High-boiling stable nanometer heat exchange fluid and preparation method thereof

Abstract

This invention discloses a high-boiling-point stable nano-heat exchange fluid and its preparation method. The heat exchange fluid uses a binary mixed base liquid composed of pure water and a polyol selected from ethylene glycol, 1,2-propanediol, and 1,2-butanediol. After adding a surfactant to the binary mixed base liquid, a nanoparticle system mainly composed of Al2O3 nanoparticles is introduced, followed by dispersion and homogenization treatment to obtain the stable nano-heat exchange fluid. The nanoparticle system may further include MWCNT nanoparticles and SiO2 nanoparticles to form composite nanoparticles, balancing enhanced thermal conductivity and dispersion stability. Compared with existing heat exchange working fluids, this invention improves the liquid-phase stable operating range, thermal conductivity, and adaptability to cyclic heat exchange by synergistically controlling the base liquid composition and the nanoparticle system. It is suitable for closed-loop high-temperature heat exchange, industrial waste heat recovery, and thermal management of electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of heat exchange fluid development technology, specifically relating to a high-boiling-point stable nano heat exchange fluid and its preparation method. Background Technology

[0002] Heat exchange media are widely used in closed-loop heat exchange equipment, industrial waste heat recovery devices, electronic device cooling systems, and medium- and high-temperature heat transfer units. They are important working media for achieving heat transfer and thermal energy utilization. The thermal conductivity, boiling point, density, specific heat capacity, and dispersion stability of the heat exchange media directly affect the heat transfer efficiency, operational stability, and applicability of the equipment during the heat exchange process.

[0003] As heat exchange systems gradually develop towards higher heat flux density, higher temperature operation, and longer cycle times, traditional water-based heat exchange media can no longer meet the requirements under certain operating conditions. For example, pure water or ordinary alcohol-water mixtures suffer from problems such as limited liquid phase operating range, insufficient thermal conductivity, and performance degradation during long-term cycling at higher temperatures, thus limiting their further application in complex heat exchange environments.

[0004] To improve the performance of heat exchange working fluids, existing technologies typically employ two methods: one is to introduce alcohol components such as ethylene glycol and propylene glycol into the base fluid to increase its boiling point and adjust its basic thermophysical properties; the other is to add functional materials such as metal oxide nanoparticles and carbon-based nanoparticles to the base fluid to improve its thermal conductivity. While these methods can improve the heat transfer effect of the heat exchange working fluid to some extent, they still have some shortcomings.

[0005] On the one hand, current technologies for designing base fluid systems often focus on simple mixtures of single alcohols and water, lacking sufficient synergistic control over the boiling point, flowability, and stability of the base fluid for different heat exchange conditions. This results in limited applicability of the heat exchange medium under medium- and high-temperature operating conditions. On the other hand, existing research on nano-heat exchange fluids often focuses on simply improving thermal conductivity, while paying insufficient attention to the compatibility between nanoparticles and the base fluid, particle dispersion stability, and long-term cycling stability. This can easily lead to problems such as particle agglomeration, sedimentation, or performance fluctuations, thus affecting the practical application effect of the heat exchange medium.

[0006] In addition, although some existing composite nano heat exchange fluids use a variety of nanoparticles for blending, the division of labor among different particles in terms of thermal conductivity enhancement, dispersion stability and overall fluid thermal property regulation is not clear enough. There is still a lack of a heat exchange fluid design scheme that takes into account high boiling point, thermal conductivity enhancement and system stability.

[0007] Patent application CN117748020A discloses a lithium battery thermal management method based on different coolants. It involves adding 0.5% alumina particles to a water and ethylene glycol solution to generate an alumina nanofluid solution. The addition of alumina to the ethylene glycol and water increases the thermal conductivity of the ethylene glycol-water mixture, thus giving the nanofluid coolant a superior cooling effect. However, due to the single nanomaterial, the resulting increase in thermal conductivity is small (only 0.05 W / m²). -1 .K -1 The problem is...

[0008] Therefore, developing a high-performance heat exchange fluid that can be synergistically controlled through base fluid formulation and nanoparticle system to improve thermal conductivity and broaden the working range of the liquid phase while ensuring fluid stability has become an urgent technical problem to be solved in this field. Summary of the Invention

[0009] To overcome the shortcomings of the existing technology and address the problems of insufficient stable operating range, limited thermal conductivity, and poor long-term cycling stability of existing heat exchange working fluids, the present invention aims to provide a high-boiling-point stable nano heat exchange fluid and its preparation method. By adding one or more nanoparticles to an alcohol-water solution, the thermal conductivity and boiling point of the heat exchange working fluid can be effectively improved, resulting in significant advantages such as enhanced heat exchange performance, broadened high-temperature operating range of the working fluid, and improved system heat exchange efficiency.

[0010] To achieve the above objectives, the technical solution adopted by the present invention includes: This invention provides a method for preparing a high-boiling-point stable nano-heat transfer fluid, comprising the following steps: Step 1: Mix polyol and pure water in a predetermined ratio to obtain a binary mixed base liquid; Step 2: Add a surfactant to the binary mixed base liquid and stir until completely dissolved to obtain a pretreated base liquid; Step 3: Add the nanoparticle system to the pretreated base liquid and disperse it to obtain a nanoparticle suspension, wherein the nanoparticle system contains at least Al2O3 nanoparticles; Step 4: The nanoparticle suspension is homogenized to obtain a high-boiling-point stable nano heat exchange fluid.

[0011] In step one, the mass fraction ratio of polyol to pure water is 10:90 to 20:80. The polyol is selected from any one of ethylene glycol, 1,2-propanediol, and 1,2-butanediol.

[0012] In step two, the surfactant is selected from one of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone.

[0013] After the surfactant mentioned in step two is completely dissolved, its volume concentration in the pretreatment base solution is 0.2% to 0.6%.

[0014] The nanoparticle system described in step three is a single nanoparticle or a mixture of nanoparticles. The single nanoparticle is an Al2O3 nanoparticle, and the mixture of nanoparticles is composed of Al2O3 nanoparticles, MWCNT nanoparticles, and SiO2 nanoparticles.

[0015] In the mixed nanoparticles, each type of nanoparticle accounts for 10% to 80% of the mass fraction, and the volume concentration of the surfactant after dissolution in step two does not exceed the volume concentration of the mixed nanoparticles in the nanoparticle suspension in step three.

[0016] The Al2O3 nanoparticles have a particle size of 10-20 nm and a purity of not less than 99.9%; the MWCNT nanoparticles have a tube diameter of 3-15 nm, a tube length of 15-30 μm, and a purity higher than 98%; the SiO2 nanoparticles have a particle size of 15-20 nm and a purity of not less than 99.5%. The homogenization treatment is carried out by a combination of mechanical stirring and ultrasonic dispersion, with an ultrasonic time of 30-100 min, an ultrasonic power of 100-300 W, and a frequency of 20-50 kHz.

[0017] The present invention also provides a high-boiling-point stable nano heat exchange fluid, wherein, by mass fraction, the nano heat exchange fluid comprises a binary mixed base liquid of 100: (0.2~1.5): (0.2~0.6), a surfactant, and a nanoparticle system; wherein, the binary mixed base liquid comprises a polyol and pure water, and the mass fraction ratio of the polyol to pure water is 10:90~20:80; the surfactant is selected from one of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone; and the nanoparticle system comprises at least Al2O3 nanoparticles.

[0018] Furthermore, the high-boiling-point stable nano heat exchange fluid of the present invention may consist only of the binary mixed base liquid, the surfactant, and the nanoparticle system; wherein the binary mixed base liquid is composed of polyol and pure water.

[0019] The heat exchange fluid according to the present invention has a high boiling point stability characteristic. Specifically, the thermal conductivity of the nano heat exchange fluid reaches 0.68 W / (m·K) at 353.15K, and increases with increasing temperature in the temperature range of 293.15K-353.15K.

[0020] Compared with the prior art, the present invention has the following technical advantages: (1) The present invention uses pure water and ethylene glycol, 1,2-propanediol or 1,2-butanediol to form a binary mixed base liquid, which can utilize the high boiling point of polyol components to improve the liquid phase stable working range of heat exchange fluid under higher temperature conditions, thereby enhancing its adaptability to medium and high temperature heat exchange conditions.

[0021] (2) The present invention introduces a nanoparticle system into a binary mixed base liquid, wherein MWCNT nanoparticles are beneficial to improving the thermal conductivity of the heat exchange fluid, Al2O3 nanoparticles are beneficial to enhancing the heat transfer enhancement effect, and SiO2 nanoparticles are beneficial to improving the dispersion stability of the system. Through the synergistic effect of each nanoparticle, the comprehensive thermal properties of the heat exchange fluid can be further improved, thereby enhancing its heat exchange performance.

[0022] (3) By co-designing the binary mixed base liquid and nanoparticle system, this invention improves the thermal conductivity of the heat exchange fluid while taking into account the working range of the liquid phase and the dispersion stability. It can provide an feasible high-performance heat exchange working fluid solution for closed-loop heat exchange, industrial waste heat recovery and thermal management of electronic devices. Attached Figure Description

[0023] Figure 1 This is a SEM image of the composite heat exchange fluid in Embodiment 1 of the present invention; Figure 2 This is a comparison diagram of the thermal conductivity of the composite heat exchange fluid in Embodiment 1 of the present invention; Figure 3 This is a comparison diagram of the thermal conductivity of the composite heat exchange fluid in Embodiment 2 of the present invention; Figure 4 This is a comparison diagram of the thermal conductivity of the composite heat exchange fluid in Embodiment 3 of the present invention; Figure 5 This is a comparison diagram of the thermal conductivity of the composite heat exchange fluid in Embodiment 4 of the present invention; Figure 6 This is a comparison diagram of the thermal conductivity of the composite heat exchange fluid in Embodiment 5 of the present invention; Figure 7 This is a comparison diagram of the thermal conductivity of the composite heat exchange fluid in Embodiment 6 of the present invention; Figure 8 This is a comparison chart of the boiling points of the binary mixed base liquids in Examples 1, 3 and 5 of this invention. Detailed Implementation

[0024] In this invention, only certain exemplary embodiments have been simply described. As those skilled in the art will recognize, the described embodiments can be modified in various ways, such as by adding, deleting, or altering, without departing from the scope of the invention. Therefore, the drawings and descriptions are considered to be exemplary in nature and not restrictive. Specific embodiments of the invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the invention.

[0025] In this embodiment of the invention, ethylene glycol, 1,2-propanediol, 1,2-butanediol, Al2O3 nanoparticles and SiO2 nanoparticles were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and MWCNT nanoparticles were purchased from Shenzhen Suiheng Graphene Technology Co., Ltd.

[0026] Compared with existing technologies that introduce alcohol components such as ethylene glycol and propylene glycol into the base fluid, this invention further expands the application of 1,2-butanediol as a key component. 1,2-Butanediol possesses a lower freezing point (-42℃), a higher boiling point (192℃), moderate low-temperature viscosity, and a unique asymmetric hydrogen bond structure, which can significantly improve the liquid-phase stability, fluidity, and thermal stability of the heat exchange medium over a wide temperature range (-40~180℃). When combined with nanoparticles, it can enhance dispersion stability and improve thermal conductivity, thus solving the technical bottlenecks of existing alcohol systems in extreme temperatures, long-term cycling, and nanofluid compatibility.

[0027] The three surfactants selected in this invention exhibit better dispersion stability in alcohol-based solutions compared to other surfactants (gum arabic and sodium dodecyl sulfate), hence these three surfactants were chosen.

[0028] In this invention, when mixed nanoparticles are used, Al2O3 nanoparticles, as high thermal conductivity hard oxide fillers, can construct a basic short-range thermally conductive framework, thereby improving the inherent thermal conductivity of the base fluid. MWCNTs, with their one-dimensional high aspect ratio structure, establish long-range continuous thermally conductive pathways, enhancing phonon transfer and fluid micro-convection effects, further improving heat transfer efficiency. SiO2 nanoparticles, rich in hydroxyl groups on their surface, can form hydrogen bonds with alcohol-based base fluids, suppressing particle entanglement, aggregation, and sedimentation through steric hindrance, while simultaneously regulating system viscosity and reducing interfacial thermal resistance. These three components form a point-to-line synergistic and complementary composite mechanism, constructing a multi-level continuous thermally conductive network that balances dispersion stability, flow characteristics, and wide-temperature-range heat transfer performance, achieving a synergistic enhanced heat transfer effect that cannot be achieved with a single nanofiller.

[0029] The following are several specific embodiments of the present invention.

[0030] Example 1 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add ethylene glycol to pure water at a mass ratio of 20:80, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; like Figure 8 As shown, the binary mixed base liquid constructed from pure water and ethylene glycol in this embodiment has good thermal stability, which solves the problem of easy decomposition of traditional base liquids under high temperature and high pressure conditions.

[0031] Step 2: Add sodium dodecylbenzenesulfonate to the binary mixed base liquid obtained in Step 1, and continue stirring until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.6% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are prepared by mixing Al2O3 nanoparticles, MWCNT nanoparticles, and SiO2 nanoparticles in a mass fraction ratio of 80:10:10. The mixed nanoparticles are added to the pretreatment base liquid obtained in Step 2, and after thorough stirring and dispersion, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The dispersion method uses a two-step method.

[0032] The parameters of each nanoparticle used in this embodiment are as follows: the particle size of Al2O3 nanoparticles is 10 nm, and the purity is ≥99.9%; the tube diameter of MWCNT nanoparticles is 3 nm, the tube length is 15 μm, and the purity is >98%; the particle size of SiO2 nanoparticles is 15 nm, and the purity is ≥99.5%. This combination of parameters can give full play to the synergistic effect of each nanoparticle and enhance the heat exchange performance. Step 4: Place the nanoparticle suspension prepared in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 60 min, the power of the ultrasonic oscillator to 180 W, and the ultrasonic frequency to 40 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid can be obtained.

[0033] like Figure 2 As shown, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid prepared in this embodiment was tested at 80 ℃. The test results showed that its thermal conductivity was 0.6247 W / (m·K), which is 20% higher than that of the pure binary mixed base liquid. Moreover, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid showed a reasonable increasing trend with the increase of temperature, which can adapt to the heat exchange scenario requirements of different temperature ranges.

[0034] Example 2 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add ethylene glycol to pure water at a mass ratio of 20:80, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; Step 2: Add sodium dodecylbenzenesulfonate to the binary mixed base liquid obtained in Step 1, and continue stirring until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.6% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of Al2O3 nanoparticles, MWCNT nanoparticles, and SiO2 nanoparticles in a mass fraction ratio of 10:80:10. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed thoroughly, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The specific parameters of each nanoparticle used in this embodiment are as follows: Al2O3 nanoparticles have a particle size of 10 nm and a purity ≥99.9%; MWCNT nanoparticles have a tube diameter of 3 nm, a tube length of 15 μm, and a purity >98%; SiO2 nanoparticles have a particle size of 15 nm and a purity ≥99.5%. Step 4: Place the nanoparticle suspension obtained in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 60 min, the power of the ultrasonic oscillator to 180 W, and the ultrasonic frequency to 40 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid is obtained.

[0035] like Figure 3 As shown, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid prepared in this embodiment was tested at 80 ℃. The test results showed that its thermal conductivity was 0.68 W / (m·K), which is 32% higher than that of the binary mixed base liquid. Moreover, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid showed a reasonable increasing trend with the increase of temperature, which can adapt to the temperature requirements of various heat exchange scenarios.

[0036] Example 3 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add 1,2-propanediol to pure water at a mass fraction ratio of 20:80, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; like Figure 8 In this embodiment, a binary mixed base liquid constructed from pure water and 1,2-propanediol exhibits good thermal stability, thus solving the problem of easy decomposition of traditional base liquids under high temperature and high pressure conditions.

[0037] Step 2: Add sodium dodecylbenzenesulfonate to the binary mixed base liquid prepared in Step 1, and stir continuously until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.6% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of Al2O3 nanoparticles, MWCNT nanoparticles and SiO2 nanoparticles in a mass fraction ratio of 80:10:10. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The specific parameters of each nanoparticle used in this embodiment are as follows: Al2O3 nanoparticles have a particle size of 10 nm and a purity ≥99.9%; MWCNT nanoparticles have a tube diameter of 3 nm, a tube length of 15 μm, and a purity >98%; SiO2 nanoparticles have a particle size of 15 nm and a purity ≥99.5%. Step 4: Place the nanoparticle suspension obtained in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 60 min, the power of the ultrasonic oscillator to 180 W, and the ultrasonic frequency to 40 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid is obtained.

[0038] like Figure 4 As shown, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid prepared in this embodiment was tested at 80℃. The test results showed that its thermal conductivity was 0.6047 W / (m·K), which is 19.77% higher than that of the binary mixed base liquid. Moreover, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid showed a reasonable increasing trend with the increase of temperature, which can be adapted to the temperature requirements of various heat exchange scenarios.

[0039] Example 4 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add 1,2-propanediol to pure water at a mass fraction ratio of 20:80, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; Step 2: Add sodium dodecylbenzenesulfonate to the binary mixed base liquid prepared in Step 1, and stir continuously until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.6% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of Al2O3 nanoparticles, MWCNT nanoparticles and SiO2 nanoparticles in a mass fraction ratio of 10:80:10. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The specific parameters of each nanoparticle used in this embodiment are as follows: Al2O3 nanoparticles have a particle size of 10 nm and a purity ≥99.9%; MWCNT nanoparticles have a tube diameter of 3 nm, a tube length of 15 μm, and a purity >98%; SiO2 nanoparticles have a particle size of 15 nm and a purity ≥99.5%. Step 4: Place the nanoparticle suspension obtained in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 60 min, the power of the ultrasonic oscillator to 180 W, and the ultrasonic frequency to 40 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid is obtained.

[0040] like Figure 5 As shown, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid prepared in this embodiment was tested at 80 ℃. The test results showed that its thermal conductivity was 0.6533 W / (m·K), which is 29.39% higher than that of the binary mixed base liquid. Moreover, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid showed a reasonable increasing trend with the increase of temperature, which can adapt to the temperature requirements of various heat exchange scenarios.

[0041] Example 5 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add 1,2-butanediol to pure water at a mass fraction ratio of 20:80, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; like Figure 8 In this embodiment, a binary mixed base liquid constructed from pure water and 1,2-butanediol has good thermal stability, which solves the problem of easy decomposition of traditional base liquids under high temperature and high pressure conditions.

[0042] Step 2: Add sodium dodecylbenzenesulfonate to the binary mixed base liquid prepared in Step 1, and stir continuously until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.6% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of Al2O3 nanoparticles, MWCNT nanoparticles and SiO2 nanoparticles in a mass fraction ratio of 80:10:10. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The specific parameters of each nanoparticle used in this embodiment are as follows: Al2O3 nanoparticles have a particle size of 10 nm and a purity ≥99.9%; MWCNT nanoparticles have a tube diameter of 3 nm, a tube length of 15 μm, and a purity >98%; SiO2 nanoparticles have a particle size of 15 nm and a purity ≥99.5%. Step 4: Place the nanoparticle suspension obtained in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 60 min, the power of the ultrasonic oscillator to 180 W, and the ultrasonic frequency to 40 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid is obtained.

[0043] like Figure 6 As shown, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid prepared in this embodiment was tested at 80℃. The test results showed that its thermal conductivity was 0.5834 W / (m·K), which is 18.66% higher than that of the binary mixed base liquid. Moreover, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid showed a reasonable increasing trend with the increase of temperature, which can adapt to the temperature requirements of various heat exchange scenarios.

[0044] Example 6 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add 1,2-butanediol to pure water at a mass fraction ratio of 20:80, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; Step 2: Add sodium dodecylbenzenesulfonate to the binary mixed base liquid prepared in Step 1, and stir continuously until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.6% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are composed of Al2O3 nanoparticles, MWCNT nanoparticles and SiO2 nanoparticles in a mass fraction ratio of 10:80:10. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The specific parameters of each nanoparticle used in this embodiment are as follows: Al2O3 nanoparticles have a particle size of 10 nm and a purity ≥99.9%; MWCNT nanoparticles have a tube diameter of 3 nm, a tube length of 15 μm, and a purity >98%; SiO2 nanoparticles have a particle size of 15 nm and a purity ≥99.5%. Step 4: Place the nanoparticle suspension obtained in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 60 min, the power of the ultrasonic oscillator to 180 W, and the ultrasonic frequency to 40 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid is obtained.

[0045] like Figure 7 As shown, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid prepared in this embodiment was tested at 80 ℃. The test results showed that its thermal conductivity was 0.6385 W / (m·K), which is 28.55% higher than that of the binary mixed base liquid. Moreover, the thermal conductivity of the high-boiling-point stable nano heat exchange fluid showed a reasonable increasing trend with the increase of temperature, which can be adapted to the temperature requirements of various heat exchange scenarios.

[0046] Example 7 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add ethylene glycol to pure water at a mass fraction ratio of 15:85, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; Step 2: Add hexadecyltrimethylammonium bromide to the binary mixed base liquid obtained in Step 1, and continue stirring until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.2% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are prepared by mixing Al2O3 nanoparticles, MWCNT nanoparticles and SiO2 nanoparticles in a mass fraction ratio of 20:60:20. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The parameters of each nanoparticle used in this embodiment are as follows: the particle size of Al2O3 nanoparticles is 15 nm, and the purity is ≥99.9%; the tube diameter of MWCNT nanoparticles is 15 nm, the tube length is 30 μm, and the purity is >98%; the particle size of SiO2 nanoparticles is 20 nm, and the purity is ≥99.5%. This combination of parameters can give full play to the synergistic effect of each nanoparticle and enhance the heat exchange performance. Step 4: Place the nanoparticle suspension prepared in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 30 min, the power of the ultrasonic oscillator to 100 W, and the ultrasonic frequency to 20 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid can be obtained.

[0047] Example 8 This embodiment provides a method for preparing a high-boiling-point stable nano-heat exchange fluid, and the specific operation steps are as follows: Step 1: Add ethylene glycol to pure water at a mass ratio of 10:90, and stir thoroughly until the system is homogeneous and stable to prepare a binary mixed base liquid; Step 2: Add polyvinylpyrrolidone to the binary mixed base liquid obtained in Step 1, and continue stirring until it is completely dissolved. Control the volume concentration of the surfactant after dissolution to 0.4% to obtain the pretreated base liquid. Step 3: Preparation of mixed nanoparticles. In this embodiment, the mixed nanoparticles are prepared by mixing Al2O3 nanoparticles, MWCNT nanoparticles and SiO2 nanoparticles in a mass fraction ratio of 60:20:20. The mixed nanoparticles are added to the pretreatment base solution obtained in Step 2, and after being stirred and dispersed thoroughly, a uniform nanoparticle suspension is obtained, wherein the volume concentration of the mixed nanoparticles in the nanoparticle suspension is 0.6%. The parameters of each nanoparticle used in this embodiment are as follows: the particle size of Al2O3 nanoparticles is 20 nm, and the purity is ≥99.9%; the tube diameter of MWCNT nanoparticles is 15 nm, the tube length is 30 μm, and the purity is >98%; the particle size of SiO2 nanoparticles is 20 nm, and the purity is ≥99.5%. This combination of parameters can give full play to the synergistic effect of each nanoparticle and enhance the heat exchange performance. Step 4: Place the nanoparticle suspension prepared in Step 3 into an ultrasonic oscillator for homogenization. Set the ultrasonic time to 100 min, the power of the ultrasonic oscillator to 300 W, and the ultrasonic frequency to 50 kHz. After the treatment is completed, a high-boiling-point stable nano heat exchange fluid can be obtained.

Claims

1. A method for preparing a high-boiling stable nanorefrigerant fluid, characterized in that, Includes the following steps: Step 1: Mix polyol and pure water in a predetermined ratio to obtain a binary mixed base liquid; Step 2: Add a surfactant to the binary mixed base liquid and stir until completely dissolved to obtain a pretreated base liquid; Step 3: Add the nanoparticle system to the pretreated base liquid and disperse it to obtain a nanoparticle suspension, wherein the nanoparticle system contains at least Al2O3 nanoparticles; Step 4: The nanoparticle suspension is homogenized to obtain a high-boiling-point stable nano heat exchange fluid.

2. The method for preparing the high-boiling-point stable nano-heat transfer fluid according to claim 1, characterized in that, In step one, the mass fraction ratio of polyol to pure water is 10:90 to 20:

80. The polyol is selected from any one of ethylene glycol, 1,2-propanediol, and 1,2-butanediol.

3. The method for preparing the high-boiling-point stable nano-heat transfer fluid according to claim 1, characterized in that, In step two, the surfactant is selected from one of hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone.

4. The method for preparing the high-boiling-point stable nano-heat transfer fluid according to claim 1 or 3, characterized in that, After the surfactant mentioned in step two is completely dissolved, its volume concentration in the pretreatment base solution is 0.2% to 0.6%.

5. The method for preparing the high-boiling-point stable nano-heat transfer fluid according to claim 1, characterized in that, The nanoparticle system described in step three is a single nanoparticle or a mixture of nanoparticles. The single nanoparticle is an Al2O3 nanoparticle, and the mixture of nanoparticles is composed of Al2O3 nanoparticles, MWCNT nanoparticles, and SiO2 nanoparticles.

6. The method for preparing the high-boiling-point stable nano-heat transfer fluid according to claim 5, characterized in that, In the mixed nanoparticles, each type of nanoparticle accounts for 10% to 80% of the mass fraction, and the volume concentration of the surfactant after dissolution in step two does not exceed the volume concentration of the mixed nanoparticles in the nanoparticle suspension in step three.

7. The method for preparing the high-boiling-point stable nano-heat transfer fluid according to claim 5, characterized in that, The Al2O3 nanoparticles have a particle size of 10-20 nm and a purity of not less than 99.9%; the MWCNT nanoparticles have a tube diameter of 3-15 nm, a tube length of 15-30 μm, and a purity higher than 98%; the SiO2 nanoparticles have a particle size of 15-20 nm and a purity of not less than 99.5%. The homogenization treatment is carried out by a combination of mechanical stirring and ultrasonic dispersion, with an ultrasonic time of 30-100 min, an ultrasonic power of 100-300 W, and a frequency of 20-50 kHz.

8. A high-boiling-point stable nano-heat transfer fluid, characterized in that, The nano-heat exchange fluid comprises, by mass fraction, a binary mixed base liquid of 100: (0.2~1.5): (0.2~0.6), a surfactant, and a nanoparticle system; wherein the binary mixed base liquid comprises a polyol and pure water, with a mass fraction ratio of polyol to pure water of 10:90~20:80; the surfactant is selected from one of cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and polyvinylpyrrolidone; and the nanoparticle system comprises at least Al2O3 nanoparticles.

9. The high-boiling-point stable nano-heat transfer fluid according to claim 8, characterized in that, The nano heat exchange fluid is composed of the binary mixed base liquid, the surfactant, and the nanoparticle system; wherein the binary mixed base liquid is composed of polyol and pure water.

10. The high-boiling-point stable nano-heat transfer fluid according to claim 8 or 9, characterized in that, The thermal conductivity of the nano heat exchange fluid reaches 0.68 W / (m·K) at 353.15K, and increases with increasing temperature in the temperature range of 293.15K-353.15K.

Images