Patent Publication Number: US-2017370655-A1

Title: Thermal battery with encapsulated phase-change material

Description:
The present invention relates to the field of thermal batteries and more specifically of thermal batteries comprising a phase-change material. 
     Thermal batteries are generally used for heating the vehicle interior, notably in electric and hybrid vehicles or for preheating a heat-transfer fluid in a thermal management circuit. Thermal batteries may also be used for preheating the engine oil or the automatic transmission fluid of vehicles with an internal combustion engine. 
     A thermal battery with phase-change materials generally comprises an enclosure forming a reservoir inside which the phase-change material is placed, generally in encapsulated form. The performance of the thermal battery is thus dependent on the quantity of phase-change material that it is able to contain, coupled with the need for the fluid to circulate within the reservoir with the lowest possible pressure drops. 
     One of the objects of the present invention is therefore to at least partially overcome the disadvantages of the prior art and to propose an improved thermal battery. 
     The present invention therefore relates to a thermal battery comprising an enclosure comprising a fluid inlet and outlet and comprising within it an encapsulated phase-change material in the form of at least one tube, at least one tube being wound in a spiral within the enclosure. 
     The fact that at least one tube of phase-change material is wound into a spiral within the enclosure means that the amount of phase-change material within the thermal battery can be maximized and the efficiency of the battery can thus be improved since this battery has a higher heat capacity. 
     According to one aspect of the invention, the spiral winding of the tube is performed about an axis of winding parallel to the circulating flow of the fluid within said thermal battery. 
     According to another aspect of the invention, the spiral winding of the tube comprises an empty central part along the axis of winding. 
     According to another aspect of the invention, the thermal battery comprises longitudinal tubes of encapsulated phase-change material, said longitudinal tubes being positioned in the central part of the spiral winding of the tube. The longitudinal tubes therefore fill in the central part of the spiral winding and thus further increase the quantity of phase-change material contained within the thermal battery. 
     According to another aspect of the invention, the thermal battery comprises spacers between the tubes so as to create a space for the circulation of the fluid. 
     According to another aspect of the invention, the spiral winding of the tube is performed using a single tube. 
     According to another aspect of the invention, the walls of the tube are made of plastic. 
    
    
     
       Further features and advantages of the invention will become more clearly apparent from reading the following description, given by way of nonlimiting illustrative example, and from the appended drawings, in which: 
         FIG. 1  is a schematic perspective depiction of the arrangement of the tubes of encapsulated phase-change material within a thermal battery according to a first embodiment, 
         FIG. 2  is a schematic perspective depiction of the arrangement of the tubes of encapsulated phase-change material within a thermal battery according to a second embodiment. 
     
    
    
     In the various figures, identical elements bear the same reference numbers. 
     A thermal battery  1  generally comprises an enclosure (not depicted), preferably thermally insulated, comprising a fluid inlet and a fluid outlet. An encapsulated phase-change material in the form of at least one tube  3  is placed inside the enclosure. As  FIGS. 1 and 2  show, at least one of the tubes  3  is wound in a spiral and arranged within the enclosure. 
     The fact that at least one tube  3  of phase-change material is wound into a spiral within the enclosure means that the amount of phase-change material within the thermal battery  1  can be maximized and the efficiency of the battery can thus be improved since this battery has a higher heat capacity. 
     The spiral winding of this tube  3  is performed about an axis of winding A which is parallel to the circulating flow of the fluid (indicated by arrows in  FIGS. 1 and 2 ) within said thermal battery  3  so that the fluid can circulate perpendicular to the spiral winding. 
     The spiral winding within the thermal battery  1  is preferably performed using a single tube  3 . That makes it possible to limit the number of ends. Specifically, at each of its ends a tube  3  containing a phase-change material has a weld or a plug in order to encapsulate said phase-change material. Limiting the number of tubes  3  and, therefore, the number of these ends makes it possible to reduce the risks of leakage of the phase-change material. 
     However, it is entirely possible, without departing from the scope of the invention, to conceive of a spiral winding made up of several tubes, or else of a stack of several spiral windings within the enclosure. 
     The tube  3  inside which the phase-change material is encapsulated is preferably made of plastic so as to allow this spiral winding. 
     Because of the limited bend radius of the tube  3 , the spiral winding has an empty central part  5  along the axis of winding A. This central part may remain empty in order to ensure good circulation of the fluid as illustrated in  FIG. 1 . For example, for a tube  3  made of a plastic such as polycarbonate, a minimum bend radius without said tube  3  kinking is of the order of 25 mm. The empty central part  5  will then have a diameter of the order of 50 mm. 
     Alternatively, and as  FIG. 2  shows, this central part  5  may be filled in with longitudinal tubes  7  of encapsulated phase-change material. These longitudinal tubes  7  are then positioned parallel to the axis of winding A. 
     These longitudinal tubes  7  therefore fill in the central part  5  of the spiral winding and thus further increase the quantity of phase-change material contained within the thermal battery. 
     In order for the fluid to be able to circulate between the turns of the spiral winding of the tube  3  and between the longitudinal tubes  7  with limited pressure drops, the tubes  3  and  7  may comprise spacers so as to create a space for the circulation of the fluid. 
     Thus it may be clearly seen that the thermal battery  1  is optimized because of the special spiral layout of at least one tube  3  of phase-change material that makes it possible to maximize the quantity of phase-change material.