Experimental Study On Thermal Storage And Heat Transfer Characteristics Of Supercritical Air Flowing Through Packed Bed

Compressed air energy storage (CAES) is a new type of large-scale storage for energy in the form of compressed air, when hours at low electric power, compressor compresses air into the underground caves or abandoned mine; when the electric power demand increases, the high pressure air is released and mixed with the fuel, then ignites in the chamber. The high temperature gas was used to drive gas turbine and the generator to generate electricity. Because of the disadvantages of energy storage density is low, the need of large caves and the fossil fuel combustion, it is restricted in application.Packed bed is a widely used as sensible heat storage device, it is considered to be one of the ideal CAES system with heat regenerator; it’s also used as the reactor and regenerator in chemical industry. In recent years, it has been widely used in solar thermal storage and Industrial heat recovery.It has the advantages of large heat transfer area, good heat transfer performance and safe and reliable.In this paper, a supercritical air energy storage system is studied; it takes advantage of the special properties of air in the supercritical state, solving the main problem faced by the compressed air energy storage. In the experiment, the supercritical compressed air is used as the heat transfer fluid, packed bed filled with rock is used as the heat reservoir, the regenerative efficiency and the inside heat transfer characteristics are studied. In the experiment, a15kW of packed bed thermal storage experiment platform is built, the main parts include:air compressor, electrical heater, high pressure packed bed, temperature sensors and a data acquisition system. In order to prevent the packed bed as well as the pipeline heat loss, rock wool insulation layer is used.After lots of different experiments in thermal energy storage and heat transfer of packed-bed, the following conclusions are obtained:for thermal energy regenerative experiment, thermal efficiency increases with the increase of mass flow rate and heat storage temperature, decreases with the increase of pressure. Changes of thermal efficiency and exergy efficiency is consistent, average wall temperature is higher, heat loss is bigger, efficiency is lower; for the internal heat transfer experiment, stones and super critical air convective heat transfer coefficient is calculated, the density, specific heat capacity, equivalent diameter, emphatically of the stone are measured. The entrance effect and the effect Re number on the Nu number are discussed, the result shows that, In the condition of the mass flow rate is the same, the entrance effect decreased with the increase of pressure, when the Re number increases, the convection heat transfer coefficient hp increases, which leads to the increase of the Nu number, so to increase air flow in a certain range, can enhance heat transfer within the packed bed convection and reduce the packed bed entrance effect.