CN101560377B - Foam metal-based high temperature phase change heat storage composite material and preparation method thereof - Google Patents

Abstract

The invention relates to a foamed-metal based high-temperature phase change heat storage composite material and a preparation method thereof, which relate to the technical field of heat storage materials. The composite material is characterized by comprising a foamed metal framework material which is attached with a solid-liquid phase change heat storage material when the temperature is more than or equal to 600 DEG C, and a high temperature phase change heat storage material which accounts for 60 to 95 percent of the total weight. The composite material has the advantages of quick heat storage and release, high heat storage density, good heat conductivity and small volume shrinkage; besides, the composite material has wide applications, and is applicable to various fields of solar energy heat power generating systems for a space station, solar electrical energy generation, high temperature waste heat recovery and the like, particularly to a heat absorber of a space solar energy heat power generating system; and the preparation method is simple and convenient, has high recombination rate, and is easy to guarantee the product quality.

Description

Foam metal-based high temperature phase change heat storage composite material and preparation method thereof

technical field

The invention relates to the technical field of heat storage materials. the

Background technique

The application of high-temperature phase change materials is mainly concentrated in the fields of solar energy utilization in space stations, industrial waste heat recovery, and power peak shaving and valley filling. In the solar thermal power generation system of the space station, the parabolic concentrator can be used to intercept solar energy, gather it into the cylindrical cavity of the heat absorber/regenerator, and convert it into heat energy, and a part of the heat energy is transferred to the circulating working fluid to drive The heat engine generates electricity, and the other part of the heat is absorbed and stored by melting in phase-change energy storage materials encapsulated in multiple small containers. During the shadow period of the orbit, the phase change energy storage material solidifies and releases heat near the phase transition point, and acts as a heat source for the heat engine to heat the circulating working fluid, so that the space station can still work continuously to generate electricity when it is in the shadow period. The heat storage container of phase change material is the main part of the heat absorption-reservoir of the solar thermal power generation system of the space station. In a solar thermal power plant, a tank-shaped concentrator is used to gather sunlight in a solar concentrator and convert it into thermal energy. Part of it is used to heat steam to generate electricity, and the other part is stored for use when sunlight is insufficient to ensure continuous power generation. . In addition, a large amount of heat will be generated in the industrial production process, and the heat is usually wasted without being used. At this time, a material is needed to recover the high-temperature waste heat for future use. the

For the heat absorber of the space solar thermal power generation system, due to the limitation of the circulation temperature of the heat engine (above 700°C), it is required to use high-temperature latent heat storage. After studying a large number of phase change materials, fluorine salts have become the main The main advantage of the selected object is that the latent heat of phase change is high, and by mixing fluorine salts with different melting points, heat storage media with different phase change temperatures can be obtained, so as to meet the requirements of the space solar thermal power generation cycle in a wide temperature range. Require. The compatibility of fluoride salts and metal container materials is also relatively good. LiF-CaF ₂ eutectic was selected as the thermal storage medium for the solar thermal power generation system of the American Liberty space station.

Fluoride salts can meet the needs of their thermal properties and compatibility, but one of its obvious disadvantages is its low thermal conductivity and large volume shrinkage during solidification (up to 23% for LiF). These two shortcomings lead to the formation of cavities in the container when the phase change material solidifies and shrinks during the shadow period, resulting in "thermal loosening" and "hot spots" during the sunshine period. Both of these phenomena will cause thermal fatigue damage to the container. It will greatly affect the heat transfer performance of the heat storage material, thereby affecting the thermal performance and reliability of the entire system. In addition, salt phase change materials are highly corrosive at high temperatures, and the container materials must be corrosion-resistant superalloys. At present, most of them focus on cobalt-based, nickel-based, niobium-based and other superalloys.

Contents of the invention

The purpose of the present invention is to provide a metal foam-based high-temperature phase-change heat storage composite material and its preparation method. The composite material has the advantages of fast heat storage and heat release, high heat storage density, good thermal conductivity, and small volume shrinkage; uses It is widely used in various fields such as space station solar thermal power generation system, solar power generation and high temperature waste heat recovery, especially for the heat absorber of space solar thermal power generation system; its preparation method is simple, the compounding rate is high, and it is easy to ensure product quality . the

One of the main technical solutions of the present invention is: a metal foam-based high-temperature phase change heat storage composite material, which is characterized in that it has a metal foam skeleton material, and a solid-liquid phase change heat storage material at ≥600°C is attached to the metal foam skeleton material. For the material, the percentage of the high-temperature phase-change heat storage material to the total weight is 60% to 95%. the

The metal foam skeleton material is preferably Ni foam or Cu metal foam skeleton material. the

The solid-liquid phase change heat storage material at ≥600°C is preferably fluoride salt LiF; or a mixture of LiF and CaF ₂ : the mass composition ratio of LiF and CaF ₂ in the mixture is 2 to 1.1:1; ≥600°C The time-solid-liquid phase change heat storage material accounts for 80-95% of the total weight.

The second main technical solution of the present invention is: the preparation method of the above-mentioned various metal foam-based high-temperature phase-change thermal storage composite materials, which is characterized in that it has the following steps:

a. Prepare the metal foam skeleton material and put it into the molding container. the

b. Prepare the solid-liquid phase change heat storage material at ≥600°C according to the required quality composition, mix well, put it in a vacuum heating furnace to heat and degas and dewater to make it molten, and the melting temperature of the heating furnace is ≥600°C °C, the phase transition temperature of the solid-liquid phase change heat storage material is 50-100 °C above; at the same time, put the molded container containing the metal foam skeleton material into the furnace for heating. the

c. The molten solid-liquid phase change heat storage material at ≥600°C is composed according to the required quality, and is quickly and accurately poured into the molding container under the argon protection gas mist, and heated and compounded in a vacuum heating furnace. The process temperature is controlled to be 80-200°C higher than the melting point of the solid-liquid phase change heat storage material at ≥600°C. the

d. After compounding, turn off the power supply of the electric furnace and slowly cool the forming container containing the metal foam-based high-temperature phase-change thermal storage composite material in the furnace, and then place the top cover of the container containing the metal-foam-based high-temperature phase-change thermal storage composite material Once packaged, the finished product is obtained. the

The material of the forming container is a cobalt-based, nickel-based or niobium-based superalloy: such as Inconel617, Haynes188, Haynes230, 316ss, etc. the

The positive effect of the present invention is that the solid-liquid phase change heat storage material is more evenly and fully distributed in the metal foam skeleton material matrix at ≥600°C, and the metal skeleton divides the solid-liquid phase change heat storage material at ≥600°C into countless Tiny heat storage units, while improving heat absorption and heat release, these tiny heat storage units also prevent the molten phase change material from flowing out due to capillary tension, and have high recombination rate, good heat storage capacity, and high thermal conductivity; And control the formation of holes to enhance heat transfer, and can also limit the large volume shrinkage during solid-liquid phase transition; the composite material has the advantages of fast heat storage and heat release, high heat storage density, good thermal conductivity, and small volume shrinkage ; Not only good heat storage capacity, especially solves the long-standing problems of low thermal conductivity and large volume shrinkage during solidification in the prior art; it has a wide range of uses and can be applied to space station solar thermal power generation systems, solar power generation and high-temperature waste heat Recycling and other fields, especially suitable for the heat absorber of the space solar thermal power generation system; its preparation method is simple, the recombination rate is high, and the product quality is easy to guarantee. the

Describe in detail below in conjunction with example, but not as limiting the present invention. the

Detailed ways

Examples The production process is as follows: Lithium fluoride, a solid-liquid phase change thermal storage material at ≥600°C, or lithium fluoride and calcium fluoride are mixed at a certain mass percentage to form a molten mixture of a certain weight, and in the molten salt eutectic Add a certain weight of metal foam skeleton material, put them together in a heat storage phase change container and carry out compounding in a vacuum heating furnace, control the compounding temperature, after compounding for a certain period of time, the finished product is cooled to a certain temperature in vacuum, then taken out, and packaged The thermal storage phase change container is a finished product. the

Step 1: Clean the porous metal foam material, remove the oil stains that may exist on its surface or in the pores, and put it into a molding container according to a certain quality. the

Step 2: According to 100% fluorine salt LiF, or the mass composition ratio of LiF and CaF ₂ mixture of LiF and CaF ₂ is 2 to 1.1:1, weigh fluoride salt, mechanically stir as evenly as possible, put it into a vacuum heating furnace to heat and remove Gas, water removal and melting; at the same time, put the forming container containing the metal foam skeleton material into the furnace for heating.

Step 3: Prepare several 100ml Al ₂ O ₃ ceramic beakers or high-purity graphite crucibles. The beakers can be filled with no less than 60g of high-temperature solid-liquid phase change heat storage materials. Pour into molding containers. Heating in a vacuum heating furnace for compounding, the temperature in the compounding process is controlled at 80-200°C higher than the melting point of the latent heat storage material, and the compounding time is 2-3 hours.

Step 4: Turn off the electric furnace and slowly cool the molded container containing the metal foam-based high-temperature phase-change heat storage composite material in the furnace. After taking it out, seal the end cover of the molded container with vacuum electron beam welding. the

Example 1: The continuous porous metal foam skeleton material is Ni foam, the high-temperature phase change heat storage material is lithium fluoride and calcium fluoride with a mass composition ratio of 1.1:1, and the heat storage metal container (that is, the molded container) is made of Haynes188 , the process conditions are as follows:

1. The heating and melting temperature of the latent heat storage material in the heating furnace is 820-870°C (that is, the high-temperature solid-liquid phase change heat storage material is melted in the heating furnace to a temperature 50-100°C above its phase transition temperature);

2. The temperature of the compounding process is 850-970°C (that is, the temperature of the compounding process is controlled to be 80-200°C higher than the melting point of the high-temperature phase change heat storage material), and the compounding time is 3 hours;

3. Lithium fluoride and calcium fluoride heat storage materials account for 95% of the total weight of the foam metal-based high-temperature phase change heat storage composite material. the

Implementation results: The phase change latent heat of the prepared composite high temperature phase change heat storage material is 870.6kJ/kg, and the phase change temperature is 769.8°C. the

Example 2: The continuous porous metal foam skeleton material is made of Ni foam, the high temperature phase change heat storage material is made of lithium fluoride and calcium fluoride in a mass composition ratio of 2:1, and the material of the heat storage metal container (i.e. the molded container) is Haynes188. The conditions are as follows:

1. The heating and melting temperature of the latent heat storage material in the heating furnace is 810-870°C (that is, the high-temperature phase change heat storage material is melted in the heating furnace to a temperature 50-100°C above its phase transition temperature);

2. The temperature of the compounding process is 850-960°C (that is, the temperature of the compounding process is controlled to be 80-200°C higher than the melting point of the high-temperature phase change heat storage material), and the compounding time is 2.8 hours;

3. Lithium fluoride and calcium fluoride heat storage materials account for 80% of the total weight of the foam metal-based high temperature phase change heat storage composite material. the

Implementation results: The latent heat of phase change of the prepared composite composite high-temperature phase change heat storage material is 851.4kJ/kg, and the phase change temperature is 762.6°C. the

Example 3: The continuous porous metal foam skeleton material is Ni foam, the high-temperature phase change heat storage material is lithium fluoride and calcium fluoride with a mass composition ratio of 1.5:1, and the heat storage metal container (that is, the molded container) is Haynes188. The process conditions are as follows:

1. The heating and melting temperature of the latent heat storage material in the heating furnace is 810-860°C (that is, the high-temperature phase change heat storage material is melted in the heating furnace to a temperature 50-100°C above its phase transition temperature);

2. The temperature of the compounding process is 840-960°C (that is, the temperature of the compounding process is controlled to be 80-200°C higher than the melting point of the high-temperature phase change heat storage material), and the compounding time is 2.5 hours;

3. Lithium fluoride and calcium fluoride heat storage materials account for 88% of the total weight of the foam metal-based high temperature phase change heat storage composite material. the

Implementation results: The latent heat of phase change of the prepared composite composite high-temperature phase change heat storage material is 832.9kJ/kg, and the phase change temperature is 758.7°C. the

Example 4: The continuous porous metal foam skeleton material is Ni foam, the high temperature phase change heat storage material is lithium fluoride, and the heat storage metal container (that is, the forming container) is made of Haynes188. The process conditions are as follows:

1. The heating and melting temperature of the latent heat storage material in the heating furnace is 900-950°C;

2. The compounding process temperature is 930-1040°C, and the compounding time is 2-3 hours;

3. The lithium fluoride heat storage material accounts for 60% of the total weight of the foam metal-based high temperature phase change heat storage composite material. the

Implementation results: The latent heat of phase change of the prepared composite high-temperature phase change heat storage material is 1032.8kJ/kg, and the phase change temperature is 850.0°C. the

Example 5: The continuous porous metal foam skeleton material is Ni foam, the high-temperature phase change heat storage material is lithium fluoride, and the heat storage metal container (that is, the forming container) is made of Haynes188. The process conditions are as follows:

1. The heating and melting temperature of the latent heat storage material in the heating furnace is 920-980°C;

2. The compounding process temperature is 950-1060°C, and the compounding time is 2-3 hours;

3. The lithium fluoride heat storage material accounts for 95% of the total weight of the foam metal-based high temperature phase change heat storage composite material. the

Implementation results: The latent heat of phase change of the prepared composite composite high-temperature phase change heat storage material is 1095.6kJ/kg, and the phase change temperature is 870.0°C. the

The product is composed of metal foam skeleton material, high temperature phase change heat storage material and phase change heat storage container, and is packaged with phase change heat storage container. The high-temperature phase change material is a solid-liquid phase change heat storage material, which is evenly distributed in the porous continuous material of inorganic metal. The capillary effect improves the reliability of the storage of phase-change substances in porous media, so that no liquid leakage occurs when the solid-liquid phase transition occurs, and at the same time, the high thermal conductivity of porous media is used to improve heat transfer efficiency. The molten salt is evenly and fully distributed in the porous network structure metal matrix. The metal skeleton divides the phase change heat storage material into countless tiny heat storage units. These tiny heat storage units improve heat absorption and heat release, Also, due to capillary tension, the outflow of the molten phase change material is prevented, the recombination rate is high, and the heat storage capacity is good. The provided composite high-temperature phase change heat storage material is used in the heat absorber of the space solar thermal power generation system, which can utilize and control the formation of holes to enhance heat transfer, limit the large volume shrinkage during solid-liquid phase change, and improve the phase efficiency. Change the thermal conductivity of the material and enhance the heat transfer capacity of the heat accumulator. the

advantage:

1. Composite the high-temperature phase-change heat storage material to the metal foam base material, which not only avoids the sintering of the inorganic salt and the matrix, but also improves the mechanical strength of the high-temperature phase-change energy storage material. the

2. Since the molten salt infiltrates spontaneously due to capillary tension, no additional pressure is required, which simplifies the preparation process. the

3. Composite high-temperature phase-change heat storage materials are used in the heat absorber of space solar thermal power generation system, which can use and control the formation of holes to enhance heat transfer and limit the large volume shrinkage during solid-liquid phase change, which is better than that without adding The volume shrinkage of the high-temperature phase-change heat storage material of foam metal is reduced by more than 15%, which improves the thermal conductivity of the phase-change material and strengthens the heat transfer capacity of the heat storage device. The latent heat of phase change of the finished product is large, up to 870.6kJ/kg, which is more than 10% higher than the latent heat of phase change of the high-temperature phase change heat storage material without adding foam metal. The energy storage density is high, and the heat output performance of the material is improved. the

Other materials of the above-mentioned solid-liquid phase change heat storage material at 600°C may also include the following high-temperature phase change materials, etc., see Table 1 (the mechanism is the same, and the examples are omitted). the

Table 1:

Phase change material name Phase transition temperature (°C) _MgF2 1263 KF 857 MgCl ₂ 714 Na ₂ CO ₃ 854 LiOH+LiF 700 Na ₂ SO ₄ /SiO ₂ 879 Na ₂ CO ₃ -BaCO ₃ /MgO 686

Claims (1)

1. the preparation method of a foamed-metal based high-temperature phase change heat storage composite material is characterized in that having following steps:

A, preparation foamed metal framework material, and put in container molding by certain mass;

B, quality on request form solid-liquid phase change heat-storing material when preparing 〉=600 ℃, mix thoroughly, put into the vacuum furnace bake out and dewater and make it be molten state, the process furnace temperature of fusion is at the high 〉=above 50-100 of transformation temperature ℃ of solid-liquid phase change heat-storing material 600 ℃ the time; Described foamed metal framework material is foamed metal Ni or foamed metal Cu framework material; During described 〉=600 ℃, the solid-liquid phase change heat-storing material is LiF and CaF ₂Mixture: LiF and CaF in mixture ₂The quality ratio of components be 2～1.1:1; The solid-liquid phase change heat-storing material accounts for 88～95% of gross weight; The container molding that will hold simultaneously the foamed metal framework material is together put into the stove heating;

C, be molten state 〉=solid-liquid phase change heat-storing material quality on request forms to add and leads in the container molding that is placed with the foamed metal skeleton 600 ℃ the time, the material of container molding is the superalloy of cobalt-based, Ni-based or niobium base; In vacuum furnace, that foamed-metal based high-temperature phase change heat storage material heating is compound, the recombination process temperature be controlled at than this 〉=fusing point of solid-liquid phase change heat-storing material is high 80～200 ℃ 600 ℃ the time;

After d, compound end, will hold container molding Slow cooling in stove of foamed-metal based high-temperature phase change heat storage composite material, with vacuum electron beam welding, that the container molding end cap seal is good after taking out.