 ⁇ , ⁇ ⁇ ⁇ ⁇ ⁇ ⁇
• the mass M g is then determined according to the relation among the relations (1), (2) and (3) involving the chosen temperature, the other two temperatures then being given by the remaining relationships.
• the effective length of the heat pipe to a temperature between 7 and Tmax ⁇ P was calculated to be as follows.
• the effective length determines in particular the percentage of heating power received by the heat pipe that is effectively transmitted to the condenser, and therefore the maximum thermal efficiency of the heat pipe. For example, if the sun-exposed portion of a heat pipe has a length of 2 meters but the effective length of the heat pipe is 1 meter, only half of the heat output received is transferred to the condenser.
• the amount of liquid phase of the coolant in a heat pipe is preferably chosen to be minimal.
• this quantity is chosen to just saturate the capillary networks used in a capillary heat pipe, and in the thermosyphon setting, the liquid phase is substantially only present in the form of a liquid film on the wall of the heat pipe.
• thermosiphon of circular geometry whose tubular parts are of identical diameter
• mass of liquid is expressed according to the relation:
• ⁇ D cal0 is the diameter of the heat pipe
• ⁇ L cal0 is the length of the functional part of the heat pipe
• ⁇ M is I e caio volume of the functional part of the heat pipe; and ⁇ efiim is the thickness of the liquid phase film covering the wall of the functional part of the heat pipe, this thickness being constant but dependent on the heat transfer fluid, the inclination of the heat pipe and the temperature.
• FIG. 10 is a diagram illustrating the effective length as a function of the temperature of a heat pipe according to the state of the art and according to the invention, the heat pipe having a cylindrical section evaporator of 8 mm internal diameter and 10 mm of external diameter and length equal to 2000 mm, no adiabatic zone, a condenser with a cylindrical section of 25 mm internal diameter and 27 mm external diameter and length equal to 84 mm.
• the heat pipe according to the invention also has a retention volume of the same section as the condenser and of length equal to 36 mm. 7 ⁇ temperature is 90 ° C and the temperature m ° ⁇ is equal to 115 ° C.
• the effective length begins to decrease from 90 ° C to zero at 115 ° C. At this temperature, the heat pipe is cut so that the heat pipe no longer transfers power beyond this temperature except the power corresponding to the flow rate of the plug 30.

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• 2013
  • 2013-03-25 FR FR1352659A patent/FR3003636B1/fr active Active
• 2014
  • 2014-03-24 WO PCT/FR2014/050674 patent/WO2014154984A1/fr active Application Filing
  • 2014-03-24 EP EP14718664.7A patent/EP2981781B1/de active Active
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