An electric vehicle thermal management system based on phase change material and air cooling and its preparation method

Abstract

The present invention proposes an electric vehicle thermal management system based on phase change material and air cooling and a preparation method, relating to the technical field of electric vehicle batteries. By optimizing the electric vehicle thermal management system and providing a preparation method for a composite phase change material with a low eutectic metastable phase change material and high thermal conductivity, it is possible to cleverly utilize the wind energy generated by the electric vehicle during driving and the high phase change enthalpy of the phase change material to achieve passive heat dissipation of the electric vehicle battery. In other words, the electric vehicle battery can be well thermally managed under different external temperature environments without the need for an additional power supply, and the thermal management effect is superior to current conventional thermal management.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle batteries, and in particular to an electric vehicle thermal management system based on phase change materials and air cooling and a preparation method thereof. Background Art

[0002] Due to their energy-saving, environmentally friendly, high energy efficiency, and low noise levels, electric vehicles have gradually become an indispensable means of transportation for Chinese people commuting and short-distance travel. However, the safety of electric vehicles has always been a major concern, primarily due to battery safety issues during use, especially during charging, which has attracted the attention of government regulators. In high-temperature conditions, the heat generated by electric vehicle battery packs cannot be dissipated to the outside world in a timely manner, causing the battery temperature to rise and causing fires, compromising the safe operation of the electric vehicle. Furthermore, high temperatures can cause irreversible capacity loss in the battery. In low-temperature conditions, the battery capacity is significantly reduced, seriously affecting the electric vehicle's range.

[0003] In the existing technology, the main methods for assisting the heat dissipation of the battery are to use a water cooling system or an air cooling auxiliary system. However, the use of a water cooling system undoubtedly adds peripheral facilities to the battery pack, which will cause the battery pack to perform additional external work and there is a risk of leakage or liquid seepage; and the heat dissipation method using air cooling to assist the phase change thermal management module is also active heat dissipation, which cannot avoid peripheral devices. When a certain temperature is reached, the air cooling module assists in heat dissipation, which also requires the battery to discharge externally, which undoubtedly increases the discharge burden of the battery. Therefore, proposing a more practical electric vehicle thermal management system that does not increase the discharge burden of the battery has certain practical and social significance. Summary of the Invention

[0004] In order to overcome the above problems or at least partially solve the above problems, an embodiment of the present invention provides an electric vehicle thermal management system based on phase change materials and air cooling and a preparation method. By optimizing the electric vehicle thermal management system, the battery of the electric vehicle can be well thermally managed without the need for additional power supply, and its thermal management effect is better than the current conventional thermal management.

[0005] The embodiment of the present invention is achieved as follows:

[0006] In the first aspect, the embodiment of the present application provides an electric vehicle thermal management system based on phase change material and air cooling, which includes a battery column, a cover, a box, a charging and discharging interface and a heat pipe. The above-mentioned box is a top opening structure, and the above-mentioned cover is used to cover the top opening of the above-mentioned box. The above-mentioned cover is provided with a heat dissipation hole adapted to the heat dissipation pipe. One end of the above-mentioned heat dissipation pipe is passed through the side wall of the above-mentioned box, and the other end passes through the above-mentioned cover through the above-mentioned heat dissipation hole. The above-mentioned box is also provided with a first metal connecting piece. The above-mentioned cover is a hollow structure. A connecting circuit is provided in the above-mentioned cover. The above-mentioned cover is provided with a heat dissipation hole adapted to the above-mentioned first metal connecting piece. The cover body is also provided with a third metal connector adapted to the battery column, the second metal connector is connected to the third metal connector through the connecting circuit, the battery column is arranged in the box body, one end of the battery column is used to be connected to the third metal connector, and the other end is connected to the first metal connector through the charging and discharging interface. The side wall of the battery column is also provided with a battery shell, the battery shell is made of a first phase change material, and the battery shell, the heat dissipation tube and the box body are filled with a filler made of a second phase change material.

[0007] Based on the first aspect, some embodiments of the present invention further include a metastable excitation device, and the metastable excitation device is connected to the outer wall of the box.

[0008] In some embodiments of the present invention, the first phase change material is a metastable phase change material, and the second phase change material is a composite phase change material.

[0009] In some embodiments of the present invention, the second phase change material includes at least one of paraffin wax, foamed aluminum, decane, magnesium chloride hexahydrate, myristic acid, stearic acid, expanded perlite, or activated carbon.

[0010] In some embodiments of the present invention, fan blades are provided in the heat dissipation pipe.

[0011] In some embodiments of the present invention, the heat dissipation pipe is spiral-shaped.

[0012] In a second aspect, an embodiment of the present application provides a method for preparing a second phase change material, comprising the following steps:

[0013] Heat lauric acid to 46-80°C to fully melt it;

[0014] adding expanded graphite to the melted lauric acid and stirring uniformly to obtain a mixture;

[0015] The mixture is subjected to vacuum impregnation and heat preservation treatment at 46-80°C;

[0016] The mixture in heat preservation treatment is stirred again for 1 to 3 minutes every 2.5 to 3.5 hours. After 11 to 13 hours, the mixture is taken out and cooled to obtain the product.

[0017] In some embodiments of the present invention, the step of adding expanded graphite to the melted lauric acid and stirring to obtain a mixture specifically comprises:

[0018] Expanded graphite is added to the melted lauric acid, with the mass ratio of the expanded graphite to the lauric acid being 8% to 18%, and the mixture is uniformly stirred to obtain a mixture.

[0019] In some embodiments of the present invention, the following steps are further included:

[0020] Fill the taken-out mixture into a mold preheated to 46-80°C;

[0021] After cooling, seal the mold, heat the mold to 46-80°C, and then cool it naturally. Repeat this process 3-6 times.

[0022] On the third side, the embodiment of the present application provides a method for preparing a first phase change material, which includes the following steps:

[0023] Calculate the raw materials by mass: 3-4 parts of sodium acetate trihydrate and 6-7 parts of urea are heated in a water bath or oil bath at 78-85°C to completely melt;

[0024] The melted sodium acetate trihydrate and urea are fully dispersed in an ultrasonicator and then encapsulated;

[0025] After packaging, keep warm in a 48-53°C water bath or oil bath for 10-30 minutes.

[0026] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0027] (1) Green and environmentally friendly, since no external power supply is required for heating or cooling, the completely passive thermal management device has no carbon emissions during use, has a long life, and can be recycled for many years;

[0028] (2) The processing and production are simple, and the preparation does not require difficult technical operations;

[0029] (3) Simple loading and maintenance. The entire system has a simple structure and is easy to install and maintain.

[0030] (4) Efficient heat dissipation, cleverly utilizing wind energy during driving and the high phase change enthalpy of phase change materials to achieve passive heat dissipation;

[0031] (5) Safe, no risk of leakage compared to liquid cooling auxiliary devices;

[0032] (6) The device is small in size and light in weight. Electric vehicles require a lighter, more compact and practical battery thermal management system, and the battery thermal management device of an electric vehicle often requires a more complex device. Thanks to the passive cooling thermal management technology provided in the embodiment of the invention, the weight and volume are reduced without external cooling devices such as water tanks, fans, and heat pumps;

[0033] (7) A method for preparing a low-eutectic metastable phase change material (first phase change material) and a high-thermal-conductivity composite phase change material (second phase change material) is also proposed, which makes it possible to use phase change materials to achieve cooling and heating, and can efficiently excite the metastable state in a low-temperature environment, providing heat for the battery to provide a healthy battery operating temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is a schematic structural diagram of an embodiment of an electric vehicle thermal management system based on phase change material and air cooling according to the present invention;

[0036] Figure 2 This is a schematic structural diagram of an embodiment of an electric vehicle thermal management system based on phase change material and air cooling according to the present invention;

[0037] Figure 3 This is a schematic structural diagram of an embodiment of an electric vehicle thermal management system based on phase change material and air cooling according to the present invention;

[0038] Figure 4 A schematic diagram of the structure of a battery column of an embodiment of an electric vehicle thermal management system based on phase change material and air cooling according to the present invention;

[0039] Figure 5 is a flow chart of a method for preparing a second phase change material in an embodiment of the present invention;

[0040] Figure 6 is a flow chart of a method for preparing a first phase change material in an embodiment of the present invention;

[0041] Figure 7 This is the cooling curve of the sodium acetate urea binary eutectic system in the embodiment of the present invention.

[0042] Icons: 1. Battery column; 2. Cover; 3. Box; 4. Charge and discharge interface; 5. Heat dissipation pipe; 6. Heat dissipation hole; 7. First metal connector; 8. Second metal connector; 9. Third metal connector; 10. Battery shell; 11. Filler; 12. Metastable excitation device. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0045] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0046] In the description of the embodiments of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is typically placed when in use. These terms are intended only to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," "third," etc., etc., are intended only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0047] Furthermore, the use of terms such as "horizontal," "vertical," and "overhanging" does not necessarily imply that the component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," not that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0048] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0049] Example

[0050] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features thereof may be combined with each other.

[0051] Please refer to Figures 1 to 4 , an embodiment of the present invention provides an electric vehicle thermal management system based on phase change material and air cooling, which includes a battery column 1, a cover 2, a box 3, a charge and discharge interface 4 and a heat pipe 5. The box 3 is a top-opening structure, and the cover 2 is used to cover the top opening of the box 3. The cover 2 is provided with a heat dissipation hole 6 adapted to the heat dissipation pipe 5. One end of the heat dissipation pipe 5 is passed through the side wall of the box 3, and the other end passes through the cover 2 through the heat dissipation hole 6. The box 3 is also provided with a first metal connector 7. The cover 2 is a hollow structure, and a connecting circuit is provided inside the cover 2. The cover 2 is provided with a first metal connector The second metal connector 8 is adapted to the connector 7, and the cover 2 is also provided with a third metal connector 9 adapted to the battery column 1. The second metal connector 8 is connected to the third metal connector 9 through a connecting circuit. The battery column 1 is arranged in the box body 3, and one end of the battery column 1 is used to be connected to the third metal connector 9, and the other end is connected to the first metal connector 7 through the charge and discharge interface 4. The side wall of the battery column 1 is also provided with a battery shell 10, and the battery shell 10 is made of a first phase change material. The battery shell 10, the heat dissipation tube 5 and the box body 3 are filled with a filler 11 made of a second phase change material.

[0052] In the above embodiment, by providing a heat dissipation pipe 5 extending through the housing 3 and the cover 2, heat generated by the battery column 1 can be dissipated into the air through the heat dissipation pipe 5. It should be noted that when the entire device is installed on an electric vehicle, the opening of the heat dissipation pipe 5 can be positioned perpendicular to the direction of travel of the electric vehicle. This allows the natural airflow generated by the vehicle's movement to flow more efficiently into the heat dissipation pipe 5, thereby improving heat dissipation throughout the device. Furthermore, the heat dissipation pipe 5 can be made of a material with a low specific heat capacity, such as metal, to provide better heat dissipation. Furthermore, by providing a battery housing 10 made of a first phase change material on the outer surface of the battery column 1, heat is supplied by the phase change of the battery housing 10 in low-temperature environments, ensuring the normal operation of the battery column 1 even in low-temperature environments and improving the stability of the device. When the battery column 1 generates heat during operation, the second phase change material begins to absorb the heat when heated to 44°C, maintaining the device temperature at a stable level of approximately 44°C. In other words, the dual passive cooling provided by the heat dissipation pipe 5 and the filler 11 made of the second phase change material effectively reduces the temperature of the entire device. Furthermore, because the cover 2 is a hollow device, the connection circuit for connecting the second metal connector 8 and the third metal connector 9 can be disposed within the cover 2. This not only prevents damage to the connection circuit but also provides a certain degree of heat dissipation for the heat generated by the connection circuit. It should be noted that because the second phase-change material filler 11 within the housing 3 is lauric acid encapsulated with a certain proportion of expanded graphite, thanks to the excellent encapsulation properties of the expanded graphite, the second phase-change material filler 11 does not leak outside the housing 3 when it undergoes a phase change due to heat, thereby affecting its normal operation.

[0053] For example, the box body 3 and the box cover can be detachably connected, which not only facilitates the installation of the entire device, but also facilitates the later inspection and maintenance of the interior of the box body 3. In addition, a sealing layer can be provided at the opening of the box body 3, so that the filler 11 can be better sealed into the box body 3.

[0054] Please refer to Figures 1 to 3 In some embodiments of the present invention, a metastable excitation device 12 is further included, and the metastable excitation device 12 is connected to the outer wall of the box 3.

[0055] In the above embodiment, a metastable excitation device 12 is provided on the outer wall of the box body 3, so that when the battery column 1 is exposed to a low-temperature cold environment, the metastable excitation device 12 can provide the battery shell 10 made of the first phase change material with sufficient energy to cause it to crystallize and release a large amount of heat, thereby increasing the temperature of the battery column 1 and maintaining the normal operating temperature of the battery column 1.

[0056] For example, the metastable state excitation device 12 may be configured as a device that excites the first phase change material to crystallize and release heat by providing ultrasonic vibration, magnetic field, electric field, and the like.

[0057] Please refer to Figures 1 to 4 In some embodiments of the present invention, the first phase change material is a metastable phase change material, and the second phase change material is a composite phase change material.

[0058] In the above embodiment, by selecting the material types of the first phase change material and the second phase change material, the heat dissipation performance of the entire system device can be integrated to enable better heat dissipation processing.

[0059] Illustratively, in some embodiments of the present invention, the second phase change material may include at least one of paraffin wax, foamed aluminum, decane, magnesium chloride hexahydrate, myristic acid, stearic acid, expanded perlite, or activated carbon.

[0060] Please refer to Figures 1 to 4 In some embodiments of the present invention, fan blades are provided in the heat dissipation pipe 5 .

[0061] In the above embodiment, by providing fan blades within the heat pipe 5, when natural air flows into the heat pipe 5, a negative pressure is generated at the rear end of the fan blades, thereby creating a suction force, allowing the natural air to continuously flow into the heat pipe 5. In other words, the heat dissipation efficiency of the heat pipe 5 can be greatly improved.

[0062] Please refer to Figures 1 to 4 In some embodiments of the present invention, the heat dissipation pipe 5 is spiral.

[0063] In the above embodiment, by arranging the heat dissipation tube 5 into a spiral shape, a swirling airflow is formed when the natural airflow flows into the heat dissipation tube 5, thereby increasing its flow rate, that is, better heat dissipation can be achieved.

[0064] Please refer to Figure 5 The present invention also provides a method for preparing a second phase change material, which comprises the following steps:

[0065] Step S101: heating lauric acid to 46-80° C. to fully melt it;

[0066] Step S102: adding expanded graphite to the melted lauric acid and stirring to obtain a mixture;

[0067] Step S103: performing vacuum impregnation and heat preservation treatment on the mixture at 46-80°C;

[0068] Step S104: stirring the mixture during heat preservation treatment for 1 to 3 minutes every 2.5 to 3.5 hours, taking out the mixture after 11 to 13 hours, and cooling it to obtain the product.

[0069] In the above embodiment, since the melting point of lauric acid is 44.07° C., it can be fully melted by heating it to 46-80° C., and then adding expanded graphite thereto can effectively improve the thermal conductivity of the material.

[0070] For example, the following examples are only used to illustrate the present invention in detail and are not intended to limit the scope of protection of the invention in any way.

[0071] (1) Example 1: Preparation of the Second Phase Change Material I

[0072] 100 parts of lauric acid are heated to 70°C to fully melt; 18 parts of expanded graphite are added to the melted lauric acid and stirred evenly to obtain a mixture; the mixture is subjected to vacuum impregnation and heat preservation treatment at 70°C; the mixture during vacuum impregnation and heat preservation treatment is stirred again for 1 to 3 minutes every 2.5 to 3.5 hours, the mixture is taken out after 11 to 13 hours, and cooled to obtain the product.

[0073] The thermal conductivity of the second phase change material prepared in this way is 1.720W / (m·K), while the thermal conductivity of lauric acid is only 0.188W / (m·K). The thermal conductivity of the composite phase change material is increased to more than 9 times that of the raw material, and its phase change enthalpy reaches 120.556J / g, and the phase change temperature is about 43°C.

[0074] (2) Example 2: Preparation of the Second Phase Change Material II

[0075] The preparation method of this embodiment is basically the same as that of embodiment 1, except that: 1. the addition ratio of expanded graphite is 8%; 2. the mixture is subjected to vacuum impregnation and heat preservation treatment at 54°C.

[0076] The thermal conductivity of the second phase change material prepared in this way is 0.9886W / (m·K), while the thermal conductivity of lauric acid is only 0.188W / (m·K). The thermal conductivity of the composite phase change material is increased to more than 5 times that of the raw material, and its phase change enthalpy reaches 138.823J / g, and the phase change temperature is about 43°C.

[0077] Please refer to Figure 5 In some embodiments of the present invention, the step of adding expanded graphite to the melted lauric acid and stirring to obtain a mixture specifically includes:

[0078] Expanded graphite is added to the melted lauric acid, with the mass ratio of the expanded graphite to the lauric acid being 8% to 18%, and the mixture is uniformly stirred to obtain a mixture.

[0079] In the above embodiment, by adjusting the mass ratio of expanded graphite to lauric acid to 8% to 18%, the overall performance of the second phase change material can be effectively improved. For example, by adding 18 parts of expanded graphite to 100 parts of melted lauric acid, the thermal conductivity of the resulting second phase change material can be optimized.

[0080] Please refer to Figure 5 In some embodiments of the present invention, the following steps are further included:

[0081] Step S105: Filling the taken-out mixture into a mold preheated to 46-80°C;

[0082] Step S106: After cooling, the mold is sealed, and the mold is heated to 46-80° C. and then naturally cooled, and repeated 3-6 times.

[0083] In the above embodiment, by subjecting the mixture filled into the mold to a heating and then cooling process, the uniformity of the entire material can be effectively improved.

[0084] For example, the removed mixture can be placed in a mold preheated to 70°C; after cooling, the mold is sealed, and the mold is heated to 70°C and then naturally cooled, repeating 3 to 6 times. Furthermore, the specific number of repetitions can be selected based on actual needs. For example, if demand is low, only about 3 repetitions can be used, while if demand is high, about 5 repetitions can be used.

[0085] Please refer to Figure 6 The embodiment of the present invention further provides a method for preparing a first phase change material, which comprises the following steps:

[0086] Step S201: 3-4 parts of sodium acetate trihydrate and 6-7 parts of urea are heated in a water bath or oil bath at 78-85° C. to completely melt the raw materials, calculated by weight.

[0087] Step S202: fully dispersing the melted sodium acetate trihydrate and urea in an ultrasonic instrument, and then encapsulating;

[0088] Step S203: After packaging, keep the mixture in a water bath or oil bath at 48 to 53° C. for 10 to 30 minutes.

[0089] In the above embodiment, the inventors discovered that mixing sodium acetate trihydrate and urea at a temperature of 78-85°C effectively improves their mixing degree and enhances the performance of the subsequent finished product. While the phase transition temperature of urea is 132.7°C, and that of sodium acetate trihydrate is 58°C, the phase transition temperature of this binary eutectic system (first phase change material) after mixing the two in the above-mentioned special ratio is only about 33°C. The battery column 1 can easily reach its phase transition temperature during operation, making it recyclable.

[0090] For example, the following examples are only used to illustrate the present invention in detail and are not intended to limit the scope of protection of the invention in any way.

[0091] (1) Example 3: Preparation of the first phase change material I

[0092] The raw materials are calculated by weight: 4 parts of sodium acetate trihydrate and 6 parts of urea are heated in a water bath or oil bath at 80°C to completely melt; the melted sodium acetate trihydrate and urea are fully dispersed in an ultrasonic instrument and then packaged; and after packaging, the packaging is kept warm in a water bath or oil bath at 50°C for 10 to 30 minutes.

[0093] The cooling curve of the binary eutectic system of the first phase change material prepared in this way is as follows: Figure 7 As shown, the prepared first phase change material is placed in a -25°C experimental box for a period of time before crystallization and heat release occur, indicating that its supercooling degree can reach above 50°C, and it can be stably in a metastable state in winter. The heat released can instantly raise the system temperature to 16.3°C, which also shows that it can provide a suitable working temperature zone for the battery column 1.

[0094] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0095] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present application is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. An electric vehicle thermal management system based on phase change material and air cooling, characterized in that: The heat dissipation device comprises a battery column, a cover, a box, a charge and discharge interface and a heat dissipation pipe, the box is a top-opening structure, the cover is used to cover the top opening of the box, the cover is provided with a heat dissipation hole adapted for the heat dissipation pipe, one end of the heat dissipation pipe is passed through the side wall of the box, and the other end passes through the cover through the heat dissipation hole, the box is further provided with a first metal connector, the cover is a hollow structure, a connecting circuit is provided in the cover, the cover is provided with a second metal connector adapted for the first metal connector, the cover is further provided with a third metal connector adapted for the battery column, the second metal connector is connected to the third metal connector through the connecting circuit, the battery column is provided in the box, one end of the battery column is used to be connected to the third metal connector, and the other end is connected to the first metal connector through the charge and discharge interface, the side wall of the battery column is further provided with a battery shell, the battery shell is made of a first phase change material, and a filler made of a second phase change material is filled between the battery shell, the heat dissipation pipe and the box; It also includes a metastable excitation device, which is connected to the outer wall of the box; Fan blades are provided in the heat dissipation pipe; The heat dissipation pipe is spiral; The first phase change material is a metastable phase change material, and the second phase change material is a composite phase change material.

2. The electric vehicle thermal management system based on phase change material and air cooling according to claim 1, characterized in that: The second phase change material includes at least one of paraffin wax, foamed aluminum, decane, magnesium chloride hexahydrate, myristic acid, stearic acid, expanded perlite, or activated carbon.

3. A method for preparing the second phase change material according to claim 1, characterized in that: The steps include: Heat lauric acid to 46-80°C to fully melt it; adding expanded graphite to the melted lauric acid and stirring uniformly to obtain a mixture; The mixture is subjected to vacuum impregnation and heat preservation treatment at 46-80°C; The mixture in heat preservation treatment is stirred again for 1 to 3 minutes every 2.5 to 3.5 hours. After 11 to 13 hours, the mixture is taken out and cooled to obtain the product.

4. The method for preparing a second phase change material according to claim 3, characterized in that: The step of adding expanded graphite to the melted lauric acid and stirring to obtain a mixture specifically comprises: Expanded graphite is added to the melted lauric acid, with the mass ratio of the expanded graphite to the lauric acid being 8% to 18%, and the mixture is uniformly stirred to obtain a mixture.

5. The method for preparing a second phase change material according to claim 3, characterized in that: The following steps are also included: Fill the taken-out mixture into a mold preheated to 46-80°C; After cooling, seal the mold, heat the mold to 46-80°C, and then cool it naturally. Repeat this process 3-6 times.

6. A method for preparing the first phase change material according to claim 1, characterized in that: The following steps are involved: Calculate the raw materials by mass: 3-4 parts of sodium acetate trihydrate and 6-7 parts of urea are heated in a water bath or oil bath at 78-85°C to completely melt; The melted sodium acetate trihydrate and urea are fully dispersed in an ultrasonicator and then encapsulated; After packaging, keep warm in a 48-53°C water bath or oil bath for 10-30 minutes.

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