High-stability latent heat transport phase change emulsion, and preparation method and application thereof

Abstract

The application discloses a kind of high stability latent heat transport phase change emulsion, belongs to phase change material technical field, including the following mass percentage raw materials: phase change heat storage material 30-45%, surfactant 5-10%, crystal nucleus agent 1-8%, antifreeze 5-12% and water 40-50%;Wherein, the HLB value of the surfactant is 10-14;Meanwhile, a kind of nanoparticle phase change fluid is proposed, including the following mass percentage raw materials: phase change emulsion 100%, nanometer material 0.1-0.5% and dispersing agent 0.1-0.5%.The phase change emulsion prepared by the formulation of the application has high stability, and by adding nanoparticles to the phase change emulsion, stirring uniformly, and then adding a dispersing agent, a nanoparticle phase change fluid with high stability, high thermal conductivity, low nucleation supercooling, high energy storage density, relatively lower viscosity, drag reduction characteristics, less prone to block the pipeline, and reduced pump consumption can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of phase change materials technology, and particularly relates to a highly stable latent heat transport phase change emulsion, its preparation method and application. Background Technology

[0002] Energy conservation and emission reduction are among the key themes of current socio-economic development. In the fields of cold and heat transfer technology, higher efficiency, lower energy consumption, and less environmental damage have become important directions for technological innovation and development. With the development of science and technology, traditional heat exchange media can no longer meet the heat transfer and cooling requirements of special environments such as high heat transfer intensity and microchannel heat dissipation. Researchers have begun to apply nanotechnology to the development of new heat exchange media, proposing the new concept of nanofluids, which are suspensions formed by adding nanoscale solid particles to a base liquid in a certain way and proportion.

[0003] Phase change fluids (PCFs) are homogeneous emulsions formed by suspending phase change materials (PCMs) in a single-phase heat transfer fluid. PCFs not only possess the excellent flow characteristics of emulsions, but also significantly enhance their heat storage capacity by absorbing or releasing a large amount of latent heat of phase change when the temperature changes. As a novel latent heat transport medium, PCFs exhibit advantages such as high energy storage density and minimal temperature variation during heat storage and release. By fabricating PCMs into microemulsions, which mainly consist of a dispersed phase of PCM and a continuous fluid medium, this system can utilize both the latent heat of the PCM and the sensible heat of the fluid medium to store thermal energy, resulting in a high energy storage density. While the dispersed phase of the PCM transitions between solid and liquid phases, the continuous fluid medium remains liquid, ensuring that the PCF system is macroscopically always in flow. However, ensuring the stability (static and dynamic stability) of phase change emulsions and ensuring that the particle size of the phase change emulsion is small enough to avoid excessively large droplet diameters that can easily clog pipelines are problems that exist in current technologies.

[0004] Meanwhile, conventional microemulsions are thermodynamically unstable systems with short lifespans. Even if they remain stable under static storage conditions, they are prone to demulsification and phase separation after repeated phase change cycles and complex operating conditions such as high-load pumping. This causes the dispersed phase to separate from the continuous phase, disrupting the equilibrium stability of the microemulsion system and leading to a decrease in its energy storage performance or even rendering it unusable. Supercooling is another drawback of conventional phase change microemulsions. Supercooling refers to a substance not undergoing solidification when its temperature reaches its freezing point; to solidify, it must be cooled below the freezing point. In practical applications, supercooling significantly increases the system's operating temperature range, causing phase change energy storage to lose its main advantage of low temperature variation. Furthermore, phase change fluids generally suffer from low thermal conductivity and corrosiveness. Some phase change materials are also prone to phase stratification, supercooling, and volatilization. These defects limit the widespread application of nanoscale phase change fluid technology.

[0005] Furthermore, adding nanoparticles and dispersants to phase change fluids (PCFs) can improve their heat transfer performance and stability. Nanoparticles can increase the thermal conductivity of PCFs to a certain extent, while dispersants can improve the stability of suspensions by ensuring uniform distribution of nanoparticles. However, PCFs themselves have low thermal conductivity and slow heat transfer rates, resulting in some PCFs not fully absorbing heat and reaching the phase change temperature when flowing through the system. Consequently, some PCFs do not undergo phase change and fail to achieve the desired enhanced heat transfer effect. The relatively low thermal conductivity of nano-PCF media cannot meet the requirements for enhanced heat transfer with small temperature differences. Measures to enhance heat transfer in equipment mainly focus on improving the heat exchange surface and manufacturing processes, but these are limited by equipment structure and manufacturing costs. Additionally, adding nanoparticles with a particle size below 100 nm exhibits a small size effect, high surface energy, and is subject to intense Brownian motion. This makes them prone to collisions, forming large aggregates with several weakly connected interfaces, leading to precipitation, reduced stability, and blockage of pipelines.

[0006] Therefore, providing a highly stable latent heat transport phase change emulsion and a nanophase change fluid is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a formulation and preparation method of a highly stable latent heat transport phase change emulsion, as well as a nanophase change fluid with high stability (thermodynamic stability, dispersion stability, and dynamic stability), high thermal conductivity, low nucleation undercooling, high energy density, and pumpability to avoid clogging pipelines, prepared by the phase change emulsion, thus solving the technical problems existing in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A highly stable latent heat transport phase change emulsion comprises the following raw materials by mass percentage: 30-45% phase change heat storage material, 5-10% surfactant, 1-8% nucleating agent, 5-12% antifreeze agent, and 40-50% water;

[0010] The surfactant has an HLB value of 10-14.

[0011] This invention prepares a stable latent heat transport phase change emulsion. By studying the effects of the type / mass fraction of phase change material, surfactant, nucleating agent, and functional additives on the properties of the phase change fluid, relevant raw materials and proportions were obtained. Simultaneously, the surfactant is crucial in determining the emulsion's stability. Since phase change materials undergo a solid-liquid phase transition upon temperature change, crystalline phase change materials easily "pierce" the interfacial film formed by the surfactant adsorbed on the surface of the emulsion particles, thus reducing emulsion stability. The surfactant used must be able to form a relatively dense or orderly adsorption layer at the interface of the emulsion's phase change material particles. Through extensive experiments, this invention ultimately determined that the emulsion formulated with a nonionic surfactant with an HLB value of 10-14 exhibits good stability.

[0012] Meanwhile, the overall mass ratio of the phase change emulsion in this invention is also crucial. Specifically, the viscosity of the phase change emulsion system affects the stability of the system, the flowability of the phase change emulsion, and the energy consumption of the pump. This invention has found that the viscosity of the phase change emulsion continuously increases with the increase of the mass fraction of n-alkane in the phase change thermal storage material; the viscosity of a 42% phase change emulsion is 360 times that of a 10wt% phase change emulsion. For emulsions with the same mass fraction of n-alkane, the viscosity decreases slowly with increasing temperature, but suddenly increases within the phase change range. This is because the viscosity of solid n-alkane is higher than that of liquid n-alkane. The viscosity of all samples is less than 2 Pa·s, meeting the requirements of a dynamic transport system.

[0013] Meanwhile, the viscosity of the entire phase change emulsion system is mainly affected by the ease with which the dispersed phase moves within the continuous phase. When the average particle size of the dispersed phase increases, the spacing between the dispersed phases increases, making movement easier and reducing the emulsion viscosity. Similarly, improved flowability of the continuous phase facilitates movement of the dispersed phase within it, further reducing emulsion viscosity. Increased water content increases the amount of water between emulsion particles, facilitating particle movement and reducing emulsion viscosity. Co-emulsifiers and mechanical stirring alter the surface tension of paraffin and water, causing the average size of the emulsion particles to increase or decrease. When the average particle size increases, the spacing between particles increases, facilitating movement and reducing viscosity; conversely, when the average particle size decreases, the spacing between particles decreases, making movement difficult and increasing viscosity. Therefore, a suitable ratio of raw materials is necessary to balance these properties and ensure optimal viscosity.

[0014] Preferably, the surfactant includes an emulsifying surfactant and a co-surfactant, with a mass ratio of 4:1.

[0015] Preferably, the emulsifying surfactant is a nonionic surfactant;

[0016] Preferably, the nonionic surfactant is at least two of propylene glycol fatty acid ester, polyoxyethylene oleyl alcohol ether, sorbitan monooleate polyoxyethylene ether, sorbitan monooleate, sorbitan monostearate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan monolaurate.

[0017] This invention employs two nonionic surfactants as compound emulsifying surfactants. The hydrophilic-lipophilic balance (HLB) value of the nonionic surfactants ranges from 0 to 20. Specifically, the HLB value of n-alkane molecules in phase change heat storage materials composed entirely of hydrophobic hydrocarbon groups is 0, the HLB value of polyoxyethylene composed entirely of hydrophilic oxyethylene groups is 20, and the HLB value of surfactants containing both hydrocarbon and oxyethylene chains falls between these two values. The HLB value of the two-component nonionic surfactant system can be calculated using the formula HLB. AB = (HLB) A ×W A +HLB B ×W B ) / (W A +W B Calculate HLB, where W A and W B These represent the amounts of surfactants A and B, respectively, in HLB. A and HLB B These are the HLB values ​​of A and B, respectively. AB The optimal ratio of compound emulsifiers is determined by the optimal HLB value of the surfactant after mixing.

[0018] The co-surfactant is any one of n-butanol, n-pentanol, stearic acid, lauric acid, and octanoic acid.

[0019] This invention, by adding a co-surfactant, further reduces interfacial tension, increases the fluidity of the interfacial film, and adjusts the HLB value of the surfactant. The co-surfactant can penetrate the intermolecular space of the surfactant in the interfacial film, reducing the rigidity of the interfacial film, increasing fluidity, and reducing the bending energy required for microemulsion formation, thus facilitating microemulsion formation. When the amount of alcohol at the interface increases to a certain extent, the excessive interfacial fluidity leads to the dominance of inter-droplet attraction, resulting in a decrease in the amount of soluble water. Moreover, with further increases in the amount of co-surfactant added, the HLB value changes significantly, thereby reducing the area of ​​the microemulsion liquid phase region.

[0020] Preferably, the phase change thermal storage material is at least one of n-alkanes with the molecular formula C2. n H 2n+2 n is an integer between 23 and 30.

[0021] By selecting alkanes with different numbers of carbon atoms, different phase change temperatures can be obtained. The phase change heat storage material used in this invention, n-alkanes, is a phase change material with a temperature range of 47-68℃, a melting enthalpy of 240-260 J / g, is non-toxic, low-corrosive, has minimal supercooling crystallization, and is relatively inexpensive. It is suitable for high-energy-density heating and heat supply latent heat transport materials, thus obtaining a phase change material system in the mid-temperature range.

[0022] The nucleating agent is any one of stearic acid, paraffin, lauric acid, and palmitic acid.

[0023] Temperature is a major challenge limiting the development of phase change emulsions. The addition of nucleating agents results in two solidification peaks due to different crystallization mechanisms. The higher-temperature solidification peak is caused by heterogeneous nucleation, where crystals form on the surface of foreign matter, such as impurities contained in n-alkanes. The other, lower-temperature solidification peak is caused by homogeneous nucleation, where crystal nuclei are generated from n-alkanes and crystals form. This invention enhances heterogeneous nucleation by adding nucleating agents, thereby reducing supercooling (heat).

[0024] The antifreeze is any one of ethylene glycol, propylene glycol, ethanol, triethanolamine, and dimethyl sulfoxide.

[0025] To prevent damage to heat exchangers caused by freezing of the heat medium in door heating curtains and heaters used in cold regions, antifreeze aqueous solutions are selected for the heating systems. Adding antifreeze to the heat medium is a common and effective method to prevent freezing, as it allows heating systems to be shut down in unoccupied buildings without freezing pipes. Using PVC high-temperature hot water pipes and antifreeze can significantly save energy and reduce pipe freezing and scale buildup.

[0026] The method for preparing a highly stable latent heat transport phase change emulsion as described above includes the following steps:

[0027] (1) Weigh the raw materials by mass percentage: 30-45% phase change heat storage material, 5-10% surfactant, 1-8% nucleating agent, 5-12% antifreeze and 40-50% water;

[0028] (2) The nucleating agent and the phase change heat storage material are mixed and heated and stirred to form a uniformly dispersed phase A;

[0029] (3) The surfactant, the water and the antifreeze are mixed and heated and stirred to obtain a continuous phase B;

[0030] (4) The dispersed phase A is added to the continuous phase B, and after high-speed homogenization, a highly stable latent heat transport phase change emulsion is obtained.

[0031] This invention prepares a latent heat transport phase change emulsion with optimal suspension stability by using a heating homogenizer for emulsification during the preparation process. The particle size of the dispersed phase in the prepared latent heat transport phase change emulsion is 0.2-1.0 μm.

[0032] Preferably, the heating temperature in steps (2) and (3) is 60-80°C;

[0033] The conditions for high-speed homogenization in step (4) are: rotation speed of 15000-25000 rpm, heating temperature of 60-80℃, and homogenization time of 5-10 min.

[0034] A nanoparticle phase change fluid, comprising the phase change emulsion described above or the phase change emulsion obtained by the preparation method described above.

[0035] Preferably, the nanoparticle phase change fluid comprises the following raw materials by mass percentage: 99.0-99.8% phase change emulsion, 0.1-0.5% nanomaterials, and 0.1-0.5% dispersant.

[0036] This invention significantly improves the stability (thermodynamic stability, dispersion stability, and dynamic stability) of phase change fluids with added nanoparticles by selectively adding dispersants. Research shows that the type / mass fraction / particle size of nanoparticles (nano-solid particles with higher thermal conductivity) and the type / mass fraction of dispersants all affect the physical properties of nano-phase change fluids with added nanoparticles. Adding nanoparticles to phase change fluids yields nano-phase change fluids with high stability (thermodynamic stability, dispersion stability, and dynamic stability), high thermal conductivity, low nucleation undercooling, high energy density, relatively lower viscosity, drag-reducing characteristics, reduced pipe blockage, and lower pump consumption.

[0037] Preferably, the nanomaterial is any one of nano-aluminum nitride, nano-boron nitride, and nano-silicon carbide;

[0038] Adding nanoparticles can enhance the heat transfer mechanism of nanofluids. Based on this principle, the nanomaterials added in this invention are high thermal conductivity nanomaterials with a thermal conductivity between 70-330 W / m·K. Currently published patents and literature mostly use metal oxides such as nano-titanium dioxide, nano-alumina, and nano-iron oxide as nanoparticles added to phase change fluids. The thermal conductivity of these materials is between 1.0-6.5 W / m·K, and the thermal conductivity of the prepared nano-phase change fluid is between 0.40-0.60 W / m·K, with a latent heat of phase change <50 J / g. The high thermal conductivity material used in this invention can effectively transfer heat and easily absorb heat from the environment. Poor thermal conductors will hinder heat flow and slowly absorb heat from the surroundings.

[0039] Furthermore, it is well known in the art that adding nanoparticles has almost no effect on the phase change initiation temperature and peak temperature of phase change fluids, but it will reduce the energy storage density of the phase change fluid, resulting in a decrease in the latent heat of phase change. Therefore, in order to improve the thermal conductivity of the phase change fluid, it is necessary to minimize the mass fraction of phase change particles. However, the latent heat of phase change will also decrease as the mass fraction decreases. In order to balance the contradiction between the two, without reducing or increasing the latent heat of phase change, the thermal conductivity of the phase change fluid is increased. This invention uses nano-solid particles with higher thermal conductivity suspended in the liquid.

[0040] This invention aims to obtain higher latent heat of phase change and better thermal conductivity of the phase change fluid. By suspending nanoparticles with higher thermal conductivity in the phase change fluid, the mass fraction of nanoparticles can be relatively reduced. The impact of increasing the mass fraction of nanoparticles on the latent heat of phase change is most pronounced. A higher nanoparticle mass fraction leads to a sharp decrease in the latent heat of phase change in the suspension, while simultaneously lowering the phase change initiation temperature and the peak phase change temperature. This is because as the mass fraction of nanoparticles increases, the number of nanoparticles per unit volume increases, resulting in stronger interactions between nanoparticles and phase change particles, and between nanoparticles themselves. The collision frequency and intensity become more intense, accelerating the energy transfer rate and enhancing the phase change capability of the suspension. Consequently, suspensions with a high nanoparticle mass fraction can undergo phase change earlier without reaching a high temperature, thus reducing both the phase change initiation temperature and the peak phase change temperature. Furthermore, similar to the reason why adding nanoparticles reduces the latent heat of phase change, a higher nanoparticle mass fraction leads to faster heat transfer and a shorter phase change completion time, resulting in less effective latent heat of phase change. Therefore, the thermal conductivity of nanophase change fluids mainly depends on the thermal conductivity of the nanoparticles themselves and the properties of the phase change base fluid. The heat transfer inside the nanoparticles is through phonons via quantum fluctuations. Phonons have particle properties, and the way they transfer energy is ballistic heat transfer. During the transfer process, they do not collide with other particles and directly transfer energy in a straight line at the speed of sound. Nanoparticles with high thermal conductivity have a faster speed. Under the action of ultrasonic stirring, the nanoparticles with high thermal conductivity are uniformly dispersed in the emulsion. Some nanoparticles are wrapped by the n-alkane microparticles of the phase change heat storage material, and some nanoparticles are dispersed in the aqueous phase, which leads to a significant increase in thermal conductivity.

[0041] Furthermore, thermal cycling stability refers to the changes in performance parameters such as dispersibility, fluidity, and stability of nanophase change fluids after repeated melting-solidification cycles. After undergoing complex operating conditions such as repeated phase change cycles and extremely high pump loads, nanophase change fluids are prone to demulsification and phase separation, causing the dispersed phase to separate from the continuous phase. This disrupts the equilibrium stability of the microemulsion system, leading to a decrease in its energy storage performance or even rendering it unusable. The higher the mass fraction of nanoparticles in the suspension, the worse its stability during thermal cycling. Suspending nanoparticles with higher thermal conductivity in the phase change fluid can relatively reduce the mass fraction of nanoparticles, thereby improving the thermal cycling stability of the nanophase change fluid. Therefore, the nanomaterials used in this invention represent a significant advancement compared to existing technologies.

[0042] Preferably, the particle size of the nanomaterial is 5-20 nm.

[0043] In the thermal cycling of nanoparticles, agglomeration is prone to occur as the collision frequency increases. Agglomerated nanoparticles precipitate from the phase change fluid, leading to a weakening of the energy transfer capacity of the suspension. At the same temperature, the larger the nanoparticle size, the lower the thermal conductivity of the phase change fluid with added nanoparticles. On the one hand, smaller nanoparticle size results in a larger specific surface area, which is more conducive to heat transfer between the nanoparticles and the base fluid. On the other hand, smaller nanoparticle size leads to more intense Brownian motion in the base fluid, which is also more conducive to heat transfer. Considering both factors, reducing the nanoparticle size can increase the thermal conductivity. As the particle size of nanoparticles increases, the phase change temperature and latent heat of phase change in the suspension tend to decrease. With increasing nanoparticle size, the energy storage density of the phase change fluid decreases, leading to a reduction in its latent heat of phase change. At the same temperature, larger nanoparticle sizes result in higher viscosity of the phase change fluid. This is because larger nanoparticle sizes reduce the spatial distance between nanoparticles at the same mass fraction, increasing the attraction between particles. This hinders relative movement between nanoparticles and increases the probability of aggregation, both contributing to increased viscosity. The thermal conductivity and latent heat of phase change fluids with different nanoparticle sizes decrease to some extent with increasing cycle count. Furthermore, larger particle sizes lead to poorer dynamic stability of the suspension. When using nanoparticles with a diameter of 5-20 nm, the change rate of both thermal conductivity and latent heat of phase change is minimized, resulting in optimal dynamic stability. Commercially available products with nanoparticles smaller than 5 nm are scarce and costly; therefore, this invention does not consider them.

[0044] Meanwhile, nanoparticles act as nucleating agents and significantly improve the thermal conductivity of phase change fluids, thereby enhancing heat transfer. Adding other substances as nucleating agents to phase change emulsions can enhance heterogeneous nucleation, thus reducing supercooling. The smaller the particle size of the nanoparticles, the larger their specific surface area, which is more conducive to enhancing heterogeneous nucleation in phase change emulsions.

[0045] The dispersant is any one of polyvinyl alcohol, xanthan gum, guar gum, gum arabic, and polyethylene glycol.

[0046] Currently, the most prominent issue in appropriately adding nanoparticles to phase change emulsions is the stability of the suspension. Phase change fluids with added nanoparticles belong to colloidal systems, and colloidal stability is defined in three aspects: thermodynamic stability, dispersion stability, and dynamic stability. Since phase change fluids with added nanoparticles are multiphase dispersion systems with high interfacial energy, they are thermodynamically unstable. Because different nanoparticles exhibit different characteristics in suspensions, the type of dispersant selected for different nanoparticles also varies. If the dispersant is not chosen appropriately, it cannot stably adsorb onto the nanoparticle surface, resulting in incomplete particle encapsulation and weakening the dispersion effect. If the mass fraction of the dispersant is too small, the dispersant adsorbed on the nanoparticle surface is insufficient to overcome the interparticle attraction, leading to nanoparticle aggregation. Conversely, adding too large a mass fraction of dispersant will cause the long polymer chains of the dispersant to become entangled, also causing particle aggregation. Therefore, when preparing phase change fluids with added nanoparticles, it is essential to select a suitable dispersant and dispersion method to obtain a stable suspension, and to control the mass fraction of the dispersant within a reasonable range.

[0047] Since the nanomaterials selected in this invention are nanomaterials with high thermal conductivity, these nanoparticle compounds are suitable for polymeric surface dispersants. Polymeric surface dispersants have the functions of emulsifiers, stabilizers, suspending agents, binders, and film-forming agents. Their relative molecular weight is very large. When added to the nanoparticle suspension, they will form non-electrical steric hindrance of particle aggregation. Although non-electrical steric hindrance will reduce or eliminate the original potential barrier between particles, its special long-chain structure prevents the particles from contacting each other. Under the condition of compression or local increase in mass fraction, the polymer on the nanoparticles will cause the repulsive force to increase, which is greater than the van der Waals attraction between particles, thereby achieving the purpose of stable dispersion. There is also an optimal concentration of polymeric dispersants. If too little is added, their long-chain structure cannot effectively prevent contact between particles. If too much is added, the polymeric surfactant will form large agglomerates with nanoparticles as the core. These agglomerates move continuously in the solution and cross-link with other agglomerates, resulting in poor solution stability. In nanofluids with added polymeric surface dispersants, the long polymeric chains coat the nanoparticles, forming a stable separating layer that prevents most particles from contacting each other, thus resulting in excellent dispersion.

[0048] This invention significantly improves the dynamic stability of nanophase change fluids by adding polymeric surface dispersants, ensuring uniform dispersion during repeated thermal cycling and enhancing the thermal cycling stability of the nanophase change fluid. The addition of polymeric surface dispersants also increases the overall thermal conductivity of the phase change fluid. After adding the dispersant, the dispersant particles adsorb onto the surface of the nanoparticles. In the suspension, the dispersant reduces the collision frequency between nanoparticles and phase change particles, and between nanoparticles themselves, thus lowering the energy transfer rate and consequently reducing the thermal conductivity of the suspension. The effect of the polymeric surface dispersant dosage fraction on the thermal conductivity of the suspension is inversely proportional: the higher the mass fraction of the added dispersant, the lower the thermal conductivity of the suspension. A lower mass fraction results in poor dispersion of nanoparticles, leading to agglomeration and sedimentation, thus reducing the thermal conductivity. Conversely, an excessively high mass fraction of dispersant causes flocculation, accelerating the aggregation of nanoparticles and further reducing the thermal conductivity. The mass fraction of dispersant has almost no effect on the phase change temperature and latent heat of phase change fluid, so the mass fraction of dispersant must be appropriate.

[0049] The preparation method of the nanoparticle phase change fluid described above specifically includes the following steps:

[0050] (1) Weigh the raw materials by mass percentage: 99.0-99.8% phase change emulsion, 0.1-0.5% nanomaterials and 0.1-0.5% dispersant, and set aside;

[0051] (2) The dispersant and the nanomaterial are added to the phase change emulsion in sequence and stirred evenly to obtain a mixture for later use;

[0052] (3) The mixture is ultrasonically treated to obtain a nanoparticle phase change fluid.

[0053] Preferably, the conditions for ultrasonic treatment in step (3) are: frequency 20-25KHZ, time 3h.

[0054] Preferably, to prevent the nanofluid from overheating, the ultrasonic treatment is stopped for 3 minutes every 40 minutes.

[0055] The application of the phase change emulsion described above, the phase change emulsion obtained by the preparation method described above, the nanoparticle phase change fluid described above, or the nanoparticle phase change fluid obtained by the preparation method described above in the preparation of heat exchange working fluids.

[0056] Combining phase change fluids (PCFs) made from phase change energy storage materials with nanomaterials leverages the surface and volume effects of nanomaterials. This reduces the viscosity coefficient of the PCF while increasing its thermal conductivity, thereby improving the thermal properties and flow characteristics of the composite PCF. Nanophase change fluids, as a novel, highly efficient, and heat-transferring energy transport medium, can effectively improve the heat transfer performance of thermal systems, enhancing their efficiency, low resistance, and compactness. They meet the high-load heat transfer and cooling requirements of thermal systems and the enhanced heat transfer requirements under special conditions (microscale conditions), and are considered a future cooling and heat dissipation technology. They have been widely applied in many industries, such as enhanced heat transfer of spacecraft thermal control fluids, nanofluid heat pipes, enhanced heat transfer of nanofluids in microchannels, and enhanced mass transfer processes using nanofluids. Nanophase change fluids refer to the preparation of a novel heat exchange medium—uniform, capable of storing cold and heat, stable, and with high thermal conductivity—by dispersing metallic or non-metallic nanoparticles into a liquid phase change heat transfer medium. Nanofluids have enormous potential applications in energy, chemical, automotive, construction, microelectronics, and information technology fields.

[0057] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: The phase change emulsion prepared by the formulation of the present invention has high stability. At the same time, by adding nanoparticles to the phase change emulsion, stirring evenly, and then adding a dispersant, a nano-phase change fluid with high stability (thermodynamic stability, dispersion stability, and dynamic stability), high thermal conductivity, low nucleation undercooling, high energy storage density, and relatively lower viscosity can be obtained. It also has drag reduction characteristics, is not easy to clog pipes, and reduces pump consumption. It has huge potential application prospects in the fields of energy, chemical industry, automobile, construction, microelectronics, and information. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0059] Figure 1 The melting and solidification DSC curves of silicon carbide phase change fluids with different mass fractions in Examples 1-3 are shown.

[0060] Figure 2 Examples 4-6 show the melting and solidification DSC curves of aluminum nitride phase change fluids with different mass fractions.

[0061] Figure 3 The melting and solidification DSC curves of boron nitride phase change fluids with different mass fractions in Examples 7-9 are shown.

[0062] Figure 4 The thermal conductivity curves of silicon carbide phase change fluids with different mass fractions in Examples 1-3 are shown.

[0063] Figure 5 The thermal conductivity curves of aluminum nitride phase change fluids with different mass fractions in Examples 4-6 are shown.

[0064] Figure 6 The thermal conductivity curves of boron nitride phase change fluids with different mass fractions in Examples 7-9 are shown.

[0065] Figure 7 DSC curves of the endothermic melting process of silicon carbide phase change fluids with different mass fractions;

[0066] Figure 8 DSC curves for the endothermic melting process of boron carbide phase change fluids with different mass fractions. Detailed Implementation

[0067] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] Example 1

[0069] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0070] 1. Preparation of phase change emulsion:

[0071] (1) Add 3 kg of stearic acid to 30 kg of n-alkane mixed phase change material (C 29 H 60 40%, C 27 H 56 20%, C 25 H 52 20%, C 23 H 48 The mixture (20%) was heated to 75°C and stirred until homogeneous to form a transparent liquid, thus obtaining a uniformly dispersed phase system A.

[0072] (2) Add 1.87 kg of dehydrated sorbitan monostearate (Span60), 2.13 kg of polyoxyethylene dehydrated sorbitan monopalmitate (Tween40), and 1.0 kg of n-pentanol to a mixture of 50 kg of water and 12 kg of ethanol, heat to 75 °C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B.

[0073] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 21000 rpm and a heating temperature controlled within 75℃. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 30% and a particle size of 0.4 μm.

[0074] 2. Preparation of nanophase change fluids

[0075] 0.3 kg of xanthan gum was slowly added to a magnetically stirred vessel containing 99.6 kg of phase change fluid, and the mixture was magnetically stirred for 10 min (1000 rpm) until homogeneous. 0.1 kg of nano-silicon carbide (5 nm) particles were slowly added to the magnetically stirred vessel in two portions (1000 rpm) and stirred until homogeneous. Ultrasonic vibration was then performed at a frequency of 25 kHz. To prevent the nano-fluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain silicon carbide nano-phase change fluid.

[0076] Example 2

[0077] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0078] 1. Preparation of phase change emulsion

[0079] (1) Add 6 kg of stearic acid to 35 kg of n-alkane mixed phase change material (C 27 H 56 60%, C 24 H 50 The mixture (40%) was heated to 62°C and stirred until homogeneous to form a transparent liquid, thus obtaining a uniformly dispersed phase system A.

[0080] (2) Add 1.12 kg of dehydrated sorbitan monostearate (Span60), 2.88 kg of polyoxyethylene dehydrated sorbitan monopalmitate (Tween40), and 1.0 kg of n-pentanol to a mixture of 45 kg of water and 9.0 kg of ethanol, heat to 62 °C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0081] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 21000 rpm and a heating temperature controlled within 62℃. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 35% and a particle size of 0.7 μm.

[0082] 2. Preparation of nanophase change fluids

[0083] 0.2 kg of guar gum was slowly added to a magnetically stirred vessel containing 99.5 kg of phase change fluid, and the mixture was magnetically stirred for 10 min (1000 rpm) until homogeneous. 0.3 kg of nano-silicon carbide (10 nm) particles were slowly added to the magnetically stirred vessel in three portions (1000 rpm) and stirred until homogeneous. Ultrasonic vibration was then performed at a frequency of 25 kHz. To prevent the nano-fluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain silicon carbide nano-phase change fluid.

[0084] Example 3

[0085] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0086] 1. Preparation of phase change emulsion

[0087] (1) Add 5 kg of stearic acid to 40 kg of n-alkane C 30 H 62 The phase change material is heated to 80°C and stirred until a transparent liquid is formed, resulting in a uniformly dispersed phase system A.

[0088] (2) 0.73 kg of sorbitan monooleate (Span80), 7.27 kg of sorbitan monooleate polyoxyethylene ether (Tween80), 2 kg of n-pentanol, 40 kg of water and 5 kg of ethylene glycol were added to a mixture and heated to 80°C and stirred until a transparent liquid was formed, thus obtaining a continuous phase system B.

[0089] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 25000 rpm and a heating temperature controlled within 80℃. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 40% and a particle size of 0.5 μm.

[0090] 2. Preparation of nanophase change fluids

[0091] 0.5 kg of water-soluble polyvinyl alcohol was slowly added to a magnetically stirred vessel containing 99 kg of phase change fluid, and the mixture was magnetically stirred for 10 min (1000 rpm) until homogeneous. 0.5 kg of nano-silicon carbide (20 nm) particles were slowly added to the magnetically stirred vessel in 5 portions (1000 rpm) and stirred until homogeneous. Ultrasonic vibration was then performed at a frequency of 25 kHz. To prevent the nano-fluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain silicon carbide nano-phase change fluid.

[0092] Example 4

[0093] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0094] 1. Preparation of phase change emulsion

[0095] (1) Add 2 kg of stearic acid to 30 kg of n-alkane phase change material mixture (C 30 H 62 40%, C 24 H 50 (60%) was heated to 70°C and stirred until a transparent liquid was formed, resulting in a uniformly dispersed phase system A.

[0096] (2) Add 3.0 kg of sorbitan monooleate (Span80), 3.4 kg of sorbitan monooleate polyoxyethylene ether (Tween80), 1.6 kg of n-butanol to a mixture of 40 kg of water and 10 kg of propylene glycol, heat to 70 °C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0097] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 25000 rpm and a heating temperature controlled within 70°C. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 30% and a particle size of 0.1 μm.

[0098] 2. Preparation of nanophase change fluids

[0099] 0.4 kg of gum arabic was slowly added to a magnetically stirred vessel containing 99.5 kg of phase change fluid, and the mixture was stirred magnetically for 10 min (1000 rpm) until homogeneous. 0.1 kg of nano-aluminum nitride (5 nm) particles were slowly added to the magnetically stirred vessel in three portions (1000 rpm) and stirred until homogeneous. Ultrasonic vibration was then performed at a frequency of 25 kHz. To prevent the nanofluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain aluminum nitride nano-phase change fluid.

[0100] Example 5

[0101] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0102] 1. Preparation of phase change emulsion

[0103] (1) Add 1 kg of lauric acid to 35 kg of n-alkane mixed phase change material (C 28 H 58 50%, C 26 H 54 30%, C 24 H 50 (20%) was heated to 65°C and stirred until a transparent liquid was formed, resulting in a uniformly dispersed phase system A.

[0104] (2) Add 1.35 kg of dehydrated sorbitan monooleate (Span80), 3.45 kg of polyoxyethylene dehydrated sorbitan monolaurate (Tween20), 1.2 kg of lauric acid to a mixture of 50 kg of water and 10 kg of ethanol, heat to 65 °C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0105] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 22000 rpm and a heating temperature controlled within 65℃. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 35% and a particle size of 0.3 μm.

[0106] 2. Preparation of nanophase change fluids

[0107] 0.5 kg of gum arabic was slowly added to a magnetically stirred vessel containing 99.2 kg of phase change fluid, and the mixture was stirred magnetically for 10 min (1000 rpm) until homogeneous. 0.3 kg of nano-aluminum nitride (10 nm) particles were slowly added to the magnetically stirred vessel in three portions (1000 rpm) and stirred until homogeneous. Ultrasonic vibration was then performed at a frequency of 20 kHz. To prevent the nanofluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain aluminum nitride nano-phase change fluid.

[0108] Example 6

[0109] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0110] 1. Preparation of phase change emulsion

[0111] (1) Add 4.5 kg of stearic acid to 40 kg of n-alkane mixed phase change material (C 28 H 56 20%, C 26 H 54 20%, C 24 H 50 20%, C 27 H 56 20%, C 25 H 52 The mixture (20%) was heated to 72°C and stirred until homogeneous to form a transparent liquid, thus obtaining a uniformly dispersed phase system A.

[0112] (2) Add 0.44 kg of dehydrated sorbitan monooleate (Span80), 4.36 kg of polyoxyethylene dehydrated sorbitan monolaurate (Tween20), 1.2 kg of stearic acid to a mixture of 41 kg of water and 7.5 kg of dimethyl sulfoxide, heat to 72°C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0113] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 24000 rpm and a heating temperature controlled within 72℃. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 40% and a particle size of 0.6 μm.

[0114] 2. Preparation of nanophase change fluids

[0115] 0.2 kg of gum arabic was slowly added to a magnetically stirred vessel containing 99.3 kg of phase change fluid, and the mixture was stirred magnetically for 10 min (1000 rpm) until homogeneous. 0.5 kg of nano-aluminum nitride (20 nm) particles were slowly added to the magnetically stirred vessel in four portions (1000 rpm) and stirred until homogeneous. Ultrasonic vibration was then performed at a frequency of 20 kHz. To prevent the nanofluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain aluminum nitride nano-phase change fluid.

[0116] Example 7

[0117] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0118] 1. Preparation of phase change emulsion

[0119] (1) Add 2 kg of stearic acid to 30 kg of n-alkane phase change material mixture (C 28 H 58 70%, C 25 H 52 The mixture (30%) was heated to 70°C and stirred until homogeneous to form a transparent liquid, thus obtaining a uniformly dispersed phase system A.

[0120] (2) Add 3.0 kg of sorbitan monooleate (Span80), 3.40 kg of sorbitan monooleate polyoxyethylene ether (Tween80), 1.6 kg of n-butanol to a mixture of 40 kg of water and 10 kg of propylene glycol, heat to 70 °C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0121] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 25000 rpm and a heating temperature controlled within 70°C. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 30% and a particle size of 0.2 μm.

[0122] 2. Preparation of nanophase change fluids

[0123] 0.40 kg of gum arabic was slowly added to a magnetically stirred vessel containing 99.5 kg of phase change fluid, and the mixture was stirred magnetically for 10 min (1000 rpm) until homogeneous. 0.10 kg of 5 nm boron nitride nanoparticles were slowly added to the magnetically stirred vessel in three portions (1000 rpm) and stirred until homogeneous. The mixture was then subjected to ultrasonic vibration at a frequency of 25 kHz. To prevent the nanofluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain boron nitride nanophase change fluid.

[0124] Example 8

[0125] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0126] 1. Preparation of phase change emulsion

[0127] (1) Add 8 kg of palmitic acid to 35 kg of n-alkane C 23 H 48 The phase change material is heated to 60°C and stirred until a transparent liquid is formed, resulting in a uniformly dispersed phase system A.

[0128] (2) Add 2.02 kg of propylene glycol fatty acid ester (PM-50), 5.18 kg of polyoxyethylene oleyl alcohol ether (OE-20), 1.8 kg of octanoic acid to a mixture of 40 kg of water and 8 kg of propylene glycol, heat to 60 °C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0129] (3) Heat the continuous phase to the same temperature, and slowly add the mixture of dispersed phase system A to the continuous phase system B while continuously stirring (1000 rpm) to form a pre-emulsion. Then, introduce the mixture into a high-speed homogenizer at 20000 rpm, controlling the heating temperature below 60℃, and homogenizing for 10 minutes. The product is an opaque, milky-white phase change microemulsion, containing a phase change material weight ratio of 35% and a particle size of 0.5 μm.

[0130] 2. Preparation of nanophase change fluids

[0131] 0.2 kg of gum arabic was slowly added to a magnetically stirred vessel containing 99.5 kg of phase change fluid, and the mixture was stirred magnetically for 10 min (1000 rpm) until homogeneous. 0.3 kg of 10 nm boron nitride nanoparticles were slowly added to the magnetically stirred vessel in three portions (1000 rpm) and stirred until homogeneous. The mixture was then subjected to ultrasonic vibration at a frequency of 25 kHz. To prevent the nanofluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration duration was 3 h to obtain boron nitride nanophase change fluid.

[0132] Example 9

[0133] This invention provides a method for preparing nanoparticle phase change fluid, comprising the following steps:

[0134] 1. Preparation of phase change emulsion

[0135] (1) Add 1.5 kg of stearic acid to 40 kg of n-alkane mixed phase change material (C 26 H 54 20%, C 24 H 50 20%, C 27 H 56 20%, C 25 H 52 20%, C 23 H 48 The mixture (20%) was heated to 62°C and stirred until homogeneous to form a transparent liquid, thus obtaining a uniformly dispersed phase system A.

[0136] (2) Add 0.51 kg of dehydrated sorbitan monooleate (Span80), 5.09 kg of polyoxyethylene dehydrated sorbitan monopalmitate (Tween40), 1.4 kg of n-butanol to a mixture of 40 kg of water and 11.5 kg of ethanol, heat to 62°C and stir until homogeneous to form a transparent liquid, thus obtaining continuous phase system B;

[0137] (3) Heat the continuous phase to the same temperature, slowly add the mixture of dispersed phase system A to the continuous phase system B, and stir continuously (1000 rpm) while adding to form a pre-emulsion. Then, introduce it into a high-speed homogenizing emulsifier with a speed of 23000 rpm and a heating temperature controlled within 62℃. The homogenization emulsification time is 10 min. The product is an opaque milky white phase change microemulsion with a phase change material weight ratio of 40% and a particle size of 0.6 μm.

[0138] 2. Preparation of nanophase change fluids

[0139] 0.1 kg of guar gum was slowly added to a magnetically stirred vessel containing 99.4 kg of phase change fluid, and the mixture was stirred magnetically for 10 min (1000 rpm) until homogeneous. 0.5 kg of nano boron nitride (20 nm) particles were slowly added to the magnetically stirred vessel in three portions (1000 rpm) and stirred until homogeneous. The mixture was then subjected to ultrasonic vibration at a frequency of 20 kHz. To prevent the nanofluid from overheating, the ultrasonic vibration was stopped for 3 min every 40 min, and the vibration time was 3 h to obtain boron nitride nanophase change fluid.

[0140] Among them, the performance of the nanophase change fluids in all the above embodiments was tested, and the results are shown in Tables 1-8 below. Figure 1-8 :

[0141] Table 1. Phase transition temperature and latent heat of phase transition of nanophase change fluids

[0142]

[0143] As shown in Table 1, the type of nano-metal compound has a significant impact on the phase transition temperature and latent heat of phase transition of nanocomposite n-alkane phase change heat storage materials. Different types of nano-metal compounds have different crystal structures, lattice constants, grain sizes, and surface energies. These characteristics affect the phase transition temperature and latent heat of phase change of nanocomposite n-alkane phase change heat storage materials. For example, adding nano-AlN powder can significantly improve the phase transition temperature and latent heat of phase change of n-alkanes. This is because nano-AlN powder has high surface energy and small grain size, which can improve the crystallinity and crystallization rate of n-alkanes, thereby increasing the phase transition temperature and latent heat of phase change. In addition, adding nano-SiC and BN and other nano-metal compounds can also improve the phase transition performance of n-alkanes. This is because these nano-metal compounds have high surface energy and small grain size, which can improve the crystallinity and crystallization rate of n-alkanes, thereby increasing the phase transition temperature and latent heat of phase change.

[0144] In summary, the type of nano-metal compound has a significant impact on the phase change temperature and latent heat of phase change of nanocomposite n-alkane phase change heat storage materials. The phase change performance of n-alkane can be improved by selecting appropriate nano-metal compounds.

[0145] Furthermore, the data in the table shows that the particle size of nano-metal compounds has a significant impact on their phase transition temperature and latent heat of phase transition. First, the smaller the particle size of nano-metal compounds, the larger the ratio of their surface area to volume, and therefore the higher their surface energy. This leads to a decrease in the phase transition temperature of nano-metal compounds, because phase transition requires overcoming the influence of surface energy. At the same time, the smaller the particle size of nano-metal compounds, the more lattice defects and interface defects they have, which affect their latent heat of phase transition.

[0146] Secondly, the particle size of nano-metal compounds also affects their crystal structure. When the particle size of nano-metal compounds is smaller than a certain size of their crystals, their crystal structure will change, thereby affecting their phase transition temperature and latent heat of phase transition. For example, the phase transition temperature and latent heat of phase transition of nano-AlN increase as the particle size decreases because the crystal structure of nano-AlN changes.

[0147] Finally, the particle size of nanomaterials also affects their thermal conductivity. Nanomaterials generally exhibit better thermal conductivity than conventional materials because their small size increases the number of heat conduction paths. This influences the rate of phase transition and heat transfer, thereby affecting their phase transition temperature and latent heat of phase transition.

[0148] Table 2. Thermal conductivity properties and improvement in thermal conductivity (compared to pure phase change fluid) of nano-phase change fluids

[0149]

[0150] Note: The thermal conductivity of water is taken as 0.59 W / mK, and the thermal conductivity of water is taken as 0.21 W / mK.

[0151] As can be seen from the data in Table 2, the addition of nano-metal compounds can significantly improve the thermal conductivity and thermal conductivity coefficient of n-alkane phase change thermal storage materials. This is because nano-metal compounds have high thermal conductivity and heat capacity, which can increase the material's thermal conductivity and heat storage capacity.

[0152] Specifically, the addition of nano-metal compounds can increase the heat conduction path of n-alkane phase change thermal storage materials, thereby improving the heat transfer rate. Furthermore, nano-metal compounds can also increase the material's heat capacity, enhancing its heat storage capability. These factors work together to significantly improve the thermal conductivity and thermal conductivity coefficient of n-alkane phase change thermal storage materials. It is important to note that the amount of nano-metal compounds added should be appropriate; excessive addition can lead to an overly long heat conduction path, which may actually reduce the thermal conductivity and thermal conductivity coefficient. Therefore, reasonable control of the addition amount is necessary in practical applications.

[0153] Table 3. Phase transition time of nanophase change fluids with different nanoparticle contents

[0154]

[0155] As shown in Table 3, nanocompounds can influence the phase transition time of n-alkane phase change fluids by altering their physical and chemical properties. Different concentrations of nanocompounds have varying effects on the phase transition time. With increasing nanocompound concentration, the phase transition time gradually decreases. This is because the addition of nanocompounds promotes nucleation and growth processes during the phase transition, thereby accelerating the transition. Furthermore, the addition of nanocompounds can improve the thermal conductivity and heat capacity of the phase change fluid, further accelerating the phase transition.

[0156] However, when the amount of nanocompound added is too high, the phase transition time may rebound, meaning the phase transition time may actually increase. This is because excessive nanocompound addition leads to an increase in the viscosity of the phase change fluid, thus hindering the phase transition. Therefore, in practical applications, it is necessary to select an appropriate amount of nanocompound added based on specific circumstances to achieve the best phase transition effect.

[0157] The effects of the amount and particle size of nanocompounds on phase transition time are complex, as they involve multiple factors such as the surface area, dispersibility, and interaction with n-alkanes. Generally, higher amounts result in shorter phase transition times because nanocompounds can act as nuclei to promote phase transition. However, excessive amounts may cause nanocompounds to aggregate, leading to longer phase transition times. Furthermore, different particle sizes of nanocompounds have varying effects on phase transition time. Smaller particle sizes can provide more nuclei, thus promoting phase transition, while larger particle sizes may hinder it. Therefore, this invention uses experimental research to determine the optimal amount of nanocompounds with different particle sizes, achieving the shortest phase transition time.

[0158] Table 4. Stability results of phase change emulsions and nanophase change fluids

[0159]

[0160]

[0161] HLB (Hydrophilic-lipophilic balance) is an index used to describe the balance between the hydrophilicity and lipophilicity of surfactants. In nanophase change n-alkane emulsions, the choice of HLB value plays a crucial role in properties such as emulsion stability and phase change temperature. According to the data in Table 4, firstly, the choice of HLB value affects emulsion stability. In nanophase change n-alkane emulsions, the choice and ratio of surfactants affect emulsion stability. Surfactants with HLB values ​​between 10 and 14 are suitable for the preparation of nanophase change n-alkane emulsions. When the HLB value is low, the surfactant tends to interact more with n-alkane molecules, leading to emulsion instability; when the HLB value is high, the surfactant tends to interact more with water molecules, also leading to emulsion instability. Therefore, choosing an appropriate HLB value can improve the emulsion stability of nanophase change n-alkane emulsions.

[0162] Secondly, the choice of HLB value also affects the phase transition temperature. In nano-phase change n-alkane emulsions, n-alkane molecules undergo a phase transition at a certain temperature, releasing stored heat energy. The choice of HLB value affects the phase transition temperature; generally, the higher the HLB value, the lower the phase transition temperature. Therefore, selecting an appropriate HLB value can control the phase transition temperature of nano-phase change n-alkane emulsions, thereby meeting the needs of different application scenarios.

[0163] In summary, HLB plays a crucial role in nanophase change n-alkane emulsions, influencing properties such as emulsion stability and phase transition temperature. Therefore, when preparing nanophase change n-alkane emulsions, it is necessary to select an appropriate HLB value to achieve the desired performance.

[0164] Table 5. Viscosity of Phase Change Emulsions and Nanophase Change Fluids

[0165]

[0166] The HLB value is an indicator of the hydrophilicity and hydrophobicity of surfactants, and it has a significant impact on the stability of nanocompound-composite n-alkane phase change fluids. Surfactants with higher HLB values ​​have stronger hydrophilicity and can be better dispersed in the aqueous phase, while surfactants with lower HLB values ​​have stronger hydrophobicity and are easier to disperse in the oil phase. Therefore, in nanocompound-composite n-alkane phase change fluids, selecting surfactants with appropriate HLB values ​​can achieve uniform dispersion of nanocompounds and stabilize the properties of the phase change fluid.

[0167] Specifically, when surfactants with lower HLB values ​​are added to phase change fluids, they interact more readily with n-alkanes, leading to decreased stability of the phase change fluid. Conversely, when surfactants with higher HLB values ​​are added to phase change fluids, they interact more readily with water, thereby promoting the dispersion of nanocompounds and improving the stability of the phase change fluid.

[0168] Therefore, when selecting surfactants, it is necessary to consider the hydrophilicity and hydrophobicity of nanocompounds, as well as the stability requirements of phase change fluids, so as to select surfactants with appropriate HLB values ​​to achieve the stability of nanocompound composite n-alkane phase change fluids.

[0169] Meanwhile, as shown in the table above, the effect of HLB value on the stability of phase change fluids composed of nanocompounds with different particle sizes and n-alkanes is related to the particle size. As the particle size decreases, the surface area of ​​the nanocompounds increases, and the effect of surfactants also increases. For larger nanocompounds, an increase in HLB value leads to an increase in the adsorption of surfactant molecules on the surface of the nanocompounds, thereby enhancing the compatibility between the nanocompounds and n-alkanes and improving the stability of the phase change fluid. For smaller nanocompounds, an increase in HLB value leads to an increase in the adsorption of surfactant molecules on the surface of the nanocompounds, but due to the small surface area of ​​the nanocompounds, the effect of surfactants is limited, so the effect of HLB value on the stability of the phase change fluid is relatively small.

[0170] Therefore, the effect of HLB value on the stability of nanocompound-composite n-alkane phase change fluid is related to the particle size of the nanocompound.

[0171] Table 6. Effect of the number of cycles of nano-SiC (5nm) phase change fluid on the phase change temperature and latent heat of phase change fluid.

[0172]

[0173] Nanocompound composite n-alkane phase change fluid is a phase change fluid with excellent performance. Its phase change temperature and latent heat of phase change are important performance indicators, and the number of cycles is one of the important factors affecting the performance of nanocompound phase change fluid.

[0174] First, regarding the effect of the number of cycles on the phase transition temperature of the nanophase change fluid, the data in the table above shows that the phase transition temperature of the nanophase change fluid changes with the increase of the number of cycles. As the number of cycles increases, the nanocompounds in the nanophase change fluid gradually aggregate, leading to an increase in the phase transition temperature. Therefore, the more cycles, the higher the phase transition temperature of the nanophase change fluid.

[0175] Secondly, regarding the effect of the number of cycles on the latent heat of phase change in nanophase change fluids, the data in the table above shows that the latent heat of phase change in nanophase change fluids changes with the increase of the number of cycles. As the number of cycles increases, the nanocompounds in the nanophase change fluid gradually aggregate, leading to a decrease in the latent heat of phase change. Therefore, the more cycles, the lower the latent heat of phase change in nanophase change fluids.

[0176] Therefore, the number of cycles affects the stability and heat transfer efficiency of the phase change fluid. The more cycles, the lower the stability of the phase change fluid may be, leading to changes in the phase change temperature and latent heat of phase change. At the same time, the number of cycles also affects the heat transfer efficiency of the phase change fluid, thereby affecting the phase change temperature and latent heat of phase change.

[0177] The addition of nano-SiC can affect the physical properties of phase change fluids, such as density, viscosity, and thermal conductivity. These changes in physical properties may affect the phase change temperature and latent heat of phase change.

[0178] Finally, the preparation methods and conditions of nanophase change fluids also affect the phase transition temperature and latent heat of phase transition. Different preparation methods and conditions may lead to different structures and properties of nanophase change fluids, thus affecting the phase transition temperature and latent heat of phase transition.

[0179] Table 7. Effect of the number of cycles of nano-AlN (5nm) phase change fluid on the phase change temperature and latent heat of phase change fluid.

[0180]

[0181] The data in the table above shows that the number of cycles of the nano-ALN composite phase change fluid has a certain impact on its phase change temperature and latent heat of phase change. As the number of cycles increases, the phase change temperature and latent heat of phase change of the nano-phase change fluid gradually decrease. This is because during the cycling process, the nanoparticles in the nano-ALN composite phase change fluid gradually aggregate, forming larger clusters, thus leading to a decrease in phase change temperature and latent heat of phase change. Furthermore, the cycling process also leads to the accumulation of impurities and bubbles in the nano-phase change fluid, further affecting its phase change performance.

[0182] Table 8. Effect of the number of cycles of 0.1% nano-BN (5nm) phase change fluid on phase change temperature and latent heat of phase change.

[0183]

[0184] As shown in the table above, the phase transition temperature and latent heat of phase transition of the nanophase change fluid may change with the increase of the number of cycles. This is because the nano-BN composite may aggregate or disperse during the cycling process, thus affecting the phase transition temperature and latent heat of phase transition. In addition, material loss or changes may occur during the cycling process, which will also affect the phase transition temperature and latent heat of phase transition.

[0185] in, Figure 1 The figures show the melting and solidification DSC curves of silicon carbide phase change fluids with different mass fractions in Examples 1-3. As can be seen from the figures, in the melting DSC curve of the nano-silicon carbide phase change fluid, a peak appears when the temperature increases, indicating that the sample is melting. During melting, the sample absorbs heat, so the peak represents the maximum amount of heat absorbed by the sample. As the temperature continues to rise, the peak gradually disappears, indicating that the sample has completely melted. In the solidification DSC curve of the nano-silicon carbide phase change fluid, a peak appears when the temperature decreases, indicating that the sample is solidifying. During solidification, the sample releases heat, so the peak represents the maximum amount of heat released by the sample. As the temperature continues to decrease, the peak gradually disappears, indicating that the sample has completely solidified.

[0186] The characteristics of the melting and solidification DSC curves of nano-silicon carbide composite n-alkane phase change fluids mainly include the following aspects:

[0187] 1. Temperatures of melting and solidification peaks: The temperatures of melting and solidification peaks of nano-silicon carbide composite n-alkane phase change fluids are usually higher than the corresponding temperatures of pure n-alkanes. This is because the addition of nano-silicon carbide increases the intermolecular forces of the phase change fluid, leading to an increase in melting and solidification temperatures.

[0188] 2. Peak values ​​of melting and solidification: The peak values ​​of melting and solidification of nano-silicon carbide composite n-alkane phase change fluid are usually higher than the corresponding peak values ​​of pure n-alkane. This is because the addition of nano-silicon carbide increases the heat capacity of the phase change fluid, leading to an increase in melting and solidification peak values.

[0189] 3. Width of melting and solidification peaks: The width of melting and solidification peaks of nano-silicon carbide composite n-alkane phase change fluids is usually narrower than the corresponding widths of pure n-alkane. This is because the addition of nano-silicon carbide increases the intermolecular forces of the phase change fluid, leading to a faster melting and solidification process.

[0190] 4. Thermal effects of melting and solidification: The thermal effects of melting and solidification of nano-silicon carbide composite n-alkane phase change fluids are usually greater than the corresponding thermal effects of pure n-alkane. This is because the addition of nano-silicon carbide increases the heat capacity of the phase change fluid, leading to a greater thermal effect of melting and solidification.

[0191] Depend on Figure 1 It is observed that with the increase of the amount of nano-silicon carbide added, the melting peak temperature and melting peak calorific value of the composite n-alkane phase change fluid both show a trend of first increasing and then decreasing. When the amount of nano-silicon carbide added is 0.1%, the melting peak temperature and melting peak calorific value reach their maximum values. As the amount of nano-silicon carbide added continues to increase, the melting peak temperature and melting peak calorific value gradually decrease. This is because an appropriate amount of nano-silicon carbide can increase the thermal stability and thermal conductivity of the composite phase change fluid, thereby increasing the melting peak temperature and melting peak calorific value. However, when the amount of nano-silicon carbide added is too large, it will lead to the aggregation of nano-silicon carbide particles, affecting the fluidity and thermal conductivity of the phase change fluid, thereby reducing the melting peak temperature and melting peak calorific value.

[0192] During solidification, with increasing amounts of nano-silicon carbide, the solidification peak temperature and calorific value of the composite phase change fluid exhibit a trend of first decreasing and then increasing. When the nano-silicon carbide content is 0.1%, both the solidification peak temperature and calorific value reach their minimum values. With further increases in the nano-silicon carbide content, both gradually increase. This is because an appropriate amount of nano-silicon carbide can increase the thermal conductivity of the composite phase change fluid, thereby accelerating the solidification rate and increasing the solidification peak temperature and calorific value. However, excessive amounts of nano-silicon carbide can lead to aggregation between the nano-silicon carbide particles, affecting the fluidity and thermal conductivity of the phase change fluid, thus reducing the solidification peak temperature and calorific value.

[0193] Figure 2 The figures show the melting and solidification DSC curves of aluminum nitride phase change fluids with different mass fractions in Examples 4-6. Figure 3 The figures show the melting and solidification DSC curves of boron nitride phase change fluids with different mass fractions in Examples 7-9. The figures also show the correlation between the curves and the solidification curves. Figure 1 same.

[0194] Figure 4 The graphs show the thermal conductivity curves of silicon carbide phase change fluids with different mass fractions in Examples 1-3. Figure 5 The graphs show the thermal conductivity curves of aluminum nitride phase change fluids with different mass fractions in Examples 4-6. Figure 6The graphs show the thermal conductivity curves of boron nitride phase change fluids with different mass fractions in Examples 7-9. As can be seen from the graphs, the latent heat of phase change gradually decreases with increasing nanocompound content. This is because nano-silicon carbide is not a phase change material; the increase in nanocompound particles reduces the content of n-alkane, thus lowering the latent heat of phase change. Furthermore, when n-alkane and nanocompound particles are combined, a portion of n-alkane is wrapped around the nanocompound particles on the surface. Within this film, the molecular arrangement of both molecules changes accordingly, and their surface free energy state also changes accordingly. Free energy accounts for a large proportion of the system's energy, thus affecting the system's thermal properties and reducing the latent heat of phase transition to some extent. For example, according to the overall scheme, the optimal content of 0.1% nano-silicon carbide results in a thermal conductivity of 0.823 W / mK. As the volume fraction continues to increase, the thermal conductivity no longer increases but decreases. When the content of nano-silicon carbide is greater than 0.5% (thermal conductivity 0.783 W / mK), this is because excessive nanoparticles inhibit the movement of particles in n-alkanes, easily leading to agglomeration and sedimentation, thereby reducing the thermal conductivity of the composite material to some extent.

[0195] Figure 7 DSC curves for the endothermic melting process of silicon carbide phase change fluids with different mass fractions. Figure 8 DSC curves of the endothermic melting process of boron carbide phase change fluids with different mass fractions are shown. In the figures, the vertical axis represents heat flux (heat transfer rate) in W / m³. 2 The horizontal axis represents time (s). The black curve represents the DSC curve of the endothermic melting process of pure n-alkanes, while the other three curves represent the DSC curves of composite materials with nanoparticle contents of 0.1%, 0.3%, and 0.5%, respectively. The curves show that adding nanoparticles can advance the phase transition point of n-alkanes and shorten the phase transition time. The specific onset time of the phase transition is shown in Table 3. As the nanoparticle content increases, the required phase transition time first decreases and then increases. The shortest time is achieved when the volume fraction is 0.1-0.5%. This is because heat transfer in a mixture occurs in two ways: conduction and convection. When the nanoparticle content is low (0.1%), the high thermal conductivity of the nanoparticles increases the thermal conductivity of the mixture, resulting in higher overall thermal conductivity and a gradually decreasing phase transition time. However, as the nanoparticle content continues to increase (above 0.1%), excessive nanoparticles will cause partial agglomeration and sedimentation. This inhibits convection between the composite material and the matrix to some extent, resulting in a decrease in the thermal conductivity of the composite material and an increase in the required phase transition time.

[0196] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nanoparticle phase change fluid, characterized in that, The nanoparticle phase change fluid comprises the following raw materials by mass percentage: 99.0-99.8% phase change emulsion, 0.1-0.5% nanomaterials, and 0.1-0.5% dispersant; The phase change emulsion comprises the following raw materials by mass percentage: 30-45% phase change heat storage material, 5-10% surfactant, 1-8% nucleating agent, 5-12% antifreeze and 40-50% water; The surfactant has an HLB value of 10-14; The surfactant includes an emulsifying surfactant and a co-surfactant, with a mass ratio of 4:

1. The emulsifying surfactant is a nonionic surfactant, and the nonionic surfactant is at least two of the following: propylene glycol fatty acid ester, polyoxyethylene oleyl alcohol ether, sorbitan monooleate polyoxyethylene ether, sorbitan monooleate, sorbitan monostearate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan monolaurate. The co-surfactant is any one of n-butanol, n-pentanol, stearic acid, lauric acid, and octanoic acid.

2. The nanoparticle phase change fluid according to claim 1, characterized in that, The phase change thermal storage material is at least one of n-alkanes, and the molecular formula of the n-alkane is C2. n H 2n+2 n is an integer between 23 and 30; The nucleating agent is any one of stearic acid, paraffin, lauric acid, and palmitic acid; The antifreeze is any one of ethylene glycol, propylene glycol, ethanol, triethanolamine, and dimethyl sulfoxide.

3. The nanoparticle phase change fluid according to any one of claims 1-2, characterized in that, The preparation method of the phase change emulsion includes the following steps: (1) Weigh the raw materials by mass percentage: 30-45% phase change heat storage material, 5-10% surfactant, 1-8% nucleating agent, 5-12% antifreeze and 40-50% water; (2) The nucleating agent and the phase change heat storage material are mixed and heated and stirred to form a uniformly dispersed phase A; (3) The surfactant, the water and the antifreeze are mixed and heated and stirred to obtain a continuous phase B; (4) The dispersed phase A is added to the continuous phase B, and after high-speed homogenization, a highly stable latent heat transport phase change emulsion is obtained.

4. The nanoparticle phase change fluid according to claim 3, characterized in that, The heating temperature described in steps (2) and (3) is 60-80℃; The conditions for high-speed homogenization in step (4) are: rotation speed of 15000-25000 rpm, heating temperature of 60-80℃, and homogenization time of 5-10 min.

5. The nanoparticle phase change fluid according to claim 1, characterized in that, The nanomaterial is any one of nano-aluminum nitride, nano-boron nitride, and nano-silicon carbide; the particle size of the nanomaterial is 5-20 nm. The dispersant is any one of polyvinyl alcohol, xanthan gum, guar gum, gum arabic, and polyethylene glycol.

6. A method for preparing a nanoparticle phase change fluid according to any one of claims 1-5, characterized in that, Specifically, the following steps are included: (1) Weigh the raw materials by mass percentage: 100% phase change emulsion, 0.1-0.5% nanomaterials and 0.1-0.5% dispersant, and set aside; (2) The dispersant and the nanomaterial are added to the phase change emulsion in sequence and stirred evenly to obtain a mixture for later use; (3) The mixture is ultrasonically treated to obtain a nanoparticle phase change fluid.

7. The application of the nanoparticle phase change fluid as described in any one of claims 1-5 or the nanoparticle phase change fluid obtained by the preparation method described in claim 6 in the preparation of heat exchange working fluid.

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