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Fig.1 Effect of inlet distance under different pressures on the heat transfer coefficient between air and packed beds
Fig. 2 Variation of average heat transfer Nu with Re of air-packed bed
The Institute of Engineering Thermophysics of the Chinese Academy of Sciences proposed and possesses a completely independent intellectual property right of the supercritical compressed air energy storage technology, which has the advantages of high efficiency, high energy density, etc., and solves the problem of the traditional compressed air energy storage system being restricted by geographical conditions and the need to consume fossils. Fuel and other issues. Different from the traditional compressed air energy storage system, one of the key features of the supercritical compressed air energy storage system is that the system uses a high-pressure cold storage heat storage device to recover and reuse compressed heat and low-temperature cold energy, thereby significantly improving the system efficiency.
When energy is stored, the supercritical air absorbs the low-temperature cold energy of the cold storage medium and then turns into high-pressure liquid air, which is then reduced to normal pressure for storage. When the energy is released, the high-pressure liquid air is converted into supercritical air after being cooled by the cold storage medium. Drive the expander to generate power. Therefore, there are a lot of flow and heat transfer under the supercritical pressure inside the narrow pores in the packed-bed cold storage and thermal storage device, as well as complex processes and phenomena such as “quasi-boiling†and “quasi-condensationâ€.
As the key parameters of heat storage process and heat storage performance, the inter-phase heat transfer coefficient between the heat transfer fluid and the heat storage medium undoubtedly becomes the focus of the entire design process of the cold storage and heat storage device. Due to the special nature of air in the supercritical state, it has a significantly different heat transfer law under atmospheric conditions. However, at present, there have been no reports of research in this area. Researchers are required to conduct independent exploration.
Recently, researchers from the Engineering Thermophysics Storage and R&D Center relying on the Zhongguancun Supercritical Air Energy Storage Foundation Test Platform have conducted experimental studies on the inter-phase heat transfer coefficient between air and packed bed at supercritical pressure and its influencing factors, and obtained working pressure. The influence of factors such as mass flow, inlet distance and other factors on the heat transfer coefficient between phases was analyzed. The internal flow and heat transfer mechanism of pores caused by the change of pressure flow velocity was analyzed.
The research results show that with the increase of pressure, the natural convection and heat transfer of the air inside the packed bed are significantly enhanced, so that the radial temperature gradient inside the packed bed tends to be gentle during the heat storage process, and the inlet effect of the heat transfer process is weakened; Under the condition of low Reynolds number, the average Nu number under normal pressure and supercritical pressure is more consistent with experimental correlations of Chandra and Willits (1981) and Yang (2012). The study of the supercritical energy of compressed air energy storage system Guiding significance.
The above work was supported by the National Natural Science Foundation of China and the National High-Tech Research and Development Program ("863" Program). Research results have been published in the International Journal of the International Journal of Heat and Mass Transfer (2014, 77:883–890).
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