A small glass tube containing oil and glass pebbles is constructed to evaluate rapidly the volumetric heat transfer characteristics during charging. An electrical hot-plate in thermal contact with a steel spiral coil is used to charge the oil/pebble-bed storage under different average charging flow rates. The heat transfer characteristics are presented in terms of the average temperature of the oil, the average temperature of the pebbles, the average charging power and the volumetric heat transfer coefficient. The results reveal that an increase in the average charging flow rate results in a linear increase in the volumetric heat transfer coefficient. An expression for the correlation between the superficial mass flow velocity, the average pebble diameter and the volumetric heat transfer coefficient is also formulated. (C) 2009 Elsevier Ltd. All rights reserved.