| Aiming at the application of thermal storage technology in peaking of the combined heat and power(CHP) plants and rene-wable energy generation,the single-tank thermocline thermal energy storage(TES) mathematical models with different transfer structure of TES material are designed.The numerical approach is verified by the corresponding single charge experiment.To discuss the TES performance of the single-tank thermocline TES system,the process including discharge,dissipation,cyclic operation and simultaneous charge and discharge are investigated by numerical simulation.The results indicate that the discharge efficiency of the high temperature is slightly higher than that of the low temperature under the condition of the same cut-off temperature factor and actual heat output.Under the influence of the initial position and thickness of thermocline,the relative growth rate and the growth rate of the thermocline varies during the dissipation.Combined with the practical application of the TES system in CHP,the temperature distribution inside the tank during the simultaneous charge and discharge process is presented.During the cyclic operation,as the number of cycles increases,the thermocline thickness increases continuously.And the effective utilization rate of the thermal storage tank is continuously reduced.In order to study the thermal performance of the packed-bed oil thermocline thermal storage system used in the high temperature thermal storage,factors including accumulation mode、charge/discharge outlet temperature、charge/discharge power and thermocline thickness are analyzed.The results indicated that when operating at the same discharge power,the TES system with small porosity has longer discharge time and small drop speed of discharge outlet temperature and discharge power.During stable simultaneous charge/discharge,the thermal exchange power of conventional TES system is small,so the charge outlet temperature raises slowly.When the heat transfer medium structure of TES is the same,the smaller the net heat storage heat flux,the longer the heat storage outlet is stable.The conventional TES tank thermocline thickness is much smaller than the packed-bed TES tank thermocline thickness when operating at the same net charge flow rate.The periodic charge process in the form of a square wave of thermal source is presented to discuss the unstable simultaneous charge/discharge thermal performance.Due to the influence of periodic superposition,the discharge outlet temperature and thermocline thickness increase after each cycle,and the discharge outlet temperature and the discharge power fluctuate periodically.The research results have guiding significance for the application of single-tank thermocline TES in the CHP plants and renewable energy generation. |
