Heating device for heating a heat transfer medium, especially in a vehicle

Abstract

Heating device for heating a heat transfer medium, in particular in a vehicle, comprising at least one heating element (14) constructed with PTC material with a plurality of heat transfer medium flow channels (30) passing through the heating element (14), wherein a housing (12) accommodating the at least one heating element (14) is provided, characterized in that at least one heating element (14) is arranged in the housing (12) such that it is possible to allow heat transfer medium to flow around it on an outer surface of at least one heating element outer wall (20, 22, 24, 26).

Description

The present invention relates to a heating device for heating a heat transfer medium, for example the air to be introduced into a vehicle interior. In vehicle manufacturing, electrically operated heating systems are increasingly used, particularly in connection with purely electric or hybrid vehicles, to provide the thermal energy required, for example, to heat the vehicle interior. These systems utilize, for instance, so-called PTC heating elements. By circulating a heat transfer medium, such as the air introduced into the vehicle interior, heat energy is transferred to the heat transfer medium by circulating heat around the PTC heating elements within the system. The PTC heating elements, which are generally block-shaped, are positioned between various supporting and electrically contacting components or material layers. This arrangement, combined with the thermal shielding of the PTC heating elements, reduces the efficiency of heat transfer to the medium being heated. US patents 5,206,476 A, DE 101 18 599 B4, US patents 3,927,300 A, 4,855,571 A, 4,232,214 A, 5,125,070 A, and 4,855,570 A each describe a heating device with a heating element made of PTC material. DE 10 2008 015 853 A1 describes a heated plastic windscreen for motor vehicles. The object of the present invention is to provide an electrically operated heating device for heating a heat transfer medium, in particular in a vehicle, which has an increased efficiency in heat transfer to the medium to be heated. According to the invention, this problem is solved by a heating device for heating a heat transfer medium, in particular in a vehicle, according to claim 1. This heating device comprises at least one heating element constructed with PTC material with a plurality of heat transfer medium flow channels passing through the heating element. By providing a heating element, or at least one element constructed with PTC material, such that it has multiple channels through which the heat transfer medium can flow, a comparatively large surface area is provided. This allows for direct heat transfer contact between the medium to be heated and the PTC material of the heating element, without any additional components obstructing the heat transfer. This results in high efficiency in the transfer of heat energy, generated by the electrical excitation of the PTC material in the heating element, to the heat transfer medium. In order to efficiently utilize the volume provided in the radiator for flow with low flow resistance, it is proposed that the heat transfer medium flow channels extend essentially parallel to each other in the radiator between an inflow end face and an outflow end face. In particular, to achieve low flow resistance, it can be provided that at least one heat transfer medium flow channel, preferably each heat transfer medium flow channel, has a cross-sectional geometry that does not change substantially in a longitudinal direction of the flow channel and / or a cross-sectional dimension that does not change substantially in a longitudinal direction of the flow channel. In a further embodiment, to adapt to different geometries of the system areas carrying the heat transfer medium to be heated, at least one heat transfer medium flow channel, preferably each heat transfer medium flow channel, can have a cross-sectional geometry that changes in a flow channel longitudinal direction and / or a cross-sectional dimension that changes in a flow channel longitudinal direction. In order to define the different heat transfer medium flow channels in the radiator, at least two heat transfer medium flow channels can be limited by a flow channel partition of the radiator separating them, or / and at least one heat transfer medium flow channel can be limited by an outer wall of the radiator. For a simple yet stable design, it is proposed that at least some, preferably all, of the flow channel partitions and / or radiator outer walls provide a radiator structure formed from a single block of material. This results in an essentially monolithic radiator structure, which ensures good structural cohesion even with comparatively complex geometries of the heat transfer medium flow channels and prevents leakage of the heat transfer medium from these channels. A simple design can be achieved by ensuring that at least some, preferably all, of the flow channel partitions and / or radiator outer walls have a substantially constant wall thickness in a circumferential direction and / or a longitudinal direction of the flow channel. Of course, it is also possible, for example, if increased mechanical stresses can occur in certain areas of the radiator, to provide flow channel partitions or radiator outer walls with varying, particularly greater or increasing, wall thicknesses in such areas. Providing the radiator with a substantially constant wall thickness can be easily achieved, for example, if at least one heat transfer medium flow channel, preferably each heat transfer medium flow channel, has a polygonal cross-sectional geometry. A stable structure of the radiator, despite a large volume of heat transfer medium flow channels and a large heat transfer surface of the radiator, can be achieved, for example, by having at least some of the heat transfer medium flow channels form a honeycomb-like opening structure. Barium titanate, for example, can be used as a PTC material for the construction of the radiator. In order to generate heat in the radiator by electrically exciting it, contact elements for electrical contacting the radiator can be provided on the radiator. A monolithic structure of the radiator, provided by a single block of material, can be achieved, for example, by manufacturing the radiator using a layer-by-layer process, such as 3D screen printing, with multiple layers of PTC material applied successively along the longitudinal direction of the flow channel. Such a layer-by-layer process makes it possible to modify the cross-sectional geometry of the radiator—that is, the flow channel partitions or radiator outer walls that define the individual heat transfer medium flow channels—by successively growing the radiator along the longitudinal direction. This allows the heat transfer medium flow channels to have essentially arbitrary cross-sectional geometries that change along their length.Cross-sectional dimensions can be provided. The heating device has a housing to accommodate at least one heating element. Within this housing, the at least one heating element is arranged such that the heat transfer medium flow channels provided in the at least one heating element are permeable to the heat transfer medium to be heated. To further increase the surface area available for heat transfer, at least one heating element is arranged in the housing according to the invention such that the heat transfer medium to be heated flows around it on an outer surface of at least one outer wall of the heating element. Additionally, at least two heating elements for parallel flow and / or at least two heating elements for series flow can be arranged in the housing. The disclosure further relates to a heating element for a heating device, in particular a heating device constructed according to the invention, wherein the heating element is constructed with PTC material and has a plurality of heat transfer medium flow channels penetrating this material. It should be noted that such a heating element can have all of the previously described heating element structural features individually or in any combination. In particular, it can be provided, for example, that at least two heat transfer medium flow channels in the radiator are limited by a flow channel partition wall of the radiator separating them, or / and at least one heat transfer medium flow channel is limited by a radiator outer wall, and that at least some, preferably all, of the flow channel partition walls and / or radiator outer walls provide a radiator structure formed from a single block of material. The disclosure further relates to a method for manufacturing such a heating element with a plurality of heat transfer medium flow channels extending in the heating element, for example for a heating device constructed according to the invention, in which the heating element is built up by successively applying PTC material layers, for example in a longitudinal direction of the flow channel, one after the other. For example, the radiator can be manufactured using a 3D screen printing process. The present invention is described below with reference to the accompanying Fig. 1, which shows in principle a perspective view of a heating device for heating a heat transfer medium. The heating device 10 shown in Fig. 1 comprises a housing 12, for example made of plastic material and only indicated in Fig. 1, which can be integrated, for example, into an air guidance system in which the air to be introduced into a vehicle interior is guided. A heating element 14 made of PTC material is arranged in the housing 12. The cross-sectional geometry of the heating element 14 is adapted to the cross-sectional geometry of the housing 12 or the air supply system into which the heating device 10 is to be integrated. In the example shown, the heating element 14 has a substantially cuboid outer contour. The radiator 14 has four outer walls 20, 22, 24, 26 that define its internal volume and extend between an inlet end face 16 (shown at the front in Fig. 1) and an outlet end face 18 (shown at the rear in Fig. 1). To provide the cuboid outer contour of the radiator 14, the outer walls 20, 22 and 24, 26 are arranged in parallel pairs opposite each other and connect to immediately adjacent outer walls at an angle of approximately 90°. Inside the radiator 14, a plurality of flow channel partitions 28, in conjunction with the radiator's outer walls 20, 22, 24, 26, define a plurality of heat transfer medium flow channels 30. The heat transfer medium flow channels 30 extend within the radiator 14 between the inlet end face 16 and the outlet end face 18, essentially parallel to each other and in a straight line along the longitudinal flow channel direction L. The heat transfer medium flow channels 30 are open at the inlet end face 16 to receive the heat transfer medium to be heated and are open at the outlet end face 18 to discharge the heat transfer medium heated during the heating operation of the heating device 10. Figure 1 illustrates an embodiment of the radiator 14 in which the flow channel partitions 28 and the radiator outer walls 20, 22, 24, 26 provide a polygonal, honeycomb-like cross-sectional geometry for the heat transfer medium flow channels 30. Each of the heat transfer medium flow channels 30, which have a substantially hexagonal cross-sectional geometry, is bounded by six partitions 28. Due to the cuboid outer contour of the radiator 14, heat transfer medium flow channels also exist that do not have a hexagonal cross-sectional geometry, but rather, for example, a triangular or quadrilateral cross-sectional geometry. In the illustrated embodiment, all flow channel partitions 28 have a substantially constant wall thickness in the circumferential direction around a respective heat transfer medium flow channel 30 and in the longitudinal direction L of the flow channel. The radiator outer walls 20, 22, 24, 26 also have a substantially constant and equal wall thickness in the longitudinal direction L of the flow channel and perpendicular to it, which can correspond to the wall thickness of the flow channel partitions 28.This results in the heat transfer medium flow channels 30 provided in the radiator 14 having a substantially constant cross-sectional dimension in the longitudinal direction L of the flow channel and preferably also being substantially cylindrical, which is achieved by ensuring that an inlet opening of the respective heat transfer medium flow channels 30 formed at the upstream end face 16 and an outlet opening of the respective heat transfer medium flow channels 30 formed at the downstream end face 18 are congruent with each other, i.e., not offset transversely to the longitudinal direction L of the flow channel. In the illustrated radiator 14, all flow channel partitions 28 and all radiator outer walls 20, 22, 24, 26 form a single, solid structure of the radiator 14, constructed from a single block of PTC material. This means that the radiator 14 is not composed of various individual parts that each partially delimit the heat transfer medium flow channels 30, but essentially forms a monolithic structure. This can be achieved, for example, by applying a multitude of layers 32 of the PTC material, as illustrated in Fig. 1, successively along the longitudinal direction L of the flow channels 30 to be formed, using a layer deposition process.For such a layer application process, for example a 3D screen printing process can be used, with which the individual layers 32 of the PTC material, for example barium titanate (BaTiO3), are applied one after the other, so that a material-coherent connection is created between the individual successively applied layers 32 and thus a virtually monolithic structure of the heating element 14 is achieved. By using such a layer deposition method, it becomes possible to produce the radiator 14 with essentially any cross-sectional geometry, in particular also any cross-sectional geometry of the heat transfer medium flow channels 30 inside the radiator 14, wherein, as in the example shown, the cross-sectional geometry and the cross-sectional dimension of the radiator 14 or of the heat transfer medium flow channels 30 formed therein can be essentially the same in the longitudinal direction L of the flow channel, i.e. between the inflow end face 16 and the outflow end face 18, or can change in the longitudinal direction L of the flow channel if required.For example, a winding or curved course of the heat transfer medium flow channels 30 inside the radiator 14 can be provided, or alternatively or additionally the heat transfer medium flow channels 30 inside the radiator 14 can have a varying cross-sectional dimension and / or cross-sectional geometry. With the inventive design of a radiator 14 with a plurality of heat transfer medium flow channels 30 penetrating it, a large surface area is provided inside the radiator 14 on which the heat transfer medium flowing through the heat transfer medium flow channels 30 can absorb heat. This ensures a very efficient heat transfer, in which the outer surface of the radiator 14, i.e., the outer surface of the radiator's outer walls 20, 22, 24, 26, is not used, or not necessarily used, for transferring heat to the heat transfer medium flowing through the radiator 14. The radiator 14 is positioned in the housing 12 such that the heat transfer medium flows not only through it in the area of ​​the heat transfer medium flow channels 30, but also around the outer surface of the outer walls 20, 22, 24, 26, in order to utilize this surface for heat transfer as well. To generate heat by electrically exciting the heating element 14, which is constructed with PTC material, electrical contacts 34, 36 are provided at two separated areas of the heating element 14, for example, on the outer surfaces of two heating element outer walls. These can be provided, for example, by applying metal material. In the area of ​​these electrical contacts 34, 36, the heating element 14 can be connected to a voltage source, for example, by soldering wires or by means of a pressure contact with contact pins or the like, in order to generate heat by applying an electrical voltage and the resulting current flowing through the heating element 14. It should be noted that, by utilizing the design principles of the present invention, the heating device 10 and / or the heating element 14 thereof can be varied in a wide variety of ways. For example, the heat transfer medium flow channels 30 can have a different cross-sectional geometry than shown. They can, for instance, have a triangular, square, or even a round cross-sectional geometry. Similarly, the heating element 14 can also have a cross-sectional geometry that differs from the rectangular cross-sectional geometry shown. Furthermore, in the heating device 10 according to the invention, a plurality of heating elements 14 can be arranged in the housing 12, for example, side by side and / or sequentially in the direction of flow.The electrical contacts 34, 36 on the heating element 14 can also be provided in a different position, the positioning of the electrical contacts 34, 36 being determined, for example, by where in the housing 12 feedthroughs for the electrical conductors leading to a voltage source are arranged.

Claims

Heating device for heating a heat transfer medium, in particular in a vehicle, comprising at least one heating element (14) constructed with PTC material with a plurality of heat transfer medium flow channels (30) passing through the heating element (14), wherein a housing (12) accommodating the at least one heating element (14) is provided, characterized in that at least one heating element (14) is arranged in the housing (12) such that it is possible to allow flow of heat transfer medium to be heated on an outer surface of at least one heating element outer wall (20, 22, 24, 26). Heating device according to claim 1, characterized in that the heat transfer medium flow channels (30) extend substantially parallel to each other in the heating element (14) between an inflow end face (16) and an outflow end face (18). Heating device according to claim 1 or 2, characterized in that at least one heat transfer medium flow channel (30), preferably each heat transfer medium flow channel (30), has a cross-sectional geometry that does not change substantially in a flow channel longitudinal direction (L) and / or a cross-sectional dimension that does not change substantially in a flow channel longitudinal direction (L). Heating device according to one of the preceding claims, characterized in that at least one heat transfer medium flow channel (30), preferably each heat transfer medium flow channel (30), has a cross-sectional geometry that changes in a flow channel longitudinal direction (L) and / or a cross-sectional dimension that changes in a flow channel longitudinal direction (L). Heating device according to one of the preceding claims, characterized in that at least two heat transfer medium flow channels (30) are limited by a flow channel partition (28) of the radiator (14) separating them, or / and that at least one heat transfer medium flow channel (30) is limited by a radiator outer wall (20, 22, 24, 26). Heating device according to claim 5, characterized in that at least a part of the, preferably all, flow channel partitions (28) and / or radiator outer walls (20, 22, 24, 26) provide a radiator structure formed from a single block of material. Heating device according to claim 5 or 6, characterized in that at least a part of the, preferably all, flow channel partitions (28) and / or radiator outer walls (30) have a substantially constant wall thickness in a flow channel circumferential direction and / or a flow channel longitudinal direction (L). Heating device according to one of the preceding claims, characterized in that at least one heat transfer medium flow channel (30), preferably each heat transfer medium flow channel (30), has a polygonal cross-sectional geometry. Heating device according to claim 8, characterized in that at least a part of the heat transfer medium flow channels (30) forms a honeycomb-like opening structure. Heating device according to one of the preceding claims, characterized in that the PTC material comprises barium titanate. Heating device according to one of the preceding claims, characterized in that contact elements (34, 36) for electrical contacting the heating element (14) are provided on the heating element (14). Heating device according to one of the preceding claims, characterized in that the heating element (14) is manufactured in a layer application process, preferably a 3D screen printing process, with a plurality of PTC material layers (32) applied successively one after the other, preferably in a flow channel longitudinal direction (L). Heating device according to one of the preceding claims, characterized in that the at least one heating element (14) is arranged in the housing (12) such that the heat transfer medium flow channels (30) provided in the at least one heating element (14) are permeable to heat transfer medium. Heating device according to one of the preceding claims, characterized in that at least two heating elements (14) for parallel flow and / or at least two heating elements (14) for serial flow are arranged in the housing (12).

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