ceramic heating element

Abstract

[Objective] To improve thermal shock resistance. [Means] A ceramic heating element 11 is a ceramic heating element 11 for heating liquids and comprises: a ceramic body 22, which includes a ceramic base 21 and extends longitudinally, and a resistance heating element 23 formed on a surface of the base 21; and a resin layer 29 configured to cover an area R1 that includes the resistance heating element 23 longitudinally on an outer surface 22A of the ceramic body 22. The resin layer 29 is heat-resistant to temperatures higher than the heating temperature of the ceramic body 22.

Description

[Technical field] The present disclosure relates to a ceramic heating element. [State of the art] To date, an electric water heater is known, which is disclosed in Japanese patent application (kokai) No. 2013-126844 (Patent 1). The electric water heater in Patent 1 comprises a housing with an inlet connection, a flow path, and an outlet connection for a heat transfer medium, as well as a ceramic heating element arranged in the flow path. The ceramic heating element comprises a ceramic support element, for example, made of aluminum oxide, silicon nitride, aluminum nitride, or silicon carbide, and a heating element embedded in the side surface of the support element. [State of the art] [Patent specification] [Patent Specification 1] Japanese patent application (kokai) No. 2013-126844 [Summary of the invention] [Problems to be solved by the invention] For example, if boiling occurs on the surface of the ceramic heating element, an air layer forms. The ceramic heating element heats up rapidly at this air layer, creating a high-temperature zone. If a liquid heat transfer medium comes into contact with this high-temperature zone, there is a risk of the ceramic heating element cracking. Therefore, the ceramic heating element is susceptible to thermal shock and prone to cracking. Consequently, the ceramic heating element must exhibit increased resistance to thermal shock in order to be used as a heat exchanger. The present disclosure was made taking into account the above circumstances, and one objective of the present disclosure is to improve resistance to thermal shocks. [Means of solving the problems] A ceramic heating element of the present disclosure is a ceramic heating element for heating liquids and comprises: a ceramic body comprising a ceramic base extending longitudinally, and a resistance heating element formed on a surface of the base; and a resin layer configured to cover an area extending longitudinally to encompass at least the resistance heating element on an outer surface of the ceramic body. The resin layer is heat-resistant to temperatures higher than the heating temperature of the ceramic body. [Effects of the invention] According to the present disclosure, resistance to thermal shock can be improved. [Brief description of the drawings] [Fig. 1] Cross-sectional view showing the entire configuration of a ceramic heating element according to embodiment 1. [Fig. 2] Cross-sectional view showing the internal structure of the ceramic heating element. [Fig. 3] View illustrating a manufacturing process for an insulating tube. [Fig. 4] Enlarged cross-sectional view of an area enclosed by an alternating long and short dashed line in Fig. 2. [Fig. 5] Perspective view showing a ceramic heating element according to embodiment 2. [Fig. 6] Perspective view showing a ceramic heating element according to embodiment 3. [Modes for carrying out the invention] [Description of embodiments of the present disclosure] First, embodiments of the present disclosure are listed and described. (1) A ceramic heating element of the present disclosure is a ceramic heating element for heating liquids and comprises: a ceramic body comprising a ceramic base extending longitudinally, and a resistance heating element formed on a surface of the base; and a resin layer configured to cover a longitudinally extending area such that it encompasses at least the resistance heating element on an outer surface of the ceramic body. The resin layer is heat-resistant to temperatures higher than the heating temperature of the ceramic body. In this configuration, the surface of the ceramic body is covered by the resin layer, thereby reducing the thermal conductivity between a liquid heat transfer medium and the ceramic body. Therefore, even with a large temperature difference between the liquid heat transfer medium and the ceramic body, rapid cooling of the ceramic body by the liquid heat transfer medium, which can lead to cracking, is prevented, and the thermal shock resistance is improved. (2) A ceramic heating element of the present disclosure is a ceramic heating element for heating liquids and comprises: a ceramic body comprising a ceramic base, having a rod-shaped form and extending longitudinally, and a resistance heating element embedded in the base; and a resin layer configured to cover a longitudinally extending area, such that it encompasses at least the resistance heating element on an outer surface of the ceramic body. The resin layer is heat-resistant to temperatures higher than the heating temperature of the ceramic body. (3) In the case of the ceramic heating element described in (1), it is advantageous if the average thickness of the resin layer is less than the distance between the resistance heating element and the outer surface. If the average thickness of the resin layer is greater than the distance between the resistance heating element and the outer surface, there is a risk that heat transfer to the liquid heat transfer medium will become less efficient. Conversely, with the configuration described above, it is possible to improve thermal shock resistance while maintaining the performance of heat transfer to the liquid heat transfer medium, since the average thickness of the resin layer is less than the distance between the resistance heating element and the outer surface. (4) In the ceramic heating element described in (1) to (3), the resin layer preferably comprises an inner resin layer that directly covers a surface of the ceramic body and an outer resin layer that covers the surface of the ceramic body over the inner resin layer, wherein the main components of the inner resin layer and the outer resin layer differ from each other. The inner resin layer can be a heat-resistant resin layer, and the outer resin layer can be a resin layer with high mechanical strength and thermal conductivity, so that the resin layer can have multiple functions. (5) In the ceramic heating element described in any one of points (1) to (4) the heat resistance temperature of the resin layer is preferably 150°C or higher. Water, coolants, and similar substances are frequently used as heat transfer media. Since the boiling point of water is 100°C and the boiling point of coolant is around 120°C, it is assumed that the resin layer can reach a temperature of 100°C or more if an air layer forms due to boiling. In this case, the resin layer can withstand temperatures up to 150°C. Suitable resins with a heat resistance temperature of 150 °C or higher include engineering plastics such as aromatic polyamide (PPA), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polysulfone (PSU), polyethersulfone (PES), polyimide (PEI), polyamide-imide (PAI), polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE). (6) In the ceramic heating element described in (1) to (5), the resin layer preferably comprises glass fibers. The inclusion of glass fibers in the resin layer can increase heat resistance and improve strength. [Details of embodiments of the present disclosure] One embodiment of the present disclosure is described with reference to Figures 1, 2, 3 to 4. The present disclosure is not limited to these examples, but is specified by the claims and is intended to encompass all modifications within the meaning and scope of the claims. In the following description, for a plurality of identical elements, one element may be designated by a reference numeral, while the reference numerals for the other elements may be omitted. <Ausführungsform 1> <Wärmetauscher> A heat exchanger 10 according to the present embodiment is a device that heats liquids such as water or coolant, which serve as a heat transfer medium. The heat exchanger 10 is, for example, installed in a vehicle such as an electric vehicle (EV) and is used to heat the passenger compartment or to warm the battery. As shown in Figures 1 and 2, the heat exchanger 10 comprises a ceramic heating element 11 and a housing 60 that accommodates the ceramic heating element 11. <keramik-heizelement> The ceramic heating element 11 comprises an insulating tube 20, a first flange 30, a second flange 40, and connection sections 25. The insulating tube 20 has a cylindrical shape centered about an axis AX. The insulating tube 20 extends longitudinally (in the direction in which the axis AX extends). The insulating tube 20 comprises a ceramic tube 20A with a cylindrical shape, a ceramic body 22 with a cylindrical shape arranged around the outer circumference of the ceramic tube 20A, and a resin layer 29 covering an outer circumferential surface 22A of the ceramic body 22. The ceramic body 22 comprises a longitudinally extending ceramic base 21, a resistance heating element 23, and a pair of internal terminals 24 formed on a surface of the base 21. The base 21 is made, for example, of a ceramic material such as aluminum oxide. As shown in Fig. 3, the resistance heating element 23 and the pair of inner terminals 24 are formed on the inner circumferential surface (the surface on the side of the ceramic tube 20A) or within the ceramic body 22. The resistance heating element 23 has a meandering, thin, wire-like shape. The inner terminals 24 each have a rectangular shape that is wider than the resistance heating element 23. The inner terminals 24 are electrically connected to the terminal sections 25 via vias (not shown). The terminal sections 25 are formed on the outer circumferential surface of the ceramic body 22. The insulating tube 20 can be manufactured, for example, by wrapping a ceramic foil 26 around the previously calcined base 21 and then firing it. Conductive layers 27 made of tungsten or similar material are formed on the surfaces or inside the ceramic foil 26. After firing, the ceramic foil 26 serves as the base 21, which forms the ceramic body 22. After firing, the conductor layers 27 serve as resistance heating element 23, internal connections 24 and connection sections 25. The resin layer 29 is configured to cover an area R1 that includes at least the resistance heating element 23 in the longitudinal direction on an outer surface 22A of the ceramic body 22. The resin layer 29 is heat-resistant to temperatures higher than the heating temperature of the ceramic body 22. The heating temperature refers to the temperature of the ceramic body 22 during heating by the resistance heating element 23. As shown in Fig. 4, the average thickness T1 of the resin layer 29 is less than the distance D1 from the resistance heating element 23 to the outer surface 22A. The resin layer 29 can comprise an inner resin layer 29A, which directly covers the outer surface 22A of the ceramic body 22, and an outer resin layer 29B, which covers the outer surface 22A of the ceramic body 22 over the inner resin layer 29A. In this case, the main components of the inner resin layer 29A and the outer resin layer 29B preferably differ from each other. The heat resistance temperature of the resin layer 29 is 150°C or higher. Suitable resins with a heat resistance temperature of 150°C or higher include engineering plastics such as aromatic polyamide (PPA), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polysulfone (PSU), polyethersulfone (PES), polyamide-imide (PAI), polyetheretherketone (PEEK), and polytetrafluoroethylene (PTFE). The resin layer 29 preferably contains glass fibers. <Gehäuse> As shown in Figs. 1 and 2, the housing 60 accommodates the ceramic heating element 11. The housing 60 forms part of a flow channel FC through which fluid flows. The ceramic heating element 11 is attached to the housing 60 in a watertight condition via the first flange 30. Furthermore, the ceramic heating element 11 is attached to the housing 60 via the second flange 40. Specifically, the ceramic heating element 11 can be attached to the housing 60 in a watertight condition via the second flange 40. Here, "attached in a watertight condition" means that several elements are connected to each other by a fastening section, and leakage of fluid through the fastening section is prevented. The housing 60 comprises a third housing 70, a second housing 80, and a first housing 90, each of which is individually formed. The third housing 70 is connected to the second housing 80. The first housing 90 is connected to the third housing 70. The third housing 70 is attached to the first flange 30 in a watertight manner. The second housing 80 is attached to the second flange 40 in a watertight manner. Here, "attached in a watertight manner" means that several elements are attached to one housing section and that leakage of liquid through the housing section is prevented. <Wirkung der Ausführungsform 1> As described above, the ceramic heating element 11 of embodiment 1 is a ceramic heating element 11 for heating liquids and comprises: the ceramic body 22, which includes the ceramic base 21 and extends longitudinally, and the resistance heating element 23 formed on the surface of the base 21; and the resin layer 29, which is configured to cover an area that includes at least the resistance heating element 23 longitudinally on the outer surface 22A of the ceramic body 22. The resin layer 29 is heat-resistant to temperatures higher than the heating temperature of the ceramic body 22. In this configuration, the thermal conductivity between the liquid heat transfer medium and the ceramic body 22 is reduced due to the resin layer 29, since the outer surface 22A of the ceramic body 22 is covered by the resin layer 29. Therefore, even with a large temperature difference between the liquid heat transfer medium and the ceramic body 22, the ceramic body 22 is prevented from being rapidly cooled by the liquid heat transfer medium and cracking, and its thermal shock resistance is improved. The average thickness T1 of the resin layer 29 is preferably thinner than the distance D1 from the resistance heating element 23 to the outer surface 22A. If the average thickness T1 of the resin layer 29 is greater than the distance D1 from the resistance heating element 23 to the outer surface 22A, there is a risk that the heat transfer to the liquid heat transfer medium will become less efficient. On the other hand, with the configuration described above, it is possible to improve the thermal shock resistance while maintaining the heat transfer to the liquid heat transfer medium, since the average thickness T1 of the resin layer 29 is thinner than the distance D1 from the resistance heating element 23 to the outer surface 22A. The resin layer 29 comprises the inner resin layer 29A, which directly covers the surface of the ceramic body 22, and the outer resin layer 29B, which covers the surface of the ceramic body 22 over the inner resin layer 29A, wherein the main components of the inner resin layer 29A and the outer resin layer 29B are preferably different from each other. The inner resin layer 29A can be a heat-resistant resin layer, and the outer resin layer 29B can be a resin layer with high mechanical strength and thermal conductivity, so that the resin layers can have multiple functions. The heat resistance temperature of the resin layer 29 is preferably 150°C or more. Water, coolants, and the like are frequently used as heat transfer media. Since the boiling point of water is 100°C and the boiling point of coolant is approximately 120°C, it is assumed that the resin layer 29 can reach a temperature of 100°C or more if an air layer forms due to boiling. In this case, the resin layer 29 can withstand temperatures of up to 150°C. The resin layer 29 preferably contains glass fibers. By incorporating glass fibers into the resin layer 29, heat resistance and strength can be improved. <Ausführungsform 2> Embodiment 2 is described with reference to Fig. 5. A ceramic heating element 12 of embodiment 2 comprises a ceramic body 122 and a resin layer 129 and, unlike the ceramic heating element 11 of embodiment 1, has a rod-shaped form. The ceramic body 122 comprises a longitudinally extending ceramic base 121 and the resistance heating element 23. The resistance heating element 23 is embedded in the longitudinally extending, rod-shaped base 121. The resin layer 129 is configured to cover an area R2 that includes at least the resistance heating element 23 longitudinally on the outer surface of the ceramic body 122. The same components as in embodiment 1 are identified by the same reference numerals as in embodiment 1, and their descriptions are omitted. <Ausführungsform 3> Embodiment 3 is described with reference to Fig. 6. A ceramic heating element 13 of embodiment 3 comprises a ceramic body 222 and a resin layer 229 and, unlike the ceramic heating element 11 of embodiment 1, has a plate-like shape. The ceramic body 222 comprises a ceramic base 221 extending longitudinally and the resistance heating element 23. The resistance heating element 23 is formed on a surface of the base 221, which has a plate-like shape and extends longitudinally. The resin layer 229 is configured to cover an area R3 that includes at least the resistance heating element 23 longitudinally on an outer surface of the ceramic body 222. The same components as in embodiment 1 are identified with the same reference numerals as in embodiment 1, and their descriptions are omitted. <Weitere Ausführungsformen> (1) In embodiments 1 to 3, the average thickness T1 of the resin layer 29 is less than the distance D1 from the resistance heating element 23 to the outer surface 22A, but the average thickness of the resin layer 29 may be equal to or greater than the distance D1. (2) In embodiments 1 to 3, the resin layer 29 consists of the inner resin layer 29A and the outer resin layer 29B, but the resin layer may consist of a single layer or of three or more layers. [Description of reference symbols] 10 Heat exchanger 11, 12, 13 Ceramic heating element 20 Insulating tube 20A Ceramic tube 21, 121, 221 Base 22, 122, 222 Ceramic body 22A Outer surface 23 Resistance heating element 24 Inner connection 25 Connection area 26 Ceramic plate 27 Conductor layer 28 Heating section 29, 129, 229 Resin layer 29A Inner resin layer 29B Outer resin layer 30 First flange 40 Second flange 60 Housing 70 Third housing 80 Second housing 90 First housing AX Axis T1 Average thickness D1 Spacing FC Flow channel R1, R2, R3 Area QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature JP 2013-126844 [0002, 0003]

Claims

A ceramic heating element for heating liquids, comprising: a ceramic body comprising a ceramic base extending longitudinally and a resistance heating element formed on a surface of the base; and a resin layer configured to cover an area encompassing at least the resistance heating element longitudinally on an outer surface of the ceramic body, wherein the resin layer is heat-resistant to temperatures higher than a heating temperature of the ceramic body. A ceramic heating element for heating liquids, comprising: a ceramic body comprising a ceramic base, having a rod-shaped form and extending longitudinally, and a resistance heating element embedded in the base; and a resin layer configured to cover an area encompassing at least the resistance heating element longitudinally on an outer surface of the ceramic body, wherein the resin layer is resistant to temperatures higher than the heating temperature of the ceramic body. Ceramic heating element according to claim 1, wherein the average thickness of the resin layer is thinner than the distance from the resistance heating element to the outer surface. The ceramic heating element according to claim 1, wherein the resin layer comprises an inner resin layer directly covering the surface of the ceramic body and an outer resin layer covering the surface of the ceramic body over the inner resin layer, and the main components of the inner resin layer and the outer resin layer differ from each other. Ceramic heating element according to claim 1 or 2, wherein the heat resistance temperature of the resin layer is 150°C or higher. Ceramic heating element according to claim 1 or 2, wherein the resin layer comprises glass fibers.

Images