Abstract:

Natural rocks are cryogenic energy storage materials and exhibit a wide suitable temperature range, low cost, and easy availability. Their thermophysical properties and cycle stabilities in cryogenic temperature regions are key factors that affect the performance of the cold storage units. An experimental bench of automatic charge and discharge was designed and constructed to explore the effects of the charge-discharge cold cycles on the properties of the cryogenic energy storage materials. The effects of 1000 charge-discharge cold cycles on the thermophysical properties and strengths of four types of natural rocks (i.e., marble, granite, limestone, and basalt) are studied. Results show that the appearance of marble, basalt, and limestone before and after the charge-discharge cold cycles remains unchanged. However, granite shows some cracks and peelings. The density, thermal conductivity, and specific heat of the rocks were not significantly affected after 1,000 charge-discharge cold cycles. The compressive strengths of marble and basalt are unchanged, and the compressive strengths of granite and limestone are observed to significantly improve. Based on the experimental results, the relations between the thermal conductivity and specific heat of four rock materials and the temperatures in the cryogenic interval from cryogenic to normal temperatures were obtained. Comparative analysis shows that the volume energy storage densities of the four types of rock exhibit a considerable difference. Limestone has the largest volume energy storage density, whereas granite has the smallest volume energy storage density. This research will provide important basic data for developing cryogenic energy storage units and systems.

Key words: packed bed, cryogenic cold storage, charge-discharge cycle, thermal physical properties, energy storage