CN101289610A - A room temperature phase change energy storage medium and preparation method thereof - Google Patents

Abstract

The invention relates to a phase change material, in particular to a room temperature phase change energy storage medium which stores thermal energy in a phase change form and a preparation method thereof. The room temperature phase change energy storage medium of the invention is composed of 57-63wt.% lithium nitrate trihydrate, 19-31wt.% magnesium nitrate hexahydrate and 12-18wt.% potassium nitrate. The preparation method is as follows: mixing lithium nitrate trihydrate, magnesium nitrate hexahydrate and potassium nitrate according to the ratio, heating to 30-100 DEG C, stirring evenly until the solid phase melts into a liquid phase, and then it can be used as a phase change energy storage medium. The energy storage material of the invention has many advantages such as stable phase transition temperature point, consistent phase composition and liquid phase composition during phase transition, sensitive phase transition with temperature change, appropriate phase transition point, and the like. When the ambient temperature is higher than 22°C, the energy storage material absorbs a large amount of heat from the environment through its own melting; when the ambient temperature is lower than 18°C, the energy storage material solidifies and releases a large amount of heat to the environment, thereby maintaining the ambient temperature of stability.

Description

A room temperature phase change energy storage medium and preparation method thereof

technical field

The invention relates to a phase change material, in particular to a room temperature phase change energy storage medium which stores thermal energy in a phase change form and a preparation method thereof.

Background technique

Room temperature phase change energy storage medium is a substance that undergoes phase change in a narrow room temperature region to store or release heat. Its mechanism of action is that when the temperature is slightly higher than room temperature (15°C-25°C), The energy medium absorbs a large amount of heat from the environment and melts to store energy. When the temperature is lower than the above temperature range, the melted room temperature phase change energy storage medium condenses into a solid and releases a large amount of heat to the indoor environment, thereby maintaining the room temperature. relatively constant. In areas with large diurnal or weekly (every week) temperature differences, the room temperature phase change energy storage medium has important application value. It can be used as an absorber of solar energy during high temperature periods, and heat indoors at night or during cooler periods. , so as to achieve the purpose of energy saving.

An ideal phase-change energy storage material should generally have a relatively constant melting point, so that when the ambient temperature is higher or lower than the phase-change temperature, the energy storage material can absorb or release energy as much as possible from the environment. This feature is of great significance for energy storage materials to absorb energy from low-grade solar energy and maintain a constant room temperature. Substances used as phase-change energy storage media may be anhydrous salts, salt water compounds and mixtures thereof, organic substances, and the like. Among them, organic substances used as phase change energy storage materials at room temperature have the disadvantages of being dangerous, flammable, expensive, and poor thermal conductivity; anhydrous molten salts are suitable for high-temperature heat storage; salt water compounds and their mixtures are suitable for storing heat from low-temperature heat sources, These materials are widely used in solar energy and urban waste heat utilization, peak shaving and valley filling of power grids, etc.

Currently, cheap and safe phase change materials, especially those with a phase transition temperature between 15°C and 25°C, are rare. However, non-flammable inorganic phase change materials with a phase change temperature in the above-mentioned range are especially rare. The applicant's invention patent application "a room temperature phase change energy storage medium" submitted on April 28, 2007, application number: 200710034840. A room temperature phase change energy storage medium composed of 70wt.% lithium nitrate trihydrate, the mechanism of action is that there is a eutectic composed of lithium nitrate trihydrate and anhydrous ammonium nitrate in the ammonium nitrate-lithium nitrate-water ternary system point, the eutectic temperature at this point is around 15°C. Encapsulate the energy storage medium in a metal or transparent glass (or plexiglass) container and place it in a building or wall, which can be used to absorb solar energy during the day and release heat at night to heat the room; During the period, it absorbs the energy of the high temperature heat source (greater than 16°C) for storage, and releases heat during the low temperature period to heat the room. The corresponding content of each component of the ternary system makes the material have stable phase transition temperature point, low toxicity, low corrosion, consistent solid phase composition and liquid phase composition during phase transition, and sensitivity to phase transition with temperature changes, etc. advantage. The applicant submitted the invention patent application "a room temperature phase change energy storage medium and its preparation method" on February 25, 2008, application number: 200810030679.3, which provides a lithium nitrate trihydrate with a weight percentage of 65-71wt.%. , 20.8-32.2wt.% magnesium nitrate hexahydrate and 2.8-8.2wt.% sodium nitrate phase change energy storage medium at room temperature, the mechanism of action is, in lithium nitrate-magnesium nitrate-sodium nitrate-water quaternary system There is a eutectic point composed of lithium nitrate trihydrate, magnesium nitrate hexahydrate and sodium nitrate, and the eutectic temperature of this point is about 24°C. The energy storage medium is packaged in a metal or transparent glass (or plexiglass) container and placed in a building room or wall to adjust the indoor temperature and keep it within a comfortable temperature range. The material has many advantages such as stable phase transition temperature point, consistent phase composition and liquid phase composition during phase transition, and sensitive phase transition with temperature changes. When the ambient temperature is higher than 25°C, the energy storage material absorbs a large amount of heat through its own melting. When the ambient temperature is lower than 22°C, the energy storage material solidifies and releases a large amount of heat to the environment, thereby maintaining the stability of the ambient temperature.

Contents of the invention

The object of the present invention is to provide an inorganic room temperature phase change energy storage medium with a phase change temperature near room temperature, which is more environmentally friendly and has a lower cost. The composition and melting point are different from the above-mentioned invention. It is prepared by mixing magnesium nitrate and potassium nitrate in a certain proportion, and the eutectic phase transition temperature is around 21°C.

A room-temperature phase-change energy storage medium and a preparation method of the present invention are realized through the following technical scheme: The room-temperature phase-change energy storage medium of the present invention is composed of 57-63wt.% lithium nitrate trihydrate and 19-31wt.% nitric acid hexahydrate Composed of magnesium and 12-18 wt.% potassium nitrate.

The preparation method is as follows: mix lithium nitrate trihydrate, magnesium nitrate hexahydrate and potassium nitrate according to the proportion and heat them to 30-100°C, stir evenly and keep them for a period of time, these solid phases melt into liquid phases, and the liquid phases are It can be used as a phase change energy storage medium. The above-mentioned lithium nitrate trihydrate can be prepared by concentrating the crystalline lithium nitrate solution, or by mixing water and anhydrous lithium nitrate at a molar ratio of 3±0.2:1. The magnesium nitrate hexahydrate is prepared by concentrating a crystalline magnesium nitrate solution, or by mixing water and anhydrous magnesium nitrate at a molar ratio of 6±0.2:1.

The energy storage material can also be formulated from magnesium nitrate solution, lithium nitrate solution and potassium nitrate solution. The formulated material contains 31.9-35.5wt.% of lithium nitrate, 10.9-18wt.% of magnesium nitrate, and 12-18wt.% of potassium nitrate. %, water 28.5-45.2wt.%.

Its mechanism of action is that there is a eutectic point composed of lithium nitrate trihydrate, magnesium nitrate hexahydrate and potassium nitrate in the lithium nitrate-magnesium nitrate-potassium nitrate-water quaternary system, and the eutectic temperature of this point is 21 ℃ or so.

Encapsulate the energy storage medium in containers made of metal or transparent glass (or plexiglass) and other materials and place it in the interior or wall of a building, which can be used to absorb solar energy during the day and release heat at night to heat the room; or During certain periods of the day, it absorbs energy from a high-temperature heat source (greater than 22°C) for storage, and releases heat during low-temperature periods to heat the room.

Compared with the prior art, the present invention has the following beneficial effects: the inventor has determined the components and corresponding contents of the room temperature phase-change energy storage medium through experimental research. The composition is consistent with the composition of the liquid phase, and the phase change is sensitive to temperature changes. When the ambient temperature is higher than 22°C, the energy storage material absorbs a large amount of heat from the environment through its own melting; when the ambient temperature is lower than 18°C, the energy storage material solidifies and releases a large amount of heat to the environment, thereby maintaining the ambient temperature of stability. The temperature adjustment range of the energy storage medium (about 20° C.) is more appropriate than that of existing energy storage materials.

Description of drawings

A room temperature phase change energy storage medium and its preparation method of the present invention have the following drawings:

Fig. 1 is a schematic diagram of the composition of the energy storage material of the present invention;

Fig. 2 is a curve diagram of the heat absorption and release temperature of the energy storage material 1 of the present invention;

Fig. 3 is a curve diagram of the heat absorption and release temperature of the energy storage material 2 of the present invention;

Fig. 4 is a curve diagram of the heat absorption and release temperature of the energy storage material 3 of the present invention;

Fig. 5 is a curve diagram of the heat absorption and release temperature of the energy storage material 4 of the present invention;

Fig. 6 is a curve diagram of the heat absorption and release temperature of the energy storage material 5 of the present invention;

Fig. 7 is a curve diagram of the heat absorption and release temperature of the energy storage material 6 of the present invention;

FIG. 8 is a graph showing the heat absorption and release temperature curves of the energy storage material 7 of the present invention.

Detailed ways

The technical scheme of a room temperature phase-change energy storage medium and its preparation method according to the present invention will be further described below in conjunction with the accompanying drawings and examples.

As shown in Figures 1 to 8, a room temperature phase change energy storage medium of the present invention is composed of 57-63wt.% lithium nitrate trihydrate, 19-31wt.% magnesium nitrate hexahydrate and 12-18wt .% composition of potassium nitrate.

The preparation method is as follows: lithium nitrate trihydrate, magnesium nitrate hexahydrate, and potassium nitrate are mixed according to the proportion and heated to 30-100°C; after stirring evenly and maintaining for a period of time, these solid phases melt into liquid phases, and the liquid phases are It can be used as a phase change energy storage medium.

The lithium nitrate trihydrate is prepared by concentrating crystalline lithium nitrate solution, or by mixing water and anhydrous lithium nitrate at a molar ratio of 3±0.2:1.

The magnesium nitrate hexahydrate is prepared by concentrating a crystalline magnesium nitrate solution, or by mixing water and anhydrous magnesium nitrate at a molar ratio of 6±0.2:1.

The preparation method is prepared by blending magnesium nitrate solution, lithium nitrate solution and potassium nitrate solution, and the blended material contains lithium nitrate 31.9-35.5wt.%, magnesium nitrate 10.9-18wt.%, potassium nitrate 12-18wt.%. , water 28.5-45.2wt.%.

Example 1.

Mix 57 grams of lithium nitrate trihydrate, 31 grams of magnesium nitrate hexahydrate and 12 grams of potassium nitrate, heat to 26-35 ° C and keep it for a period of time until the solid is completely melted into a liquid. The composition of the liquid is shown at point 1 in Figure 1. As shown, the liquid contained 31.95 grams of lithium nitrate, 17.93 grams of magnesium nitrate, 12 grams of potassium nitrate in 38.12 grams of water. Put the liquid in a closed container and place the container in an air environment of 15°C. The temperature change of the measured medium is shown in the solid line in Figure 2. It can be seen that there is an obvious temperature plateau at around 19°C, which is due to the medium Solidification at this temperature releases a large amount of heat to the environment, thereby maintaining the stability of its own temperature. Observation of the crystallization behavior of the medium shows that at 25°C the medium is completely liquid and at 18°C the medium is almost completely transformed into a solid state.

Then place the container containing the fully cured energy storage medium in an environment with a room temperature of 26°C. The temperature of the medium rises as shown by the solid line in Figure 2. It can be seen that there is an obvious temperature plateau at around 20.5°C, which is the temperature of the medium. Due to the large amount of heat absorbed from the environment, the medium is completely melted above 21°C, thus accelerating the temperature rise.

Repeat the above process with the same weight of pure water, and the measured temperature rise and fall curves are shown in the dotted line in Figure 2. It can be seen that the water reaches the ambient temperature in a very short time, and the heat storage capacity is limited.

Comparing the two, it can be seen that the energy storage medium of the present invention can absorb a large amount of heat from an environment higher than 21°C, and release a large amount of heat to an environment lower than 18°C, thereby maintaining the constant temperature of the medium itself and the environment, and its temperature regulation ability It is many times larger than pure water.

Example 2.

Mix 57 grams of lithium nitrate trihydrate, 25 grams of magnesium nitrate hexahydrate and 18 grams of potassium nitrate, heat to 26-35 ° C and keep for a period of time until the solid is completely melted into a liquid. The liquid composition is shown in Figure 1. As shown in the dot, the liquid contained 31.95 grams of lithium nitrate, 14.46 grams of magnesium nitrate, 18 grams of potassium nitrate and 35.59 grams of water. Pack this liquid in airtight container, carry out temperature rise and fall experiment by the condition described in embodiment 1, the result is as shown in Figure 3 solid line. It can be seen that the material also has an obvious temperature plateau between 19-21 ° C, and the maintenance time is also very long. Compared with pure water, the energy storage medium still has good energy storage performance, and can also be used as a phase change energy storage material at room temperature.

Example 3.

Mix 63 grams of lithium nitrate trihydrate, 19 grams of magnesium nitrate hexahydrate and 18 grams of potassium nitrate, heat to 26-35 ° C and keep it for a period of time until the solid is completely melted into a liquid. The liquid composition is shown as 3 in Figure 1 As shown in the dot, the liquid contained 35.31 grams of lithium nitrate, 10.99 grams of magnesium nitrate, 18 grams of potassium nitrate and 35.7 grams of water. Pack this liquid in airtight container, carry out temperature rise and fall experiment by the condition described in embodiment 1, the result is as shown in Figure 4 solid line. It can be seen that the material also has an obvious temperature plateau between 19-21 ° C, and the maintenance time is also very long. Compared with pure water, the energy storage medium still has good energy storage performance, and can also be used as a phase change energy storage material at room temperature.

Example 4.

Mix 63 grams of lithium nitrate trihydrate, 25 grams of magnesium nitrate hexahydrate and 12 grams of potassium nitrate, heat to 26-35 ° C and keep it for a period of time until the solid is completely melted into a liquid. The liquid composition is shown as 4 in Figure 1 As shown in the dot, the liquid contained 35.31 grams of lithium nitrate, 14.46 grams of magnesium nitrate, 12 grams of potassium nitrate and 38.23 grams of water. Pack this liquid in airtight container, carry out heating and cooling experiment according to the condition described in embodiment 1, the result is as shown in Figure 5 solid line. It can be seen that the material also has an obvious temperature plateau between 19-21 ° C, and the maintenance time is also very long. Compared with pure water, the energy storage medium has good energy storage performance, and can also be used as a phase change energy storage material at room temperature.

The above examples are to explain the present invention in more detail, but not to limit the present invention, and the present invention can be implemented according to any mode described in the content of the present invention.

Comparative example 1.

Mix 52.5 grams of lithium nitrate trihydrate, 39 grams of magnesium nitrate hexahydrate and 8.5 grams of potassium nitrate, heat to 26-35 ° C and keep for a period of time, it is found that the solid is completely melted into a liquid, and the composition of the liquid is shown as 5 in Figure 1 As shown in the dot, the liquid contained 29.43 grams of lithium nitrate, 22.56 grams of magnesium nitrate, 8.5 grams of potassium nitrate and 39.51 grams of water. Pack this liquid in airtight container, carry out heating and cooling experiment according to the condition described in embodiment 1, the result is as shown in Fig. 6 solid line. It was observed that even if the temperature was raised to 26° C., some solids in the liquid still remained unmelted. Although the material with this ratio has an obvious temperature plateau during the heating and cooling period, the maintenance time of the platform is too short, and some solids have not melted during the heating period, which contributes little to the constant room temperature, so the material with this ratio is not suitable as a Use of energy storage materials at constant room temperature.

Comparative example 2.

Mix 58.4 grams of lithium nitrate trihydrate, 9.4 grams of magnesium nitrate hexahydrate and 32.2 grams of potassium nitrate, heat to 26-35 ° C and keep it for a period of time. It is found that some solids are still not melted into liquids. The composition of the liquid is shown in Figure 1 As shown in point 6, the liquid contains 32.73 grams of lithium nitrate, 5.44 grams of magnesium nitrate, 32.2 grams of potassium nitrate and 29.63 grams of water. Pack this liquid in airtight container, carry out heating and cooling experiment according to the condition described in embodiment 1, the result is as shown in Figure 7 solid line. It can be seen that the material has a very short platform during the cooling process, but no obvious platform during the heating process. Since some solids have not melted during the entire heating and cooling period, the contribution to the constant room temperature is minimal. Therefore, the composition The specific material is not suitable for use as an energy storage material at a constant room temperature.

Comparative example 3.

82.7 grams of lithium nitrate trihydrate, 10.8 grams of magnesium nitrate hexahydrate and 6.5 grams of potassium nitrate are mixed together, heated to 26-35 ° C and kept for a period of time, the composition of the mixture is shown at point 7 in Figure 1, and the mixture contains 46.35 grams of lithium nitrate, 6.25 grams of magnesium nitrate, 6.5 grams of potassium nitrate and 40.9 grams of water. Pack this liquid in airtight container, carry out heating and cooling experiment according to the condition described in embodiment 1, the result is as shown in Figure 8 solid line. It can be seen that the material has no obvious platform in the process of heating and cooling, so it cannot be used as an energy storage material at a constant room temperature.

Claims (5)

1, a kind of phase-change and energy-storage medium at room temperature is characterized in that: described energy-accumulating medium is the nitrate trihydrate lithium of 57-63wt.% by weight percentage, and the magnesium nitrate hexahydrate of 19-31wt.% and the saltpetre of 12-18wt.% are formed.

2, a kind of preparation method of phase-change and energy-storage medium at room temperature is characterized in that: described preparation method comprises the steps: the nitrate trihydrate lithium, magnesium nitrate hexahydrate, and saltpetre arrives 30-100 ℃ by the proportioning Hybrid Heating; After stirring and keeping for some time, these solid phases are molten into liquid phase, and this liquid phase promptly can be used as phase-change and energy-storage medium and uses.

3, the preparation method of a kind of phase-change and energy-storage medium at room temperature according to claim 2, it is characterized in that: described nitrate trihydrate lithium makes by the condensing crystal lithium nitrate solution, or by water and anhydrous nitric acid lithium by 3 ± 0.2: 1 mol ratio mixed makes.

4, the preparation method of a kind of phase-change and energy-storage medium at room temperature according to claim 2, it is characterized in that: described magnesium nitrate hexahydrate makes by the condensing crystal magnesium nitrate solution, or by water and anhydrous nitric acid magnesium by 6 ± 0.2: 1 mol ratio mixed makes.

5, a kind of preparation method of phase-change and energy-storage medium at room temperature, it is characterized in that: described preparation method is by magnesium nitrate solution, lithium nitrate solution and potassium nitrate solution allotment form, material after the allotment contains lithium nitrate 31.9-35.5wt.%, magnesium nitrate 10.9-18wt.%, saltpetre 12-18wt.%, water 28.5-45.2wt.%.

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