| With the deepening of global modernization and industrialization,the demand for energy is increasin,therefore,the energy issue is still a major concern in the world today.Combined Cooling Heating and Power(CCHP)system,which follows the principles of energy cascade utilization and provides users with cold,hot and electric loads at the same time,is a potential energy-saving and emission reduction technology.Meanwhile the energy efficiency of CCHP system is 70%~90%,and energy saving rate is 20%~40%.However,due to the mismatch between the three-dimensional fluctuations of the user's loads and the one-dimensional output of the CCHP system,the output of the CCHP system is too large or the over-combustion is excessive.As a result,the energy saving rate of China's current actual CCHP system is relatively low(less than 20%)compare to distribution production system,far from achieving the system energy saving potential.In theory,the introduction of energy storage technology can effectively solve this problem,but the traditional passive energy storage does not participate in system regulation and operation.Therefore,this study is based on the need to integrate the energy storage system into the CCHP system's control unit,and study the energy charging or discharging characteristics of the energy storage device from the perspective of system control and operation.In this research,a shell-and-tube latent heat storage devices(LHST)using stearic acid(SA)and stearic acid/expanded graphite(SA/EG)composites as phase change materials(PCM)was studied with experimental and numerical simulation methods.The variation of the properties of phase change materials in the process of energy charging and discharging of LHST devices was studied experimentally and a series of experiments under different working conditions of the heat transfer fluid(HTF)were carried out.In the experimental study,the melting and solidification properties of the phase change materials were obtained with the change of temperature and flow rate of the heat transfer fluid.And comprehensive assessment indicators for evaluation of LHST devices,such as charging/discharging energy time,charging/discharging energy,average charging/discharging energy,energy storage efficiency,and energy storage density,were calculated.Meanwhile,a three-dimensional mathematical model based on the enthalphy-porosity model was established to study the heat transfer mechanism of the charging/discharging process and to analyze the flow and heat transfer uniformity.In addition,the concept of thermal resistance is introduced in this study.Taking the energy storage unit as the research object,the mathematical model in the process of charging/discharging energy is established with similar solution of the phase change heat transfer problem.And analyzing the change of charging/discharging energy and estimate the range of storage power.Then the calculation result of a single energy storage unit was extended to the entire energy storage device with the form of a parallel connection of thermal resistance.After the introduction of the correction factor,it was found that the theoretical calculations of stored energy and cumulative heat storage were in agreement with the experimental results.This study will provide guidance and reference for the study of LHST devices in other temperature zones in the CCHP system.At the same time,the energy storage model established in this study will provide theoretical support for the integration and regulation of CCHP system. |
PDF Full Text Request