The volumetric coefficient of heat transfer and the energy storage capacity in a direct contact thermal energy storage system using Na(2)CO(3)(.)10H(2)O Solution as thermal energy storage medium have been investigated. Hot kerosene was used as a heat transfer fluid. The experiments were carried out by bubbling hot kerosene from the bottom of a column containing Na(2)CO(3)(.)10H(2)O solution. The column used in this experiment was made from glass of 3 mm in thickness with the inside diameter of 7 cm and 100 cm in height. The effects of kerosene flow rate and kerosene bubble diameter to the volumetric coefficient of heat transfer and the storing rate of energy have been studied. The volumetric coefficient of heat transfer was strongly affected by the flow rate of the kerosene. The effect of the kerosene flow rate on the storing rate of energy was relatively high, while the effect of the bubble diameter was small. (C) 2004 Elsevier Ltd. All rights reserved.