Study On The Performance Of Single-tank Ceramic Packed Bed Heat Storage System

The heat storage system can solve the intermittent and instability of energy in solar thermal power generation,the single tank packed bed heat storage system can realize the effective storage and release of heat energy,a 1 k Wβdish solar Stirling engine heat storage system is established,using albite/blast furnace slag and graphite composite,ceramic composite heat storage materials with different graphite contents were prepared,the ceramic composite material with the best comprehensive performance was used in the heat storage tank,the heat storage and release performance of the system was studied.Design single tank heat storage system,water as a single-phase fluid,the heat storage and release process of single tank heat storage system is numerically calculated,the influence of initial conditions and geometric parameters on the heat transfer and flow of the heat storage tank is analyzed,the results showed:reducing inlet velocity and heat storage temperature difference can reduce the thickness of the thermocline,improve the heat storage efficiency;increasing the aspect ratio increases the thickness of the thermocline,and the heat storage efficiency is improved,height becomes the main factor affecting efficiency;changing the initial temperature has little effect on the thickness of the thermocline;The best working conditions are₄9))=0.005 m/s,=40 K,H/D=4.3;as the heat storage and release process proceeds,the average Nu gradually decreases and then tends to be stable,it is consistent with the change trend of thermocline thickness;the average Nu of the heat storage process increases with the increase of the inlet flow rate,it decreases with the increase of heat storage temperature difference and height-diameter ratio.Albite/blast furnace slag and graphite ceramic composites were prepared,the thermal properties and compressive strength of the composites were characterized,results showed:the graphite content increases from 10%to 30%,the thermal conductivity of albite composites increased from 0.88 W/（m·K）to 3.05 W/（m·K）,The thermal diffusivity increases from 0.35 m²/s to 0.95 m²/s;the thermal conductivity of slag composites increased from 1.44 W/（m·K）to 11.34 W/（m·K）,the thermal diffusivity increases from0.45 m²/s to 2.77 m²/s;the specific heat capacity and compressive strength decreased,after adding 30%graphite,the compressive strength of the composite material is not suitable for the heat storage tank filler;two ceramic composites containing 20%graphite have good skeleton structure and dense porous structure,no chemical reaction to form new substances,suitable for single tank packed bed filler.Blast furnace slag composite material is used as the filler of heat storage tank,a single tank ceramic packed bed heat storage model is established,the study found:reducing the porosity and particle size of the composites can reduce the thickness of the thermocline,reducing the porosity and particle size of the composite material can reduce the thickness of the thermocline layer and improve the heat storage and release efficiency,after adding the filler,the thickness of the thermocline under different initial conditions can be reduced by 37.5 mm-70 mm compared with the pure water heat storage tank,the heat storage and release efficiency is increased by about 6%,through theπtheorem,the linear multiple regression method is used to analyze the influence of inlet velocity,heat storage temperature difference,tank height-diameter ratio and packing on the thickness of the thermocline of the heat storage tank,the dimensionless function relation of the thickness ratio of the thermocline is obtained;the effects of height,initial conditions,particle temperature and temperature difference between particles and hot water on the heat storage process were analyzed;the continuous cycle heat storage and release process is simulated,it is found that the temperature distribution in the tank gradually tends to be stable as the cycle progresses,the heat storage cut-off temperature and the heat release cut-off temperature have a great influence on the steady-state operation of the heat storage tank,and the inlet flow rate has little effect on the steady-state operation,When^*₍（8）=0.16,the heat release cut-off temperature is reduced from 345 K to 335 K,and the capacity utilization rate is increased by 15.5%,When^*=0.1,the heat storage cut-off temperature increases from 308 K to 324 K,and the capacity utilization rate increases by17.05%.Reasonable operation strategy is the key to improve the efficiency of single tank thermocline heat storage system,the performance of heat storage tank under different working conditions was simulated,It lays a theoretical foundation for the realization of high performance heat storage system.