Optimization Of Eutectic Salt Phase Change Cold Storage Materials And Heat Exchangers

Air conditioning storage technology can effectively relieve the power supply pressure during the peak period through"peak shifting and valley filling"of electricity,which is an effective measure for building energy conservation and emission reduction.Phase change heat exchanger is a key component of energy storage and energy release in cold storage technology.The eutectic salt cold storage material with Na₂SO₄·10H₂O as the main energy storage material has the advantages of high thermal conductivity,high energy storage density and safety and non-toxicity,and has been widely concerned in the field of air conditioning cold storage.However,phase separation,cyclic thermal attenuation and other problems restrict its application and promotion.It is very difficult to solve the phase change heat transfer problem in complex heat exchangers.At present,the performance and heat transfer process of the cooler are mainly studied through numerical simulation and experiment,among which numerical simulation is more flexible and economical.In this paper,the cycling stability of the Na₂SO₄·10H₂O material system is optimized by changing thickener,the influence of eutectic salt thermal attenuation characteristics on the cooling performance of the accumulator is studied in COMSOL simulation software,a kind of split ring-ribbed heat exchange tube is designed to enhance heat transfer,and the influence of its structure parameters and operating parameters on the cooling process is discussed.The main contents are as follows:Firstly,a new thickener,PAC,is added to the Na₂SO₄·10H₂O system to compare the thickening effect with the three thickeners commonly used at present by observing the separation degree of samples,analyzing the step cooling curve,and testing the circulating latent heat value.The experimental results show that the system with PAC as thickener had the best stability,and the latent heat value only decreases by 13.1%after 200 frost-melt cycles.Secondly,COMSOL simulation software is used to establish the numerical model of the ring-ribbed tube cooler,and the specific heat capacitance-temperature curve of the prepared material is used to correct the equivalent specific heat term in the sensible heat capacity model.The experimental results are compared with the numerical results of the modified and modified type to verify the correctness of the modified model.Then,according to the DSC curve,the physical property change of eutectic salt material caused by thermal attenuation is analyzed,the influence of material thermal attenuation on cooling power and effective cooling time under different heat exchange temperature difference is analyzed in typical annular tube cooler by using the aforementioned model,and the improvement effect of optimized phase change materials on cooling performance is compared.The results show that when the heat transfer temperature difference of 2℃,eutectic salt thermal decay make effective interpretation of the cold storage tanks time dropped by 32.5%,modified materials have extended their effective interpretation of the cold by 30.8%.Finally,a kind of open-ended ring-ribbed structure is proposed through the numerical study of the heat transfer process of the ring-ribbed heat exchange tube,which can improve the heat transfer effect of the region far from the wall of the heat exchange tube and shorten the melting time of phase change material by 24.3%.The control variable method is used to study the structural parameters of the split ring ribs,and it is found that when the junction distance is 30mm,the wing thickness ratio is 0.9,and the span is 7mm,good heat transfer effect can be achieved under the condition of less fin consumption.The optimal dimensionless span is 0.55 in the range of fin spacing between 9mm and 15mm.Increasing the inlet temperature and velocity of the heat transfer fluid can improve the heat transfer effect,but the lifting effect will weaken after a certain degree.The optimal values are 14℃and 1.4m/s,respectively.