The internal melt ice-on-coil tank with horizontal tubes is used widely for thermal storage. Its discharge process is greatly affected by the ice-water density different. The existing models developed for internal melt ice-on-coil tanks are concentric cylinder models which are applicable to tanks with vertical tubes or when all the water in the tank is frozen, but they do not describe the effect of the ice-water density difference on discharge. This paper introduces an eccentric cylinder model developed especially for the discharge process in a tank with horizontal tubes. The model is simple and is suitable for system simulation. Experimental validation proved the reliability of the model. (C) 2001 Elsevier Science B.V. All rights reserved.