Experimental Determination of the Influence of Shape on the Heat Transfer Process in a Crushed Granite Storage Bed

Magdalena Nemś
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Magdalena Nemś: Department of Thermodynamics and Renewable Energy Sources, Faculty of Mechanical and Power Engineering, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland

Energies, 2020, vol. 13, issue 24, 1-16

Abstract: The article presents the problem of modelling the charging of a constant-phase bed storage in the first hours of the process. The places of errors in the heat transfer calculations for the packed beds were indicated. Granite in the shape of spheres and crushed rocks, with a characteristic dimension of 50 mm, was used for the experimental tests. The material was subjected to tomographic examination and then used as a storage material. The charging process was carried out for three flow rates: 0.006, 0.008 and 0.010 m 3 /s. After three hours of testing, the temperature of the outlet air for the granite sphere as the storage material was the same as for the granite crushed rock. However, the biggest differences occurred after 1 h of charging. They were equal to: 40.4% for the flow rate of 0.006 m 3 /s, 22.0% for the flow rate of 0.008 m 3 /s, and 18.5% for the flow rate of 0.010 m 3 /s. The differences were greater than the uncertainty of the measurements. As a result, different temperatures of the storage material were obtained. After three hours, they were equal to: 25.2%, 12.3% and 8.6% for the lowest, medium, and highest airflow, respectively. The conducted heat transfer analysis and the relationship Nu = f ( Re ) was determined. The influence of the calculated and actual surface of the crushed rock on the heat exchange process was explained. For all the tested air flow rates through the bed, higher thermal parameters were obtained for the crushed rock than for the sphere. The maximum differences in the Nu number were: 222.6%, 151.4% and 161.3% for the flow of 0.006, 0.008 and 0.010 m 3 /s, respectively. This means that the description of the heat exchange process in the piled beds would require a parameter that takes into account the geometry of the storage material.

Keywords: heat storage; sensible heat; heat transfer; rock bed storage; rock shape (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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