CN108645260B

CN108645260B - Containing structure for realizing low supercooling degree phase change energy storage material and method for preparing structure

Info

Publication number: CN108645260B
Application number: CN201810456269.9A
Authority: CN
Inventors: 张波; 何振辉
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2018-05-14
Filing date: 2018-05-14
Publication date: 2020-08-11
Anticipated expiration: 2038-05-14
Also published as: CN108645260A

Abstract

The invention provides a containing structure for a phase change energy storage material with low supercooling degree, which comprises a framework main body, wherein the framework main body comprises a plurality of holes for containing the phase change material; and the holes are internally provided with covering layers capable of inducing the nucleation of the phase-change material. The invention also provides an energy storage structure based on the containing structure and a method for reducing the supercooling degree of the phase-change material. The invention has the following beneficial effects: 1. the holes are formed in the framework main body, the covering layers are arranged in the holes, the structure is simple, and the supercooling degree of the phase change material placed in the holes can be greatly reduced; 2. the framework main body, the covering layer, the anti-corrosion layer and the phase-change material can be matched in various ways, so that the application range is wide and the manufacturing cost is low; 3. the phenomenon that supercooling property is uneven due to the sedimentation of the nucleating agent is avoided, the foam framework ensures that heat transfer property is even, and the heat exchange efficiency is greatly improved.

Description

Containing structure for realizing low supercooling degree phase change energy storage material and method for preparing structure

Technical Field

The invention relates to the technical field of phase change material heat storage and cold storage, in particular to a phase change material containing structure, an energy storage structure and a method for preparing the structure.

Background

The energy problem is a prominent problem for human survival in the 21 st century. The world population is rapidly expanding and the energy demand is rapidly increasing. In the face of limited resources and for long-term survival, people must conserve energy and make efficient storage use. Phase change energy storage is a way to save and effectively store energy in the process of utilizing energy. The technology is to solve the contradiction that the energy supply and demand are not matched in time and space. Especially in the fields of peak regulation of power systems, manned space and deep space exploration, solar energy utilization, waste heat recovery, heating and air conditioning and household appliance industrial energy, the method can be widely used.

The excellent phase change energy storage material has the advantages of large phase change latent heat, low supercooling degree, high heat conductivity, proper phase change cold storage temperature point and the like. The energy storage material comprises: organic phase change material, inorganic phase change material, and mixed material of organic and inorganic materials.

All materials have supercooling phenomena during condensation, including transition from gaseous to liquid and transition from liquid to solid. Supercooling occurs from the cooling of molten metal to solid metal to the cooling and solidification of crystalline hydrated salts to solid crystals. In general, supercooling can be viewed as the difference between the temperature at which the phase change material begins to condense and the melting point (melting point is almost or equal to the point at which two phases coexist). The temperature point at which the phase change material starts to condense needs to be distinguished from the point at which two phases coexist. Supercooling is a hysteresis phenomenon of phase change of a substance.

In the application research and development and application process of the phase change energy storage material, the feasibility of the material in application can be restricted by the size of the supercooling degree. The high supercooling degree of the material means that the material cannot release latent heat near the equilibrium point of two phases, so that the material loses the advantage of the suitable phase transition temperature. In addition, the method brings greater design technical difficulty to the material refrigeration equipment and is not beneficial to energy conservation.

For example, for cold storage engineering in a living temperature region (requiring a phase transition equilibrium point at-30 to 10 degrees celsius), high supercooling degree means that higher requirements are imposed on the refrigeration capacity of the equipment, resulting in greater energy consumption for refrigeration. Among materials with proper phase change equilibrium points, the ice storage material is widely applied, the phase change equilibrium temperature is proper, the phase change latent heat of the ice storage material is very high in all applied phase change materials, and particularly the latent heat of pure water is the highest. It is commonly used for life preservation, food and medicine long-distance refrigeration and transportation, large-scale freezing cold storage air conditioner and the like. However, the supercooling degree of the water-containing ice cold storage material is often large, particularly the supercooling degree of pure water can reach 39 ℃ (freezing and nucleation are carried out only at minus 39 ℃), and the supercooling degree of common cold storage gel is often very large (dozens of DEG). If one does not try to reduce the supercooling degree, the refrigerating equipment must have strong low-temperature refrigerating capacity and heat-insulating performance. As a result, the design and manufacturing costs of the refrigeration system are increased. In addition, the refrigeration system is in a low-temperature state for a long time, so that the heat leakage phenomenon cannot be avoided, and the power of the system for consuming energy is increased, so that more and a large amount of energy is consumed. Is not beneficial to energy saving. Therefore, the supercooling degree is reduced, the design and manufacturing cost of equipment is reduced, and the energy conservation is facilitated.

The prior method for reducing the supercooling degree comprises the following steps: ultrasonic method, elastic potential energy method, stirring method, doping, adding nucleating agent and microcapsule method. Ultrasonic wave, elastic potential energy and stirring methods all belong to methods which need dynamic interference to help nucleation, and a motion structure or an additional equipment unit is needed, so that the technical complexity and the control complexity are increased, and the method is not simple enough. Impurities often appear in the mixed nucleating agentAnd the phenomena of agglomeration and the like caused by the precipitation of nucleating agents and the extrusion of particles by a phase-change solidification interface are not beneficial to the dispersion of the particles in the phase-change material (the phase-change material mainly refers to fluids such as liquid and the like), so that the uniformity and the stability of low supercooling of a phase-change matrix are ensured. Through the verification of a unified measurement experimental means and through research reports, the addition of various foreign particles (novel materials such as carbon nanotubes, nano CuO and nano Al) which are generally researched at present can be known₂O₃Etc.) are generally in the range of-ten to twenty degrees celsius, and the reduction effect is not very stable. The microcapsule energy storage technology is to embed solid, liquid or gas materials in micron-sized microcapsules and control the embedded materials to release required heat or cold in expectation under certain conditions. Although the energy storage technology of the microcapsule method can reduce the supercooling degree, the preparation process of the capsule is complicated, the preparation method is different and the universality is poor aiming at different phase-change materials, and the research on the phase-change materials containing water only appears on a few kinds of crystal hydrated salts. The supercooling of these microencapsulated waters and salts is still large (up to thirty or more degrees celsius). Compared with pure water, the crystalline hydrated salt has obviously smaller latent heat of phase change, and the integral macroscopic energy storage density of the energy storage material is obviously reduced under the same volume due to the pores among the microcapsules.

In summary, there are many structures or methods for reducing the supercooling degree of the phase change material in the prior art, but these structures or methods are complicated, have high application cost, and have undesirable energy storage effect.

Disclosure of Invention

The invention aims to provide a containing structure for realizing a phase change energy storage material with low supercooling degree and a method for preparing the structure, mainly aims to solve the problems of over-complexity and poor energy storage effect of the existing structure and method for reducing the supercooling degree of the phase change material, and can also solve the defects of uneven and stable sedimentation and supercooling property caused by using a common particle-shaped nucleating agent.

The invention provides a containing structure for a phase change energy storage material with low supercooling degree, which comprises a framework main body, wherein the framework main body comprises a plurality of holes for containing the phase change material; and the holes are internally provided with covering layers capable of inducing the nucleation of the phase-change material.

Preferably, the holes are in communication with each other.

Preferably, the holes have a PPI value of 5 or more.

Preferably, the porosity of the pores is between 70% and 95%.

Preferably, an anti-corrosion layer is arranged between the inner wall surface of the hole and the covering layer.

Preferably, the corrosion protection layer comprises a first protection layer and a second protection layer.

The invention also provides an energy storage structure with low supercooling degree, which comprises the accommodating structure and the phase change material filled in the hole.

Preferably, the skeleton body is a foam metal, and the phase change material is a water-based phase change material.

The invention also provides a method for preparing the containment structure, comprising the steps of: cleaning the framework main body, wherein the framework main body comprises a plurality of holes for containing the phase-change material; carrying out chemical dip plating or electroplating on the inner surface of the hole of the framework main body to form an anti-corrosion coating; and preparing the covering layer on the surface of the plating layer.

The invention also provides a method for preparing the energy storage structure, which comprises the following steps: taking foam metal as the framework main body; cleaning the surface of the foam metal; carrying out chemical immersion plating or electroplating on the inner surface of the hole of the foam metal to form an anti-corrosion plating layer; preparing the covering layer on the surface of the plating layer; and filling the phase change material into the skeleton body with the covering layer.

The invention has the following beneficial effects:

1. the holes are formed in the framework main body, the covering layers are arranged in the holes, the structure is simple, and the supercooling degree of the phase change material placed in the holes can be greatly reduced;

2. the framework main body, the covering layer, the anti-corrosion layer and the phase-change material can be matched in various ways, so that the application range is wide and the manufacturing cost is low;

3. the phenomenon that supercooling property is uneven due to the sedimentation of the nucleating agent is avoided, the foam framework ensures that heat transfer property is even, and the heat exchange efficiency is greatly improved.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic diagram of the structure of an energy storage structure in one embodiment;

fig. 2 is a schematic diagram showing the structure of the hole in fig. 1 in detail.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative only and should not be construed as limiting the invention.

As shown in fig. 1 and fig. 2, a holding structure for a phase change material 3 includes a skeleton body 1, where the skeleton body 1 includes a plurality of holes for holding the phase change material 3; the holes are provided with covering layers 2 which can induce the nucleation of the phase-change material.

One of the main functions of the skeleton body 1 is to provide a space (i.e. a hole) for accommodating the phase change material 3, so in general, the skeleton body 1 may be a solid body composed of a single substance, such as metallic copper, aluminum or a carbon-based material, which may be solid or hollow; of course, it is not excluded that the carcass body 1 is composed of different substances, and in some cases, the carcass body 1 may also have a detachable structure. In the prior art, foam materials (e.g., open-cell metal foams, foam plastics, carbon foams) are particularly suitable as the carcass body 1, because these materials are directly available on the market, and in addition, they are produced with cells that can be directly used as holes.

The holes may be of various sizes and shapes, and they may or may not be interconnected, or partially interconnected, in some particular cases. Of course, communication is preferred, which facilitates filling and placement of the phase change material therein. The interior surface of the cavity may or may not be corrosion protected.

In order to reduce the supercooling degree of the phase-change material, the PPI (also called poreseper Linear inc, "in chinese meaning" void density unit ") value and the porosity of the pores are considered. Generally, the PPI value of the pores is above 5, and the porosity of the pores is between 70% and 95%, which is good. When the foam material with the porosity of 85-95% is adopted, a space for filling the phase-change material can be fully reserved, and the composite material filled with the phase-change material is ensured to have latent heat which is close to the latent heat of the phase-change material under the same volume.

As for the phase change material 3, it may be of various types or phases. It may be a mixture or may be a pure substance. It may be a solid material, or it may be a liquid material or a gaseous material. Even solid-liquid materials, solid-gas materials, liquid-gas materials and solid-liquid-gas materials can be used. In some cases, the phase change material may specifically be water vapor (gas), an aqueous solution to which dispersed nanoparticles are added (solid-liquid), paraffin in a molten state (liquid), or water filled with bubbles (gas-liquid), or the like.

The containment structure is particularly useful for containing materials that exhibit significant supercooling when condensed. For example, inorganic materials have a large degree of supercooling by condensation of materials such as aqueous gel, crystalline hydrated salt, and pure water. For example, organic materials having functional groups having water-absorbing properties such as alcohols, esters, saccharides, and carboxylic acids have a large supercooling degree. These materials are all adapted to be placed into the containment structure.

The cover layer 2 employs a nucleating material (nucleating agent) for inducing nucleation of the phase change material 3, so that the cover layer 2 is in direct contact with the phase change material 3 when the containment structure is in use. The theory and practice of using nucleating agents to induce nucleation of phase change materials is well established.

The covering layer 2 can be a coarse structure substance with micro-nano size morphology, and can also be a solid substance which has the same crystal structure and approximate lattice constant with the crystal after the phase-change material is condensed. Or the solid substance not only has micro-nano morphology, but also has a crystal structure similar to that of the crystal after the phase-change material is condensed and a lattice constant approximate to that of the crystal.

In the prior art, the nucleation is generally induced by adding a nucleating agent to the phase-change material (e.g., adding the nucleating agent to water); the nucleating material is used as a wrapping object (namely the covering layer 2) of the phase-change material 3, and an unexpected and better effect can be achieved in the aspect of reducing the supercooling degree of the phase-change material 3; meanwhile, the problem of particle sedimentation caused by directly adding a nucleating agent into the phase-change material is also avoided.

In most cases, the materials of the covering layer 2 and the carcass body 1 are not the same, but it is not excluded that they are integrally formed and have the same material.

In some cases, the presence of the cover layer 2 may completely isolate the phase change material 3 from the inner wall of the hole; in other cases, however, the covering layer 2 may not completely cover the inner wall of the hole.

The covering layer 2 is usually made by coating or chemical immersion plating, but other techniques can be used according to the actual needs by those skilled in the art.

In some cases, the inner wall of the hole is directly engaged with the cover layer 2; in some cases, an anti-corrosion layer is disposed between the inner wall surface of the hole and the covering layer 2, and the main purpose of the anti-corrosion layer is to prevent the covering layer 2/the phase change material 3 from directly contacting with the skeleton body 1 to corrode.

The means for corrosion protection may be a single layer of a corrosion-resistant material such as gold, tungsten, molybdenum, platinum, and the like corrosion-resistant metals. It is also possible to plate a protective layer having a multilayer structure. In some cases, the corrosion protection layer comprises a first protection layer and a second protection layer, wherein the inner wall of the hole is connected with the first protection layer, the first protection layer is connected with the second protection layer, and the second protection layer is connected with the covering layer 2. For example, for a gold foam copper surface, a layer of nickel is plated on the surface of the copper foam before gold plating, and then gold plating is performed. The nickel layer thus constitutes together with the gold layer an anti-corrosion layer.

Of course, the corrosion protection layer may have a structure with more layers, which is not described in detail herein.

Based on the accommodating structure, after the phase change material is filled in the accommodating structure, the accommodating structure is an energy storage structure with low supercooling degree.

In order to further understand the technical solutions and effects mentioned above, two more specific examples are listed below to illustrate the preparation of the energy storage structure and the technical effects brought by the energy storage structure.

Example 1

The implementation steps are as follows:

(1) an open-cell copper foam with PPI of 100 and porosity of 90% is selected, and subjected to cleaning and surface activation, degreasing → water washing → oxidized film → water washing → acid washing → water washing.

(2) And (3) chemically plating nickel on the cleaned foam copper, wherein the thickness is controlled to be between hundreds of nanometers and 1 micron, cleaning, plating gold, the thickness of the gold plating is controlled to be 100 nanometers, and then cleaning and storing the plated part. In this case, a foamed metal material (i.e., the skeleton body 1) is obtained, and such a foamed material is subjected to an anticorrosive treatment.

(3) The covering layer 2 for inducing the phase change material to condense and nucleate is prepared on the surface of the foam metal material subjected to the anti-corrosion treatment, namely, the surface of the pore is chemically plated with silver. The thickness of the silver plating is based on the condition that the plating layer is almost or completely expressed as pure silver. The thickness is usually controlled to be 100 nm or more. And then cleaning and drying. And then soaking the substrate in an iodine absolute ethyl alcohol solution for 2 hours in a dark place. Taking out, washing with anhydrous ethanol for at least 3 times, and soaking for more than 10 min. And finally taking out and airing. A containment structure covered with an ice nucleation overlayer 2 inducing pure water freezing is obtained.

(4) Since the porous material (i.e., the containing structure) covered with the pure water ice-formation inducing and nucleation covering layer 2 is made to be super-hydrophilic, the porous material covered with the pure water ice-formation inducing and nucleation covering layer 2 is directly immersed in pure water to be filled with water. Thus, the composite phase change cold storage material (namely the energy storage structure) capable of realizing low supercooling degree icing is obtained.

In this embodiment, DSC measurement means is used to find that the accommodation structure plated with the covering layer 2 for inducing pure water to freeze and nucleate can reduce the supercooling degree of pure water to 2 ℃. This result indicates that the supercooling degree improving effect is excellent in this field. Compared with other ice cold storage materials in the research field, the composite material has low supercooling degree, and has incomparable high thermal conductivity and high latent heat compared with other materials. The composite material also maintains a low superheat (melting point is almost unchanged) of the phase change process. There is no settling problem (which would lead to non-uniform and unstable energy storage properties) with the added particles. The result is also much better than the effect of reducing supercooling degree by using the foam copper alone.

Example 2

Under the condition that the cold storage material is required to be light, the implementation steps can be as follows:

(1) an open cell aluminum foam with a PPI of 100 and a porosity of 90% was selected. It is cleaned and surface activated. Degreasing → washing with water → oxidized film → washing with water → acid washing → washing with water.

(2) The cleaned aluminum foam is subjected to an anti-corrosion treatment, and a metal such as platinum can be selected, but the cost of gold plating is relatively low. The specific process comprises the following steps: zinc plating → cleaning → nickel plating → cleaning → electroless gold plating → cleaning. The thickness of the plating zinc is tens of nanometers and above (the first protective layer), the thickness of the plating nickel (the second protective layer) is hundreds of nanometers to 1 micron, and the thickness of the plating gold (the third protective layer) is 100 nanometers.

(3) Silver plating → washing → drying. Then soaking in iodine absolute ethanol solution for 2 h. The soaking process needs to be performed in a dark or dark room location. The thickness of the silver plating (coating layer 2) is based on the fact that the plating layer shows almost or completely pure silver. Typically 100 nm or more.

(4) The foam pieces were removed from the iodine in absolute ethanol. And (3) washing the container in a dark place for 3 times by using absolute ethyl alcohol, soaking for 10min, and finally drying in the air to obtain the containing structure.

(5) The containment structure was mixed with 4% alcohol. The composite phase change material (namely the energy storage structure) which has low supercooling degree, light weight, high heat conductivity and high phase change latent heat and maintains low superheat degree is obtained.

The supercooling degree can be reduced to about 0.4 ℃ by adopting DSC measurement means for detection. This result is excellent compared to other research results in this field. Without overheating. And the structure can also take the advantages of light weight and high energy storage density into consideration.

In conclusion, the two embodiments can show that the energy storage structure is not only suitable for pure water icing, but also suitable for phase change materials such as alcohol. In various phase-change materials (organic or inorganic), the supercooling degree of water is very large, and if the energy storage structure can obviously reduce the supercooling degree of water freezing, the supercooling degree of any other phase-change material can be reduced in the same way as long as the phase-change material is ensured not to have chemical reaction with a covering layer for inducing condensation and nucleation of the phase-change material and the foam material. The effect of reducing the supercooling degree is obviously superior to the effect of independently adding the covering particles for inducing the phase-change material to condense and nucleate as the nucleating agent and the effect of directly mixing the original foam material and the phase-change material.

In summary, the present invention discloses a method for preparing said containment structure comprising the steps of: cleaning the framework main body, wherein the framework main body comprises a plurality of holes for containing the phase-change material; carrying out chemical dip plating or electroplating on the inner surface of the hole of the framework main body to form an anti-corrosion coating; and preparing the covering layer on the surface of the plating layer.

In summary, the present invention discloses a method for preparing the energy storage structure, comprising the steps of: taking foam metal as the framework main body; cleaning the surface of the foam metal; carrying out chemical immersion plating or electroplating on the inner surface of the hole of the foam metal to form an anti-corrosion plating layer; preparing the covering layer on the surface of the plating layer; and filling the phase change material into the skeleton body with the covering layer.

The foregoing is only a partial embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. The utility model provides a realize low supercooling degree's phase change energy storage material's containment structure, includes the skeleton main part, its characterized in that: the framework main body comprises a plurality of holes for containing phase-change materials;

the containing structure is suitable for containing inorganic materials or organic materials with obvious supercooling degree during condensation; the inorganic material is selected from aqueous gel with large condensation supercooling degree, crystalline hydrated salt and pure water material; the organic material is selected from alcohols with larger supercooling degree, esters, saccharides and carboxylic acids with-OH, -COOH water-absorbing functional groups;

a covering layer capable of inducing nucleation of the phase-change material is arranged in the hole; the covering layer is a coarse structure substance with micro-nano size morphology, or a solid substance with a crystal structure and an approximate lattice constant which are the same as those of the crystal condensed by the phase change material, or the covering layer is a solid substance with micro-nano morphology and a crystal structure and an approximate lattice constant which are the same as those of the crystal condensed by the phase change material;

the framework main body is made of foam metal, and the holes are communicated with each other; an anti-corrosion layer is arranged between the inner wall surface of the hole and the covering layer; the anti-corrosion layer comprises a first protective layer and a second protective layer; the inner wall of the hole is connected with the first protective layer, the first protective layer is connected with the second protective layer, and the second protective layer is connected with the covering layer.

2. The containment structure of claim 1, wherein: the pores have a PPI value of 5 or more.

3. The containment structure of claim 1, wherein: the porosity of the pores is between 70% and 95%.

4. A method of making a containment structure according to any of claims 1 to 3, wherein: the method comprises the following steps:

cleaning the framework main body, wherein the framework main body comprises a plurality of holes for containing the phase-change material; carrying out chemical dip plating or electroplating on the inner surface of the hole of the framework main body to form an anti-corrosion coating;

and preparing the covering layer on the surface of the plating layer.

5. An energy storage structure with low supercooling degree is characterized in that: the containing structure prepared by the preparation method of the containing structure as claimed in claim 4, and the phase change material filled in the hole.

6. A method for preparing the energy storage structure of claim 5 having a low degree of subcooling, characterized in that: the method comprises the following steps:

taking foam metal as the framework main body;

cleaning the surface of the foam metal;

carrying out chemical immersion plating or electroplating on the inner surface of the hole of the foam metal to form an anti-corrosion plating layer;

preparing the covering layer on the surface of the plating layer;

and filling the phase change material into the skeleton body with the covering layer.