FR3038705B1 - THERMAL EXCHANGE METHOD AND DEVICE WITH A GEAR PUMP WITH BEARINGS LUBRICATED EXCLUSIVELY BY THE HEAT TRANSFER FLUID - Google Patents

Abstract

The invention relates to a heat exchange process in which a coolant is driven in displacement in a circuit by at least one gear pump having bearings (34, 35). The heat transfer fluid is chosen so as to be able to lubricate the bearings, and the bearings, permeable to the coolant, are free of any lubricant other than the coolant and lubricated exclusively by the coolant.

Description

The invention relates to a method and a device for heat exchange, in particular of the monophasic or two-phase type, comprising at least one gear pump. FR2946100 discloses a method and a device for two-phase heat exchange with a gear pump on bearings with a low speed of rotation and gaps less than one hundredth of a millimeter. Such a known two-phase heat exchange device comprises a heat-transfer fluid capable of exhibiting at least partially in the liquid state and at least partially in the vapor state, and means for pumping the heat-transfer fluid to drive it moving in motion. a circuit comprising heat exchange means with at least one cold source and at least one hot source external to this circuit, said heat transfer fluid changing at least partially in contact with at least a part of said heat exchange means . Since the circuit is generally in the form of a loop (the heat transfer fluid flowing continuously in a closed network), it is called a "two-phase loop". Such a two-phase loop has many advantages, especially in space applications, and more generally in all applications where a high heat exchange efficiency is sought in terms of the power transported, the power density exchanged, the efficiency of the heat exchanges and, together, a great compactness and a minimum mass. Such a two-phase heat exchange device is therefore particularly useful on board space systems, and must, for this purpose, be able to operate in a wide temperature range (which can be between -50 ° C and + 75 ° C), with a mass flow of heat transfer fluid that is not very sensitive to changes in pressure and loss of charge (that is to say, in particular to the difference in pressure between the outlet and the inlet of the pump), which are different on Earth and in space, the device to be able to function in both situations.

The ball bearings described in this document are "O" -shaped contact bearings axially clamped against each other with axial preload resulting in radial preload of the bearings bearing to the bearing flange and radial preloading of the balls of the bearings. bearings in the rings of these. Such an assembly makes it possible in particular to avoid any vibration and any deterioration when launching a space system, and to precisely guide the axes of the bearings and to minimize the play in the pumping chamber.

The bearings are self-lubricating, that is to say incorporate a powder forming a lubricant film held between the balls and the bearing rings. In order to maintain the lubricating film in the rings and to prevent the unwanted diffusion of the lubricating film on the outside thereof, the rings are systematically coated either with lateral sealing flanges or with a lacquer of lower surface tension ( see for example "Materials Engineering Branch TIP" publication, Charles E. Vest, NASA No. 068 Anti-creep Films for Lubricants Oil, September 2002, fattps; // code541 .gsfc.nasa.gov / Uploads materials tips PDFs / TIP 20068R.pdf%). However, since the coolant used is of low viscosity and sometimes corrosive, the heat transfer fluid must be chosen so as to be compatible with the lubricant, which considerably limits the choice of heat transfer fluid and that of the lubricant. Indeed, although the lubricated bearings are necessarily closed by sealing flanges and / or coated with varnish at the rings (to prevent the lubricant to mix with the heat transfer fluid, to pollute and become less effective point tribologically or to be completely carried away by it, despite the low rotational speed), the coolant always succeeds in creeping into the bearing when the sealing of the flanges decreases under the pressure of the coolant and / or according to their wear. Similarly, if the sealing flanges are replaced by a varnish deposited on the outer faces of the rings (as in some mechanisms embedded on board space systems, this varnish then having the function of preventing as much as possible the loss of the lubricating film, in particular in micro gravity), given the mixing of the coolant in the bearings, despite the low speed of rotation, this varnish does not prevent the heat transfer fluid from contacting the balls.

The problem that arises then is that of the lifetime of such a device, which must be able to be guaranteed for many years, in particular in space systems applications, throughout the operating range of the control loop. heat exchange, and in particular throughout the range of flow, and therefore rotational speed, of the gear pump.

However, despite the low rotational speed, it turns out that the lubricant bearings is subject to wear phenomena and can even, as we have seen, gradually disappear in microgravity and contaminate the heat transfer fluid and the heat transfer loop. heat exchange, despite the presence of sealing flanges, the sealing is subject to wear preventing the certification of a long life, or the sealing varnish, whose installation is delicate and expensive, and is not always sufficient to prevent any penetration of the corrosive coolant and low viscosity into the bearing rings. In addition, in this known device, the low rotation speed imposed on the pump limits, for equal weight, the performance, particularly in terms of mass flow, of the heat exchange loop.

Accordingly, the invention aims to overcome these disadvantages by providing a method and a heat exchange device whose life can be guaranteed more reliably.

It aims in particular to provide a method and a heat exchange device having a greater mass flow / weight ratio.

It also aims at proposing a method and a device of heat exchange more particularly adapted to the applications in the space systems (space probes, artificial satellites of the Earth of all dimensions and applications, space station ...).

To this end, the invention relates to a method of heat exchange - especially on board a space system - in which: a heat transfer fluid is pumped in displacement in a circuit comprising heat exchange means with at least a cold source and with at least one heat source external to the circuit, the coolant is driven by at least one gear pump comprising: a housing, at least two toothed wheels in meshing engagement with each other; other, where each toothed wheel is integral with a shaft guided in rotation and aligned relative to the housing by bearings, characterized in that: - the heat transfer fluid is chosen so as to be able to lubricate the bearings, - said bearings are permeable to the coolant, are free of any lubricant other than the coolant and lubricated exclusively by the coolant.

The bearings are permeable to the coolant in that they have internal and external rings spaced apart from each other with an open space between them, without sealing flange, allowing the passage of heat transfer fluid. In complete contradiction with all the previous teachings in the field, the inventors have now surprisingly found that it is in fact possible, desirable and advantageous not to use self-lubricated bearings dry, whose lubricant can be denatured and / or pollute the heat transfer fluid, but on the contrary to lubricate the bearings exclusively by the coolant itself which, thanks to its low viscosity, penetrates appropriately between and in the rings, the balls (or other rolling members) and the bearing cages and actually has satisfactory lubricating properties. Thus said bearings are free of any lubricant other than the coolant.

In particular, said bearings comprise rings housing rolling members (such as balls, rollers, needles, etc.), and these rings are permeable to the heat-transfer fluid so as to let the latter pass inside the bearing rings on contact. rolling bodies. Advantageously and according to the invention, each bearing comprising an inner ring and an outer ring each having side flanks between which the rolling members are housed, a free radial space is provided between the lateral flanks of the inner ring and the outer ring for the passage of the coolant.

Advantageously and according to the invention the coolant is selected from the group of heat transfer fluids containing more than 30% of at least one heat transfer compound selected from the group consisting of water, ammonia, hydrocarbons, and halogenated hydrocarbons. In particular, advantageously and according to the invention, the coolant is selected from the group of heat transfer fluids containing more than 30% of at least one heat transfer compound selected from the group consisting of ammonia, water and , RI34a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), R1234ze (1,3,3,3-tetrafluoropropene), perfluorinated polyethers (such as Galden® HT 80 ), nitrogen, helium, ethane, methane, propene, and mixtures thereof.

In some embodiments, the heat exchange process is a monophasic process, the heat transfer fluid being a monophasic liquid, that is to say selected to remain liquid throughout the heat exchange loop, for the entire range of temperature of use chosen. The liquid monophasic heat transfer fluid may be chosen especially from the group consisting of liquid ammonia, liquid water, RI34a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), R1234ze (1,3,3,3-tetrafhioropropene), perfluorinated polyethers (such as Galden® HT 80), liquid nitrogen, liquid helium, liquid ethane, liquid methane, propene liquid and their mixtures.

In other embodiments, advantageously and according to the invention: the heat transfer fluid is chosen from the group of fluids likely to be at least partially in the liquid state and at least partly in the vapor state; coolant fluid at least partially changing state in contact with said heat exchange means.

Advantageously, the two-phase heat transfer fluid can be chosen from the group consisting of ammonia, water, RI34a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), R1234ze ( 1,3,3,3-tetrafluoropropene), perfluorinated polyethers (such as Galden® HT 80), nitrogen, helium, ethane, methane and propene.

In addition, advantageously and according to the invention, the coolant is chosen with a viscosity less than or equal to that of water.

According to the invention, the heat transfer fluid must be chosen so as to lubricate the bearings. In particular, it must be compatible with the constituent materials of the bearings. Nevertheless, advantageously and according to the invention, the coolant is free of any lubricating oil (or other agent).

Against all odds, while liquid ammonia is not considered to have good dynamic lubrication properties, good results have been obtained with a coolant consisting of ammonia, in the liquid state in the pump, and with bearings comprising ceramic rolling members.

Advantageously and according to the invention the coolant is selected from the group of heat transfer fluids containing more than 30% of at least one heat transfer compound selected from the group consisting of 1,1,1,2-tetrafluoroethane, 1 , 1-difluoroethane, 1,3,3,3-tetrafluoropropene and mixtures thereof. Throughout the text, the proportions indicated are proportions in mass.

According to particular embodiments, the heat transfer fluid according to the invention is advantageously chosen from the group consisting of binary compositions (consisting of two heat transfer compounds), ternary compositions (consisting of three heat transfer compounds), and of quaternary composition (consisting of four heat transfer compounds).

Furthermore, one of the unexpected effects of the invention is to allow to significantly increase the speed of rotation of the gear pump, as well as internal clearances to the pump, without affecting the life or performance of the pump. Indeed, it turns out that an increase in the rotational speed actually improves the lubricating effect by the coolant, whose circulation within the bearings itself also has the function of improving the thermal homogeneity and in particular to avoid heating, and therefore wear or nuisance micro-welding phenomena in the bearings. An increase in the rotation speed also makes it possible to improve the pumping efficiency and, for the same mass flow rate, to reduce the size of the pump.

Thus, advantageously and according to the invention, at least one of the shafts of the gears is coupled to a drive motor adapted to be able to drive the latter in rotation at a speed greater than 250tr / min.

In some embodiments, advantageously and according to the invention at least one drive motor is chosen to be able to drive at least one of the shafts of the rotating gears at a speed between 260tr / min and 5000tr / min-notably between 300 rpm and 2000 rpm, for example of the order of 600 rpm. The invention also extends to a heat exchange device for implementing a method according to the invention. It therefore also relates to a heat exchange device comprising: - a heat transfer fluid, - a circuit comprising heat exchange means of said heat transfer fluid with at least one cold source and with at least one external heat source to the circuit, - at least a gear pump for driving the coolant in said circuit comprising: o a housing, o at least two toothed wheels -in particular two externally toothed gears-in meshing engagement with each other, o each gear wheel being mounted integral with a shaft guided in rotation and aligned with the housing by bearings, characterized in that: - the heat transfer fluid is adapted to lubricate the bearings, - said bearings are permeable to the coolant, are free of any lubricant other than the coolant and lubricated exclusively by the coolant.

A device according to the invention is also advantageously characterized by all or some of the characteristics mentioned above in relation to the method according to the invention.

In addition, advantageously and according to the invention at least one of the shafts of the gears is coupled to a drive motor adapted to be able to drive the latter in rotation at a speed greater than 250tr / min, in particular less than 5000tr / min. min -notamment between 300tr / min and 2000tr / min, for example of the order of 600tr / min.

Furthermore, in certain embodiments, a device according to the invention is also advantageously characterized in that the gear pump comprising in the housing, a pumping chamber and heat transfer fluid circulation, this chamber being delimited by internal walls , containing the gears, and comprising at least one inlet for the coolant on one side of the meshing of the gears and at least one discharge outlet of the coolant on the other side of the meshing of the wheels toothed games are formed radially and axially between the inner walls of said chamber and the gear wheels, these games being all greater than one hundredth of a millimeter and less than one millimeter and, in operation, filled with heat transfer fluid. Also, in certain embodiments, advantageously and according to the invention, the gear wheels of the gear pump are of external straight teeth without offset and the shafts of the toothed wheels are parallel to one another. The invention also extends to a heat exchange process implemented in a device according to the invention. The invention also extends to a space system comprising at least one heat exchange device according to the invention. It therefore also extends to a space system in which a heat exchange method according to the invention is implemented. The invention also relates to a heat exchange method, a heat exchange device and a space system characterized in combination by all or some of the characteristics mentioned above or below. Other objects, features and advantages of the invention will become apparent on reading the following non-limiting description which refers to the appended figures in which: FIG. 1 is a diagram of an exemplary device of FIG. According to the invention, FIG. 2 is a schematic perspective exploded view of a gear pump of a device according to one embodiment of the invention. FIG. 3 is a schematic perspective view of the invention. FIG. 4 is a diagrammatic sectional view through a plane passing through the axes of rotation of the pinions of the pump of FIG. 2; FIG. 5 is a diagrammatic view in FIG. Section 6 is a schematic sectional view of a detail along the line VI-VI of Figure 5; Figure 7 is a diagrammatic sectional view of a detail; along the line VII-VII of FIG.

The heat exchange device according to the invention shown in FIG. 1 comprises a heat exchange loop 10 in which a two-phase heat transfer fluid circulates. Such diphasic heat transfer fluids which may be at least partly in the liquid state and at least partially in the vapor state, have for the most part a very low viscosity, lower than that of water.

Advantageously and according to the invention, the coolant is selected from the group of heat transfer fluids containing more than 30% of at least one heat transfer compound selected from the group consisting of water, ammonia, hydrocarbons and halogenated hydrocarbons (alkyl halides). More particularly heat transfer fluid comprises at least one heat transfer compound selected from hydrocarbons, hydrofluorocarbons, ethers, hydrofluoroethers and fluoroolefins.

According to particular embodiments, the heat transfer fluid according to the invention is advantageously chosen from the group consisting of compositions comprising a single heat transfer compound, binary compositions (consisting of two heat transfer compounds), ternary compositions ( consisting of three heat transfer compounds), and quaternary composition (consisting of four heat transfer compounds).

In particular, at least one heat transfer fluid heat transfer compound may be chosen from refrigerants whose classification is given for example by the publication "Classification of refrigerants", International Institute of Refrigeration, Paris, France http: // www.iifiir.org/userfiles/file/webfiles/sum.maries/Refrigerant classification F Rjgdr.

According to a particular embodiment, the coolant is free of any lubricating oil.

According to one embodiment, the heat transfer fluid further comprises: one or more additives chosen from stabilizers, surfactants, tracer agents, fluorescent agents, odorants, solubilizing agents and mixtures thereof; preferably one or more additives selected from stabilizers, surfactants, tracer agents, fluorescers, odorants, solubilizers and mixtures thereof.

The stabilizer (s), when present, preferably represent at most 5% by weight in the heat transfer composition. Among the stabilizers, there may be mentioned in particular nitromethane, ascorbic acid, terephthalic acid, azoles such as tolutriazole or benzotriazole, phenol compounds such as tocopherol, hydroquinone, t-butyl hydroquinone, 2,6-di-tert-butyl-4-methylphenol, 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid, epoxides (optionally fluorinated or perfluorinated alkyl or alkenyl or aromatic) such as n-butylglycidyl ether, hexanedioldiglycidyl ether, allylglycidyl ether, butylphenylglycidyl ether, phosphites, phosphates such as tricresyl phosphates, thiols and lactones. As tracer agents (which can be detected) mention may be made of deuterated hydrofluorocarbons or not, deuterated hydrocarbons, perfluorocarbons, fluoroethers, brominated compounds, iodinated compounds, alcohols, aldehydes, ketones, nitrous oxide and combinations thereof. The tracer agent is different from the one or more heat transfer compounds composing the heat transfer fluid. As solubilizing agents, mention may be made of hydrocarbons, dimethyl ether, polyoxyalkylene ethers, amides, ketones, nitriles, chlorocarbons, esters, lactones, aryl ethers, fluoroethers and magnesium compounds. 1-trifluoroalkanes. The solubilizing agent is different from the one or more heat transfer compounds composing the heat transfer fluid. Fluorescent agents that may be mentioned include naphthalimides, perylenes, coumarins, anthracenes, phenanthracenes, xanthenes, thioxanthenes, naphthoxanhthenes, fluoresceins and derivatives and combinations thereof. As odorants, mention may be made of alkyl acrylates, allyl acrylates, acrylic acids, acrylilsters, alkyl ethers, alkyl esters, alkynes, aldehydes, thiols, thioethers, disulphides, allyl isothiocyanates and alkanoic acids. , amines, norbornenes, norbornene derivatives, cyclohexene, heterocyclic aromatic compounds, ascaridole, o-methoxy (methyl) phenol and combinations thereof.

The coolant according to the invention may also comprise, or even consist of, at least one of the following heat transfer compounds: - ammonia, - water, - 1,1,1,2-tetrafluoroethane ( RI34a), 1,1-difluoroethane (RI52a), 1,3,3,3-tetrafluoropropene (R1234ze), a perfluorinated polyether such as Galden® HT 80, nitrogen, helium, - ethane, - methane, - propene.

The coolant is delivered from a diphasic tank 11 whose output 12 is connected to a pipe 13 connected to a gear pump 14 according to the invention. In this pipe 13, the coolant is mainly liquid, normally substantially monophasic (that is to say only liquid). However, it is possible that the fluid in the pipe 13 is at least partly vapor, and it is an advantage of the invention to allow the operation of the two-phase loop and the pumping of the heat exchange fluid, even in the where it is partially vapor in the pipe 13.

The pump 14 delivers the liquid in the pressurized liquid state to an evaporator exchanger group adapted to collect the thermal power (calories) released by exothermic components 16 (for example electronic circuits of a space system). At the outlet of the evaporator group, the fluid is brought to the two-phase liquid / gas state (the proportion of fluid in the vapor state depending on the power absorbed in the evaporator group) in a line 17 connected to a group 18 condenser exchanger supplying the fluid in the liquid state in the pipe 13 upstream of the outlet 12 of the tank 11, after extracting the thermal power of the fluid in the two-phase state to a cold source 19 (for example the external environment).

The pump 14 is driven by any motor 20, preferably a brushless synchronous electric motor, for example via a magnetic sealing coupling 21 or a rotor motor immersed in a sealed bell.

Figures 2 to 6 show an embodiment of a pump 14 can be used in a device according to the invention. This pump 14 comprises a sealed peripheral casing 22 formed of a parallelepipedal casing 22a, the dimensions of which are adapted to contain the different elements constituting the pump, this casing being closed by a flange forming a cover 22b tightened on the casing by screws or bolts. 23.

The lid 23 has a fluid inlet orifice 24, and a discharge port 25 of the fluid under pressure. These orifices 24, 25 communicate through the cover 22b with the inside of the casing 22. Inside the casing 22, a chamber 26 for pumping and circulating the coolant is formed between two parallel flanges 27, 28 separated by a flange 29 spacer. These three flanges 27, 28, 29 are tightened against each other by screws or bolts (not shown), and the assembly formed by these three flanges 27, 28, 29 is itself fixed rigidly on the inner face of the cover 22b by screws or bolts (not shown). The flanges 27, 28, 29 are housed in the housing 22, but have a slightly smaller dimension than the internal enclosure 25 defined in the housing 22, so as to provide a discharge space 42 for the circulation of the fluid on the discharge side as described below.

The flanges 27, 28, 29 are recessed so as to delimit, with the external teeth of two gears 30, 31, the chamber 26 for pumping and circulation, the latter having dimensions and a shape suitable for housing the two gears 30 , 31 with external straight teeth in meshing cooperation with each other without offset. Each pinion 30, 31 is mounted integral with a shaft 32, respectively 33, guided in rotation and aligned relative to the housing by bearings 34, respectively 35.

The shafts 32, 33 of the pinions are parallel to each other, and at least one of the shafts, said shaft 32 leading, extends towards and in the cover 22b so as to have a end carrying a series of internal permanent magnets 50 adapted to form the magnetic coupling 21 allowing the coupling of this shaft 32 leading to the motor shaft 20, and thus the drive by the latter of the driving shaft 32 and the pinion 30, said pinion 30 leading. As seen in FIG. 4, the internal magnets 50 of the end of the driving shaft 32 are housed in a cavity 51 of the cover 22b delimited by a wall 52 forming a protuberance extending outwardly from the latter. to be able to be hatched by a bell 53 also carrying external permanent magnets 54 adapted to be able to cooperate magnetically through the wall 52 with the internal magnets 50, thereby constituting the magnetic coupling 21. When the bell 53 is rotated, it drives itself in rotation the internal magnets 50, and thus the leading shaft 32. This bell 53 is adapted to receive the end of the motor shaft 20 and be integral in rotation with the latter. The other pinion 31, called pinion 31 driven, as well as its shaft 33, said shaft 33 led, are rotated by the pinion 30 driving due to the meshing engagement of the pinions 30, 31.

The chamber 26 for pumping and circulation comprises a first lobe 36 of cylindrical general shape of revolution about the axis of the driving shaft 32, this first lobe 36 being adapted to fit more closely, with the minimum of radial clearances and axial, the driving pinion. Similarly, the circulation pumping chamber 26 comprises a second lobe 37 of cylindrical general shape of revolution about the axis of the driven shaft 33, this second lobe 37 being adapted to fit more closely, with the minimum of games radial and axial, the pinion 31 led.

The chamber 26 for pumping and circulation also comprises, between the two lobes 36, 37, on the one hand an inlet chamber 38 located on one side of the meshing of the pinions, on the other hand a chamber 39 discharge located on the other side of the gear meshing. The inlet chamber 38 is in communication with the inlet orifice 24. The discharge chamber 39 is in communication with the discharge port 25. To do this, the flange 29 spacer and / or the flange 27, said flange 27 bearing, interposed between the flange 29 spacer and the cover 22b have through-holes.

In the embodiment shown, the spacer flange 29 has a discharge lumen 43 extending laterally (in a direction orthogonal to the axis of the shafts 32, 33 of the gears) from the discharge chamber 39 to unblock at the edge 44 outer periphery of the flange 29 spacer so that the pressurized fluid escaping through the discharge port 43 flows into the discharge space 42 extending between the flanges 27, 28, 29 and the wall internal of the housing 22, to the discharge port 25 which is in communication with the space 42 of discharge. The spacer flange 29 also has an inlet lumen 40 extending laterally (in a direction orthogonal to the axis of the shafts 32, 33 of the gears) from the inlet chamber 38 and up to a light 41 of FIG. connection made in the spacer flange 29 and opening on the face of the flange 29 spacer in contact with the flange 27 bearing carrier, this connection light 41 receiving sealingly the end 45 of an intake tube 46 passing through a light passage 47 of the flange 27 bearing carrier and the cover 22b to form the orifice 24 of admission (Figure 7).

Each of the shafts 32, 33 of the pinions 30, 31 extends axially on only one side of the pinion 30, 31 and is guided relative to the housing 22 cantilevered only by bearings 34, 35 cooperating only with the flange 27 bearing housing 22 (Figures 4 and 6).

To ensure alignment, each shaft 32, 33 of the pinion is guided relative to the housing 22 by two ball bearings 34a, 34b, respectively 35a, 35b which are adjacent to the axially, namely a proximal bearing 34a, 35a which is axially the closer to the pinion 30, 31, and a distal bearing 34b, 35b which is axially furthest from the pinion 30, 31. Each bearing has an inner ring 63a, 63b, 64a, 64b, an outer ring 69a, 69b, 70a, 70b, and beads 71a, 71b, 72a, 72b. Each inner ring and each outer ring are spaced from each other, the space between them being left free, without lateral flange, so as to let the heat transfer fluid between them, inside the bearing.

In addition, the two angular contact ball bearings 34a, 34b, respectively 35a, 35b of each pinion shaft 32, 33 are mounted in a so-called "O" (or "back-to-back") oblique contact arrangement, tight axially against each other with a so-called solid axial preload (by compensating for play and clamping in axial compression of the parts in contact, without elastic bending member such as a Belleville washer) resulting in a radial preload of the bearings to report to the flange 27 door bearings and a radial preload ball bearings in the rings of the latter.

To do this, the shaft 32, 33 of the pinion has a bore 55, 56 through which axial through which is passed the rod 57, 58 of a bolt 59, 60 having a head or nut 61, 62 resting on the ring 63b, 64b of the bearing 34b, 35b distal, and at its other axial end, a head or nut 65, 66 bearing on the face 67, 68 external radial pinion 30, 31 extending opposite the 32, 33. The inner ring 63b, 64b of the bearing 34b, 35b distally extends axially beyond the end of the shaft 32, 33, so that the tightening of the bolt 59, 60 causes a axial clamping stress of the inner rings 63a, 63b canceling the clearance between the inner rings and determining the desired preload, and, respectively, 64a, 64b of the two bearings which are adjacent to one another. Thus, the directions of the contact forces between the balls and the tracks of the inner and outer rings are oblique and substantially draw an O. Such an assembly in "O" ensures a very high axial stability without tilting.

A spacer 73, 74 for wedging is interposed between the inner ring 63a, 64a of the proximal bearing 34a, 35a and a shoulder 75, 76 radial of the pinion 30, 31 so as to determine (according to the width of the spacer 73, 74). the axial position of the pinion 30, 31.

The outer rings 69a, 69b, 70a, 70b of the bearings are fixed to the flange 27 bearing seats and clamped against each other axially. To do this, the flange 27 bearing carrier has a shoulder 77, 78 receiving the outer ring 69a, 70a of the proximal bearing, and a ring 79, 80 clamping is applied opposite against the outer ring 69b, 70b of the distal bearing , and this clamping ring 79, 80 is clamped axially against the flange 27 bearing carrier by screws 81, 82.

It follows from this assembly that the bearings are perfectly fixed, without play, on the flange 27 door bearings, they are perfectly aligned along the axis of the shaft 32, 33, that each shaft 32, 33 pinion is him - Even perfectly positioned and aligned with the flange 27 door bearings, and that the operating clearance in the bearings are canceled. Such an assembly "O" without clearance increases the tilt stiffness of each axis and not only has the advantage of avoiding any vibration and damage when launching a space system, but also and above all also allows to precisely guide the axes and minimize the play in the circulating pump chamber and ensure the pumping of a low viscosity heat transfer fluid with such a gear pump.

The constituent materials of the bearings must be chosen so as to be compatible with the coolant used to lubricate them. In particular, the balls 71a, 71b, 72a, 72b are formed of a non-metallic material, in particular ceramic. In addition, the bearings advantageously have cages formed of metallic or plastic materials or composites.

In addition, the parts of the pump may come into contact with the heat transfer fluid may have a surface coating resistant to corrosion-in particular chemical deposition of nickel metal-. In practice, in such a pump according to the invention, the clearances extending radially and axially between the inner walls of the pumping chamber and the pinions may all be greater than one hundredth of a millimeter, for example between one hundredth and five hundredths of a millimeter. millimeter, and, in operation, filled with heat transfer fluid.

The circulation of the coolant in the pump is shown schematically in FIG. 4. As can be seen, the heat transfer fluid flows in the bearings 34, 35 and lubricates them.

The service life and operation of such a pump can be guaranteed over a large number of years.

Furthermore, there is a regime of operation of such a pump in which the pump has the desired performance in terms of independence of the flow with respect to the variation of pressure drop in the loop, which can be encountered in this type. two-phase loop and this in a wide temperature range, and in which on the other hand the leaks are minimized. In practice, the drive motor 20 can be adapted and controlled to drive the driving shaft 32 and the pinions 30, 31 in rotation at a speed greater than 250 rpm, preferably less than 5000 rpm - in particular between 300 rpm min and 2000tr / min, for example of the order of 600tr / min. EXAMPLE 1

Tests were conducted with a test bench dedicated to gear pump insulated bearings, free of any lubricant, and immersed in ammonia as a two-phase heat transfer fluid.

The rotation speed of the pre-loaded bearings is 1800 rpm with an outside temperature corresponding to the ambient temperature. After more than two billion turns, the bearings are removed and the bearings are in new condition. EXAMPLE 2

Tests have been conducted with a two-phase loop according to the invention comprising ammonia as a two-phase heat transfer fluid and a gear pump whose bearings are free of any lubricant, the general characteristics of the two-phase loop of the pump being the following.

The volume of the two-phase loop is 1. 54f. 512g of ammonia are injected into this loop. The gear pump has a volume of 1.8dm for a mass of 4 kg. The internal clearances in the pump are of the order of 2 hundredths of a millimeter. The volume flow delivered by the pump is a linear function of its rotational speed. It delivers about 3f / min for a speed of rotation of 575rpm.

The rotational speed of the pump is varied in the following range: 100 rpm, 300 rpm, 578 rpm, 685 rpm. The external temperature is also varied: -20 ° C., 25 ° C., 50 ° C., and 75 ° C. The variation of the mass flow rate delivered by the pump is measured as a function of the pressure increase between the outlet and the outlet. pump inlet.

It can be seen with a speed of rotation at 100 rpm that the mass flow rate can not exceed 5 g / s, and that the increase in pressure can not exceed 0.7 hPa.

On the other hand, it can be seen that for higher rotational speeds, the mass flow rate increases as a function of the rotational speed, the pressure difference being at least equal to 1.5 hPa. With a mass flow rate of the order of 25 g / s at 75 ° C., a decrease in mass flow rate of the order of 13% (from 26.21 g / s to 22.88 g / s) is observed for increase of the pressure difference delivered by the pump from 0.1 hPa to 1 hPa. This value is sufficiently small to be acceptable in relation to the regulatory requirement of flow independence with respect to the pressure drop variation in a two-phase fluid loop (maximum 20% decrease in mass flow for an increase of multiplicative factor equal to 10 of the pressure drop in the loop).

It can also be seen that the pump operates in the same way throughout the external temperature range. EXAMPLE 3

The identical diphasic loop of Example 2 is used, but replacing the ammonia with 662 g of heat transfer fluid RI52a.

In a first period of 117 days, the operation of the pump is adjusted so that it produces a pressure increase of 0.3 hPa. The speed of rotation of the pump and 577 rpm, the mass flow delivered is of the order of 40 g / s and the torque at the inlet of the pump is of the order of 0.1 N.m. The operating parameters (supply voltage, output pressure, mass flow, rotation speed, torque) are measured every 10 min. The temperature of the fluid at the inlet of the pump is of the order of 60 ° C. It is noted that the parameters of the pump do not change during this first period of 117 days during which the pump has achieved 97, 4 million rounds. At the end of this first period of 117 days, the operation of the pump is modified so as to deliver a pressure increase of 1 hPa with a rotation speed of 578 rpm. After a second period of 39 days, the pump has completed more than 130 million rounds. The delivered mass flow rate is 37.21 g / s, for a torque at the pump inlet of 0.18 Nm. Again, no significant change in the operating parameters of the pump is found at the end of this second period, that is to say after 156 days of operation. EXAMPLE 4

The same two-phase loop and the same gear pump as in Example 3 are used.

The rotational speed of the pump is varied in the following range: 100 rpm, 300 rpm, 680 rpm. The external temperature is also varied: -20 ° C., 0 ° C., and 80 ° C. The variation of the mass flow rate delivered by the pump is measured as a function of the pressure increase between the outlet and the inlet of the pump. pump.

It can be seen with a rotation speed at 100tr / min that the mass flow rate can not exceed 10g / s, and that the pressure increase can not exceed 0.9hPa at 80 ° C.

On the other hand, it can be seen that for higher rotational speeds, the mass flow rate increases as a function of the rotational speed, the pressure difference being at least 1.5 hPa. The mass flow rate is equal to 50 g / s at 80 ° C for a pressure increase of 0.1 hPa, and goes to 38 g / s at 80 ° C for a pressure increase of 1.5 hPa, the mass flow rate decrease varying. according to an affine function of the value of the pressure increase delivered by the pump. In particular, a decrease in mass flow of the order of 14% is noted for an increase in the pressure difference from 0.1 hPa to 1 hPa. It can also be seen that the pump operates in the same way throughout the external temperature range. Thus, a mass flow rate of the order of 70 g / s is delivered by the pump at -20 ° C. for a rotation speed of 680 rpm and a pressure increase delivered by the pump of 0.1 hPa. The decrease in mass flow is of the order of 7.7% for an increase in the pressure difference of 0.1 hPa to 1 hPa. These values are sufficiently low to be acceptable, the standards imposing a maximum decrease of 20% mass flow. The invention may in particular be applied for the thermal control of exothermic components, for example electronic circuits, in a space system such as a satellite or a space station, or in terrestrial electrical and / or electronic systems such as the electronic control centers. recording of digital data ("data centers") or farms of computer servers (for example of the type used for "Cloud" technologies on the Internet). The device according to the invention is then a device for thermal control of exothermic components 16 of an electrical and / or electronic system, the circuit 13, 17 forming a diphasic heat transfer fluid loop, said components 16 forming a hot spring which is external to the circuit and is associated with the latter by means 15 of heat exchange for cooling.

It goes without saying that the invention is the subject of numerous alternative embodiments with respect to the embodiment described above and shown in the figures, given solely by way of non-limiting example. For example, it applies equally well to a liquid monophasic heat transfer fluid exchange loop, to a gearwheel pump, at least one of which is a ring gear, or to a pump comprising a plurality of gears.

Claims (12)

1 / - Heat exchange process - especially aboard a space system - wherein: - a coolant is driven by pumping in displacement in a circuit (13, 17) comprising means (15, 18) of heat exchange with at least one cold source (19) and with at least one heat source (16) external to the circuit, - the coolant is driven by at least one gear pump (14) comprising: o a housing (22), o at least two wheels (30, 31) toothed in meshing engagement with each other, o each toothed wheel (30, 31) being mounted integral with a shaft (32, 33) guided in rotation and aligned relative to the casing (2) by bearings (34, 35), o in the casing (22), a chamber (26) for pumping and circulating the coolant, this chamber (26) being delimited by internal walls, containing the toothed wheels (30, 31), and comprising at least one inlet (38) for the admission of the heat transfer fluid to one side of the gripping of the wheels (30, 31) and at least one discharge outlet (39) of the coolant on the other side of the meshing of the toothed wheels (30, 31), play being formed radially and axially between the inner walls of said chamber (26) and the toothed wheels (30, 31), characterized in that: - the drive motor (20) is adapted to be able to drive at least one (32) of the shafts of the rotating gears at a speed greater than 250 rpm and less than 5000 rpm, the coolant is chosen with a viscosity less than or equal to that of the water and so as to be able to lubricate the bearings, the said bearings are permeable to the coolant, are free of any lubricant other than the coolant and lubricated exclusively by the coolant. 2 / - Method according to claim 1 characterized in that: - the coolant is selected from the group of fluids likely to be at least partially in the liquid state and at least partially in the vapor state, - the heat transfer fluid at least partially changing state in contact with said heat exchange means (15, 18). 3 / - Method according to one of claims 1 or 2 characterized in that the heat transfer fluid is selected from the group of heat transfer fluids containing more than 30% of at least one heat transfer compound selected from the group consisting of water, ammonia, hydrocarbons, and halogenated hydrocarbons. 4 / - Method according to one of claims 1 to 3, characterized in that the coolant is selected from the group of heat transfer fluids containing more than 30% of at least one heat transfer compound selected from the group of ammonia, water, RI34a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), R1234ze (1,3,3,3-tetrafluoropropene), perfluorinated polyethers, nitrogen, helium, ethane, methane, propene, and mixtures thereof. 5 / - Method according to one of claims 1 to 4, characterized in that said bearings (34, 35) comprise rolling members ceramic. 6 / - Method according to one of claims 1 to 5, characterized in that at least one (32) of the shafts of the wheels is coupled to a drive motor (20) adapted to be able to drive the latter in rotation at a speed between 300 rpm and 2000 rpm. 7 / - heat exchange device comprising: - a heat transfer fluid, --a circuit (13, 17) comprising means (15, 18) for heat exchange of said coolant with at least one cold source (19) and with a least one heat source (16) external to the circuit, - at least one pump (14) gear for driving the coolant in said circuit comprising: o a housing (22), o at least two wheels (30, 31) toothed in meshing cooperation with each other, where each toothed wheel (30, 31) is integral with a shaft (32, 33) guided in rotation and aligned with the housing (2) by bearings ( 34, 35), o in the housing (22), a chamber (26) for pumping and circulating the coolant, this chamber (26) being delimited by internal walls, containing the wheels (30, 31) toothed, and comprising at least one inlet (38) for the admission of the coolant on one side of the meshing of the wheels (30, 31) and at least one outlet (39) of flow of the heat transfer fluid on the other side of the meshing of the toothed wheels (30, 31), play being formed radially and axially between the internal walls of said chamber (26) and the toothed wheels (30, 31), characterized in that: - the drive motor (20) is adapted to drive at least one (32) of the rotating gear shafts at a speed greater than 250rpm and less than 5000rpm; heat transfer fluid has a viscosity less than or equal to that of water, and is adapted to lubricate the bearings, - said bearings are permeable to the coolant, are free of any lubricant other than the coolant and lubricated exclusively by the coolant. 8 / - Device according to claim 7, characterized in that each bearing (34, 35) comprising an inner ring and an outer ring each having side flanks between which the rolling members are housed, a free radial space is formed between the flanks side of the inner ring and the outer ring for the passage of heat transfer fluid. 9 / - Device according to one of claims 7 or 8 characterized in that at least one (32) of the shafts of the toothed wheels is coupled to a drive motor (20) adapted to be able to drive the latter in rotation at a speed between 300 rpm and 2000 rpm. 10 / - Device according to one of claims 7 to 9 characterized in that said bearings (34, 35) comprise rolling members ceramic. 11 / - Device according to one of claims 7 to 10 characterized in that said clearances are all greater than one hundredth of a millimeter and less than one millimeter -particularly between one hundredth and five hundredths of a millimeter- and filled with heat transfer fluid. 12 / - Space system comprising at least one device according to one of claims 7 to 11.