Hydrothermal PTC heater and preparation method thereof

Abstract

The invention discloses a hydrothermal PTC heater and a preparation method thereof. The hydrothermal PTC heater comprises a PTC heating bag, a metal shell, a composite phase change material and inorganic glue, wherein the space between the PTC heating bag and the metal shell is filled with the composite phase change material and the inorganic glue; the PTC heating bag comprises a PTC heating chip, an electrode plate and an insulating ceramic plate; the phase change temperature of the composite phase change material is higher than 20 DEG C and lower than the Curie temperature of the insulating ceramic plate; according to the invention, the high-thermal-conductivity inorganic insulating ceramic plate is adopted to replace a traditional organic insulating film, and the composite phase-change material is combined for filling, so that the air thermal resistance in an assembly gap is effectively eliminated, and an efficient and stable heat-conducting path is constructed between the PTC chip and the metal shell; meanwhile, the inorganic glue buffer layer with matched components is matched, mechanical stress is effectively relieved in the press-fitting process, brittle elements are prevented from being damaged, and the power density, the operation stability, the structural durability and the electrical safety of the heater are remarkably improved while the good heat conduction capacity is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of PTC heater technology, and in particular to a hydrothermal PTC heater and its preparation method. Background Technology

[0002] Hydrothermal PTC heaters serve as key heating components in the thermal management systems of new energy electric vehicles, transferring heat to the coolant to achieve overall vehicle thermal management. As electric vehicles increasingly demand compact and efficient thermal management, the power density and reliability requirements for hydrothermal PTC heaters are also rising.

[0003] In existing technologies, PTC heating elements are typically fixed to a metal housing groove using wedge-shaped blocks. An unavoidable assembly gap exists between them. Due to the extremely low thermal conductivity of air (approximately 0.026 W / (m·K)), this gap creates significant thermal resistance, severely hindering heat conduction from the PTC chip to the housing. This not only reduces overall heat transfer efficiency but also causes localized temperature increases in the chip. Since PTC material has a positive temperature coefficient, its resistance increases rapidly with temperature rise, leading to a decrease in output power and limiting the improvement of power density per unit volume. Furthermore, traditional solutions often use polyimide film as the electrical insulation layer. While this organic material possesses certain insulating properties, its extremely low thermal conductivity further exacerbates the thermal resistance problem, resulting in low heat transfer efficiency and impacting power density improvement.

[0004] Therefore, it is essential to provide a technical solution for a hydrothermal PTC heater that can improve power density. Summary of the Invention

[0005] In view of this, this application provides a hydrothermal PTC heater and its preparation method to solve the problem of how to improve the power density of the hydrothermal PTC heater.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a hydrothermal PTC heater, comprising a PTC heating element, a metal shell, and a composite phase change material and inorganic adhesive filled between the PTC heating element and the metal shell; the PTC heating element comprises a PTC heating chip, electrode plates, and an insulating ceramic plate; the PTC heating chip is disposed inside the PTC heating element; two electrode plates are respectively tightly attached to the two heating surfaces of the PTC heating chip; two insulating ceramic plates are respectively covered on the outer sides of the two electrode plates; the phase change temperature of the composite phase change material is higher than 20°C and lower than the Curie temperature of the insulating ceramic plate.

[0007] Preferably, the composite phase change material is a microencapsulated phase change material or a framework-based composite phase change material; the phase change degree of the composite phase change material is 50-110℃; and the thermal conductivity of the composite phase change material in the solid state is ≥1.5 W / (m·K).

[0008] Preferably, the microencapsulated phase change material includes a core material and a shell material encapsulating the core material; the core material includes one or more of octadecyl alcohol, eicosyl alcohol, dioctyl alcohol, palmitic acid, and stearic acid, and the shell material includes one or more of alumina, aluminum nitride, silicon nitride, and boron nitride.

[0009] Preferably, the framework-based composite phase change material includes a framework and a phase change material loaded inside the framework; the framework includes one or more of porous alumina materials, porous aluminum nitride materials, porous silicon nitride materials, and porous boron nitride materials, and the phase change material includes one or more of octadecyl alcohol, eicosyl alcohol, eicosyl glycol, palmitic acid, stearic acid, paraffin wax, polyethylene glycol, and pentaerythritol.

[0010] Preferably, the material of the inorganic adhesive is the same as the material of the skeleton or shell of the composite phase change material.

[0011] Preferably, the microencapsulated phase change material is obtained by in-situ polymerization, sol-gel method or interfacial polymerization.

[0012] Preferably, the framework-based composite phase change material is obtained by vacuum impregnation.

[0013] Secondly, this application provides a method for preparing a hydrothermal PTC heater, comprising the following steps: S1. Apply inorganic adhesive to the inner surface of the metal casing and the outer surface of the PTC heating pack; S2. Place the PTC heating pack and composite phase change material inside the metal shell, and then press and cure them to obtain the hydrothermal PTC heater.

[0014] Preferably, the specific process of step S2 is as follows: placing the PTC heating pack inside the metal shell and applying pressure to the PTC heating pack; injecting composite phase change material into the gap between the metal shell and the PTC heating pack and performing heat curing treatment.

[0015] Preferably, the specific process of step S2 is as follows: the PTC heating pack and the composite phase change material are placed inside the metal shell and subjected to pressure treatment, followed by heat curing treatment.

[0016] The beneficial effects of this application are as follows: By replacing the traditional organic insulating film with a high thermal conductivity inorganic insulating ceramic plate and combining it with composite phase change material filling, this application effectively eliminates the air thermal resistance in the assembly gap, and constructs an efficient and stable heat conduction path between the PTC chip and the metal shell; at the same time, with the inorganic adhesive buffer layer with matching composition, it effectively relieves mechanical stress during the pressing process, prevents damage to brittle components, and meets the insulation safety requirements under high voltage applications while ensuring good thermal conductivity, avoiding the reliability risks caused by high temperature aging of organic materials, and significantly improving the power density, operational stability, structural durability and electrical safety of the heater. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the cross-section of a hydrothermal PTC heater. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] like Figure 1 As shown, this application provides a hydrothermal PTC heater, including a PTC heating pack 1, a metal shell 2, and a composite phase change material 4 and inorganic adhesive filled between the PTC heating pack 1 and the metal shell 2; the PTC heating pack 1 includes a PTC heating chip, electrode plates, and an insulating ceramic plate; the PTC heating chip is disposed inside the PTC heating pack 1; two electrode plates are respectively tightly attached to the two heating surfaces of the PTC heating chip; two insulating ceramic plates are respectively covered on the outer sides of the two electrode plates; the phase change temperature of the composite phase change material 4 is higher than 20°C and lower than the Curie temperature of the PTC heating chip.

[0020] The increased power density in this application is based on two synergistic mechanisms. First, using an insulating ceramic plate with high thermal conductivity (≥20 W / (m·K)) as the insulating and heat-conducting layer reduces the basic thermal resistance from the source. Simultaneously, it works synergistically with a composite phase change material with high thermal conductivity to establish an efficient heat transfer path, enabling the heat generated by the PTC heating chip to be efficiently transferred to the heater channel, directly increasing the output power. Second, utilizing the positive temperature coefficient of resistance of the PTC heating chip, the aforementioned heat dissipation channel effectively reduces its operating temperature. The decrease in temperature leads to a reduction in chip resistance, thereby further increasing its power output at the same voltage. Based on the synergistic effect of these two mechanisms, this embodiment can significantly improve its heating power and power density without increasing the overall volume of the PTC heater.

[0021] In some embodiments, the composite phase change material 4 is a microencapsulated phase change material or a framework-based composite phase change material; the phase change degree of the composite phase change material 4 is 50-110℃; the thermal conductivity of the composite phase change material 4 in the solid state is ≥1.5 W / (m·K).

[0022] In this embodiment, by filling the gaps with a highly thermally conductive composite phase change material, the huge thermal resistance caused by air in the traditional assembly gaps due to its low thermal resistance (thermal conductivity of only 0.026 W / (m·K)) is eliminated. Together with the insulating ceramic plate, a heat conduction channel is established from the internal PTC chip to the external metal shell. On the other hand, the latent heat of phase change of the composite phase change material absorbs a large amount of heat in the PTC operating temperature range (50-110℃), forming a dual mechanism of heat conduction and heat storage, which effectively reduces the operating temperature of the PTC chip, thereby enabling it to operate on a more optimal resistance-temperature curve. Furthermore, the heat absorption and thermal buffering effect of the composite phase change material effectively suppresses the temperature rise of the PTC heating chip, avoids local overheating, and helps to improve the reliability and service life of the heater.

[0023] In some embodiments, the microencapsulated phase change material includes a core material and a shell material covering the core material; the core material includes one or more of octadecyl alcohol, eicosyl alcohol, dodecyl alcohol, palmitic acid, and stearic acid, and the shell material includes one or more of alumina, aluminum nitride, silicon nitride, and boron nitride.

[0024] In this embodiment, the shell material is an inorganic insulating material with good thermal conductivity, which is conducive to effectively transferring heat to the flow channel, increasing the output power of the PTC heating chip, and thus increasing the power density of the heater.

[0025] In some embodiments, the framework-based composite phase change material includes a framework and a phase change material loaded inside the framework; the framework includes one or more of porous alumina materials, porous aluminum nitride materials, porous silicon nitride materials, and porous boron nitride materials, and the phase change material includes one or more of octadecyl alcohol, eicosyl alcohol, dodecyl alcohol, palmitic acid, stearic acid, paraffin wax, polyethylene glycol, and pentaerythritol.

[0026] In this embodiment, the skeleton is an inorganic insulating porous material, which not only provides electrical insulation but also benefits from the inherent high thermal conductivity of inorganic materials, thereby improving power density.

[0027] In some embodiments, the material of the inorganic adhesive is the same as the material of the skeleton or shell of the composite phase change material.

[0028] In this embodiment, the insulating ceramic plate, the microcapsule shell / skeleton of the composite phase change material, and the inorganic adhesive are all made of inorganic insulating materials with high thermal conductivity. While ensuring thermal conductivity, this ensures that the overall structure meets the insulation safety requirements of high-voltage PTC electrical applications and solves the hidden dangers of organic materials (such as polyimide) aging and deterioration of insulation performance at high temperatures.

[0029] In some embodiments, the microencapsulated phase change material is obtained by in-situ polymerization, sol-gel polymerization, or interfacial polymerization.

[0030] In some embodiments, the framework-based composite phase change material is obtained by vacuum impregnation.

[0031] In this embodiment, the microencapsulated phase change material and the framework-based composite phase change material can ensure that the material does not leak during the solid-liquid phase change process, has no risk of leakage during long-term use, and maintains stable thermal conductivity.

[0032] This application provides a method for preparing a hydrothermal PTC heater, comprising the following steps: S1. Apply inorganic adhesive to the inner surface of the heating groove formed by the metal shell 2 itself and the outer surface of the insulating ceramic plate of the PTC heating pack 1; S2. Place the PTC heating pack 1 and the composite phase change material 4 into the heating tank formed by the metal shell 2, and perform pressing and curing treatment to obtain the hydrothermal PTC heater.

[0033] In this application, during the curing process, the composite phase change material undergoes a single melt-recrystallization, further penetrating and optimizing the interfacial contact with the skeleton and inorganic adhesive, forming a highly thermally conductive pathway.

[0034] In some embodiments, step S2 specifically involves: placing the PTC heating pack 1 inside the metal housing 2 and applying pressure to the PTC heating pack 1; injecting the composite phase change material 4 into the gap 3 between the metal housing 2 and the PTC heating pack 1, and then performing a heat curing process.

[0035] In some embodiments, the application of inorganic adhesive further includes pre-curing; the pre-curing temperature is 80°C and the pre-curing time is 5 minutes. The purpose of pre-curing is to bring the inorganic adhesive to a semi-cured viscous state, thereby providing optimal cushioning and bonding properties.

[0036] In this application, during the pressing and buffering process, the inorganic adhesive layer in a "semi-cured" state undergoes elastic deformation under pressure, becoming an ideal stress buffer layer that evenly disperses the concentrated compressive stress, effectively avoiding the risk of the brittle alumina ceramic plate and PTC chip breaking due to point stress. During co-curing molding, the inorganic adhesive is fully cured to form a robust thermally conductive skeleton. At the same time, due to the consistency of materials and thermal processes, the composite phase change material, inorganic adhesive, and ceramic plate form an integrated thermally conductive structure with tight interfacial bonding and extremely low thermal resistance.

[0037] In some embodiments, step S2 specifically involves placing the PTC heating pack 1 and the composite phase change material 4 into the gap 3 formed by the metal shell 2, applying pressure, and then performing a heat curing process.

[0038] In some embodiments, the pressing force for the pressure treatment is 1500-2000N.

[0039] In some embodiments, the temperature for the heat curing treatment is 100-120°C and the time is 20-30 minutes to cure the inorganic adhesive.

[0040] In this application, before pressing, an inorganic adhesive with the same composition as the microcapsule shell / skeleton of the phase change material is coated on the surface of the shell and the insulating ceramic plate. This design not only greatly reduces the interfacial thermal resistance, but also plays a key mechanical buffering role when a pressing force of 1500-2000N is applied, effectively preventing the brittle insulating ceramic plate and PTC heating chip from breaking due to stress concentration, thereby improving the structural strength and durability of the entire module.

[0041] The following specific embodiments further illustrate this solution.

[0042] The source of raw materials in Example 1: PTC heating pack: includes a PTC heating chip and electrode plates. A 0.5 mm thick 96% alumina insulating ceramic plate serves as the insulating thermal interface with the metal shell. The thermal conductivity of the insulating ceramic plate is 25 W / (m·K). The PTC heating chip is located inside the PTC heating pack. Two electrode plates are tightly attached to the two heating surfaces of the PTC heating chip. Two insulating ceramic plates cover the outer sides of the two electrode plates.

[0043] Microencapsulated phase change material: Eicosanol was heated to complete melting, and nano-alumina modified with a silane coupling agent was added. The resulting oil phase was slowly added dropwise to an aqueous phase formed by a mixture of polyvinyl alcohol and deionized water, and high-speed shear emulsification was performed to form a water-in-oil structure. Subsequently, a crosslinking agent was added, and the mixture was stirred for several hours and dried to form a microencapsulated phase change material with eicosanol as the core material (phase change temperature 65℃), nano-alumina as the shell material, a particle size controlled at 100-150 μm, and a shell thickness of about 8 μm, resulting in a thermal conductivity of 2 W / (m·K).

[0044] Inorganic adhesives: adhesive materials with alumina powder as the main component and aluminum phosphate as the binder phase.

[0045] The source of raw materials in Example 2: PTC heating pack: Includes PTC heating chip and electrode plate, and uses aluminum nitride insulating ceramic plate as the insulating thermal interface with metal shell. The thermal conductivity of aluminum nitride insulating ceramic plate is as high as 170 W / (m·K).

[0046] Framework-based composite phase change material: Boron nitride porous ceramic with a three-dimensional network structure (porosity of 92% and average pore size of 50μm) is used as the framework. Paraffin wax with a phase change temperature of 58℃ is loaded into its pores by vacuum impregnation to form a framework-based composite phase change material bulk. The overall thermal conductivity of this material is 5 W / (m·K), which is significantly improved compared with the thermal conductivity of pure paraffin wax.

[0047] Inorganic adhesive: an equimolar mixture of aqueous solution of aluminum chromium phosphate and aluminum nitride.

[0048] Example 1 A hydrothermal PTC heater includes a PTC heating element, a metal shell, and a composite phase change material and inorganic adhesive filled between the PTC heating element and the metal shell; the PTC heating element includes a PTC heating chip, electrode plates, and an insulating ceramic plate; the phase change temperature of the composite phase change material is 65°C.

[0049] The preparation method of the hydrothermal PTC heater includes the following steps: Adhesive application and pre-curing: A layer of the above-mentioned alumina inorganic adhesive is uniformly applied to the inner wall of the heating tank of the aluminum alloy shell and the outer surface of the alumina insulating ceramic plate of the PTC heating pack. The wet film thickness of the coating is about 100μm. It is pre-cured at 80℃ for 5 minutes, and the alumina inorganic adhesive forms a semi-cured viscous state. Pressing and buffering: Place the PTC heating pack into the heating tank and apply a pressing force of 1800N along the axial direction; Injection of phase change material: The microencapsulated phase change material is mixed with silicone resin (5% of the total weight) into a paste, and then vacuum-injected into the gap (0.3 mm) between the heating pack and the shell; Co-curing molding: Place the entire component in an oven at 100°C and cure for 30 minutes to obtain a hydrothermal PTC heater.

[0050] Example 2 A hydrothermal PTC heater includes a PTC heating element, a metal shell, and a composite phase change material and inorganic adhesive filled between the PTC heating element and the metal shell; the PTC heating element includes a PTC heating chip, electrode plates, and an insulating ceramic plate; the phase change temperature of the composite phase change material is 58°C.

[0051] The preparation method of the hydrothermal PTC heater includes the following steps: Adhesive application: Use dispensing equipment to apply aluminum nitride inorganic adhesive to the inner wall of the heating tank of the aluminum alloy shell, ensuring uniform coating and a wet film thickness of about 100μm; Pressing and buffering: The skeleton-based composite phase change material is pre-placed in the heating tank, then the PTC heating pack is placed in and a pressing force of 2000N is applied. During this process, the composite phase change material block undergoes slight deformation under pressure, fully adhering to the coated inorganic adhesive and expelling the air at the interface. Curing and molding: Place the entire component in an oven at 110°C and cure for 40 minutes to obtain a hydrothermal PTC heater.

[0052] Example 3 A hydrothermal PTC heater is identical to that in Example 2, except that the PTC heating element, skeleton-based composite phase change material, and inorganic adhesive in Example 2 are replaced with the corresponding PTC heating element, skeleton-based composite phase change material, and inorganic adhesive in Example 1.

[0053] Comparative Example 1 A hydrothermal PTC heater is identical to that in Example 1, except that it does not include a pre-curing step.

[0054] Comparative Example 2 A hydrothermal PTC heater, otherwise identical to Example 1, except that the inorganic adhesive is an equimolar mixture of aluminum chromium phosphate aqueous solution and aluminum nitride as in Example 2.

[0055] Comparative Example 3 A hydrothermal PTC heater is the same as in Example 1, except that it does not include composite phase change materials.

[0056] Comparative Example 4 A hydrothermal PTC heater is identical to that in Example 1, except that the insulating ceramic plate is replaced with a polyimide film.

[0057] Comparative Example 5 A hydrothermal PTC heater, otherwise identical to Example 1, except that no inorganic adhesive is added.

[0058] Comparative Example 6 A hydrothermal PTC heater is otherwise identical to that in Example 2, except that a pressing force of 1200N is applied.

[0059] Comparative Example 7 A hydrothermal PTC heater is identical to that in Example 1, except that it does not include a composite phase change material and the insulating ceramic plate is replaced with a polyimide film.

[0060] Testing and Evaluation The power, thermal buffering performance, and reliability of the hydrothermal PTC heaters obtained in different embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0061] Steady-state power: The stable output power maintained by a hydrothermal PTC heater after reaching thermal equilibrium under conditions of 60°C inlet water temperature and 10 L / min flow rate. Without changing the boundary dimensions of the PTC heater, the higher the stable power, the higher the power density of the PTC heater. Thermal buffer performance: The evaluation index is the temperature fluctuation range of the PTC chip center. The test conditions are the same as the steady-state power. When a power step or ambient temperature change is applied, the maximum fluctuation range of the chip center temperature (ΔTmax) is used as the standard to measure the thermal buffer performance. The better the thermal buffer performance, the better the heat transfer efficiency of the heater, and the PTC power will not decrease due to a sharp increase in temperature. Structural reliability: After 500 thermal cycles (room temperature - 100℃), the PTC heating chip is disassembled and tested for creepage and breakdown. If the structure is undamaged, it indicates that the PTC heater has a longer lifespan and better value. Ultimate power: Under the same test conditions as steady-state power, it is the peak output power that can be reached instantaneously before the temperature rise causes a significant increase in its resistance. The higher the ultimate power, the better the heating rate of the PTC heater.

[0062] Long-term stability: The power decay rate after 1000 hours under high-temperature aging conditions at 150℃. The better the stability, the longer the service life of the PTC heater.

[0063] Table 1 Test Results

[0064] This application effectively eliminates air thermal resistance in the assembly gap by replacing the traditional organic insulating film with a high thermal conductivity inorganic insulating ceramic plate and combining it with composite phase change material filling. This creates an efficient and stable thermal conduction path between the PTC chip and the metal shell. At the same time, the use of a component-matched inorganic adhesive buffer layer effectively relieves mechanical stress during the press-fitting process, preventing damage to brittle components. While ensuring good thermal conductivity, it meets the insulation safety requirements under high voltage applications, avoids the reliability risks caused by high-temperature aging of organic materials, and significantly improves the power density, operational stability, structural durability, and electrical safety of the heater.

[0065] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydrothermal PTC heater, characterized by, The water heat PTC heater comprises a PTC heating package (1), a metal shell (2), and a composite phase change material (4) and inorganic glue filled between the PTC heating package (1) and the metal shell (2); the PTC heating package (1) comprises a PTC heating chip, an electrode sheet and an insulating ceramic plate; the phase change temperature of the composite phase change material (4) is higher than 20 DEG C and lower than the Curie temperature of the PTC heating chip.

2. The hydrothermal PTC heater according to claim 1, characterized in that, The composite phase change material (4) is microencapsulated phase change material or skeleton-based composite phase change material; the phase change temperature of the composite phase change material (4) is 50-110 DEG C; the thermal conductivity of the composite phase change material (4) in solid state is greater than or equal to 1.5 W / (m*K).

3. The hydrothermal PTC heater according to claim 2, wherein The microencapsulated phase change material comprises core material and shell material coated on the core material; the core material comprises one or more of octadecanol, eicosanol, docosanol, palmitic acid and stearic acid; the shell material comprises one or more of aluminum oxide, aluminum nitride, silicon nitride and boron nitride.

4. The hydrothermal PTC heater according to claim 2, wherein The skeleton-based composite phase change material comprises skeleton and phase change material loaded in the skeleton; the skeleton comprises one or more of aluminum oxide porous material, aluminum nitride porous material, silicon nitride porous material and boron nitride porous material; the phase change material comprises one or more of octadecanol, eicosanol, docosanol, palmitic acid, stearic acid, paraffin, polyethylene glycol and pentaerythritol.

5. The hydrothermal PTC heater according to any one of claims 3-4, characterized in that, The material of the inorganic glue is the same as the material of the skeleton or shell of the composite phase change material (4).

6. The hydrothermal PTC heater according to claim 2, wherein The microencapsulated phase change material is obtained by in-situ polymerization method, sol-gel method or interfacial polymerization method.

7. The hydrothermal PTC heater according to claim 2, wherein The skeleton-based composite phase change material is obtained by vacuum impregnation method.

8. A method of manufacturing a hydrothermal PTC heater according to any one of claims 1 to 7, characterized by, The method comprises the following steps: S1. applying inorganic glue on the inner side surface of the metal shell (2) and the outer surface of the PTC heating package (1); S2. placing the PTC heating package (1) and the composite phase change material (4) in the metal shell (2), and performing compression and curing treatment, thereby obtaining the water heat PTC heater.

9. The production method according to claim 8, characterized by, The specific process of step S2 is: placing the PTC heating package (1) in the metal shell (2), and performing pressure treatment on the PTC heating package (1); injecting the composite phase change material (4) into the gap (3) between the metal shell (2) and the PTC heating package (1), and performing heating and curing treatment.

10. The preparation method according to claim 8, characterized in that, The specific process of step S2 is: placing the PTC heating package (1) and the composite phase change material (4) in the metal shell (2), and performing pressure treatment, and then performing heating and curing treatment.

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