Abstract:
A thermal generator ( 1 ) comprises at least one thermal flow generation unit ( 2 ) that is provided with at least one thermal module ( 3 ) each containing a magnetocaloric member ( 4 ) through which a coolant flows. A magnetic arrangement ( 9 ) is actuated for alternatively subjecting each magnetocaloric member ( 4 ) to a variation in magnetic field, the alternating movement of the coolant is synchronized with the magnetic field variation, the magnetocaloric member ( 4 ) is integrated into a closed flow circuit ( 6 ) that connects the two opposite ends ( 7 ) of the magnetocaloric member ( 4 ), and the closed circuit includes a single element ( 5 ) for moving the coolant through the magnetocaloric member ( 4 ).

Description:
This application is a National Stage completion of PCT/FR2009/001129 filed Sep. 23, 2009, which claims priority from French patent application serial no. 08/05278 filed Sep. 25, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to a heat generator with magnetocaloric material comprising at least one thermal flux generation unit provided with at least one thermal module containing a magnetocaloric element across which a heat transfer fluid circulates according to an alternating movement on both sides of the magnetocaloric element, the heat generator comprising also a magnetic arrangement put in motion to alternately subject the magnetocaloric element to a magnetic field variation and create alternately in the magnetocaloric element a heating cycle and a cooling cycle, generating the creation of, and then maintaining, a temperature gradient between the two opposite ends of the magnetocaloric element, the alternating displacement of the heat transfer fluid being synchronized with the magnetic field variation, the magnetocaloric element being integrated in a closed heat transfer fluid circulation circuit connecting the two opposite ends of the magnetocaloric element and the closed circuit comprising a single means of displacement of the heat transfer fluid through the magnetocaloric element in both displacement directions. 
     BACKGROUND OF THE INVENTION 
     Magnetic refrigeration technology at ambient temperature has been known for more than twenty years and the advantages it provides in terms of ecology and sustainable development are widely acknowledged. Its limits in terms of its useful calorific output and its efficiency are also well known. Consequently, all the research undertaken in this field tends to improve the performance of such a generator, by adjusting various parameters, such as the magnetization power, the performance of the magnetocaloric element, the surface for heat exchange between the heat transfer fluid and the magnetocaloric elements, the performance of the heat exchangers, etc. 
     One of the difficulties in the realization of generators that use one or more magnetocaloric elements lies in the exchange of thermal energy between these magnetocaloric elements and the circuit(s) that use, consume or exchange the thermal energy with the generator, and that are connected with the latter. A solution for performing this exchange consists in making a heat transfer fluid, liquid or not, circulate through the magnetocaloric elements, in synchronization with the variation of the magnetic field which the magnetocaloric elements are subjected to and to perform then a thermal exchange between the heat transfer fluid and the circuits. 
     The publication WO 03/016794 gives an example of implementation in which the magnetocaloric elements are in a closed fluid circuit including a circulation pump for the heat transfer fluid, located outside of the thermal module and requiring specific control and connection means. 
     In the French patent application no. 07/07612, the applicant presents a heat generator with magnetocaloric material in which the heat transfer fluid is circulated between the magnetocaloric elements and two exchange chambers called a hot chamber and a cold chamber. This circulation is carried out by means of two sets of pistons that are positioned opposite the magnetocaloric elements and driven by a control cam connected to an actuator. 
     This generator nevertheless has a disadvantage related to the need for two cams to drive the two sets of pistons positioned opposite each magnetocaloric element. This leads to an increase of the number of parts making up the generator, and more specifically of the number of moving parts and thus to an increase of the risk of malfunction, to a higher risk of wear due to the permanent contact between the cam and the pistons, and to a degradation of the efficiency of the generator. Furthermore, the high number of parts also increases the space requirement of the generator and thus limits its ability to be integrated in environments in which the available space is reduced and limited. 
     SUMMARY OF THE INVENTION 
     The present invention aims to overcome these disadvantages by offering a heat generator in which the number of moving elements is reduced and whose configuration allows an important reduction of the space requirement of the generator. 
     For this purpose, the invention concerns a heat generator comprising a thermal flux generation unit comprises a field closing device arranged to loop the magnetic flux generated by the magnetic arrangement and in that the field closing device is provided with a control device of the means of displacement. 
     The closed circuit can be made of one or several conduits or channels connecting the opposite ends of the magnetocaloric element. 
     The integration of a single means of displacement allows limiting the number of parts of the heat generator and thus reducing its production cost. Likewise, the use of a device necessary for the operation of the generator as a device allowing to actuate the means of displacement of the heat transfer fluid allows for an even further reduction of the number of parts making up the generator and, furthermore, to reduce its space requirement. 
     The means of displacement can be a piston that moves in a jacket formed in the corresponding closed circuit. 
     Advantageously, the field closing device can be made out of a magnetizable material and be coupled magnetically with the mobile magnetic arrangement. 
     In a first embodiment variant, the control device can be a cam profile with an approximately sinusoidal shape whose amplitude determines the stroke of the pistons and whose sinusoidal phase corresponds globally to a heating cycle and to a cooling cycle of the magnetocaloric elements. 
     For that purpose, the piston can comprise a groove in which the cam profile circulates. 
     In a second embodiment variant, the piston can include a zone of magnetizable material and can be coupled magnetically with the field closing device making up the control device. 
     In a first embodiment, the thermal flux generation unit can be provided with several thermal modules and have a circular structure in which the magnetocaloric elements are arranged on a circle around a central axis, the magnetic arrangement can be rotated around the central axis and the magnetocaloric elements can be arranged between the magnetic arrangement and the field closing device. 
     In this configuration, the field closing device can be coupled magnetically with the magnetic arrangement and the closed circuit and the jacket of the piston can be made of two circular parts meant for being assembled, the circular parts can be approximately symmetrical with respect to their assembly plane, and can each comprise at least one recess forming a part of the jacket of a piston and a groove with open ends and forming a connection channel between the recess and the corresponding magnetocaloric element. 
     According to a second embodiment, the thermal flux generation unit can have a linear structure in which the magnetocaloric elements are aligned and the magnetic arrangement can be driven in reciprocating translation along the magnetocaloric elements. 
     In this embodiment, the field closing device can have a yoke-shaped profile whose both legs are provided, on their internal faces, with permanent magnets with opposite polarities and making up the magnetic arrangement and the control device can have the shape of a driving pin housed in a corresponding groove of each piston. 
     As a variant, the field closing device can also have a yoke-shaped profile whose both legs are provided, on their internal faces, with permanent magnets with opposite polarities and making up the magnetic arrangement, the control device can nonetheless comprise two permanent magnets with different polarities located at a distance and opposite from each other and the piston can comprise a magnet arranged with respect to the permanent magnets of the control device so as to be pushed back by each of the latter, and thus follow their displacement. The movement of the control device thus leads to that of the piston, without contact between them, apart from the magnetic arrangement. For that purpose, the piston can be located approximately between the two permanent magnets of the control device and preferably above them. 
     In order to ensure that the heat exchange between the magnetocaloric element and the heat transfer fluid occurs after a phase change of the magnetocaloric element, the generator can also comprise, in its linear version, an offset means suitable for anticipating and/or delaying the movement of the piston with respect to that of the magnetic arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention and its advantages will be better revealed in the following description of an embodiment given as a non limiting example, in reference to the drawings, in which: 
         FIG. 1  is an exploded view of a heat generator with a circular configuration, according to a first embodiment of the invention, 
         FIG. 2  is a transparent front view of the thermal module of the generator of  FIG. 1 , 
         FIG. 3  is a section view along plane III-Ill of  FIG. 2 , 
         FIG. 4  is a view of detail B of  FIG. 3 , 
         FIG. 5  is an exploded view of an embodiment variant of a circular heat generator, 
         FIG. 6  is a longitudinal sectional view of the generator represented in  FIG. 5 , 
         FIGS. 7A and 7B  are perspective views of a heat generator with a linear configuration, according to a second embodiment of the invention, in two positions of the magnetic arrangement, and 
         FIG. 8  is a partial section view of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the implementation examples shown, identical parts or sections have the same numerical references. 
       FIGS. 1 to 6  represent a heat generator  1  according to a first embodiment of the invention, in which the structure of the generator  1  is circular. 
     The heat generator  1  represented in  FIGS. 1 to 4  comprises only one thermal flux generating unit  2 . This unit is provided with several thermal modules  3  each comprising a magnetocaloric element  4  across which a heat transfer fluid is circulated by a means of displacement  5  in the form of a piston. For simplification reasons, only one piston  5  is represented in  FIG. 1 . The magnetocaloric elements  4  are arranged in a circle around a central axis A and a magnetic arrangement  9  rotates around the central axis A so as to submit the magnetocaloric elements  4  to a variable magnetic field to perform alternately a heating cycle and a cooling cycle in the latter. 
     The magnetocaloric elements  4  are permeable to the heat transfer fluid and can be made of one or several magnetocaloric materials. They comprise open fluid passages that can be made of the pores of a porous material, the mini or micro-channels machined in a full block or obtained by assembling for example superposed grooved plates. 
     The heat transfer fluid is moved in each thermal module  3  in a reciprocating movement through the magnetocaloric element  4 , on either side of the latter. For that purpose, the thermal module  3  also comprises a closed circuit  6  for the circulation of the heat transfer fluid. This circuit is made of channels connecting the two opposite ends  7  and  8  of the magnetocaloric element  4  and comprises a means of displacement  5  that moves the heat transfer fluid in a reciprocating movement. In the represented examples, the means of displacement  5 ,  50 ,  60  is a piston. It can nevertheless be realized in any other form, such as a membrane for example, suitable for generating reciprocating movement of the heat transfer fluid. 
     All the described embodiments show that by fluidly connecting both ends  7  and  8  of the magnetocaloric element  4  only one means of displacement  5 ,  50 ,  60  is needed to circulate the heat transfer fluid in both directions through the magnetocaloric element  4 . This makes the construction of the heat generator according to the invention easier and also limits its space requirement since, on the one hand, only one means of displacement  5 ,  50 ,  60  is required for the circulation of the heat transfer fluid in each thermal module and, on the other hand, this implies the installation of only one control device of the means of displacement. 
     The heat generator  1  also comprises a magnetic arrangement  9  put in motion to subject alternately each magnetocaloric element  4  to a magnetic field variation and create alternately in the magnetocaloric element  4  a heating cycle and a cooling cycle, generating the creation of, and then maintaining, a temperature gradient between the two opposite ends  7  and  8  of the magnetocaloric element  4  and the reciprocating movement of the heat transfer fluid is synchronised with the variation of the magnetic field. 
     The piston  5  is moved in a jacket  11  by means of a cam profile  19  forming a control device, provided on the side of a field closing device  30  arranged to loop the magnetic flux generated by the magnetic arrangement  9 . This field closing device  30  is located opposite the jacket  11  of the piston  5 . For minimizing the space requirement, all pistons  5 , the magnetocaloric elements  4 , the magnetic arrangement  9  and the field closing device  30  are arranged concentrically around the central axis A. The jacket  11  comprises an opening  17  to facilitate positioning the cam profile  19  in a corresponding groove  18  of the piston  5  in order to actuate the latter. For that purpose, the cam profile  19  has an approximately sinusoidal shape, with an amplitude that determines the stroke of the pistons  5  and a sinusoidal phase that corresponds globally to a heating cycle and a cooling cycle of the magnetocaloric elements  4 . Rotation of the field closing device  30 , and thus of the cam profile  19 , leads to the displacement of the pistons  5 , according to a reciprocating movement. This rotation is generated through the intermediary of the rotation of the magnetic arrangement  9 , with which the field closing device  30  is coupled magnetically. 
     For that purpose, the magnetic arrangement  9  is made of an assembly of magnetized parts  20  and non magnetized parts  21  and the field closing device  30  is made in the shape of a ring out of a magnetizable material, for example iron, comprising bosses or protuberances  22  located opposite the magnetized parts  20  to allow magnetic coupling with the magnetic arrangement  9  and obtain this way the rotational drive of the field closing device  30  when the magnetic arrangement  9  rotates. Even though the field closing device  30  represented comprises four bosses  22 , only one boss is sufficient to obtain the magnetic coupling. 
     The magnetic arrangement  9  can be coupled with an actuator (not represented) in order to be mobile in rotation with respect to the magnetocaloric elements  4 . The simultaneous movement of the magnetic arrangement  9  and of the field closing device  30  in particular avoids the generation of eddy currents. The magnetocaloric elements  4  are arranged around the magnetic arrangement  9  and between the latter and the field closing device  30 . This way, displacement of the magnetic arrangement  9  subjects the magnetocaloric elements  4  to a magnetic field variation and simultaneously leads to displacement of the field closing device  30 . 
     The heat generator  1  represented in  FIGS. 1 to 4  has a configuration that favours a limited space requirement, in particular thanks to the concentric structure around the central axis A and formed by the magnetic arrangement  9 , the field closing device  30  in form of a ring, the magnetocaloric elements  4  also arranged concentrically around the central axis A and finally the pistons  5  integrated in the jackets  11  provided in two circular parts  12  and also concentric with the above-mentioned elements. Such a heat generator  1  can thus have a width of a few centimeters. 
     The two circular parts  12  are symmetrical with respect to their assembly plane and comprise recesses  15  which form a part of the jacket  11  of the pistons  5  and a groove  16  fluidly connecting each recess  15  with the corresponding magnetocaloric element  4 . The circular parts  12  are arranged so that the cam profile  19  is positioned in the groove  18  of each piston  5 . The recesses  15  and the grooves  16  of the circular parts  12  can be produced by boring, drilling, moulding or any other similar process and form a part of the closed circuit  6  for the circulation of the heat transfer fluid. 
     The generator  1  also comprises two protective covers  23  that tightly close the grooves  16  of the circular parts  12 . 
     The heat generator  100  represented in  FIGS. 5 and 6  is made according to a variant of the embodiment in which the structure of the generator  100  is circular and comprises a circular thermal flux generation unit  102 . The configuration of this generator is approximately identical with that of the generator  1  represented in  FIGS. 1 to 4  and offers the same advantages, in particular regarding the reduced space requirement. However, the piston  50  is driven differently. As previously, the control device of the pistons  50  is made up of the field closing device  31 . But the pistons  50  are provided with a ring  51  made of a magnetisable material that couples magnetically with the field closing device  31  and follows the rotation of the latter without contact. The field closing device  31  can also comprise a cam profile  19  like that of the heat generator  1  of  FIGS. 1 to 4 . However, in this example, it is not necessary to provide a groove in each piston  50 , since the field closing device  31  drives each piston  50  without any contact, by magnetic coupling. There is thus no risk of wear between the control device and the pistons  50 . The pistons  50  are preferably approximately cylindrical and have an area of magnetizable material  51  in the form of a ring mounted in a circular groove of the piston  50 . 
     Any other piston form can also suit and can be determined to minimize the hydraulic head losses. 
       FIGS. 7A ,  7 B and  8  represent a heat generator  200  according to a second embodiment of the invention, in which the structure of the generator  200  is approximately linear.  FIG. 8  represents more specifically, at the level of the cut section, the closed heat transfer fluid circulation circuit  6 , the magnetocaloric element  4  and the piston  60 . 
     The thermal flux generation unit  202  is linear, the magnetocaloric elements  4  being aligned. In the represented example, the heat generator  200  is made up of only one unit  202  comprising a thermal module  3 . The invention covers, of course, heat generators comprising several thermal flux generation units. The number of units and thermal modules will be determined as a function of the power of the heat generator. 
     The field closing device  32  has a yoke-shaped profile whose both legs are provided, on their internal faces, with permanent magnets  24  with opposite polarities and making up the magnetic arrangement  9 . The reciprocating translational movement (according to arrow F) of the field closing device  32  and of the magnetic arrangement  9  subjects the magnetocaloric elements  4  aligned between the magnets  24  to a magnetic field variation. Furthermore, the field closing device  32  comprises, for each piston  60 , a driving pin  192  to drive it. The driving pin ensures the mechanical coupling between the field closing device  32  and the heat transfer fluid displacement means, here in the form of pistons  60 . This way, the movement of the magnetic arrangement  32  leads on the one hand to a variation of the magnetic field in the magnetocaloric elements  4 , and thus to an alternation of heating and cooling cycles of the latter and, on the other hand, to the simultaneous movement of the driving pins  192  which in turn move the pistons  60  in the corresponding jacket  11 , and thus the heat transfer fluid in the closed circuit  6 . 
     Furthermore, the represented generator  200  comprises an offset means  10  that allows offsetting the movement of the piston  60  with respect to that of the magnetic arrangement  32 . This means is implemented in the form of two stops  13 ,  14  made in a U-shaped part that is mounted on the field closing device  32 . These two stops  13 ,  14  are arranged underneath the piston  60  and co-operate with the driving pin  192 . The latter is thus driven by these two stops  13 ,  14  when the field closing device  32  moves according to arrow F. They allow controlling the movement of the piston  60  in synchronism with the movement of the field closing device  32 . 
     So, in  FIG. 7A , when the field closing device  32  moves towards the right, it only drives the driving pin  192 , and thus the piston  60  associated to the latter, when the stop  14  comes in contact with the driving pin  192 , position represented in  FIG. 7B . During this movement, the magnetocaloric element  4  has left the magnetic field of the magnets  24  and was subjected to a cooling cycle without movement of the piston  60 . The heat exchange between the hear transfer fluid and the magnetocaloric element  4  thus takes place when the stop  14  arrives in contact with the driving pin  192  and the field closing device  32  moves further towards the right in the figure, thus moving the piston  60  in the closed circuit  6 . The complete stroke of the field closing device  32  is not transmitted totally to the piston  60 . 
     Conversely, during the movement of the field closing device  32  towards the left on  FIG. 7B , the magnetocaloric element  4  is subjected to a magnetic field and thus to a heating cycle, without any move of the piston  60 , and thus of the heat transfer fluid. When the driving pin  192  comes in contact with the stop  13 , the latter drives it, which induces a movement of the corresponding piston  60 , and thus movement of the heat transfer fluid in the closed circuit  6  and thus heat exchange between the latter and the magnetocaloric element  4 . 
     Such an offset means enables optimizing the heat exchange between the heat transfer fluid and the magnetocaloric element  4  by performing it after a phase change of the magnetocaloric element  4 , and thus increasing the efficiency of the generator  200 . 
     In a non represented variant, the field closing device can have a yoke-shaped profile whose both legs are provided, on their internal faces, with permanent magnets with opposite polarities and making up the magnetic arrangement, the control device can nonetheless comprise two permanent magnets with different polarities located at a distance and opposite of each other and the piston can comprise a magnet arranged with respect to the permanent magnets of the control device so as to be pushed back by each of the latter, and thus follow their displacement. The displacement of the control device thus leads to that of the piston, without contact between the latter, apart from the magnetic arrangement. For that purpose, the piston can be located approximately between the two permanent magnets of the control device and preferably above them. 
     Even though all attached drawings illustrate heat generators  1 ,  100 ,  200  comprising only one thermal flux generation unit  2 , the invention also provides for the production of a heat generator having a stepped structure with several thermal flux generation units  2 ,  102 ,  202 . Such a configuration allows increasing the efficiency of the heat generator according to the invention. 
     Possibilities for Industrial Application: 
     This description shows clearly that the invention allows reaching the goals defined, that is to say to offer a heat generator  1 ,  100 ,  200  with a simple design and with a reduced space requirement, limiting the number of moving elements for the circulation of the heat transfer fluid in the thermal modules  3 . 
     Such a heat generator  1 ,  100 ,  200  can find an application, in industry as well as domestic, in the area of heating, air conditioning, tempering, cooling or others, at competitive costs and with reduced space requirements. 
     Furthermore, all parts making up this heat generator  1 ,  100 ,  200  can be manufactured according to reproducible industrial processes. 
     The present invention is not restricted to the example of embodiment described, but extends to any modification or variant which is obvious to a person skilled in the art while remaining within the scope of the protection defined in the attached claims.