Plastic high-thermal-conductivity composite cold storage material and preparation method thereof

Abstract

The invention discloses a plastic high-thermal-conductivity composite cold storage material and a preparation method thereof. The composite cold storage material comprises a porous framework and a cold storage medium which is immersed in the porous framework and wraps the porous framework, the porous framework is made of an alloy material, a metal material or a ceramic material; the solid-state cold storage medium is made of water, a salt solution or an organic cold storage material; the appearance of the composite cold storage material can be any one of an olive shape, a golf ball shape, a calabash shape, an oval shape, a ball shape, a pulmonary alveolus shape, a water drop shape, a bullet shape and a spindle shape. The composite cold storage material disclosed by the invention has extremely strong plasticity in appearance, can reduce the flow resistance of external fluid in a cryogenic packed bed, has higher heat conductivity coefficient and higher thermal reaction rate in thermal performance, and can realize a more efficient cold storage / release process.

Description

Technical Field

[0001] The invention relates to the technical field of solid-phase sensible heat cold storage and the technical field of deep-cold packed bed energy storage, and in particular to a plastic high-thermal-conductivity composite cold storage material and a preparation method thereof. Background Art

[0002] Liquid air energy storage (LAES) is a type of compressed air energy storage. It stores electrical energy in the form of liquid air by introducing cold storage technology, which not only greatly improves the energy density of compressed air energy storage system (CAES), but also greatly reduces the requirements of CAES system for geographical factors. At present, most of the research on LAES system remains at the system design level. The design of the cold storage subsystem is too ideal, resulting in a large difference between the theoretical round-trip efficiency of the system and the efficiency of the corresponding pilot system. In order to accelerate the process of engineering application of LAES system, attention must be paid to the cold storage technology used in LAES system.

[0003] Cold storage technology is a special form of thermal energy storage technology. Thermal energy storage technology refers to the use of heat storage materials to store or release heat in a certain way, which can solve the time and space problems in the heat supply and demand relationship. The materials used for thermal energy storage technology must have suitable properties, such as high specific heat capacity, high thermal conductivity, low cost, thermal stability, chemical stability, low volume change, non-toxicity and low flammability. Thermal energy storage technology that stores and utilizes heat below ambient temperature is usually called cold storage technology. Cold storage technology is widely used in air conditioning, food and drug processing, energy storage and other fields.

[0004] According to the cold storage materials used, cold storage technology is divided into two types: sensible heat storage and latent heat storage. Sensible heat storage uses the sensible heat properties of materials to complete cold storage. Common sensible heat storage materials include low-temperature water, rocks, etc. Latent heat storage uses the phase change properties and sensible heat properties of materials to complete cold storage. Usually, phase change materials (PCM) such as ice and eutectic salts are used as cold storage media. Since water is a relatively cheap, easy to obtain, safe and simple working fluid with large heat capacity, the current cold storage technology in industrial production mainly uses water storage and ice storage technology. Compared with sensible heat storage with water as the working fluid, cold storage technology has an energy capacity of about 7 to 8 times that of water storage by utilizing the latent heat of phase change of water.

[0005] At present, due to the advantages of mature technology and good economy, the cold storage technology in LAES mostly uses sensible heat materials that can meet the temperature requirements of LAES, mainly including liquid cold storage materials such as methanol and propane and solid materials such as rocks and pebbles. In order to seek high energy density, high compactness and high economy cold storage technology, and further reduce the requirements of LAES system for geographical conditions, focusing only on sensible heat storage technology can no longer meet the development requirements of LAES system. Latent heat storage technology has received widespread attention in industries such as textiles, air conditioning, construction and food. However, due to the low liquefaction temperature of air and the large-scale cold storage required by LAES, finding a latent heat storage material suitable for LAES still faces great challenges. Therefore, latent heat storage technology suitable for LAES is still in the exploratory stage, and some researchers have been trying to find PCM suitable for LAES.

[0006] With the continuous development of society, people's demand for environmentally friendly and renewable cold energy is constantly expanding, especially in the fields of refrigeration, air conditioning and other temperature control. Solid phase cold storage technology has become an important means of energy saving. At the LNG receiving station, LNG needs to be gasified by the gasifier before use. It is estimated that the gasification process of each ton of LNG is equivalent to releasing 860MJ of cold energy (about 230kWh), but this part of cold energy is unstable with the amount of gasified LNG and cannot be directly used for stable grid-connected power generation. Therefore, cold storage technology is needed to store cold energy to achieve peak shaving and valley filling of power generation, carbon dioxide capture, alkane separation, low-temperature refrigeration and other purposes. Common cold storage materials include low-temperature water, rock, ice, eutectic salts, etc. However, the current cold storage materials have problems such as low thermal conductivity and large fluid flow resistance inside and outside the packed bed, which leads to a slow overall thermal reaction rate of the cold storage system and a low storage / release rate.

[0007] In order to solve the problems existing in the above-mentioned cold storage materials, Wu liangyu (Wu liangyu, Yu Jie, et al. International Journal of Refrigeration, 2024, Volume 158, Pages 144-156) et al. proposed bionic fins based on traditional fins to enhance the thermal properties of spherical cold storage materials. They found that the presence of bionic metal fins caused minimal loss of ice hockey cold storage capacity, and proved that aluminum is the best fin material. From the perspective of macroscopic structure optimization, Zhai Xiaoqiang proposed an efficient phase change energy storage package, which looks like a red blood cell. Its special structural parameters ensure heat exchange efficiency while also reducing the flow resistance of the external fluid. (Zhai Xiaoqiang, Cheng Xiwen. A high-efficiency phase change energy storage package, 2017, CN107062971A).

[0008] Although the existing method of adding bionic fins can improve the thermal performance of cold storage materials and increase the thermal conductivity and thermal response time of existing cold storage materials, the complex structural design of the bionic fins limits the possibility of mass production; although the design of the red blood cell-shaped package ensures the heat exchange efficiency and reduces the flow resistance of the external fluid, its complex geometric structure can only be achieved through 3D printing and cannot be mass-produced.

[0009] Therefore, how to obtain a high thermal conductivity composite cold storage material that can be mass-produced and can reduce the flow resistance of the external fluid in a cryogenic packed bed, and at the same time has a higher thermal conductivity and a faster thermal reaction rate in thermal performance, is still a technical problem that needs to be solved urgently. Summary of the invention

[0010] In view of this, the purpose of the present invention is to provide a plastic high thermal conductivity composite cold storage material and a preparation method thereof. Specifically, in response to the above-mentioned existing problems, the inventors have proposed a high thermal conductivity composite cold storage material structure type and a batch preparation method that is externally plastic and internally filled with a porous skeleton, which effectively solves the problems of low thermal conductivity, large flow resistance of the internal and external fluids in the packed bed, slow thermal reaction rate of the cold storage system, and low storage / release rate of the existing cold storage materials. It has significant advantages such as low raw material cost, simple preparation method, and batch production. The shape of the material can be customized according to the requirements of the application scenario, and has broad application prospects in the fields of solid-phase sensible heat storage technology and deep-cold packed bed energy storage technology.

[0011] In a first aspect, the present invention provides a composite cold storage material, comprising a porous skeleton and a cold storage medium immersed in the porous skeleton and wrapped outside the porous skeleton;

[0012] The porous skeleton is made of alloy material, metal material or ceramic material;

[0013] The material of the cold storage medium is water, salt solution or organic cold storage material, the salt solution is selected from one or more of KCl, NaCl, BaCl2, CaCl2, KNO3, NaNO3, Na2CO3, K2CO3 solution, and the organic cold storage material is selected from one or more of tetradecane, lauric acid, ethylene glycol, paraffin, fatty acid, polyethylene glycol laurate;

[0014] The composite cold storage material has an outer shape of any one of an olive shape, a golf ball shape, a gourd shape, an oval shape, a sphere shape, an alveolar shape, a water drop shape, a bullet shape, and a spindle shape.

[0015] In the above-mentioned composite cold storage material, further, the alloy material includes one or more of chromium alloy, copper alloy, iron alloy, nickel alloy, aluminum alloy, stainless steel, and molybdenum alloy; the metal material includes one or more of copper, iron, nickel, chromium, aluminum, and molybdenum; the ceramic material includes one or more of silicon carbide, silicon boride, aluminum oxide, boron carbide, zinc oxide, zirconium oxide, and silicon nitride;

[0016] Furthermore, the shape of the porous skeleton includes any one of a foam porous shape, a loofah shape, a honeycomb shape, and a lotus root shape.

[0017] In the above-mentioned composite cold storage material, further, the cold storage medium wrapped outside the porous skeleton accounts for 20% to 80% of the volume of the composite cold storage material.

[0018] In a second aspect, the present invention provides a method for preparing the composite cold storage material described in any of the above items, comprising the following steps: (1) filling the porous skeleton into a mold having the described shape, and then pouring the cold storage medium into the mold until the porous skeleton is completely immersed; (2) freezing the mold obtained in step (1) until the cold storage medium is completely solidified, and obtaining the composite cold storage material by demolding.

[0019] In the above-mentioned method for preparing the composite cold storage material, further, the material of the mold is metal, alloy metal, silicone, plastic or high molecular polymer.

[0020] In a third aspect, the present invention provides a packed bed cold storage system, comprising a shell and a composite cold storage material as described in any one of the above items or a composite cold storage material prepared by any one of the above methods filled in the shell.

[0021] In the above-mentioned packed bed cold storage system, further, the composite cold storage material is filled in the shell in a random arrangement, a close arrangement, a radial gradient layered arrangement or an axial gradient layered arrangement.

[0022] In a fourth aspect, the present invention provides a method for releasing and storing cold using any of the above-mentioned packed bed cold storage systems, comprising the following steps:

[0023] A high-temperature cold medium is introduced into the packed bed cold storage system, the high-temperature cold medium contacts the composite cold storage material to absorb the cold in the composite cold storage material, and the cold medium after heat exchange flows out of the packed bed cold storage system to complete cold release; wherein the cold release temperature is controlled to be lower than the melting point of the cold storage medium used to maintain the shape of the composite cold storage material;

[0024] A low-temperature refrigerant is introduced into the packed bed cold storage system, the low-temperature refrigerant contacts the composite cold storage material to transfer cold to the composite cold storage material, and the refrigerant after heat exchange flows out of the packed bed cold storage system to complete cold storage.

[0025] In the above-mentioned method for releasing and storing cold, further, the shape parameters of the composite cold storage material filled in the packed bed cold storage system are obtained by the following steps:

[0026] The geometric shape and geometric parameters of the fluid channel of the packed bed cold storage system, the type and physical properties of the cold medium, the geometric model of the pre-designed shape of the composite cold storage material, the type of cold storage medium and the physical properties of the cold storage medium are input into the multi-physics field simulation software, and the fluid flow module is selected to determine the shape parameters of the composite cold storage material according to the flow characteristics of the composite cold storage materials with different geometric shapes.

[0027] In the above-mentioned method for releasing and storing cold, further, the characteristic length of the composite cold storage material filled in the packed bed cold storage system is obtained by the following steps:

[0028] The characteristic length in the composite cool storage material is determined according to the determined shape parameters of the composite cool storage material and the resistance coefficients at different characteristic lengths.

[0029] In the above-mentioned method of releasing and storing cold, further, the porosity of the porous skeleton in the composite cold storage material filled in the packed bed cold storage system is obtained by the following steps: inputting the geometric model of the random porous medium in the multi-physics field simulation software, selecting the pore domain as the cold storage material domain, selecting the continuous channel domain as the high thermal conductivity skeleton domain, selecting the solid heat transfer module, and determining the volume percentage of the porous skeleton in the composite cold storage material according to the heat transfer characteristics of the composite cold storage material.

[0030] In a fifth aspect, the present invention provides a liquid air energy storage system, comprising the composite cold storage material described in any one of the above items or the composite cold storage material prepared by the method described in any one of the above items, or the packed bed type cold storage device described in any one of the above items.

[0031] The present invention has the following beneficial effects:

[0032] 1. The present invention proposes a composite cold storage material with plasticity and high thermal conductivity and a preparation method thereof. Thanks to the low cost of the filling material and the internal porous metal and the simple preparation method, low-cost mass production of the composite cold storage material is achieved.

[0033] 2. Compared with traditional cold storage materials, the composite cold storage material of the present invention has extremely strong plasticity in appearance, which can reduce the flow resistance of external fluid in the cryogenic filling bed. At the same time, it has higher thermal conductivity and faster thermal reaction rate in thermal performance, so it can achieve a more efficient cold storage / release process, which opens up a new way for the design of high-performance cryogenic filling bed filling materials based on cold storage systems.

[0034] 3. The present invention gives plasticity to traditional cold storage materials and improves the feasibility of theoretical design of cold storage materials. The heat transfer area, resistance coefficient and heat transfer performance of the composite cold storage material are calculated according to the parameters of the refrigerant medium in different actual application conditions using the continuity equation, momentum equation, energy equation and transport theorem. The outer surface of the composite cold storage material is mathematically described and the design shape is optimized on this basis to minimize the external fluid flow resistance under actual working conditions, thereby maximizing the cold storage performance of the deep-cold packed bed and accelerating the system thermal reaction rate of the deep-cold packed bed, thereby greatly expanding the application scope of cold storage materials in the field of sensible heat cold storage.

[0035] 4. The present invention adopts a porous skeleton as the internal main structure of the composite cold storage material, and uses the energy transport equation to obtain the optimal solution of the porous skeleton ratio through heat transfer calculation simulation. It not only enhances the overall thermal conductivity of the composite material, but also solves the problem of low thermal conductivity of a single cold storage material, and ensures that the overall structure has a certain mechanical strength, strengthens the peak-cutting and valley-filling effect of the cold storage material in the process of grid-connected power generation, and reduces the waste of high-grade electric energy. The economic benefits generated are significant, which is of great significance for saving resources, improving the utilization efficiency of cold energy, and developing a circular economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the structure of a composite cold storage material in one embodiment of the present invention;

[0037] Figure 2 Schematic diagrams of the appearance of the composite cold storage material in one embodiment of the present invention, which are olive-shaped (a), golf ball-shaped (b), gourd-shaped (c), oval-shaped (d), alveolar-shaped (e), teardrop-shaped (f), bullet-shaped (g) and spindle-shaped (h);

[0038] Figure 3 Schematic diagrams of the shapes of porous skeletons in one embodiment of the present invention, which are foam porous shape (a), loofah shape (b), honeycomb shape (c) and lotus root shape (d);

[0039] Figure 4 Schematic diagram of the arrangement of the composite cold storage material in one embodiment of the present invention, which are radial gradient layered arrangement (a) and axial gradient layered arrangement (b);

[0040] Figure 5A schematic diagram of the COMSOL Multiphysics 6.0 workflow in one embodiment of the present invention;

[0041] Figure 6 It is a schematic diagram of the calculation and design results of the composite cold storage material in one embodiment of the present invention;

[0042] Figure 7 It is a schematic diagram of calculating the performance differences of spherical, olive-shaped and elliptical composite cold storage materials in one embodiment of the present invention;

[0043] Figure 8 Schematic diagram of the change of the specific resistance coefficient of the elliptical composite cold storage material with the semi-major axis a in one embodiment of the present invention;

[0044] Fig. 9 Schematic diagram of the variation of the specific resistance coefficient of the olive-shaped composite cold storage material with the radius R in one embodiment of the present invention;

[0045] Fig.10 The effect of the porosity of the composite cold storage material on the internal temperature distribution during the cold storage / release process in one embodiment of the present invention;

[0046] Fig.11 The effect of the porosity of the composite cold storage material on the thermal properties of the material in one embodiment of the present invention;

[0047] Fig.12 This is a schematic diagram of the preparation process of the foam copper / ice composite cold storage material in one embodiment of the present invention;

[0048] Fig.13 Schematic diagram of the arrangement of composite cold storage materials in a cryogenic packed bed cold storage tank in one embodiment of the present invention.

[0049] The numbers in the figure are as follows:

[0050] 100-composite cold storage material; 101-porous skeleton; 102-cold storage medium;

[0051] 200-housing;

[0052] 300-Mold. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] As described in the background technology, the current cold storage materials have low thermal conductivity, large resistance to the flow of external fluids in the packed bed, and other problems, which lead to a slow overall thermal reaction rate of the cold storage system and a low storage / release rate. The design of adding bionic fins and red blood cell-shaped packaging bodies in the prior art cannot achieve mass production and has a high production cost. The inventor of the present invention has taken a different approach by adopting a method of filling a highly thermally conductive porous skeleton inside and a plastic cold storage medium outside to prepare a plastic high thermal conductivity composite cold storage material. The cold storage medium wrapped on the outside is designed into a specific shape through optimization calculation. While achieving high thermal conductivity, the flow resistance of the external fluid can be reduced in the deep cold packed bed, thereby obtaining a higher thermal conductivity coefficient and a faster thermal reaction rate in terms of thermal performance.

[0055] The first part, such as Figure 1 As shown, the present invention provides a composite cold storage material 100, including a porous skeleton 101 and a cold storage medium 102 immersed in the porous skeleton and wrapped outside the porous skeleton; the porous skeleton 101 is made of an alloy material, a metal material or a ceramic material, the material of the solid cold storage medium 102 is water, a salt solution or an organic cold storage material, the salt solution includes one or more of KCl, NaCl, BaCl2, CaCl2, KNO3, NaNO3, Na2CO3, and K2CO3 solutions, and the organic cold storage material includes tetradecane, lauric acid, ethylene glycol, paraffin, fatty acid, and polyethylene glycol laurate; the shape of the composite cold storage material 100 includes any one of an olive shape, a golf ball shape, a gourd shape, an oval shape, a sphere, an alveolar shape, a teardrop shape, a bullet shape, and a spindle shape.

[0056] Based on the above technical solution, the present invention makes the porous skeleton and the plastic cold storage medium into Figure 2 The composite material shown, wherein the cold storage medium 102 is liquid at room temperature and can be quickly formed into the shape in the mold by freezing to achieve mass production, and on the other hand, the porous skeleton 101 with high thermal conductivity will increase the thermal conductivity of the composite cold storage material 100, and the cold storage medium 102 with plasticity is frozen into a specific low flow resistance shape by mold.

[0057] It should be noted that Figure 1 The shapes listed in the figure are only for demonstrating the structure of the composite cold storage material of the present invention, and they do not limit the shapes of the composite cold storage material of the present invention. On the contrary, the shapes of the composite cold storage material of the present invention include any one of olive shape, golf ball shape, gourd shape, oval shape, spherical shape, alveolar shape, tear drop shape, bullet shape and spindle shape.

[0058] The term "olive-shaped" refers to Figure 2 The shape shown in a is similar to an olive, with a large middle and small ends.

[0059] The term "golf ball shaped" refers to Figure 2 The surface shown in b has a golf ball-like shape with dimples.

[0060] The term "gourd-shaped" refers to Figure 2 c shows a gourd-like shape.

[0061] The term "oval" refers to Figure 2 The shape shown in d is similar to an oval.

[0062] The term "alveolar shape" refers to Figure 2 The shape shown in e is similar to that of alveoli.

[0063] The term "teardrop shape" refers to Figure 2 f shows a water droplet-like shape.

[0064] The term "bullet-shaped" refers to Figure 2 The bullet-like shape shown in g.

[0065] The term "spindle-shaped" refers to Figure 2 The spindle-like shape shown in h.

[0066] The above-mentioned shapes can reduce the flow resistance of the external fluid in the cryogenic packed bed, thereby obtaining a higher thermal conductivity and a faster thermal reaction rate in terms of thermal performance. Taking the golf ball shape as an example, there are many dimples on the golf ball surface, which help to disrupt the airflow behind the sphere and reduce the formation of vortices. Vortex is one of the main reasons for the increase in resistance. By reducing vortices, the flow resistance can be reduced. In order to form the above-mentioned shape, it is undoubted that the cold storage medium wrapped outside the porous skeleton exists in a solid state.

[0067] The plastic shape can be further described by mathematical parameters, and its mathematical description is but not limited to ellipse. Olive Shape Teardrop shape (x=a(1-cos(t)) n , y = bsin(t) n ), super elliptical wait.

[0068] In at least one embodiment of the present invention, the alloy material includes one or more of chromium alloy, copper alloy, iron alloy, nickel alloy, aluminum alloy, stainless steel, and molybdenum alloy, the metal material includes one or more of copper, iron, nickel, and chromium, and the ceramic material includes one or more of silicon carbide, silicon boride, aluminum oxide, boron carbide, zinc oxide, zirconium oxide, and silicon nitride. The porous skeleton 101 can not only provide certain mechanical properties, but also improve the thermal conductivity of the composite cold storage material and accelerate the heat exchange process.

[0069] like Figure 3As shown, the shape of the porous skeleton includes any one of a foam porous shape, a loofah shape, a honeycomb shape, and a lotus root shape.

[0070] The term "cellular foam" refers to Figure 3 The shape shown in a.

[0071] The term "loofah-shaped" refers to Figure 3 The shape shown in b.

[0072] The term "honeycomb" refers to Figure 3 The shape shown in c.

[0073] The term "lotus root-shaped" refers to Figure 3 The shape shown in d.

[0074] The cold storage medium in the present application can provide the composite cold storage material with the desired shape on the one hand, and on the other hand, the pores of the porous skeleton are filled with the cold storage medium, which increases the heat exchange area between the cold storage medium and the porous skeleton and accelerates the heat exchange process. It can be understood that the salt solution in the cold storage medium refers to its aqueous solution.

[0075] In at least one embodiment of the present invention, the volume percentage of the cold storage medium wrapped outside the porous skeleton accounts for 20% to 80% of the composite cold storage material. This volume percentage is more conducive to achieving an efficient cold storage / release process, because when the volume percentage of the cold storage medium wrapped outside is too low, it cannot form the shape to reduce the flow resistance of the external fluid, and when the volume percentage of the cold storage medium wrapped outside is too high, it is not conducive to improving the thermal conductivity of the composite cold storage material.

[0076] The parameters in the mathematical description and the porosity of the porous skeleton can be adjusted within a reasonable range according to the actual application conditions, such as the density and viscosity of the cold medium used, the cold storage medium in the composite cold storage material, and the size of the fluid channel. Preferably, the flow characteristics and heat transfer characteristics under the corresponding plastic shape and porosity can be calculated and optimized to obtain the theoretical optimal value. The optimization method is detailed below and will not be described here.

[0077] In at least one embodiment of the present invention, the characteristic length of the composite cold storage material can be adjusted within a reasonable range according to the actual application conditions, specifically in combination with the plastic shape and the size of the fluid resistance (flow performance). Preferably, the theoretical optimal value of the characteristic length can be calculated based on the flow characteristics under the corresponding plastic shape. The optimization method is detailed below and will not be repeated here. The term "characteristic length" is a dimension that defines the scale of a physical system, and the characteristic length l = V / S = volume divided by the surface. Among them, when the shape is elliptical, the characteristic length is the length of the major semi-axis (hereinafter referred to as the semi-axis length).

[0078] The second part, such as Fig.12 As shown, the present invention provides a method for preparing the composite cold storage material described in any of the above items, comprising the following steps: (1) filling the porous skeleton 101 into a mold 300 having the described shape, and then pouring the cold storage medium 102 into the mold until the porous skeleton 101 is completely immersed; (2) freezing the mold 300 obtained in step (1) until the cold storage medium is completely solidified, and demolding to obtain the composite cold storage material.

[0079] In at least one embodiment of the present invention, the material of the mold is metal, alloy metal, silicone, plastic or polymer, the metal is iron or copper, the alloy is iron alloy or nickel alloy; the polymer is polydimethylsiloxane (PDMS), polypropylene (PP), polyethylene (PE), polycarbonate (PC) or polytetrafluoroethylene (PTFE). The selection of the material is conducive to the demolding of the composite cold storage material while shaping the composite cold storage material, and it is easy to obtain and has low cost. The processing method of the mold is determined by the material. For alloy metal materials, stamping molding, casting and other methods can be adopted. For polymer materials such as plastics and silicone, curing molding can be adopted. The porous skeleton 4 is filled in the mold 3, and the volume ratio occupied by the filling is the volume percentage of the porous skeleton in the composite cold storage material, which can be obtained by the optimal solution of the heat transfer calculation below.

[0080] In the third part, the present invention provides a packed bed cold storage system, comprising a shell 200 and any one of the composite cold storage materials 100 described above filled in the shell.

[0081] In at least one embodiment of the present invention, Figure 4 As shown, the composite cold storage material 100 is filled in the shell 200 in a random arrangement, a close arrangement, or a radial gradient layered arrangement (such as Figure 4 (a)), axial gradient layered arrangement (as shown Figure 4 (b)). The specific conditions depend on the actual working conditions, so as to minimize the flow resistance of the composite cold storage material in the packed bed and the external fluid; when storing cold, maximize the cold storage rate of the composite cold storage material for the low-temperature heat exchange fluid; when releasing cold, maximize the cold release rate of the composite cold storage material to the high-temperature heat exchange fluid.

[0082] In the fourth part, the present invention provides a method for releasing and storing cold using any of the above-mentioned packed bed cold storage systems, comprising the following steps:

[0083] A high-temperature cold medium is introduced into the packed bed cold storage system, the high-temperature cold medium contacts the composite cold storage material to absorb the cold in the composite cold storage material, and the cold medium after heat exchange flows out of the packed bed cold storage system to complete cold release; wherein the cold release temperature is controlled to be lower than the melting point of the cold storage medium used to maintain the shape of the composite cold storage material;

[0084] A low-temperature refrigerant is introduced into the packed bed cold storage system, the low-temperature refrigerant contacts the composite cold storage material to transfer cold to the composite cold storage material, and the refrigerant after heat exchange flows out of the packed bed cold storage system to complete cold storage.

[0085] In at least one embodiment of the present invention, preferably, the shape parameters of the composite cold storage material filled in the packed bed cold storage system are obtained by the following steps: the geometric shape and geometric parameters of the fluid channel of the packed bed cold storage system, the type and physical properties of the cold medium, the geometric model of the pre-designed shape of the composite cold storage material, the type of cold storage medium and the physical properties of the cold storage medium are input into the multi-physics field simulation software, and the fluid flow module is selected to determine the shape parameters of the composite cold storage material according to the flow characteristics of the composite cold storage materials with different geometric shapes. More preferably, the characteristic length of the composite cold storage material filled in the packed bed cold storage system is obtained by the following steps: the characteristic length of the composite cold storage material is determined according to the determined shape parameters of the composite cold storage material and the resistance coefficient at different characteristic lengths.

[0086] In at least one embodiment of the present invention, preferably, the porosity of the porous skeleton in the composite cold storage material filled in the packed bed cold storage system is obtained by the following steps: inputting a geometric model of a random porous medium in a multi-physics field simulation software, selecting the pore domain as the cold storage material domain, selecting the continuous channel domain as the high thermal conductivity skeleton domain, selecting a solid heat transfer module, and determining the volume percentage of the porous skeleton in the composite cold storage material according to the heat transfer characteristics of the composite cold storage material.

[0087] In at least one embodiment of the present invention, the multi-physics field simulation software is commercial software such as COMSOL. It is understandable that those skilled in the art can also use the corresponding equations listed below to implement the corresponding calculations using open source software.

[0088] In the above embodiment, specifically, the mathematical parameters of the shape are determined according to the flow characteristics of the plastic cold storage materials with different structures under the forced convection of the external fluid, such as the basic shape of the outer surface is determined according to the parameters of the cold medium under different actual application conditions, including density, viscosity, etc., and the outer surface of the composite cold storage material is mathematically described and parameterized. More specifically, the geometric model of the pre-designed shape of the composite cold storage material is obtained by the following steps: the shape points of the composite cold storage material (1) described by the discrete corresponding streamline equations are drawn into a combined model by a drawing tool (such as CAD), and exported into a format recognizable by commercial software such as COMSOL.

[0089] In the above embodiments, specifically, the flow characteristics of the geometric shape are calculated and analyzed using the corresponding continuity equation, momentum equation, energy equation, transport theorem, and discrete analysis method. After post-analysis processing, the best geometric shape is selected to regenerate the model for new flow characteristic calculations. For example, the heat exchange area, resistance coefficient, and heat exchange performance of the composite cold storage material are calculated using the continuity equation, momentum equation, energy equation, and transport theorem. The parameters of the outer surface shape are changed and the heat exchange area, resistance coefficient, and heat exchange performance are used as the evaluation criteria for the optimization design to optimize the design shape so as to minimize the external fluid flow resistance in accordance with actual working conditions.

[0090] Among them, when the continuity equation, momentum equation, energy equation and transport theorem are When it is less than or equal to 2000, the laminar boundary condition is selected for calculation, and the specific continuity and momentum equations of the external fluid can be expressed as:

[0091]

[0092]

[0093] The external fluid energy equation can be expressed as:

[0094]

[0095] At the same time, the drag coefficient C D It can be expressed as:

[0096]

[0097] Where u and v are the components of the heat transfer fluid velocity in the x and y directions respectively; ρ, μ, k, C p are density, dynamic viscosity, thermal conductivity and specific heat at constant pressure, respectively, where the subscript f represents the heat transfer fluid; U in is the inlet flow rate; L is the characteristic length; C D is the resistance coefficient of the cold storage composite material; F Dis the resistance of the composite material; T is the temperature; D is the characteristic length.

[0098] Among them, when the continuity equation, momentum equation and transport theorem are at the Reynolds number When it is larger, the turbulent boundary conditions are selected for calculation, and the specific continuity and momentum equations can be expressed as:

[0099]

[0100] where u i ,u j The speed of the heat transfer fluid at x is i , x j Component in direction; ρ f , μ are the density and dynamic viscosity of the heat transfer fluid respectively; τ ij and σ ij is the stress tensor; U in is the inlet flow rate.

[0101] In the above-mentioned embodiments, specifically, the cold storage material under the optimized determined shape parameters is studied to explore the heat transfer performance of the cold storage material under different porosities and high thermal conductivity porous skeleton filling, that is, the optimal volume ratio of the porous skeleton to the composite cold storage material, that is, the optimal porosity of the composite cold storage material is calculated by the energy transfer equation, and the optimal solution is obtained by heat transfer characteristic calculation simulation of the thermal physical parameters of the porous skeleton and the cold storage medium. Specifically, a model of a random porous medium is established and combined into a whole through drawing tools including CAD, and then exported into a format recognizable by software such as COMSOL. The pore domain is selected as the cold storage material domain, and the continuous channel domain is selected as the high thermal conductivity skeleton domain. Under the solid heat transfer module, the energy storage density and thermal conductivity of the composite cold storage material (1) are calculated using the corresponding energy equation and discrete analysis method, and the optimal porous skeleton (4) volume ratio is selected after analysis and processing to regenerate the model for new heat transfer characteristic calculation.

[0102] The energy equation and transport theorem can be expressed as:

[0103]

[0104] The meanings of the parameters in the energy equation are the same as those in the previous equation.

[0105] Part V. The present invention provides a liquid air energy storage system, comprising the composite cold storage material described in any one of the above items, or the packed bed type cold storage device described in any one of the above items.

[0106] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0107] The methods used in the following examples, unless otherwise specified, are all conventional methods, carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0108] Example 1

[0109] This embodiment takes the preparation process of elliptical foam copper / ice composite cold storage material and olive-shaped foam copper / ice composite cold storage material as an example, and takes the laminar flow condition as an example as follows: dry air is selected as the cold medium in the packed bed cold storage system (2), and the air flow channel length is 4m and the height is 1m. The spherical diameter of the control group is taken as 0.125m. The air flows in from the left inlet of the channel and fully develops the flow in the initial section, and the pressure at the right outlet of the channel is zero. The upper and lower walls of the channel and the boundaries of the cold storage material are considered to be fixed to avoid the generation of viscous effects near the end of the boundary.

[0110] The continuity, momentum equation, and energy equation of the external fluid flow model of the composite cold storage material can be expressed as:

[0111]

[0112]

[0113] at the same time,

[0114]

[0115] Where u and v are the components of the velocity of the heat transfer fluid in the x and y directions respectively; ρ, μ, k, C p are density, dynamic viscosity, thermal conductivity and specific heat at constant pressure, respectively, where the subscript f represents the heat transfer fluid; U in is the inlet flow rate; L is the characteristic length; C D is the resistance coefficient of the cold storage composite material; F D is the resistance of the composite material; T is the temperature; D is the characteristic length. The above units are all in the International System of Units. The partial differential equations created by the law of conservation of momentum and mass are solved by the commercial software COMSOL Multiphysics. The specific operation process is as follows: Figure 5 shown.

[0116] In the geometry interface window of COMSOL Multiphysics, determine the rectangular fluid channel with a length of 4m and a height of 1m. Select dry air as the coolant medium, and import the density, viscosity and other physical properties of dry air in the material window (built-in software). Use CAD software to draw the elliptical and olive-shaped points of the discrete composite cold storage material (1) into a model, and export it to a format recognizable by COMSOL Multiphysics software. Import the elliptical and olive-shaped geometric models into the geometry interface of COMSOL Multiphysics respectively. Select ice as the internal area, and input the density, thermal conductivity and other physical properties of ice in the material window (built-in software). According to the solution results of COMSOL Multiphysics, the composite cold storage material is designed to be elliptical, as shown in Figure 6 As shown in (c1), its external shape curve can be expressed as:

[0117]

[0118] Its volume and surface area can be calculated using the following equations:

[0119]

[0120] S=4πab

[0121] In addition, according to the COMSOL Multiphysics solution, the composite cold storage material is designed to be olive-shaped, and its external shape curve can be expressed as:

[0122]

[0123]

[0124] When C = 1 / 3, it is called the LV-Haack curve, which is the minimum resistance curve under a given length and volume. When the curve is symmetrical about the x-axis and the right boundary, the closed curve formed resembles an olive shape, such as Figure 6 As shown in (b1) in .

[0125] Its volume and surface area can be calculated using the following equations:

[0126]

[0127] The entire calculation range uses free triangle meshes to divide the flow channel. To ensure accurate results, about 260,000 meshes are used to divide the entire area. Adjust the parameters to calculate the flow characteristics of composite cold storage materials with different geometric shapes. The flow state of a sphere with the same volume is used as a reference for analysis, such as Figure 6As shown in (a3) ​​in the figure. In the fully developed stage of the sphere in the coolant flow field, a vortex street will be generated behind the sphere, which will deteriorate the flow state of the coolant, causing energy loss and a decrease in the cold transfer rate. Figure 6 (b3) in Figure 2) and the ellipse (as shown in Figure 2 Figure 6 (c3) in the figure) has better flow characteristics under the same incoming flow field. To more intuitively describe the differences between the three, we can use the heat transfer area S and the resistance coefficient C D Take the sphere of the same volume as the reference point and normalize the calculated data, such as Figure 7 It can be found that the elliptical and olive shapes increase the heat exchange area and reduce the resistance coefficient to varying degrees while ensuring the same volume as the reference sphere.

[0128] The ellipse selected in this example, while ensuring the same volume as the reference sphere, has a drag coefficient that varies with the semi-axis length a as shown below: Figure 8 As shown, as the semi-axis length a increases, the resistance coefficient decreases continuously, and the elliptical external fluid flow resistance is smaller, but its actual shape needs to be determined in combination with the actual application conditions.

[0129] The olive shape selected in this example is equal to a constant while ensuring that the volume is the same as that of the reference sphere. The variation trend of its drag coefficient with radius R is as follows: Fig. 9 As shown in the figure, with the increase of radius R, the resistance coefficient shows a trend of first decreasing and then increasing. It can be seen that the olive shape has the best flow performance, but different application conditions will correspond to different optimal sizes and minimum flow resistances. Its actual shape needs to be determined in combination with the actual application conditions.

[0130] The porosity of the composite cold storage material will affect the internal temperature distribution of the material during the cold storage / release process. On the basis of the above research, the heat transfer performance of the cold storage material with different porosities and high thermal conductivity porous skeleton filling is further explored for the cold storage material with optimized determined shape parameters. The model of the random porous medium is established through CAD and combined as a whole, and exported into a format recognizable by COMSOL Multiphysics. The geometric model of the random porous medium is imported into the geometric interface of COMSOL Multiphysics. The pore domain is selected as the cold storage material domain, and the continuous channel domain is selected as the high thermal conductivity skeleton domain. Under the solid heat transfer module, the energy storage density and thermal conductivity rate of the composite cold storage material (1) are calculated using the corresponding energy equation and discrete analysis method. After analysis and post-processing, the optimal porous skeleton (4) volume ratio is selected to regenerate the model for new heat transfer characteristic calculations. The energy equation of the composite cold storage material is:

[0131]

[0132] The meaning of the symbols is the same as that of the above equation. Taking the elliptical composite cold storage material as an example, Fig.10 As shown, the smaller the porosity, that is, the larger the volume ratio of the filled porous skeleton to the composite cold storage material, the smaller the temperature difference inside the cold storage material during the cold storage / release process, the more uniform the internal temperature distribution, and the faster the heat transfer speed.

[0133] The effect of the porosity of the composite cold storage material on the thermal performance of the composite cold storage material can be described from the energy density and heat transfer efficiency, such as Fig.11 As shown, the energy density of the composite cold storage material with a porosity of 100%, i.e., no porous skeleton filling, is used as the reference point. The energy density data obtained is normalized. It can be found that the energy density decreases with the decrease of porosity. The energy density when the porosity is equal to 45% is 27% compared with that when it is 100%, and the energy density when the porosity is equal to 55% is 30% compared with that when it is 100%. The heat exchange efficiency decreases with the increase of porosity. The heat exchange efficiency when the porosity is equal to 45% is 80 times that when the porosity is equal to 100%, and the heat exchange efficiency when the porosity is equal to 55% is 53 times that when the porosity is equal to 100%. The porosity selected in this example is 55%, but its actual porosity needs to be determined in combination with the actual application conditions.

[0134] After post-processing optimization calculation, this example selects an elliptical foam copper / ice composite cold storage material with a semi-axis length a equal to 0.08m and a porosity equal to 45%, and an olive-shaped foam copper / ice composite cold storage material with a semi-axis length R equal to 0.05m and a porosity equal to 45%, and describes the preparation process in detail.

[0135] At a temperature of 25°C, the PDMS main agent and the curing agent are mixed in a ratio of 10:1, and shaped into an oval and olive shape. The temperature is controlled at -20°C using a cold box, and the PDMS is frozen for 24 hours to solidify the PDMS to prepare an oval and olive-shaped PDMS mold; with the solidified PDMS mold as the bottom, a foam copper metal skeleton is filled in the PDMS mold until the foam copper occupies 45% of the volume of the PDMS mold, and pure water as a filling material is poured into the PDMS mold until the pure water completely immerses the foam copper metal skeleton, and the temperature is controlled at -20°C using a cold box, and frozen for 24 hours until the pure water is completely solidified and completely wraps the foam copper metal skeleton, and the outer PDMS mold is peeled off to obtain an oval and olive-shaped foam copper / ice composite cold storage material. The specific preparation flow chart is as follows Fig.12 The arrangement of the oval and olive-shaped composite cold storage materials in the deep cold packed bed cold storage tank is shown in FIG. Fig.13The figure shows a close arrangement to minimize the external fluid flow resistance of the composite cold storage material in the deep cold packed bed and maximize the cold storage performance, and accelerate the system thermal reaction rate of the deep cold packed bed. When in use, high-temperature dry air is introduced into the packed bed cold storage system, and the high-temperature dry air contacts the composite cold storage material to absorb the cold in the composite cold storage material. The dry air after heat exchange flows out of the packed bed cold storage system to complete the cold release; wherein, the temperature in the composite cold storage material should be controlled below the melting point (0°C) of the cold storage medium ice; low-temperature dry air is introduced into the packed bed cold storage system, and the low-temperature dry air contacts the composite cold storage material to transfer the cold to the composite cold storage material. The cold medium after heat exchange flows out of the packed bed cold storage system to complete the cold storage.

[0136] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by a person skilled in the art within the scope of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A composite cold storage material, characterized in that: It includes a porous skeleton and a cold storage medium immersed in the porous skeleton and wrapped outside the porous skeleton; The porous skeleton is made of alloy material, metal material or ceramic material; The material of the cold storage medium is water, salt solution or organic cold storage material, the salt solution is selected from one or more of KCl, NaCl, BaCl2, CaCl2, KNO3, NaNO3, Na2CO3, K2CO3 solution, and the organic cold storage material is selected from one or more of tetradecane, lauric acid, ethylene glycol, paraffin, fatty acid, polyethylene glycol laurate; The composite cold storage material has an outer shape of any one of an olive shape, a golf ball shape, a gourd shape, an oval shape, a sphere shape, an alveolar shape, a water drop shape, a bullet shape, and a spindle shape.

2. The composite cold storage material according to claim 1, characterized in that: The alloy material includes one or more of chromium alloy, copper alloy, iron alloy, nickel alloy, aluminum alloy, stainless steel, and molybdenum alloy; The metal material includes one or more of copper, iron, nickel, chromium, aluminum, and molybdenum; The ceramic material includes one or more of silicon carbide, silicon boride, aluminum oxide, boron carbide, zinc oxide, zirconium oxide, and silicon nitride; The shape of the porous skeleton includes any one of a foam porous shape, a loofah shape, a honeycomb shape, and a lotus root shape.

3. The composite cold storage material according to claim 1, characterized in that: The volume percentage of the cold storage medium wrapped outside the porous skeleton in the composite cold storage material is 20% to 80%.

4. The method for preparing the composite cold storage material according to any one of claims 1 to 3, characterized in that: The steps include: (1) filling the porous skeleton into a mold having the shape, and then pouring the cold storage medium into the mold until the porous skeleton is completely immersed; (2) Freezing the mold obtained in step (1) until the cold storage medium is completely solidified, and then demolding to obtain the composite cold storage material.

5. The method for preparing the composite cold storage material according to claim 4, characterized in that: The material of the mold is metal, alloy metal, silicone, plastic or high molecular polymer.

6. A packed bed cold storage system, characterized in that: The invention comprises a shell and the composite cold storage material according to any one of claims 1 to 3 filled in the shell or the composite cold storage material prepared by the method according to any one of claims 4 to 5.

7. The packed bed cold storage system according to claim 6, characterized in that: The composite cold storage material is filled in the shell in a random arrangement, a close arrangement, a radial gradient layered arrangement or an axial gradient layered arrangement.

8. A method for releasing and storing cold using the packed bed cold storage system according to any one of claims 6 to 7, characterized in that: The steps include: A high-temperature cold medium is introduced into the packed bed cold storage system, the high-temperature cold medium contacts the composite cold storage material to absorb the cold in the composite cold storage material, and the cold medium after heat exchange flows out of the packed bed cold storage system to complete cold release; wherein the cold release temperature is controlled to be lower than the melting point of the cold storage medium used to maintain the shape of the composite cold storage material; A low-temperature refrigerant is introduced into the packed bed cold storage system, the low-temperature refrigerant contacts the composite cold storage material to transfer cold to the composite cold storage material, and the refrigerant after heat exchange flows out of the packed bed cold storage system to complete cold storage.

9. The method for releasing and storing cold according to claim 8, characterized in that: The shape parameters of the composite cold storage material filled in the packed bed cold storage system are obtained by the following steps: The geometric shape and geometric parameters of the fluid channel of the packed bed cold storage system, the type and physical properties of the cold medium, the geometric model of the pre-designed shape of the composite cold storage material, the type of cold storage medium and the physical properties of the cold storage medium are input into the multi-physics field simulation software, and the fluid flow module is selected to determine the shape parameters of the composite cold storage material according to the flow characteristics of the composite cold storage materials with different geometric shapes.

10. The method for releasing and storing cold according to claim 8, characterized in that: The characteristic length of the composite cold storage material filled in the packed bed cold storage system is obtained by the following steps: The characteristic length in the composite cool storage material is determined according to the determined shape parameters of the composite cool storage material and the resistance coefficients at different characteristic lengths.

11. The method for releasing and storing cold according to claim 8, characterized in that: The porosity of the porous skeleton in the composite cold storage material filled in the packed bed cold storage system is obtained by the following steps: inputting a geometric model of a random porous medium into a multi-physics field simulation software, selecting a pore domain as a cold storage material domain, selecting a continuous channel domain as a high thermal conductivity skeleton domain, selecting a solid heat transfer module, and determining the volume percentage of the porous skeleton in the composite cold storage material according to the heat transfer characteristics of the composite cold storage material.

12. A liquid air energy storage system, characterized in that: It comprises the composite cold storage material according to any one of claims 1 to 3 or the composite cold storage material prepared by the method according to any one of claims 4 to 5, or the packed bed type cold storage device according to claim 6 or 7.

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