CN102173114A - Phase-change energy-storage hot pad and preparation method thereof - Google Patents

Abstract

The invention provides a phase change energy storage heat pad and a preparation method thereof, belonging to the technical field of functional composite materials. As a new form of energy utilization, phase change thermal storage materials have their own shortcomings such as supercooling, precipitation and low thermal conductivity. The invention utilizes and improves the shortcomings of the phase change material itself, and combines the knowledge of chemical thermodynamics and physiological hygiene to invent a phase change energy storage heat pad. The heat pad product is composed of fabric layer, protective layer, sponge layer, heat storage layer, heating layer and heat insulation layer. The preparation of heat storage layer material is the key point of the present invention. The heat storage layer is a physical fusion of stearic acid and Na ₂ HPO ₄ ·12H ₂ O, the mass ratio of fusion is 2:3, and polyacrylamide with a mass percentage of 1% is added at the same time, which makes up for the organic and inorganic materials. own shortcomings. The heat pad product has very good stability and good heat storage and release performance. It can not only keep warm but also improve the comfortable conditions and convenient and practical requirements for people to rest or exercise.

Description

A kind of phase change energy storage heat pad and preparation method thereof

technical field

The invention belongs to the technical field of functional composite materials, and in particular relates to a phase change energy storage heat pad and a preparation method thereof.

Background technique

The most important issues in the field of energy utilization are energy saving and environmental protection, and phase change energy storage technology is a new type of environmental protection and energy saving technology that utilizes the phase change latent heat of phase change materials for energy storage (heat storage, cold storage), which can alleviate the energy consumption of both parties. The mismatch in time, intensity and location is an effective way to use energy rationally and reduce environmental pollution, and it is also an effective means to improve energy utilization. Use energy storage technology to store the energy when the supply exceeds the demand and use it when needed, which can not only improve the utilization rate of energy, but also alleviate the urgency of energy utilization. Making full use of phase change latent heat energy storage has become a hot spot in the field of scientific research.

Phase-change energy storage materials can absorb heat (cold) from the external environment or release heat (cold) to the environment during the phase change process, thereby realizing energy storage and release. Utilizing this feature of phase change energy storage materials, it can be applied to solar energy utilization, "peak shifting and valley filling" of electric power, waste heat and waste heat recovery, energy saving of industrial and civil building heating and air conditioning, and aerospace and textile industries. and other fields. Therefore, phase change energy storage materials have been paid more and more attention and have broad application prospects.

Foreign researches on phase change materials (PCMs) started as early as the 1960s. At that time, the researches were mainly for the purpose of energy saving, and mainly focused on inorganic salt hydrates. However, the disadvantages of inorganic salt hydrate materials are that there is a large degree of supercooling and obvious precipitation, as well as thermal stability problems under periodic operation. Even with the addition of nucleating agents and dispersants, it cannot be effectively solved, which limits the application of eutectic salts. However, organic substances represented by paraffin, alkanes, and fatty acids are the focus of research on organic phase change materials at home and abroad. Their advantages are mainly in good thermal stability, relatively cheap price, high thermal storage density, good thermal stability, and no corrosion. properties, supercooling and phase stratification of non-hydrated salt phase change materials; the disadvantage is that the thermal conductivity is very low, which leads to the disadvantages of poor heat transfer performance and low heat storage utilization in the application of heat storage systems, thus The efficiency of the system is reduced, and the application field of the organic phase change material is greatly limited. The present invention uses the characteristics of poor thermal conductivity of phase change materials, utilizes and improves this shortcoming, and combines the knowledge of chemical thermodynamics and physiological hygiene to change the traditional passive way of keeping warm for human beings to active heating and temperature regulation. The way of starting from the development of intelligent "phase change heat storage pad".

Contents of the invention

The purpose of the present invention is to provide a phase change energy storage heat pad and its preparation method to improve the supercooling and phase separation of crystalline hydrated salts, the small thermal conductivity of stearic acid, etc., and at the same time make the phase change material have high strength , high thermal conductivity, high modulus, high scratch resistance, corrosion resistance, low density, good flexibility, strong heat storage capacity and other characteristics. In addition, it also has the advantages of simple operation, easy process control, and low synthesis temperature.

The invention provides a phase change energy storage heat pad. The heat pad is composed of a fabric layer, a protective layer and a main structure. The main structure is composed of four parts: a sponge layer 1, a heat storage layer 2, a heating layer 3, and an insulation layer 4. The innermost layer of the main structure is a heating layer 3. The upper layer outside layer 3 is heat storage layer 2, the lower layer is heat insulation layer 4, and the outside of heat insulation layer 4 and heat storage layer 2 is sponge layer 1; the periphery of the main structure is protective layer 5 and fabric layer 6 in turn from inside to outside, The material of the protective layer 5 is hydrogen fiber, and the material of the fabric layer 6 is cotton material.

The phase change energy storage material filled in the heat storage layer 2 is a physical fusion of stearic acid and Na ₂ HPO ₄ ·12H ₂ O, the fusion mass ratio is 2:3, and at the same time, 1% by mass of poly Acrylamide.

In the phase change material used in the present invention, stearic acid has a molecular formula of C ₁₈ H ₃₆ O ₂ , is a white monoclinic prism, and is a saturated fatty acid existing in animal fat in the form of glyceride. The melting point is generally between 60-70°C. The boiling point (1 standard atmosphere) is 383°C. It is not easy to undergo chemical reactions such as self-oxidation, reduction, and addition. Fatty acids have the properties of dehydration and thermal decomposition at the same time, but thermal decomposition and dehydration can only occur at temperatures above 350°C. As a commonly used phase change material, stearic acid has the advantages of high latent heat value, no supercooling and precipitation, and stable performance. It is a non-toxic and non-corrosive substance. The disadvantage is that the thermal conductivity is small.

Na ₂ HPO ₄ ·12H ₂ O, also known as disodium hydrogen phosphate dodecahydrate, white or colorless monoclinic prismatic crystal, non-toxic, melting point around 35°C, specific gravity 1.52, not in strong acid environment, Not prone to chemical reactions. When the temperature is 125°C, it loses all crystal water and becomes anhydrous, and decomposes into sodium pyrophosphate at 250°C. It has the advantages of high latent heat value, good heat storage and thermal conductivity, but the disadvantage is that there is supercooling phenomenon.

The layered sponge used in the present invention can make people feel comfortable, and can play the role of indirect heat transfer. The thickness of the sponge depends on the quality of the selected sponge material, generally 4-5cm.

The thermal storage material and the heating layer used in the present invention are the main body of the thermal pad. The heating is mainly through the use of a power source to heat the thermal storage material. When the environment is warm and comfortable and no heating is required, the thermal pad is stored by the power source. Heat to conserve heat. When the environment changes and people need heating, the energy is transferred to the human body through the heat storage material to realize the intermittent utilization of energy. In order to avoid or reduce the inhomogeneity of the heating surface of the heat pad caused by the inhomogeneity of the material in the heat storage layer due to the flow of the liquid phase during the phase change process, a supporting frame is encapsulated in the heat storage layer. To a certain extent, the flow deformation of the heat storage material can be fixed. The thickness of the heating layer is between 1-2cm.

The material of the insulation layer used in the present invention is open-cell sponge rubber with a thickness of 2-3cm, and its function is to transfer heat to the useful side as much as possible during heating and heat release.

The heating film adopted in the present invention is a self-made simple, practical and cheap film. The heating surface is heated by the high thermal resistance silicone spiral heating wire wrapped around the polyester cloth surface. The heating wire part is a heating material with high temperature resistance, corrosion resistance, high insulation of the skin rubber, and good heat radiation performance. The heating power of the entire heating part is 40W, and when the surface heating temperature is 120°C, no abnormal phenomenon occurs. Of course, if the heating time is too long, you can consider installing a constant temperature device in the heating pad heating film.

The present invention also provides a preparation method of this phase change energy storage heat pad, the preparation method includes two steps, the first step, the preparation of phase change energy storage material, mainly adopts the sol-gel method, the second step, " Phase change energy storage thermal pad". Specifically include the following steps:

Step 1: Preparation of phase change energy storage materials:

Step 1.1: Put the stearic acid in a three-necked flask, heat the stirrer with a constant temperature magnetic force, and heat and stir at 75°C until the stearic acid is completely dissolved;

Step 1.2: Grind the dried _{Na 2} HPO ₄ ·12H ₂ O into powder, and slowly and _evenly add the stearic acid to the molten stearic acid at a mass ratio _of 3:2 , while adding 1% polyacrylamide by mass percentage;

Step 1.3: Stir continuously for 10 minutes to obtain a milky white gel;

Step 1.4: Heat the colloid repeatedly for 3-5 times, and cool it to 33-35 degrees under airtight conditions. When the colloidal state remains unchanged, the phase change energy storage material is obtained;

Step 2: Forming and preparation of the thermal pad, the specific process is as follows:

Step 2.1: Encapsulate the phase-change energy storage material into small pieces with PEEK heat-resistant plastic film, and use a sealer to encapsulate the plastic film, and finally attach a layer of tin foil to the outer surface of the packaging bag to complete the preparation of the heat storage layer ;

Step 2.2: Wrap the polyester cloth surface with a high thermal resistance silicone spiral heating wire to form a heating layer;

Step 2.3: Put the insulation layer under the heating layer and sew it together with thread;

Step 2.4: Place the heat storage layer on top of the sewn heating layer and insulation layer;

Step 2.5: Process the sponge into a groove shape with the same size as the heat storage layer block, and then fix the heat storage layer block in the groove of the sponge;

Step 2.6: Wrap the sponge around the insulation layer to fix the entire main part of the heat pad;

Step 2.7: Tightly wrap a layer of hydrogen fiber around the sponge as a protective layer, and then wrap a layer of cotton material fabric layer, and sew it with thread to get the heat pad product.

The protective layer adopted in the present invention is hydrogen fiber, and the fabric layer is cotton material. Hydrogen fiber has small thermal conductivity, which can reduce the rapid loss of stored heat to a certain extent. Cotton can adjust the microclimate environment in the human body clothing to meet the comfort requirements of the human body.

The present invention has the following beneficial effects:

The phase change heat storage heat pad is mainly processed and designed according to the temperature regulation function of heat storage textiles. As a daily necessities that actively regulate the microclimate of the human body and the surroundings, heat storage heat pads not only meet people's needs for comfort and convenience in life in the 21st century, but also meet the heat preservation requirements of people who have been outside for a long time or in a relatively cold environment. The invention of this product breaks through the concept of traditional electric heating pads and other supplies that simply use electricity for heating. From the perspective of human comfort and safety, the human body temperature is kept in a comfortable state as much as possible, so as to not only keep warm but also improve people's health. Comfortable conditions and convenient and practical requirements for rest or exercise.

The property of the thermal pad product in the present invention does not change after repeated heat storage and discharge, and the thermal pad has very good stability. The heat storage and release time of heat pad products is basically about 3 hours and 8 hours. The maximum surface temperature of the heat pad is basically around 55°C, and the final temperature of the heat release is basically maintained at around 26°C. This temperature is very suitable for human body requirements in the external environment or indoor heating, and has good heat storage and release performance.

Description of drawings

Figure 1: The main structure of the thermal pad;

Figure 2: Product structure diagram of thermal pad;

In the figure, 1-sponge layer, 2-heat storage layer, 3-heating layer, 4-heat insulation layer, 5-protective layer, 6-fabric layer.

Detailed ways

The present invention will be described in detail below in combination with specific embodiments.

The phase-change thermal storage material layer in the present invention is a physical fusion of stearic acid and Na ₂ HPO ₄ ·12H ₂ O, the fusion mass ratio is 2:3, and 1% polyacrylamide is added at the same time.

The test of the latent heat and melting point of the phase change heat storage material of the present invention can use a differential scanning calorimeter (DSC), and it is found that: stearic acid begins to partially melt from 50°C, and the latent heat of phase change is about 200J/kg . The melting point (phase transition temperature) of Na ₂ HPO ₄ ·12H ₂ O is 35° C., and the latent heat of phase transition is 246 J/kg. It can be seen that the melting point and latent heat of Na ₂ HPO ₄ ·12H ₂ O are very suitable for the human body's own sense of cold and heat. As a heat pad material itself has the effect of thermal insulation, so stearic acid with a higher melting point is selected to adjust the ratio of Na ₂ HPO ₄ ·12H ₂ O, so as to adjust the phase transition temperature and balance The contact temperature between people and the heat pad can achieve both comfortable and long-term effective effects.

In the present invention, the supercooling degree of Na ₂ HPO ₄ ·12H ₂ O is not very high, generally about 10 degrees. Experiments show that stearic acid is effective as a nucleating agent of Na ₂ HPO ₄ ·12H ₂ O. For the precipitation of Na ₂ HPO ₄ ·12H ₂ O, polyacrylamide is mainly added therein as a thickener. By adding 1% by mass of polyacrylamide to Na ₂ HPO ₄ ·12H ₂ O, the phase separation problem during crystallization of Na ₂ HPO ₄ ·12H ₂ O can be well prevented.

The preparation method of the phase-change heat storage material in the present invention is as follows: First, weigh a certain amount of stearic acid and Na ₂ HPO ₄ ·12H ₂ O with a balance, weigh them according to the set ratio, and put them in different beakers , and put a glass cover slip on top of the beaker. Put the beaker on a magnetic heating stirrer to heat and melt. When stearic acid and Na ₂ HPO ₄ ·12H ₂ O respectively reach their own melting points and melt completely, put the Na ₂ HPO ₄ ·12H ₂ O solution together with the The water is poured into the beaker filled with the stearic acid solution by means of glass rod drainage, and 1% polyacrylamide is added thereto. At this time, the temperature of the constant magnetic stirrer remains unchanged, and the two mixed materials are stirred continuously at a constant rate until the final material is mixed evenly and gelatinous. At this time, the magnetic stirrer can be turned off, and the material is taken out. The mixing process is over.

The infrared spectrum analysis of the mixed material shows that there is no reaction between Na ₂ HPO ₄ ·12H ₂ O and stearic acid itself, which is a kind of physical fusion, so the latent heat value of the mixed material should also be the neutralization of the two. In fact, the DSC test of the mixed material shows that the phase change latent heat value of the mixed material is 238.4J/g, which is in good agreement with the values measured separately for the two materials. This shows again that this material is simply physically fused without chemical reaction, that is, the respective physical and chemical properties do not change.

The design method and steps of the phase change heat storage pad in the present invention are as described above, and the heat storage and release performance of the heat pad is mainly evaluated from two indicators of temperature and time. Tests show that the heat storage and release time of heat pad products is basically about 3 hours and 8 hours. The maximum surface temperature of the heat pad is basically around 55°C, and the final temperature of the heat release is basically maintained at around 26°C. This temperature is very suitable for human body requirements in the external environment or indoor heating, and has good heat storage and release performance.

Claims (4)

1. A phase-change energy storage heat pad is composed of a fabric layer, a protective layer and a main structure, and is characterized in that the main structure is composed of a sponge layer (1), a thermal storage layer (2), a heating layer (3), The heat insulation layer (4) consists of four parts, the innermost layer of the main structure is the heating layer (3), the upper layer outside the heating layer (3) is the heat storage layer (2), the lower layer is the heat insulation layer (4), and the heat insulation layer (4) and the heat storage layer (2) is a sponge layer (1); the periphery of the main structure is a protective layer (5) and a fabric layer (6) from the inside to the outside, the protective layer (5) is made of hydrogen fiber, and the fabric layer (6) The material is cotton material. 2. A phase-change energy storage heating pad according to claim 1, characterized in that, the phase-change energy storage material is filled in the heat storage layer (2), and the phase-change energy storage material is stearin Physical fusion of acid and Na ₂ HPO ₄ ·12H ₂ O, the mass ratio of fusion is 2:3, and polyacrylamide with a mass percentage of 1% is added at the same time. 3. A phase-change energy storage heating pad according to claim 1, characterized in that the thickness of the sponge layer (1) is 4-5cm, and the heat-insulating layer (4) is an open-cell sponge rubber with a thickness of The heating layer (3) is a self-made heating film formed by winding a polyester cloth surface with a high thermal resistance silicone spiral heating wire, and the thickness is between 1-2cm. 4. The preparation method of the phase-change energy storage heat pad according to claim 1, characterized in that, the method is carried out in the following steps: Step 1, preparation of phase change energy storage material: Step 1.1: Put the stearic acid in a three-necked flask, heat the stirrer with a constant temperature magnetic force, and heat and stir at 75°C until the stearic acid is completely dissolved; Step 1.2: Grind the dried _{Na 2} HPO ₄ ·12H ₂ O into powder, and slowly and _evenly add the stearic acid to the molten stearic acid at a mass ratio _of 3:2 , while adding 1% polyacrylamide by mass percentage; Step 1.3: Stir continuously for 10 minutes to obtain a milky white gel; Step 1.4: Heat the colloid repeatedly for 3-5 times, and cool it to 33-35 degrees under airtight conditions. When the colloidal state remains unchanged, the phase change energy storage material is obtained; Step 2, preparation of phase change energy storage heat pad: Step 2.1: Encapsulate the phase-change energy storage material into small pieces with PEEK heat-resistant plastic film, and use a sealer to encapsulate the plastic film, and finally attach a layer of tin foil to the outer surface of the packaging bag to complete the preparation of the heat storage layer ; Step 2.2: Wrap the polyester cloth surface with a high thermal resistance silicone spiral heating wire to form a heating layer; Step 2.3: Put the insulation layer under the heating layer and sew it together with thread; Step 2.4: Place the heat storage layer on top of the sewn heating layer and insulation layer; Step 2.5: Process the sponge into a groove shape with the same size as the heat storage layer block, and then fix the heat storage layer block in the groove of the sponge; Step 2.6: Wrap the sponge around the insulation layer to fix the entire main part of the heat pad; Step 2.7: Tightly wrap a layer of hydrogen fiber around the sponge as a protective layer, and then wrap a layer of cotton material fabric layer, and sew it with thread to get the heat pad product.

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