Preparation Of Sodium Sulfate Decahydrate-Disodium Hydrogen Phosphate Dodecahydrate Composite Phase Change Material And Its Application In Solar Greenhouse

Solar greenhouse is an important energy-saving building in northern China for agricultural production.Its main function is to provide suitable growth environment for crops by using clean and renewable energy solar energy.However,it is difficult to guarantee the crop growth temperature(20?25?)in the cold area at night due to the instability of solar energy.Traditional heating methods such as coal and oil not only consume non renewable energy,but also pollute the environment.In order to solve this problem,this paper uses energy-saving and environmental friendly phase change energy storage technology based on phase change materials to adjust the thermal environment of greenhouse,in order to achieve the ideal temperature control effect.The ratio of binary eutectic mixed salt composed of sodium sulfate decahydrate and disodium hydrogen phosphate dodecahydrate was determined by experiments.It was modified by adding auxiliary materials such as melting point regulator,nucleating agent and thermal conductivity enhancer through physical blending.The phase transformation properties of phase change materials were characterized by step cooling curve method and differential scanning calorimetry(DSC).Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O based composite phase change materials for solar greenhouse were prepared.The phase change temperature was 24.9?and the latent heat was 143.7 J/g.The composition of the phase change material is:21.37%Na₂SO₄·10H₂O+64.10%Na₂HPO₄·12H₂O+4.27%KCl+4.27%H₂O+4.27%Na₂Si O₃·9H₂O+0.85%graphite powder+0.85%CMC.After 80 cycles,the phase change material can still maintain good phase change properties.In order to verify the application effect of self-made Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O based composite phase change materials in solar greenhouse,square plastic barrel and polyethylene plastic bag were used to package the phase change materials,which were defined as package scheme 1 and package scheme 2respectively.The packaged materials were placed in the solar greenhouse,and the temperature changes of the phase change greenhouse and the control greenhouse were compared.The results showed that:in package scheme 1,the maximum temperature of phase change greenhouse on sunny day was 2.0?lower than that of the control greenhouse,the minimum air temperature was 0.8?1.4?higher than that of the control greenhouse;the minimum soil temperature was always about 0.5?higher than that of the control greenhouse;the maximum wall temperature was 2.2?lower than that of the control greenhouse,and the minimum temperature was 3.4?higher than that of the control greenhouse.In package 2,the maximum indoor temperature of the phase change greenhouse can be reduced by 3.1?in sunny days,and the minimum temperature can be increased by 1.7?2.7?at night;during the test period,the soil temperature of the phase change greenhouse is always 0.3?1.4?higher than that of the control greenhouse;the wall temperature decreases by 1.5?in the maximum temperature,and increases by 2.4?in the minimum temperature.Both of them can reduce the indoor maximum temperature,improve the indoor minimum temperature and reduce the indoor temperature fluctuation,indicating that the composite phase change material has good thermal storage and insulation performance,and can be effectively used to improve the thermal environment of greenhouse.