FR2463372A1 - Thermocouple generator with heat exchanger - consists of air heater and water cooling coils fitted with thermocouple pads - Google Patents

Abstract

The heat pump consists of a number of vertically arranged elements which are identical and arranged in parallel rows. Each of the elements consists of a pipe wound in a coil and contains the circulating water. The air circulator has a number of vertical passages in the distributor. The air flow is channelled in a duct to circulate between the water pipes. The system is fitted with an electrical network which provides power from the thermocouples.

Description

The present invention, due to the work of MM. Michel BERTHET, Jean
Claude KERMARREC and Robert RAVELET from MARCOUSSIS Laboratories, Compagnie Générale d'Electricité's research center, concerns a thermoelectric device for heat transfer between a first liquid fluid and a second fluid.

 Such a device comprises thermoelements (thermoelectric elements) mounted between thermal conductors associated with hot exchangers traversed by a hot fluid and cold exchangers traversed by a cold fluid.

There are two types of thermoelements, namely P type thermoelements, which transfer heat in the direction of the electric current, and N type thermoelements, which transfer it in the opposite direction to the electric current.

 Such devices can be used to generate a direct electric current when the thermal conductors are maintained at different temperatures by the hot fluid and the cold fluid, or, on the contrary, to maintain these thermal conductors at different temperatures in order to heat or to cool one fluid with respect to the other by circulating a direct electric current in the thermoelements.

In this case the heat is brought to the thermoelements and to the thermal conductors by the cold exchangers and transferred to the hot exchangers.

 The invention applies more particularly, but not exclusively to this latter type of device, the thermoelements being supplied with direct electric current to maintain a temperature difference between the thermal conductors. Such a device, called a "heat pump", can also be used for air conditioning purposes by heating or cooling a fluid from the ambient atmosphere.

For the construction of thermoelectric devices, it has already been proposed to make them comprise rows of thermoelements arranged in a direction OZ and traversed by a direct electric current whose direction is, when the row is followed, alternately in a direction OX and according the opposite direction XO. (To indicate the various directions in space, we refer to a OXYZ trirectangle trihedron defining OX directions, for example from left to right, OY, for example from front to back,
OZ for example from bottom to top, and vertical planes such as XOZ or YOZ, and horizontal planes such as XOY). On the two opposite faces of these thermoelements parallel to YOZ are welded heat exchangers allowing the transfer of heat from a cold fluid to a hot fluid.

 The mechanical structure is designed to reconcile the sealing requirements concerning the fluid circuits with the presence of differential thermal expansions. In the case of devices of large dimensions, the relative displacements due to these expansions are also important and the production of this structure is made particularly delicate by the fact that the known thermoelements based on bismuth telluride are extremely fragile. In practice, this results in fractures of these thermoelements.

 The object of the present invention is to produce a thermoelectric device for heat transfer between a first liquid fluid and a second fluid making it possible to avoid fractures of fragile thermoelements in a simple manner while having good thermal efficiency and maintaining a low size.

 It relates to a thermoelectric device with heat transfer between a first liquid fluid and a second fluid comprising - a row of thermoelements arranged in an OZ direction, each of these thermoelements having a first face towards an inclined OX direction, on the OZ direction , and a second face opposite the first, - this row being provided with thermal conductors of a first type welded on the first faces of the thermoelements, - thermal conductors of a second type welded on the second faces of the thermoelements, - and means for causing the thermoelements to pass through an electric current parallel to the direction OX, this current flowing in the direction OX or in the opposite direction XO depending on whether the thermoelement is of type P or N so that the thermoelement transfers heat in the same direction whatever its type between the exchangers of the first type and the exchangers of the second type, - the device if further comprising a first liquid fluid circuit in thermal contact with the conductors of the first type, and a second fluid circuit for circulating a second fluid in thermal contact with the conductors of the second type so as to carry out heat transfer between the two fluids, characterized in that the thermal conductors of the first type and the first fluid circuit constitute a sufficiently flexible structure so that, when expansions or contractions occur under the action of temperature variations, the displacements of the thermoelements and thermal conductors of the first type are imposed by the movements of the thermal conductors of the second type.

 Using the attached schematic figures, we will describe below, without limitation, how the invention can be implemented. It should be understood that the elements described and shown can, without departing from the scope of the invention, be replaced by other elements ensuring the same technical functions. When the same element is represented in several figures, it is designated by the same reference sign.

 Figure 1 shows a partially exploded perspective view of a device according to the invention.

 Figure 2 shows a partially torn side view of the same device.

FIG. 3 represents a cut front view of the same device.

 The device described operates thermally between a first fluid which is a strip constituting the cold source, and a second fluid which is air constituting the hot source. This air is heated by cooling the cooler water, that is to say that the device constitutes a water-air heat pump.

 This pump comprises a certain number of vertical rows (direction OZ) of thermoelements such as R1, R2, R10; R'1, R'2 identical and arranged along two lines of direction OY such as R1, R2, ... Rn, and R'1, R'2 .... arranged symmetrically with respect to a median plane parallel to YOZ not shown. Row R1 will be more particularly described.

The thermoelements are evenly spaced in each row, as are the rows in each row. Each row can be described as a succession of stages, each comprising a water thermal conductor, that is to say of the first type forming part of a water heat exchanger, a thermoelement of a type of conductivity P or N , an air thermal conductor, that is to say of the second type forming part of an air heat exchanger, the preceding stage and the following stage comprising a thermoelement of an opposite type of conductivity.

 Three circuits are connected to these rows, namely an electrical circuit, and a first and a second fluid circuit which are a water circuit and an air circuit.

The electric circuit is intended to make the thermoelements cross by a direct electric current directed according to OX, for example for thermoelements of even rank such as T2, and according to XO for thermoelements of odd rank such as T1 and T3, the necessary electrical connections being carried out between successive thermoelements of each row via the thermal conductors of the first and second type alternately. The rows are successively supplied in series from two terminals such as 2 each arranged at a suitable end of one of the two rows located at the two ends of a line. Such a connection
in series makes it possible to obtain an acceptable impedance of the heat pump despite the very low impedance of each row. The connections between rows are made by bars such as 4 arranged alternately in the lower part and in the upper part.

All of the device's air circuits are essentially constituted by two vertical air ducts such as 28 each corresponding to a line and forming two symmetrical air layers to the left and right of the device.

 Each conduit such as 28 is mainly limited by two vertical walls parallel to the plane YOZ (FIGS. 2 and 3), an internal wall 34 constituted by a sheet of steel or aluminum, and an external wall 32 rendered for example insulating by the presence of a lining layer 33 and whose role is to channel the air circulation and to avoid the introduction of objects liable to obstruct the duct. It can also be limited at the front and rear by two plates parallel to the XOZ plane and not shown.

 The entire volume of the duct is occupied by a set of heat exchange blocks such as 26 constituted by vertical fins having a large surface area for heat exchange with air, as known. Each of these blocks is part of one (or more) air heat exchangers comprising an air thermal conductor. These blocks follow one another vertically opposite a row, and horizontally from front to back, opposite the successive rows of the line. They are made of a metal that is a good thermal conductor such as aluminum. They are fixed to the internal wall 34 by welding. To prevent them from creating short thermal circuits they can be separated from each other if they are made of a very good conductive metal such as copper or aluminum; The air exchanger can be in one piece if it is made of steel strip.

The thermoelements are thermally connected to the sheet 34 by the intermediary of thermal conductors of the second type constituted for example by heat conduction blocks 36, made of aluminum, and glued by their external face to this sheet via a thin layer of electrically insulating glue.

 The opposite face carries a protuberance on which a thermoelement is welded, the thickness decreasing from this protuberance to avoid as much as possible thermal short-circuits relative to the water exchangers.

 To ensure the necessary electrical connections between two successive thermoelements such as T2 and T3 or more generally T2n and T2n + 1, n being an integer, and to facilitate the manufacture and assembly of thermal air conductors, these are produced in pairs , except at the beginning (and at the end of the row if, as shown - the number of thermoelements is even). Each pair consists of a single block such as 36, the internal face of which carries two protrusions.

 The water circuit comprises, for each line, an inlet manifold 6 bringing lukewarm water (150C) and an outlet manifold 8, bringing cooled water (oc), these two collectors being arranged parallel to OY above and below the row of rows. The rows are supplied in parallel between these two collectors, each by a conduit such as 10 which passes in series through all the water heat exchangers in the row.

The lower end of this duct is situated substantially vertically from its upper end, but it presents between the two a complex sinuous shape constituted by an alternating succession of connecting sections such as 14 and of heat exchange sections such as 12 (see figure 2).

Each heat exchange section is arranged in a vertical plane parallel to OY, in contact with a thermal water conductor 16. It is curved so as to enter and exit the thermal conductor on the same side of the row, for example the rear side. It has in this plane, the shape of a U whose branches are parallel to the direction OY, and welded in grooves formed by bending in the copper plate constituting this conductor, this arrangement in U increasing the heat exchange surface and facilitating assembly. One branch is above a thermoelement soldered to the copper plate and the other below. Its section is substantially circular to facilitate its manufacture.

Each connecting section has the shape of a median U between two extreme U's. The median U is arranged in a plane parallel to YOZ, the branches of the U being parallel to OY, one above the other below.

The two extreme U's are superimposed in the two horizontal planes of the two branches of the middle U so as to be connected on the one hand to these two branches and on the other hand to the ends of the heat exchange sections passing through two thermal water conductors succeeding in the stack.

All the heat exchange sections overlap, as do the connection sections. The median U has in particular the function of making the water circuit sufficiently flexible by facilitating the deformation of the heat exchange section.

The heat exchange sections must have a low thermal resistance when crossing their wall. The connecting sections must have a strong longitudinal electrical resistance and could in some cases be made of an insulating material such as polyvinyl chloride. It has however been found preferable to avoid collages, expensive in terms of labor if we want them to be certainly waterproof, and, for this, to constitute the whole of the conduit by a single uniform metal tube with a thickness of sufficiently weak wall - (less than 0.3 mm), made of a relatively electrically and mechanically resistant metal. This material is stainless steel. In the example described, the thickness is 0.1 mm, the outside diameter being 2.5 mm. It currently seems difficult to further reduce this thickness. The electrical resistance is increased by the elongation resulting from the presence of the median U.

The heat exchange sections are welded to the water heat conductors, such as 16, and cooperate with them to form water heat exchangers, that is to say that these heat conductors, which are part of the row, transmit directly the heat between the water and the thermoelements of the stack.

In order to ensure the necessary electrical connection between two successive thermoelements such as T1 and T2 or more generally such as
T2n-1 and T2n, n being an integer, and to facilitate the manufacture and assembly of thermal water conductors, these are produced in pairs. Each pair is formed from a suitably folded copper strip (see Figures 1 and 3). The length of this strip is arranged along OZ and its width along OY. The two end portions of this strip constitute the two thermal conductors and are flat, except for the grooves intended to receive the water conduit. The intermediate portion 17 of the length of the strip is folded in U shape with the branches of the U substantially perpendicular to the extreme portions, that is to say parallel to OX, and the base of the U in the shape of a semicircle being further from the row of thermoelements than the extreme portions. The length of these branches is chosen to be sufficient to ensure flexibility avoiding excessive force on the thermoelements via the mechanical connection thus created, the shape of this U can be possibly modified to further increase flexibility.

This length is for example 6mm if the strip has a width of 25mm and a thickness of 0.8mm, this thickness being able to be reduced to 0.6mm in the base of the U. The electrical connection can of course, instead of being produced by a copper strip folded in a U, the entry by a stack of copper foil strips welded on the two thermal conductors.

 The thermoelements are welded to the end portions by means of circular pins 18.

The rigidity of each row and of the row line is ensured by the sheet 34, which is fixed by the usual means to the frame of the device, the two rows of rows being disposed between the two sheets 34 which hold them.

 The water-air heat pump thus produced can advantageously be used for heating the air in a living room from a water circuit.

Claims (9)

1 / Thermoelectric device for heat transfer between a first liquid fluid and a second fluid comprising - a row (R1) of thermoelements (T1, T2, T3) arranged in a direction OZ, each of these thermoelements having a first face towards a direction OX inclined to the direction OZ, and a second face opposite to the first, this row being provided with - thermal conductors of a first type (16) welded on the first faces of the thermoelements, - thermal conductors (36) of a second type welded on the second faces of the thermoelements, - and means (2, 4) for making the thermoelements travel through an electric current parallel to the direction OX, this current flowing in the direction OX or in the opposite direction XO according that the thermoelement is of type P or N so that the thermoelement transfers heat in the same direction whatever its type between the exchangers of the first type and the exchangers of the second typ e, - the device further comprising a first fluid circuit (10) for circulating a first liquid fluid in thermal contact with the conductors of the first type, - and a second fluid circuit (28) for circulating a second fluid in thermal contact with the conductors of the second type so as to produce a heat transfer between the two fluids, characterized in that the thermal conductors of the first type (16) and the first fluid circuit (10) constitute a structure which is sufficiently flexible to that, when dilations or contractions occur under the action of temperature variations, the displacements of thermoelements (T1, T2, T3) and thermal conductors of the first type (16) are imposed by the displacements of thermal conductors of the second type (36). 2 / Device according to claim 1, wherein the first fluid circuit is con # constituted by a liquid conduit (10) comprising a succession of heat exchange sections (12) welded to thermal conductors of the first type (16) so as to constitute heat exchangers of a first type, the successive heat exchange sections being connected in series by connection sections (14), characterized in that these connection sections (14) have a sinuous shape which is easily deformable elastically so as to increase the flexibility of the circuit (10). 3 / Device according to claim 2, characterized in that each thermal conductor of the first type (16) has the form of a metal plate substantially perpendicular to the direction OX, - each heat exchange section (12) of said conduit liquid (10) being constituted by a metal tube bent in a U shape and welded at least by its branches to this plate, its branches being parallel to an OY direction substantially perpendicular to the OX and OZ directions. 4 / Device according to claim 3, characterized by the fact that each connection section (14) has the form of a succession of three U connected to the two U of the two heat exchange sections on either side of this section of connection, with alignment of the outlet branch of a U with the inlet branch of the next U, these three U being a median U between two extreme U's, the median U being arranged in a plane parallel to YOZ with branches parallel to OY, the two extreme U's being superimposed in two planes perpendicular to OZ. 5 / Device according to claim 2, characterized in that the thermal conductors of the first type (16) are joined by pairs of two consecutive thermal conductors, each pair being formed by a strip whose length is arranged according to OZ, the two portions extremities of this strip being flat and constitute the two thermal conductors (16), an intermediate portion (17) of this strip being folded in a U shape with the branches of the U substantially perpendicular to the end portions, so that the presence of this portion intermediate provides a flexible electrical connection between the two thermal conductors (16) of the first type of the pair and between the two consecutive thermoelements (T1, T2) soldered to these thermal conductors, - an electrical connection being provided between two consecutive thermal conductors of the second type (36) when these two conductors are soldered to the second faces of two thermoelements (T2, T3), the first of which s faces are soldered to two thermal conductors of the first type (16) appearing in two consecutive pairs, so as to allow the electric current to pass from one thermoelement (T2) to the next (T3) alternately by these electrical connections between thermal conductors of the second type and by said strips comprising a pair of thermal conductors of the first type (16). 6 / Device according to claim 5, characterized in that said strips are further folded in their two end portions (16) to form grooves receiving the branches of the U of said heat exchange sections (12). 7 / Device according to claim 5, characterized in that said electrical connection between two thermal conductors of the second type is made by the fact that these two thermal conductors are constituted by the same block of thermal conduction (36), - the blocks of successive thermal conduction (36) of the row being glued by an external face to an internal face of the same flat metal sheet (34) by means of an electrically insulating adhesive.  8 / Device according to claim 7, characterized # in that the thermoelements (T2, T3) are welded on protrusions of an internal face of said heat conduction blocks, the thickness of these blocks decreasing from these protuberances so as to increase the average distance and the thermal resistance between these blocks and the thermal conductors of the first type (16). 9 / Device according to claim 8, characterized in that the heat exchange blocks with fins (26) are welded to the outer face of said metal sheet (34) to ensure good heat exchange with a second gaseous fluid.