| The harvest season of pasture in northern China is also the period of annual rainfall.If the forage grass was not seasonablely dried and stored,it may be washed in the field and the loss of its nutrients would be serious,resulting in some grass degeneration.Due to the intermittent characteristics of solar energy resources,the actual running time of the equipment is limited.In order to speed up the harvest period,a high performance phase change storage equipment was developed,and the uninterrupted operation of the solar pasture drying equipment was realized.The following research work has been carried out in detail:1.Through researching literature review and analysing the principle of phase change material screening,the structure and physical properties of mannitol and compound algal alcohol were characterized and analyzed systematically in medium temperature phase change materials.The results show that mannitol and compound trehalo alcohol have the advantages of high phase change latent heat,high temperature stability and low expansion coefficient,while its disadvantage is that the thermal conductivity is low still exists.Thus,the heat transfer enhancement should be carried out in practical application.2.In order to enhance the thermal conductivity of mannitol,we will study several kinds of finned tube shell structures.Using the heat transfer oil as the heat transfer medium,and the mannitol and the compound alginol as the phase change heat storage material,we will study the finned tube shell phase transformation heat transfer model.And then we will also discuss the effects of the structure parameters of the fin tube,the inlet temperature,the velocity of the heat conduction oil on the liquid phase rate and the supercooling of the phase change of the phase change material step by step.Shell structure,which effectively enhances the heat transfer capability of phase change materials.Compared with the circular tube heat exchanger,the solid liquid phase transition time is shortened by 62.4%.The research in this chapter provides the design basis for the structural of phase change thermal storage device.3.For the two phase change materials with high solid-liquid phase transition temperature(120 degree and 165 degree Celsius),a line focusing solar collector system is designed and developed.The heat collector and its loss performance of evacuated collector tube are under deep consideration,and the influencing factors of improving the collector efficiency will be found.Through the experimental research,the system can increase the temperature of the heat transfer oil to 280 C,meeting the requirements of the heat transfer temperature of the phase change material.4.Trough designing and developing phase change material storage heat and device,we’ll further study the storage and exothermic characteristics of phase change materials and the heat transfer characteristics of heat storage materials in the heat storage system,which are able to provide a theoretical basis for the optimization of the structure of the regenerator.Besides,we could study the heat storage of the multi-phase change heat storage device under the inlet temperature of 210 and the inlet velocity 2.0m/s.-heat transfer law and heat transfer enhancement mechanism during exothermic process.The heat transfer efficiency of heat transfer oil and phase change material is enhanced by using multi-phase combined heat storage structure.At the same time,the low temperature heat conduction oil recirculation collector improves the heat and light conversion efficiency of the trough type solar collector.The thermal storage time of the multi-phase combined heat storage structure is shortened by 63min compared with the single phase change thermal storage structure,and the shortening rate of effective heat storage time is 21%.5.the CFD finite volume module of COMSOL Multiphysics software is used as the basis for the numerical calculation of the phase change heat transfer,and the physical modeling of the square coil solar heat storage device is carried out.And we need to test the simulation of the thermal storage and exothermic of the phase change heat storage device,by which we know that the simulated temperature variation is similar to the experimental data,so the correctness of the physical mathematical model is verified.Through the change of the liquid phase ratio of the single phase change heat storage unit with time,we found the non synchronism of the phase change melting,and the inhomogeneity of the phase change melting in the heat storage device,in the upper,middle and lower parts of the regenerator.According to simulation data,the structural parameters of the heat storage device were optimized.What’s more,the uniformity of phase change melting in the upper,middle and lower parts of the phase change heat storage device is further improved by using the multi thickness fin structure.6.a test bed for the drying characteristics of the day-and-night alternate solar pasture was designed and built,we would carry out the application of the trough solar phase change storage technology in the alfalfa drying system.The trough solar multi phase heat storage device using 12m2 can provide 45 centigrade hot air continuous heat relea sing time of 295min,which can meet the day-and-night alternate type of solar pasture drying test bed for a batch of pasture drying.C ompared three kinds of thermal storage materials,including the heat collecting methods of mannitol,compound algal alcohol and water,if under the same heat storage capacity,the heat storage time of the 12m2 trough solar multi-phase heat storage device is shortened by 41%than that of the 20.4m2 vacuum tube type solar energy water regenerator,and the volume of the phase change device is reduced by 52.9%.The heat discharge rate of the regenerative material was increased by 4.0 times.Meanwhile,the multi-phase heat storage device has obvious advantage of thermal storage. |
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