| The modernization process of human civilization has been based on the exploitation and utilization of energy,and the demand and consumption of energy have been accelerating day by day especially since the fossil energy age.It is obviously necessary to make our energy development sustainable when faced with more and more severe energy shortage,environment pollution and climate change.On the one hand,it is significant to develop renewable and clean energy.On the other hand,we should spare no effort to improve energy efficiency.The development of distributed combined cooling,heat and power(CCHP)systems have been aimed to use energy according to energy grade and match the temperature to improve energy efficiency.They are built near users and can provide cooling,heat and power at the same time by themselves,which can achieve the goal to save energy and reduce emission.They have been acting as important supplements for central energy systems.The new generation CCHP systems which introduce energy storage controlling can deal with the mismatch between the three-dimensional fluctuations of users' load and the one-dimensional output of CCHP systems in time and space due to the shifting peak loads.In addition,the middle temperature(200?300?)energy storage can reduce the installation capacity and further increase the efficiency of the energy systems.However,the prerequisite and basis of active energy storage controlling's smooth and effective performance is that it owns sufficient controlling competence,which means energy storage device should have abundant energy storage capacity,big charge/discharge power and big energy storage density.And the 3 goals depend on the energy storage materials and the structure of energy storage device.To be specific,it means selecting proper energy storage material,enhancing thermal conductivity and improving the long-term melting-solidification cycle stability,optimally designing energy storage device to increase its heat transfer area,improve heat transfer uniformity and reduce heat loss.Therefore,this thesis selects myo-inositol as middle temperature phase change energy storage material whose overall properties are relatively good.This thesis also tries some methods to enhance the thermal conductivity of myo-inositol and finds theaddition of a specific heat-conducting carbon fiber plays an obvious role in enhancing thermal conductivity.Moreover,experiments have been carried out to test the thermal conductivity,melting-solidification cycle characteristics,the period and enthalpy of phase change after long-term melting and solidification cycle,infrared spectroscopic analysis of diffierent addition rate myo-inositol with heat-conducting carbon fiber composite material in this thesis.These researches find low addition of heat-conducting carbon fiber not only can enhance conductivity,but also can improve the long-term melting and solidification cycle stability.Meanwhile,this thesis designs U-type tube middle temperature phase change energy storage device.Compared with ordinary tube and shell energy storage device,it has better performance at heat transfer area,heat transfer uniformity and work efficiency.Based on the study on phase change materials and energy storage device,this thesis designs and builds energy storage experiment system,carries out the research on storage/release characteristics of U-type tube middle temperature phase change energy storage device,analyzes the law of whole storage and release period,compares the influence on charge/discharge power,average power,latent heat power,accumulated storage/release energy and charge/discharge efficiency under different inlet temperatures and mass flow rates of heat transfer fluid.Last but not the least,this thesis also computes energy storage density and overall energy storage efficiency.This study will provide the value of data support and theoretical guidance to active energy shorage controlling. |
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