Estimation of volumetric heat transfer coefficient in randomly packed beds of uniform sized spheres with water as working medium

The advent of technology and development has led to a surge in energy demands by both developing and developed nations. Since 2000, the energy usage pattern in India has doubled. The majority of the power sector is dependent on the fossil fuel sources for energy generation. While energy generation is of prime concern the storage and retrieval with minimum losses is also significant. The packed beds system form a significant part of the solar power systems which are used to store energy during day time and retrieve it during the night. The present work investigates on the issues related to energy storage capability in packed beds. In the present work, volumetric heat transfer coefficient is measured using a transient technique in packed beds with uniformly sized spheres. The experiments are conducted for bed to particle diameter ratios of 5, 10 and 21. The temperatures inside the packed bed are measured at four axial locations with thermocouples placed inside the spheres and positioned 112 mm apart along the central axis. The temperatures are measured at four radial locations 5, 10, 15 and 20 mm apart from the solid wall along different axial planes from the entry of packing. The experimental results are compared with Schumann's curves and the volumetric heat transfer coefficient is estimated. It is found that the estimated volumetric heat transfer coefficient (h(v)) is higher for smaller particle diameter 2.38 mm as compared to larger diameter spheres with random packing. There is an increase in the volumetric heat transfer coefficient (h(v)) with the increase in the particle Reynolds number. (C) 2016 Elsevier Masson SAS. All rights reserved.