Cooling medium for charging cable liquid cooling heat dissipation system and preparation method

Abstract

The invention relates to the field of cooling media, in particular to a cooling medium for a charging cable liquid cooling heat dissipation system and a preparation method. A cooling medium for a liquid cooling heat dissipation system of a charging cable comprises the following components in percentage by weight: 85-92% of a basic liquid, 5-12% of a heat conduction and phase change functional filler and 1-3% of a functional additive, the heat-conducting and phase-change functional filler comprises a nano boron nitride sheet and a microencapsulated phase-change material in a weight ratio of (3-6): (2-6); the microencapsulated phase change material takes paraffin or fatty acid ester as a core material and takes polymethyl methacrylate as a wall material. The thermal conductivity and the wide temperature range stability are improved.

Description

Technical Field

[0001] This application relates to the field of cooling media, and in particular to a cooling media and preparation method for a liquid cooling heat dissipation system for charging cables. Background Technology

[0002] With the rapid development of new energy vehicles, high-power DC fast charging technology has become crucial for solving the problem of long charging times. The increased charging power leads to a dramatic increase in heat generation in charging cables, making liquid cooling technology the mainstream solution. As a key medium in the liquid cooling system, the performance of the coolant directly affects the safety and efficiency of the charging system.

[0003] Currently, the main types of coolants on the market are water-glycol-based, mineral oil-based, and silicone oil-based. Water-glycol-based coolants are low in cost and have a high specific heat capacity, but their dielectric strength is insufficient, and leakage may cause short circuits. Mineral oil and silicone oil-based coolants have higher dielectric strength, but their thermal conductivity is relatively low, resulting in limited heat dissipation efficiency. In addition, existing coolants also have shortcomings in performance under extreme temperatures: their viscosity increases sharply at low temperatures, affecting flow, and they are prone to oxidation and decomposition at high temperatures.

[0004] Especially for high-power DC charging cables, the operating current can reach over 500A, resulting in large instantaneous thermal shocks. Relying solely on the sensible heat absorption of the liquid is insufficient to effectively control the temperature rise. Furthermore, the internal structure of charging cables is complex, containing various metallic materials (copper conductors), polymer materials (TPU / PE tubing, insulation layers), and sealing materials, requiring the coolant to have good material compatibility.

[0005] Therefore, developing a coolant that simultaneously possesses high insulation, high thermal conductivity, wide temperature range stability, and good compatibility is of great significance for advancing the development of high-power charging technology. Summary of the Invention

[0006] To improve thermal conductivity and wide temperature range stability, this application provides a cooling medium and its preparation method for a liquid cooling heat dissipation system for charging cables.

[0007] In a first aspect, this application provides a cooling medium for a liquid cooling heat dissipation system for charging cables, employing the following technical solution: A cooling medium for a liquid cooling heat dissipation system for charging cables comprises, by weight percentage: 85-92% base fluid, 5-12% thermally conductive and phase-change functional filler, and 1-3% functional additives; The thermally conductive and phase change functional filler comprises nano-boron nitride sheets and microencapsulated phase change materials in a weight ratio of (3-6):(2-6); The microencapsulated phase change material uses paraffin or fatty acid esters as the core material and polymethyl methacrylate as the wall material.

[0008] By adopting the above technical solution and designing a ternary system of "base fluid-functional filler-additives," synergistic performance optimization is achieved. The core material is selected from paraffin wax or fatty acid esters, with a phase change point of 40-50℃. The base fluid constitutes the continuous phase, providing basic insulation and fluidity; the thermally conductive and phase change functional filler serves as the dispersed phase, with nano-boron nitride constructing an efficient thermal conduction path, and microencapsulated phase change materials absorbing / releasing a large amount of latent heat within a specific temperature range (40-50℃), acting as a "thermal buffer"; the functional additives ensure long-term stable operation. This formulation system enables the cooling medium to simultaneously possess high dielectric strength, excellent active heat dissipation capability, and wide temperature range stability, fundamentally solving the contradiction of traditional coolants in simultaneously achieving insulation and heat dissipation, and low-temperature flow and high-temperature stability.

[0009] Furthermore, the wall thickness of the microencapsulated phase change material is 0.1-2 μm.

[0010] By employing the above technical solution, the thickness of the microcapsule wall material is limited to 0.1-2 μm, based on a balance between mechanics and heat transfer. Too thin a wall material results in insufficient mechanical strength, making it prone to breakage and leakage under cyclic shear; too thick a wall material significantly increases thermal resistance, hindering the efficient transfer of latent heat of phase change in the core material. This thickness range ensures sufficient durability of the microcapsules during long-term operation in the liquid cooling system, while maximizing their thermal buffering response speed and efficiency.

[0011] Furthermore, the microencapsulated phase change material has a bimodal particle size distribution, comprising particles with a first peak of 5-10 μm and a second peak of 15-20 μm in a weight ratio of (1-2):1.

[0012] By adopting the above technical solution, the microcapsule particle size is specified to exhibit a bimodal distribution with a specific weight ratio. Particles of a single size tend to form a regular arrangement in the suspension, leading to accelerated sedimentation. In the bimodal distribution, smaller particles can fill the gaps between larger particles, forming a denser packing structure, thereby significantly reducing particle settling velocity and enhancing the long-term stability of the suspension. Simultaneously, the slightly different thermal response characteristics of microcapsules of different sizes help to smooth the overall temperature buffer curve.

[0013] Furthermore, the preparation method of the microencapsulated phase change material is as follows: (1) The oil phase is slowly added dropwise to the aqueous phase and continuously sheared to form a stable oil / water emulsion; The oil phase includes: paraffin or fatty acid esters, methyl methacrylate, oil-soluble initiators, and surface modifiers; The aqueous phase includes: deionized water, dispersant stabilizer, dispersant co-dispersant, and pH adjuster; (2) Through interfacial polymerization reaction, a polymer wall material is formed to obtain primary microcapsules; (3) The product obtained in step (2) is contacted with an organic swelling agent for swelling and strengthening treatment, and then the swelling agent is removed to densify the wall material; (4) Separate, wash and dry the microcapsules.

[0014] By employing the above technical solution, interfacial polymerization can form a complete and uniform polymer wall material in situ at the oil-water interface, achieving a high encapsulation rate. "Swelling reinforcement" uses an organic swelling agent to swell and relax the initially formed polymer chain segments of the wall material, followed by removal of the swelling agent to allow the chain segments to rearrange and solidify in a denser state. This process eliminates micro-defects, significantly improving the density, mechanical strength, and impermeability of the wall material, thereby extending the service life of the microcapsules under harsh operating conditions.

[0015] Furthermore, the dispersant stabilizer is polyvinyl alcohol and the dispersant co-dispersant is sodium alginate.

[0016] By adopting the above technical solution, polyvinyl alcohol (PVA) is selected as the main dispersant and stabilizer. Its long molecular chains can form a strong protective layer on the surface of oil droplets, preventing the emulsion droplets from coalescing before polymerization. Sodium alginate is used as a co-dispersant. Its anionic properties and thickening effect can further adjust the viscosity and interfacial properties of the aqueous phase. Together with PVA, it can precisely control the particle size and distribution of emulsion droplets, which is a key process guarantee for obtaining a bimodal distribution.

[0017] Furthermore, the boron nitride nanosheets have a particle size of 50-200 nm, a thickness of less than 5 nm, and their surface is modified by grafting with a silane coupling agent.

[0018] By employing the above technical solution, the particle size of the boron nitride nanosheets is controlled within 50-200 nm, and the thickness is <5 nm, in order to maximize its specific surface area and thermal anisotropy. h-BN has extremely high in-plane thermal conductivity, and its nanosheet morphology easily overlaps in liquids to form a three-dimensional thermally conductive network. Surface grafting modification with a silane coupling agent transforms the hydrophilic h-BN surface into a hydrophobic one, greatly improving its dispersibility and compatibility in organic base liquids, preventing the aggregation and sedimentation of nanoparticles, thereby stably and efficiently enhancing the overall thermal conductivity of the cooling medium.

[0019] Furthermore, the base liquid comprises hydrogenated terphenyl and pentaerythritol ester in a weight ratio of (6-7):(4-3).

[0020] By adopting the above technical solution, the base fluid is compounded with hydrogenated terphenyl and pentaerythritol ester in a specific ratio of (6-7):(4-3), achieving a synergistic effect. Hydrogenated terphenyl has extremely high dielectric strength and thermal oxidation stability, but its viscosity is relatively high at low temperatures; pentaerythritol ester, on the other hand, possesses excellent low-temperature fluidity and wetting compatibility with polymer materials. This ratio optimizes low-temperature fluidity at -40℃ while ensuring an overall dielectric strength >35 kV / mm, and enhances compatibility with the internal materials of the cable.

[0021] Furthermore, the functional additives include a composite corrosion inhibitor, a high-temperature antioxidant, a flame retardant synergist, and an antifoaming agent in a weight ratio of (3-8):(5-12):(2-5):(0.5-1).

[0022] Furthermore, the composite corrosion inhibitor is composed of benzotriazole compounds and sulfonate compounds; the high-temperature antioxidant is composed of hindered phenolic compounds and amine compounds; the flame retardant synergist is microencapsulated red phosphorus or organophosphorus ester; and the defoamer is polyether-modified siloxane.

[0023] By adopting the above technical solutions, the composite corrosion inhibitor protects various metals through different mechanisms; the composite antioxidant resists high-temperature oxidation through synergistic effects; the flame retardant synergist improves the safety level of the coolant; and the defoamer ensures the reliability of system operation. This additive system can achieve comprehensive performance of corrosion inhibition, oxidation resistance, flame retardancy, and defoaming with minimal dosage, ensuring the long-term stable operation of the cooling medium in complex and demanding cable liquid cooling systems.

[0024] Secondly, this application provides a method for preparing a cooling medium for a liquid cooling heat dissipation system for charging cables, employing the following technical solution: A method for preparing a cooling medium for a liquid cooling heat dissipation system of a charging cable includes the following steps: S1. Under high-speed shearing conditions, add nano boron nitride sheets to the base liquid and shear continuously for 30-60 minutes to form a uniformly dispersed suspension; the high-speed shearing condition is a rotation speed ≥ 5000 rpm; S2. Reduce the stirring speed to 300 rpm, add the microencapsulated phase change material and functional additives, and stir until evenly mixed; S3. Dehydrate and degas for 1-2 hours under vacuum conditions < -0.095 MPa and temperature < 80℃, then filter to obtain the cooling medium.

[0025] The key to this preparation method, employing the aforementioned technical solution, lies in step-by-step, differentiated process control. The first step, using high-speed shearing at ≥5000 rpm, aims to fully peel and disperse the nano-boron nitride sheets, breaking down their agglomerates to form a uniform and stable thermally conductive network. The second step significantly reduces the stirring speed to 300 rpm to provide a sufficiently gentle mixing environment when adding the microencapsulated phase change material, preventing high-speed shearing forces from damaging the fine structure of the microcapsules and ensuring their integrity. Subsequent vacuum dehydration and degassing thoroughly removes moisture and air bubbles, a necessary step to obtain extremely high and stable dielectric strength. The entire process flow is scientifically designed, combining high efficiency with protective features.

[0026] In summary, this application has the following beneficial effects: 1. High-efficiency active heat dissipation: Through the dual mechanisms of "nano boron nitride thermal conductive network" and "microcapsule phase change thermal buffer", rapid heat conduction and peak heat load management are achieved.

[0027] 2. Ultra-wide temperature range applicable: Maintains good fluidity at -40℃, has a high flash point, and meets the needs of all scenarios from cold to hot regions, from cold start to continuous high-power operation.

[0028] 3. Excellent long-term stability: The optimized formula and bimodal distribution design ensure that the functional filler has almost no sedimentation and minimal performance degradation under long-term high-temperature static and thermal cycling, guaranteeing the lifetime maintenance-free reliability of the liquid cooling system. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the embodiments.

[0030] Example of raw material and intermediate preparation raw material It should be noted that: in the following examples, unless otherwise specified, the conditions shall be in accordance with conventional conditions or the manufacturer's recommended conditions; and the raw materials used in the following examples, unless otherwise specified, shall be from commercially available sources. Hydrogenated terphenyl: Industrial grade, purity ≥99.5%; Pentaerythritol ester: Industrial grade, purity ≥98%; Nano-boron nitride sheets: purity ≥99%, average particle size 50-200 nm, thickness <5 nm, specific surface area >40 m² 2 / g; Silane coupling agent: used for boron nitride surface modification, γ-aminopropyltriethoxysilane (KH-550). Paraffin wax: Refined paraffin wax, phase transition point 45±2℃; Fatty acid esters: Methyl palmitate, butyl stearate, etc. can be selected, with a phase transition point of 40-50℃ and a purity of ≥95%; Methyl methacrylate (MMA): Chemically pure, polymerization grade, purity ≥99.5%; Oil-soluble initiator: azobisisobutyronitrile (AIBN), chemically pure, purity ≥98%; Vinyltriethoxysilane: chemically pure, purity ≥97%, used for prefunctionalization of microcapsule wall materials; Polyvinyl alcohol: Dispersant and stabilizer, degree of alcoholysis 88%, degree of polymerization 1700±50; Sodium alginate: dispersant, chemically pure, viscosity (1% aqueous solution, 20℃) ≥200 mPa·s; pH adjuster: Citric acid-sodium citrate buffer, analytical grade; Organic swelling agent: ethyl acetate, analytical grade, purity ≥99.5%; Methylbenzotriazole (TTAA), industrial grade, purity ≥98%; Sulfonates, sodium petroleum sulfonate, industrial grade; Hindered phenols: 2,6-Di-tert-butyl-p-cresol, industrial grade; Amines: phenothiazine or alkylated diphenylamine, industrial grade; Microencapsulated red phosphorus, with an average particle size of 5-20 μm and a red phosphorus content of ≥85%; Organophosphorus esters: Tris(2-chloroethyl) phosphate, industrial grade; Polyether-modified siloxanes, such as BYK-016, BYK-022, or similar non-silicone polyether defoamers, industrial grade.

[0031] Preparation Example Preparation Example 1 A microencapsulated phase change material, the preparation method of which is as follows: (1) Emulsification Oil phase preparation: Dissolve 1 kg of refined paraffin (phase transition point 45℃), 0.2 kg of methyl methacrylate, 0.002 kg of azobisisobutyronitrile and 0.003 kg of vinyltriethoxysilane by stirring at 60℃; Aqueous phase preparation: Dissolve 0.03 kg polyvinyl alcohol and 0.002 kg sodium alginate in 3 kg deionized water, heat to 60°C, and add sodium citrate buffer to adjust the pH to 7.0; Under high-speed shearing at 10,000 rpm, the oil phase was slowly added dropwise to the aqueous phase at a rate of 1 mL / min, and shearing was continued for 20 minutes to obtain a uniform and stable oil / water emulsion. (2) Interface aggregation The emulsion was transferred to a reaction vessel, heated to 78°C under nitrogen protection, and reacted for 5 hours to form a polymer wall material, thus obtaining primary microcapsules. (3) Swelling enhancement The temperature was lowered to 35°C, 0.2 kg of ethyl acetate was added, and the mixture was gently stirred for 3 hours. Then the temperature was raised to 50°C, and the ethyl acetate was recovered by vacuum distillation at -0.085 MPa. (4) Post-processing After the reaction solution was cooled, it was filtered, washed three times each with warm water and ethanol, dried under vacuum at 45°C for 12 hours, and sieved to obtain microencapsulated phase change material with a particle size mainly distributed in the range of 8-15 μm. The cross-section of the microcapsules was observed by scanning electron microscopy (SEM), and the average value and range of 50 random points were taken. The wall thickness of the microcapsules was 0.9-1.3 μm.

[0032] Preparation Example 2 (1) Emulsification The preparation of the oil phase and the aqueous phase are the same as in Preparation Example 1; Step-by-step independent emulsification: Preparation of small particle size emulsion: Take 60% of the total oil phase weight and slowly add it dropwise to the corresponding proportion of aqueous phase under high-speed shearing at 12000 rpm for 30 minutes until a uniform and stable emulsion A is formed, so as to form fine emulsion droplets with the main particle size peak at 5-10 μm, which can be used as templates for subsequent generation of small particle size microcapsules. Preparation of large particle size emulsion: Take the remaining 40% of the oil phase and slowly add it dropwise to the corresponding proportion of the aqueous phase under medium-high speed shearing conditions of 8000 rpm. Continue shearing for 20 minutes until a uniform and stable emulsion B is formed to form larger emulsion droplets with the main particle size peak of 15-20 μm, which can be used as templates for the subsequent generation of large particle size microcapsules. Emulsion mixing: The emulsion A and emulsion B, after emulsification, are mixed evenly at a weight ratio of 1.5:1 at 400 rpm, with the aim of ultimately forming microcapsules with bimodal particle size characteristics; The subsequent steps were the same as in Preparation Example 1, resulting in a microencapsulated phase change material with a bimodal particle size distribution. The two characteristic peaks were measured by a laser particle size analyzer and found to be located in the 5-10 μm and 15-20 μm ranges, respectively, with a weight ratio of approximately 1.5:1.

[0033] Preparation Example 3 A surface-modified boron nitride nanoparticle is prepared by the following method: 100g of boron nitride nanosheets with an average particle size of 100 nm and a thickness of 3 nm were dispersed in 2L of anhydrous ethanol, sonicated for 30 minutes, 15g of silane coupling agent was added, and the mixture was refluxed and stirred at 80℃ for 6 hours. After the reaction was completed, the nanosheets were centrifuged, washed three times with ethanol, and dried under vacuum at 80℃ to obtain surface-modified boron nitride nanosheets.

[0034] Example Examples 1-3 A cooling medium for a liquid cooling heat dissipation system of charging cables, the preparation method of which is as follows: S1. According to the raw material ratio in Table 1, add the nano boron nitride sheet to the base liquid under high-speed shearing at 6000 rpm and continue shearing for 45 minutes to form a uniformly dispersed suspension. S2. Reduce the stirring speed to 300 rpm, add the microencapsulated phase change material and other functional additives, and stir until evenly mixed; S3. Dehydrate and degas at -0.098 MPa and 75℃ for 90 minutes, then filter through a 5μm filter element to obtain the cooling medium.

[0035] Table 1 Raw Material Proportions (kg) The base solution comprises hydrogenated terphenyl and pentaerythritol ester in a weight ratio of 6:3; the thermally conductive and phase change functional filler comprises nano-boron nitride sheets and microencapsulated phase change material in a weight ratio of 3:6, wherein the microencapsulated phase change material is derived from Preparation Example 1; the functional additives comprise a composite corrosion inhibitor, a high-temperature antioxidant, a flame retardant synergist, and an defoamer in a weight ratio of 3:12:2:1; the composite corrosion inhibitor comprises methylbenzotriazole and sodium petroleum sulfonate in a weight ratio of 2:3; the high-temperature antioxidant comprises 2,6-di-tert-butyl-p-cresol and phenothiazine or alkylated diphenylamine in a weight ratio of 1:2; the flame retardant synergist is an organophosphate ester; and the defoamer is a polyether-modified siloxane.

[0036] Example 4 Unlike Example 2, the base liquid in Example 4 is hydrogenated terphenyl.

[0037] Example 5 Unlike Example 2, the thermally conductive and phase change functional filler in Example 5 includes nano-boron nitride sheets and microencapsulated phase change materials in a weight ratio of 6:2.

[0038] Example 6 Unlike Example 2, the phase change functional filler used in Example 6 was derived from Preparation Example 2.

[0039] Example 7 Unlike Example 2, in Example 7, the nano-boron nitride was replaced with an equal amount of modified nano-boron nitride from Preparation Example 3.

[0040] Comparative Example Comparative Example 1 Comparative Example 1 is a conventional water-glycol coolant consisting of 50% ethylene glycol and 50% deionized water.

[0041] Comparative Example 2 Unlike Example 1, in Comparative Example 2, an equal amount of nano-boron nitride was used to replace the microencapsulated phase change material.

[0042] Comparative Example 3 Unlike Example 1, in Comparative Example 3, an equal amount of microencapsulated phase change material was used to replace the nano-boron nitride.

[0043] Performance testing The following performance tests were conducted on the cooling media obtained in Examples 1-7 and Comparative Examples 1-3. The test methods and results are as follows: I. Basic Physical, Chemical and Electrical Performance Tests Test method: Dielectric strength: Tested according to GB / T 507 (equivalent to ASTM D877).

[0044] Thermal conductivity: Tested at 25℃ according to GB / T 10297 (hot wire method).

[0045] Kinematic viscosity (-40℃): Tested according to GB / T 265 (equivalent to ASTM D445).

[0046] Flash point: Test according to GB / T 3536 (Cleveland open cup method).

[0047] Copper sheet corrosion (100℃, 3h): Rating according to GB / T 5096.

[0048] Phase change latent heat: Differential scanning calorimetry (DSC) was used to measure the endothermic peak area in the range of 20-80℃ at a heating rate of 5℃ / min. The test results are shown in Table 2.

[0049] Table 2. Results of Basic Physicochemical Properties Tests As can be seen from Table 2: High insulation: The dielectric strength of all embodiments is ≥40 kV / mm, which is much higher than that of Comparative Example 1, demonstrating the high insulation advantage of the base liquid system.

[0050] High thermal conductivity: The thermal conductivity of Examples 1-7 is between 0.35 and 0.45 W / m·K. Comparative Example 3 has a thermal conductivity of only 0.16 W / m·K, demonstrating the key role of nano-boron nitride in improving thermal conductivity.

[0051] Excellent low-temperature flowability: The viscosity of all examples is ≤20 cSt at -40°C, which meets the requirements for use in extremely cold environments. Comparative Example 1 has a viscosity as high as 780 cSt, and it is basically unable to flow at low temperatures.

[0052] High safety: All examples have a flash point ≥220℃, classifying them as flame-retardant liquids. In contrast, Comparative Example 1 has a flash point of only 108℃, posing a flammable risk.

[0053] Thermal buffering capacity: Significant latent heat of phase transition (15-38 J / g) was measured in all examples containing microcapsules. Comparative Example 2 (without microcapsules) had a latent heat of 0, and Comparative Example 3 (with microcapsules but without boron nitride) had a latent heat of 30 J / g, demonstrating the successful encapsulation and functionality of the microcapsules.

[0054] II. Thermal Cycling Stability and Suspension Stability Tests Test method: Thermal cycling stability: The sample was cycled 100 times alternately between -40℃ (held for 4 hours) and 120℃ (held for 4 hours). The rate of change in viscosity and dielectric strength before and after the cycle was tested, and the appearance was observed.

[0055] Suspension stability: The sample was placed in an 80℃ oven and left to stand for 30 days (simulating long-term thermal storage). The volume ratio of the bottom sediment was observed, and the difference in thermal conductivity between the upper clear liquid and the lower sediment was tested by sampling. The results are shown in Table 3.

[0056] Table 3 Results of thermal cycling and suspension stability tests As can be seen from Table 3: Thermal stability and material compatibility: After 100 severe thermal cycles, the viscosity and dielectric strength of the sample in the example showed very small changes (<±6%), indicating that the formulation system was stable, the additives were effective, and the material compatibility was good.

[0057] Suspension stability: Example 6 (using bimodal microcapsules) exhibited excellent suspension stability with a sedimentation rate of <0.2% and almost no difference in performance between the upper and lower layers. Comparative Example 3 (with microcapsules but no boron nitride, and the microcapsules were unimodal) had a sedimentation rate as high as 12% and a difference of 25% in thermal conductivity between the upper and lower layers, indicating that the synergistic effect of the bimodal distribution design and surface-modified nano-boron nitride is crucial for preventing filler sedimentation and maintaining system homogeneity.

[0058] III. Simulated Cable Temperature Rise Test Test method: Construct a simulated liquid-cooled cable test platform, and test a 5-meter-long cable with a nominal cross-sectional area of ​​50 mm². 2 The copper conductor was placed in an insulating sleeve, with a cooling medium circulating outside the sleeve at a flow rate of 5 L / min. A constant current of 600 A was applied through a DC power supply to simulate high-power charging. The conductor temperature at a distance of 3 meters from the power supply was monitored using thermocouples. The time it took for the conductor temperature to reach a steady state (change of <1℃ within 10 minutes) and the final equilibrium temperature were recorded from an ambient temperature of 25℃. The results are shown in Table 4.

[0059] Table 4 Simulated cable temperature rise test results As can be seen from Table 4: The "heat buffering" effect is clearly demonstrated by the fact that the temperature rise curves of Examples 2 and 6 show a significant "plateau" in the 45-50℃ range. This is direct evidence of the latent heat absorption of the microencapsulated phase change material, which significantly slows down the temperature rise rate. Comparative Example 2 (without microcapsules) has the fastest temperature rise, with an equilibrium temperature as high as 95℃.

[0060] Synergistic heat dissipation advantages: Examples 2 and 6 not only exhibit a gradual temperature rise but also the lowest equilibrium temperature (81-82℃). This is attributed to the efficient thermal conductivity of nano-boron nitride, which rapidly dissipates heat, and the latent heat of phase change in the microcapsules, which buffers peak heat loads. The synergistic effect of these two factors achieves optimal heat dissipation.

[0061] Limitations of individual functions: Comparative Example 3 (microcapsules only) had a plateau period, but due to poor thermal conductivity, heat could not be effectively dissipated, and the final equilibrium temperature was still relatively high (91℃). Comparative Example 1 (conventional coolant) had the worst performance due to insulation and low-temperature limitations.

[0062] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A cooling medium for a liquid cooling heat dissipation system of charging cables, characterized in that, By weight percentage, it comprises the following components: base fluid 85-92%, thermally conductive and phase change functional filler 5-12%, and functional additives 1-3%; The thermally conductive and phase change functional filler comprises nano-boron nitride sheets and microencapsulated phase change materials in a weight ratio of (3-6):(2-6); The microencapsulated phase change material uses paraffin or fatty acid esters as the core material and polymethyl methacrylate as the wall material. The base liquid comprises hydrogenated terphenyl and pentaerythritol ester in a weight ratio of (6-7):(4-3); The functional additives include a composite corrosion inhibitor, a high-temperature antioxidant, a flame retardant synergist, and an antifoaming agent in a weight ratio of (3-8):(5-12):(2-5):(0.5-1).

2. The cooling medium for a liquid cooling heat dissipation system for charging cables according to claim 1, characterized in that, The wall thickness of the microencapsulated phase change material is 0.1-2 μm.

3. The cooling medium for a liquid cooling heat dissipation system for charging cables according to claim 1, characterized in that, The microencapsulated phase change material has a bimodal particle size distribution, comprising particles with a first peak of 5-10 μm and a second peak of 15-20 μm in a weight ratio of (1-2):

1.

4. The cooling medium for a liquid cooling heat dissipation system for charging cables according to claim 1, characterized in that, The preparation method of the microencapsulated phase change material is as follows: (1) The oil phase is slowly added dropwise to the aqueous phase and continuously sheared to form a stable oil / water emulsion; The oil phase includes: paraffin or fatty acid esters, methyl methacrylate, oil-soluble initiators, and surface modifiers; The aqueous phase includes: deionized water, dispersant stabilizer, dispersant co-dispersant, and pH adjuster; (2) Through interfacial polymerization reaction, a polymer wall material is formed to obtain primary microcapsules; (3) The product obtained in step (2) is contacted with an organic swelling agent for swelling and strengthening treatment, and then the swelling agent is removed to densify the wall material; (4) Separate, wash and dry the microcapsules.

5. The cooling medium for a liquid cooling heat dissipation system for charging cables according to claim 4, characterized in that, The dispersant stabilizer is polyvinyl alcohol, and the dispersant co-dispersant is sodium alginate.

6. The cooling medium for a liquid cooling heat dissipation system for charging cables according to claim 1, characterized in that, The boron nitride nanosheets have a particle size of 50-200 nm, a thickness of less than 5 nm, and their surface is modified by grafting with a silane coupling agent.

7. The cooling medium for a liquid cooling heat dissipation system for charging cables according to claim 1, characterized in that, The composite corrosion inhibitor is composed of benzotriazole compounds and sulfonate compounds; the high-temperature antioxidant is composed of hindered phenolic compounds and amine compounds; the flame retardant synergist is microencapsulated red phosphorus or organophosphorus ester; and the defoamer is polyether-modified siloxane.

8. A method for preparing a cooling medium for a liquid cooling heat dissipation system for charging cables as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Under high-speed shearing conditions, add nano boron nitride sheets to the base liquid and shear continuously for 30-60 minutes to form a uniformly dispersed suspension; the high-speed shearing condition is a rotation speed ≥ 5000 rpm; S2. Reduce the stirring speed to 300 rpm, add the microencapsulated phase change material and functional additives, and stir until evenly mixed; S3. Dehydrate and degas for 1-2 hours under vacuum conditions < -0.095 MPa and temperature < 80℃, then filter to obtain the cooling medium.

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