EP3004773A1

EP3004773A1 - Heat transfer device with diphasic fluid

Info

Publication number: EP3004773A1
Application number: EP14727210.8A
Authority: EP
Inventors: Vincent Dupont
Original assignee: Euro Heat Pipes SA
Current assignee: Euro Heat Pipes SA
Priority date: 2013-05-29
Filing date: 2014-05-28
Publication date: 2016-04-13
Also published as: WO2014191512A1; US10209008B2; FR3006431B1; US20160116226A1; FR3006431A1

Abstract

A heat transfer device with diphasic fluid with capillary or gravity pumping, with a diphasic working fluid contained in a closed general circuit, comprising an evaporator (1), a condenser (2), a reservoir (3) having an internal volume (30) with a liquid portion (6) and a gas portion (7), a first vapour communication circuit (4), a second liquid-phase communication circuit (5), in which the reservoir (3) comprises a plurality of floating bodies (8) separating the liquid portion from the gas portion, whereby the heat exchanges between the liquid portion and the gas portion are slowed down, helping to lessen the effect of movements of the liquid portion or of an inflow of cold or hot liquid into the reservoir.

Description

Two-phase fluid heat transport device

The present invention relates to two-phase fluid heat transport devices, in particular mechanically passive devices with a two-phase fluid loop with capillary pumping or using gravity.

It is known from FR-A-2949642 such devices used as cooling means for electrotechnical power converter.

These devices can be regulated in temperature via a pressure control in the tank. This control can be active (electrical heating resistance) or totally passive (introduction of an auxiliary gas into the tank).

However, it appeared that the starting phases were particularly delicate for large thermal powers, it can occur a drying of the capillary wick and thus a failure of startup.

In addition, if the device is subjected to accelerations, it can occur a phenomenon of cold shock ^y 'in the tank that abruptly lowers the pressure and deteriorates the performance.

Moreover, significant variations in the thermal load can lead to instabilities in the operation of the two-phase loop.

It has therefore appeared a need to increase, on the one hand, the reliability of the start-up and, on the other hand, the reliability of the operation of such loops under thermal load conditions which present strong variations.

For this purpose, the subject of the invention is a capillary pumping thermal transfer device adapted to extract heat from a hot source and to restore this heat to a cold source by means of a two-phase working fluid contained in a enclosed general circuit, comprising: at least one evaporator (1), having an inlet and an outlet,

at least one condenser (2),

a reservoir (3) having an interior volume with a liquid portion and a gas portion, and at least one inlet and / or outlet orifice (31; 31a, 31b),

a first communication circuit (4), for essentially vapor phase fluid, connecting the outlet of the evaporator to an inlet of the condenser,

a second communication circuit (5), for fluid essentially in the liquid phase, connecting an outlet of the condenser to the tank and to the inlet of the evaporator, characterized in that the reservoir (3) comprises a plurality of floating bodies separating the liquid portion from the gas portion, whereby the heat exchange between the liquid portion and the gas portion is slowed down.

Thanks to these provisions, the floating bodies form a thermal barrier which provides a slowing of heat exchange between the liquid portion and the gaseous portion, which has several beneficial effects explained below.

Indeed, the two-phase loop can be subject to significant variations in thermal load, and therefore the flow of liquid entering the liquid part can both have a variable or even chaotic flow and secondly a temperature quite different from that of the tank.

First of all we can lessen the effect of an influx of cold liquid in the tank. Such cold liquid influx can lead to an effect of ^y cold shock ", namely a sudden lowering of the upper surface temperature of the liquid in the tank which causes a drop in pressure and a sudden increase in pressure adverse loads operation of the loop. Thanks to the presence of floating bodies, the temperature variation the surface of the liquid phase will be much slower. This effect is particularly sensitive if the tank is thermally controlled by means of a heating cartridge.

In other circumstances, for example in the case of a pressurization by voluntary introduction of an inert auxiliary gas into the reservoir, the influx of liquid may be at a temperature substantially greater than the average temperature of the reservoir which can lead to to effect ^there hot shock ", namely a rapid increase of the upper surface temperature of the liquid in the tank which causes an increase in pressure and temperature, with potentially near operating conditions the maximum limits in temperature and pressure. Here again, the presence of the floating bodies then acts as a thermal resistance to slow the variations of the gas-liquid surface temperature (upper surface temperature of the liquid in the tank).

Finally, there may be significant fluid movements in the reservoir when the device is subjected to accelerations, for example if it is on board a transport vehicle. This can then lead to a mixing effect in the reservoir, which can lead to rapid and undesirable changes in the temperature of the surface of the liquid in contact with the gas phase in the reservoir, and consequently the instability of operation of the two-phase loop. . Here again, the floating bodies form a barrier that dampens the mixing effect in the liquid.

In various embodiments of the invention, one or more of the following provisions may also be used:

the plurality of floating body walls forms several superimposed layers; This gives a good efficiency the thermal barrier while allowing liquid-gas exchanges;

said floating bodies are interconnected by a flexible structure; This prevents one or more floating bodies remains stuck on a wall or disengages from other floating bodies;

the reservoir comprises a low grid and a high grid, respectively arranged at a distance from the bottom wall and from the upper wall of the tank, so that these two grids prevent the floating bodies from passing through them and thus forming lower limits and upper for the displacement of the floating bodies inside the tank; This avoids one or more floating bodies do not stick on the inner wall or on the upper wall;

all said floating bodies have substantially the same shape; which represents an easy solution to industrialize, because one uses only one type of elements which one counts or that one weighs to determine the necessary quantity;

said floating bodies are made of a material selected from stainless steel, teflon, borosilicate, carbon, ceramic; whereby a chemically neutral material is chosen which does not age unfavorably over time;

said floating bodies may have a spherical shape, preferably with a diameter of between 0.5 and 10 mm; which facilitates the spatial rearrangement of the floating bodies in the event of a change in the geometry of the liquid surface;

the volume occupied by the plurality of said floating bodies is between 3% and 12% of the total volume of the tank; whereby a sufficient and optimal thickness of floating bodies is obtained, in particular for a tank having the usual dimensions for this kind application;

the reservoir comprises an inlet jet deflector in the vicinity of the inlet orifice; This prevents the jet of entry from having a direct influence on the layer of floating bodies;

The evaporator comprises a microporous mass adapted to provide capillary pumping of fluid in the liquid phase; so that a capillary pumping solution is used without resorting to the effect of gravity for the pumping function; whereby the device can be used in a microgravity environment;

- the device can further comprise an anti member ^¬ back as a float arranged between the internal volume of the container and the microporous mass of one evaporator and arranged to prevent the liquid present in one evaporator only moves to the volume inside the tank; which makes the start of the two-phase loop more reliable;

the device being mainly subjected to gravity, the evaporator can be placed below the condenser and the tank, so that the gravity is used to move the liquid towards the evaporator; which represents an alternative to capillary pumping.

Other aspects, objects and advantages of the invention will appear on reading the following description of several embodiments of the invention, given by way of non-limiting examples, with reference to the accompanying drawings, in which:

FIG. 1 is a general view of a device according to one embodiment of the invention,

FIG. 2 shows in more detail the reservoir of the device of FIG. 1,

FIG. 3 shows a variant of the reservoir of FIG. 2,

FIG. 4 shows a second embodiment of the device of the invention, in which gravity is mainly used to ensure the pumping of the two-phase loop.

In the different figures, the same references designate identical or similar elements.

FIG. 1 shows a capillary pumping heat transport device with a two-phase fluid loop. The device comprises an evaporator 1, having an inlet 1a and an outlet 1b, and a microporous mass 10 adapted to provide capillary pumping. For this purpose, the microporous mass 10 surrounds a blind central longitudinal recess 15 in communication with the inlet 1a to receive working fluid 9 in the liquid state from a reservoir 3.

The evaporator 1 is thermally coupled to a hot source 11, such as an assembly comprising electronic power components or any other element generating heat, for example by joule effect, or by any other process.

Under the effect of the supply of calories to the contact 16 of the microporous mass filled with liquid, fluid passes from the liquid state to the vapor state and is evacuated by the transfer chamber 17 and by a first circuit. communication 4 which conveys said vapor to a condenser 2 having an inlet 2a and an outlet 2b.

In the evaporator 1, the cavities released by the evacuated vapor are filled with liquid sucked by the microporous mass 10 from the aforementioned central recess 15; it is the phenomenon of capillary pumping well known in itself.

Inside said condenser 2, heat is transferred by the fluid in the vapor phase to a cold source 12, which causes a cooling of the vapor fluid and its phase change to the liquid phase, ie its condensation.

At the level of the condenser 2, the temperature of the working fluid 9 is lowered below its equilibrium liquid-vapor temperature, which is also called sub-cooling ('sub-cooling' in English) so that the fluid can not do not iron in the vapor state without any heat input.

The vapor pressure pushes the liquid towards the outlet 2b of the condenser 2 which opens onto a second communication circuit 5, also connected to the tank 3. Said second communication circuit 5 may comprise two distinct portions 5a, 5b as it will be seen further.

The second communication circuit 5 comprises working fluid essentially in the liquid phase, whereas the first communication circuit 4 comprises fluid essentially in the vapor phase.

The reservoir 3 has at least one inlet and / or outlet orifice 31, here in this case in FIG. 1 an inlet orifice 31a and a separate outlet orifice 31b, and the reservoir 3 has an interior volume 30, filled with the coolant 9 in diphasic form. The working fluid 9 can be, for example, ammonia or any other suitable fluid, but methanol can preferably be chosen. The working fluid 9 is in two-phase form in the tank 3 partly in the liquid phase 6 and partly in the vapor phase 7. In an environment in which a gravity is exerted (vertical in Z), the gas phase part 7 is located above the liquid phase portion 6 and a liquid-vapor interface 19 separates the two phases (upper surface of the liquid in the tank).

It is the temperature of this separation surface 19 which determines the pressure in the loop, this pressure corresponds to the saturation pressure of the fluid at the temperature prevailing at the separation surface 19, by virtue of a one-to-one relationship that connects Psat and Tsat under saturation conditions.

It should be noted that, in the case where the heat transfer device is located in a moving vehicle, the reservoir can undergo various inertial forces and varied. In addition, the reservoir may be inclined with respect to its normal reference position, as shown in Figure 3.

Advantageously according to the invention, there is a plurality of floating bodies 8 inside the tank. These floating bodies 8 are positioned naturally in the upper part of the liquid portion, generally at the interface between the liquid portion 6 and the gas portion 7.

Their buoyancy relative to the liquid of the working fluid must be sufficient, and therefore their density must be substantially less than the density of the liquid. Depending on the chosen material, these floating bodies 8 may be solid or hollow, the hollow internal volume being adapted according to desired buoyancy.

Preferably, a material that is chemically inert with respect to the working fluid will be chosen. Preferably, stainless steel, teflon, borosilicate, carbon, ceramic, or other materials may be used.

These floating bodies are designed to resist without bursting at a relatively low external pressure, for example up to a few hundredths of an atmosphere in the case of use of low-pressure fluid such as methanol at -50 ° C. or during the pre-emptied filling of the system.

Furthermore, these floating bodies are designed to withstand the maximum pressure that can prevail in the two-phase loop temperature and maximum thermal load, which can go up to ten bars. Advantageously, a sufficient number of floating bodies 8 are provided so that they form several superimposed layers, as shown in particular in FIGS. 2 and 3, whereby the floating bodies can be reconfigured spatially according to the surface and the geometry of the liquid-gas interface. For example, when the reservoir is inclined (Figure 3), the surface of the liquid-gas interface is greater and therefore, the floating bodies are reconfigured spatially to occupy all this surface but on a slightly smaller thickness.

In other words, all the floating bodies 8 form a thermal barrier with variable geometry.

Depending on the application and the shape of the tank, several shapes can be chosen for the floating bodies. Advantageously, it will be possible to choose a sphere shape, whereby the plurality of floating bodies will constitute a carpet of floating balls.

For example, we can choose a diameter for the balls between 0.5mm and 10 mm, or between 2mm and 5mm.

According to an advantageous aspect, all the floating bodies can have substantially the same shape, spherical or other. We then use a single type that is counted or weighed to arrive at the required amount of insertion into the tank.

Alternatively, when for example the reservoir may be a cylinder of a certain length and axis A, the floating bodies may be chosen as round rods of small diameter extending parallel to the axis A along the entire length of the cylinder, and arranged next to each other.

The reservoir 3 serves as expansion vessel for the working fluid of the two-phase loop and for possible pressure regulation. Therefore, the The liquid portion in the tank varies between a minimum non-zero volume in the tank and a maximum volume that does not occupy the entire interior volume 30 of the tank 3.

In order to prevent floating bodies 8 from sticking to the walls, in particular to the upper wall 32 at the bottom wall 33 of the tank, provision is made to arrange horizontal grids, namely an upper grid 82, and lower grid 83, their position being compatible with the minimum volume and the maximum volume of the liquid portion in the tank as mentioned above.

The mesh of the grids is small enough to prevent the floating bodies from crossing the grids. It is arranged to have the lower grid 83 a little below the minimum volume of liquid and the upper gate 82 a little above the maximum volume of liquid in the tank.

For systems subjected to violent or periodic longitudinal accelerations, vertical grids 13 (see Fig. 4) can prevent rapid movements of the liquid which could disturb the efficiency of the floating bodies. The free surface is then compartmentalized to obtain this anti-sloshing function.

The volume occupied by the plurality of said floating bodies can advantageously be between 3% and 12% of the total volume of the tank, so that a sufficient and optimal thickness of floating bodies is obtained, in particular for a tank having usual dimensions for this kind of application, namely three relatively small dimensions.

According to an optional feature, provision is made to wrap the floating bodies in a flexible structure, for example of the net or gauze type as shown in FIG. 3. In this case, at least one end of the envelope containing the floating bodies is attached to one side of the tank at a point of attachment 40.

It is not excluded to have several attachment points, provided that the flexible structure is extensible or has a certain length of slack. The floating bodies are trapped inside the net, which avoids one or more floating bodies does not separate from the group.

In addition, advantageously according to the invention, the reservoir comprises an inlet jet deflector 38 in the vicinity of the inlet orifice 31a or the inlet / outlet port 31 according to the configuration of the second conduit.

This inlet jet deflector 38 prevents a rapid inflow of liquid into the reservoir from creating a stream in the liquid phase directed directly to the liquid-gas interface. This deflector may be in the form of a U-shaped profile oriented downwards, or a bell or any other shape creating a sufficient deflection of the path of the liquid entering vertically upwards.

At the inlet orifice 31a and / or the outlet inlet 31 of the tank, a strainer 34, shown in FIG. 4, may optionally be provided to prevent one or more floating bodies from being introduced into the pipe. liquid to the evaporator.

The strainer 34 may be for example an iron straw type structure, or a sponge-type structure or a macroporous structure.

It can be further provided a filling port

39 closed after the initial filling of working fluid.

The first and second fluid communication circuits 4,5 are preferably tubular conduits, but could be other types of fluid communication conduits or channels (rectangular conduits, flexible, etc. ).

Similarly, the second fluid communication circuit 5 may be in the form of two separate independent pipes 5a, 5b (see Fig 1) or a single pipe with a 'T' connection 5c (see Fig 4).

These pipe configurations remain relevant when multiple and / or multiple condensers are connected in parallel.

In all cases, the second fluid communication circuit 5 connects the outlet of the condenser 2b to the inlet of the evaporator 1a, either indirectly via the reservoir (in the case of two independent conduits) or directly (case or single driving with 'T').

The device may further comprise a non-return member 60 in the form of a float arranged between the internal volume of the reservoir and the evaporator. This non-return member forms a valve intended to prevent the liquid present in the evaporator from moving towards the interior volume of the tank, in particular at the time of the sudden start.

Advantageously according to the invention, the device is devoid of any mechanical pump although the invention does not exclude the presence of a mechanical booster pump.

Claims

A heat transfer device, mainly subjected to earth gravity, adapted to extract heat from a hot source (11) and to return this heat to a cold source (12) by means of a two-phase working fluid contained in a closed general circuit, comprising:

at least one evaporator (1), having an inlet and an outlet,

at least one condenser (2),

a reservoir (3) having an internal volume (30) with a liquid portion 6 and a gas portion 7, and at least one inlet and / or outlet (31; 3a, 3b),

a second communication circuit (5), for fluid essentially in the liquid phase, connecting an outlet of the condenser to the tank and to the inlet of the evaporator, characterized in that the reservoir (3) comprises a plurality of floating bodies (8) separating the liquid portion from the gas portion, whereby the heat exchange between the liquid portion and the gas portion is slowed down.

2. Device according to claim 1, wherein said plurality of floating bodies (8) forms several superimposed layers.

3. Device according to one of claims 1 to 2, wherein said floating bodies (8) are interconnected by a flexible structure (35).

4. Device according to one of claims 1 to 2, wherein the reservoir (3) comprises a low grid (83) and a high grid (82), respectively arranged remotely the bottom wall and the upper wall of the tank, so that these two grids prevent the floating bodies from crossing.

5. Device according to one of claims 1 to 4, wherein all said floating bodies have substantially the same shape.

6. Device according to one of claims 1 to 5, wherein said floating bodies (8) are made of a material selected from stainless steel, teflon, borosilicate, carbon, ceramic.

7. Device according to one of claims 1 to 6, wherein said floating bodies have a spherical shape, preferably with a diameter of between 0.5 and 10 mm.

8. Device according to one of claims 1 to 7, wherein the volume occupied by the plurality of said floating bodies (8) is between 3% and 12% of the total volume of the tank.

9. Device according to one of claims 1 to 8, wherein the reservoir comprises an inlet jet deflector (38) in the vicinity of the inlet port.

10. Device according to one of claims 1 to 9, wherein 1 'evaporator (1) comprises a microporous mass (10) adapted to provide capillary pumping fluid in the liquid phase.

11. Thermal transfer device according to one of the preceding claims, mainly subjected to gravity, wherein 1 'evaporator (1) is placed below the condenser (2) and the tank, so that the gravity is used to move the liquid to the evaporator.