[Packaging News, China] 2.3 Sealing stability analysis of composite phase change energy storage material The material's sealing performance was studied by thermogravimetric analysis of the sample. Figure 4 is a TG plot of different sodium acetate trihydrate samples.
From Figure 4, it can be seen that under the condition of a constant temperature of 70 minutes at 70°C, the sample with 50% sodium acetate trihydrate and 60% of the sample has a 90.332% weight loss rate, and the sealing effect is comparable. The weight loss of the sample is mainly the weight loss of the free water, because the free water on the surface of the sodium acetate trihydrate and the small amount of moisture in the air will be enveloped by the carrier material during the preparation of the material. When the material is heated, this part of the water should be taken off first. The phase change energy storage material in the composite material did not produce a great loss. However, when the content is 70%, the bearing rate is 81.922%, the weight loss rate becomes significantly larger, the sealing performance becomes worse, and water loss occurs in the crystal water. Therefore, in the case of increasing the energy storage unit as much as possible to maintain a good sealing effect, sodium acetate trihydrate content of 60% is appropriate.
FIG. 5 is a TG curve of a composite phase change energy storage material filled with different expanded graphite content when the sodium trihydrate acetate mass fraction is 60%. From Figure 5, it can be seen that the rate of maintenance is 91.264%, 90.619% and 90.332%, respectively, and the weight loss rate of composite phase change energy storage material with expanded graphite is lower than that of unexpanded graphite. This fact indicates that due to the porous adsorption properties of the expanded graphite, it contributes to the improvement of the sealing stability of the composite phase change energy storage material.
2.4 Analysis of thermal conductivity of composite phase change energy storage materials The thermal conductivity of composite phase change energy storage materials was measured using a steady-state plate method. Figure 6 shows the amount of composite graphite phase-change materials with different contents of sodium acetate trihydrate added with expanded graphite. Change in thermal conductivity.
It can be seen from Figure 6 that under the same sodium acetate trihydrate content, the thermal conductivity of the composite phase change energy storage material becomes larger with the increase of the mass fraction of expanded graphite, and the growth rate tends to increase. At the same time, when the content of expanded graphite is constant, the thermal conductivity of the composite phase change energy storage material increases with the increase of the content of sodium acetate trihydrate. The above facts indicate that the effect of adding expanded graphite on the thermal conductivity of composite phase change energy storage materials is obvious. When the content of expanded graphite is 5% and the content of sodium acetate trihydrate is 60%, the thermal conductivity of composite phase change energy storage material is 0.891. W/(m°C) increases the thermal conductivity by 57.7% compared to the case where no expanded graphite is added. In addition, sodium acetate trihydrate is not only an energy storage material in the composite phase change energy storage material system, but also functions as a thermal conductive filler. Under the condition that no expanded graphite is added, when the content of sodium acetate trihydrate is 50%, the thermal conductivity of the composite phase change energy storage material is 0.488 W/(m°C), while the thermal conductivity of the trihydrate sodium acetate content is 60%. It is 0.563w/(m°C), an increase of 15.4%; when the sodium acetate trihydrate content is 70%, the thermal conductivity of the composite phase change material is 1.03W/(m°C), which is higher than that of the composite phase change material without added expanded graphite. The thermal conductivity increased by 77.6% but the sealing performance of the material was poor at this time.
2.5 Composite Phase Change Energy Storage Material Conversion Rate
FIG. 7 is a thermal energy storage (discharge) curve of a composite phase change energy storage material having a sodium trihydrate acetate mass fraction of 60%. As can be seen from FIG. 7 , the material is stored during the gradual increase of the composite phase change material from 40° C. to 80° C. The energy storage time of the composite phase change energy storage material without added expanded graphite was 690 seconds, while the addition of 3% expanded graphite energy storage time was only 330 seconds. In the process of the composite phase change energy storage material dropping from 80°C to 40°C, the material is discharged. The time required for the energy release of the composite phase change material without added expanded graphite was 1260S, whereas the time required for the addition of 3% expanded graphite was 930S. This fact shows that with the addition of expanded graphite, the thermal conductivity of the material increases, and the rate of energy exchange increases.
3 Conclusions a) Sodium acetate trihydrate is not only an energy storage material in the composite phase change energy storage material system, but also functions as a thermally conductive filler. Under the condition that no expanded graphite is added, when the content of sodium acetate trihydrate is 50%, the thermal conductivity of the composite phase change energy storage material is 0.488 W/(m°C), while the thermal conductivity of the trihydrate sodium acetate content is 60%. It is 0.563 W/(m°C), an increase of 15.4%.
b) The composite phase change energy storage material prepared from sodium acetate trihydrate and the epoxy resin can well prevent the leakage of the liquid phase when the material is used; through the material, the OIA expanded graphite can further improve the composite phase change energy storage. Material's thermal conductivity and liquid-phase sealing properties. When the content of expanded graphite is 5% and the content of sodium acetate trihydrate is 60%, the thermal conductivity of composite phase change energy storage material is 0.891w/(m°C), which is 57.7% higher than that when no expanded graphite is added; c) The time required for the thermal storage of the composite phase change energy storage material to increase its storage (discharge) heat is greatly shortened, so that the energy exchange rate of the material is greatly improved.