A NUMERICAL-EXPERIMENTAL STUDY CONCERNING ICE STORAGE TANKS Cleyton Senior Stampa Fluminense Federal University, Department of Mechanical Engineering, ZIP: 24210-240, Niterói, RJ, Brazil. E-mail: cleytonstampa@aol.com. Angela Ourívio Nieckele Pontifical Catholic University of Rio de Janeiro, Department of Mechanical Engineering, ZIP: 22453-900, Rio de Janeiro, RJ, Brazil. E-mail: nieckele@mec.puc-rio.br Sergio Leal Braga Pontifical Catholic University of Rio de Janeiro, Department of Mechanical Engineering, ZIP: 22453-900, Rio de Janeiro, RJ, Brazil. E-mail:slbraga@mec.puc-rio.br Abstract: A numerical-experimental investigation of a typical operation condition, associated with indirect, area-constrained, ice- on-pipe storage tanks is presented. The storage tank is simulated through a vertical annulus with the inner vertical wall representing one of the tubes packed into a typical storage tank. The outer vertical wall represents the maximum possible border for some ice layer growth, before it intersects another neighboring ice layer. In order to learn about the effect of loss in surface area and heat transfer rate, when two adjacent ice layers intersect during the ice making process, an experiment with a vertical annulus was carried out. Our task was to measure the temperature profile along the outer vertical wall over the time, with thermocouples positioned at specific locations and, to compare it with the correspondent numerical results. Regarding the annulus, the top and bottom walls of the cavity, as well as the outer vertical one were thermally insulated. The experiment begins with the water in the liquid phase, which is confined into the cavity, at the environment temperature. For the time greater than 0, it was imposed to the inner wall a prescribed typical cold temperature, smaller than the melting temperature of water (0°C). The mathematical model used to simulate transient natural convection of water with phase-change (solidification) was based on the finite volume method in order to solve the set of coupled conservation equations of mass, momentum and energy. It was adopted a fixed and regular grid of 140x140 nodal points and it was considered the fully-implicit time marching technique as well. Key words: Ice Storage Tanks, Annular cavity, Natural convection. 1. Introduction The present work aims to learn about the behavior of the formed solid around one vertical tube pertaining to a typical fusion latent heat storage system, such as indirect, area-constrained, ice-on-pipe storage tanks, during a process of full charging (ice making) Inside these equipments the tubes are usually positioned very close to one another and, whenever two or more ice layers intercept themselves, the thermal exchange is affected due to a reduction in the superficial heat transfer area. Other problem observed during a water solidification process is the appearance of a complex flow structure and uncommon patterns of temperature distribution in the melt, caused by the inversion density phenomenon for water around 4°C (Lin and Nansteel, 1987). This fact also affects significantly the thermal exchange between one tube of the device and its involving environment. In this sense, the shape and the growing velocity of an ice layer around and along a tube are functions of the velocity and temperature fields in the liquid region, which depend on the initial and boundary conditions to be considered. Natural convection problems considering cold water in vertical rectangular and horizontal cylindrical annular cavities, have been dominated the research studies (Lin and Nansteel, 1987; Inaba and Fukuda, 1988; Tong and Koster, 1994; Vasseur and Robbilard, 1983 and Ho and Lin, 1990). Ho and Tu (1998) carried out a numerical study on vertical annulus, regarding natural convection of cold water from a stable laminar to oscillatory regime. The result showed that under specific conditions of the density inversion parameter, the buoyancy-driven flow experienced a Hopf bifurcation into a periodic oscillation regime at critical Rayleigh numbers. Phase-change processes around a cylinder or inside cylindrical cavities are of particular interest in thermal storage devices. Those one represent an important area and studies of performance concerning energy storage systems have been the target of many works (Laouadi and Lacroix, 199; Ismail and Abugderah, 2000 and Ismail et al., 2000). The main goal of the researches related to these systems has been the determination of the higher capacity of energy accumulation per unit volume. West and Braun (1999) presented a numerical and experimental study of the partial charging and discharging processes, with icing, in tanks of ice storage. Stampa et al. (2001) have also presented a numerical study of natural convection in vertical annular cavity, considering the density inversion phenomenon of the water, however, without formation of the solid phase. In that study, the influence of the multi-cellular regime in the rate of heat transfer was investigated. In other study, Stampa et al. (2002) analyzed the growth of an ice layer around a vertical tube. In a numerical-experimental work presented by Benta et al. (2000), it was studied the solidification of water outside tubes, where the moving of the solid-liquid interface and the influence of the conditions for the secondary fluid in the process were experimentally investigated by using photographs. Abugderah and Ismail (2000) also investigated the solidification outside tubes vertically disposed within a shell and tube heat storage system. The results were concerned with temperature distribution for the whole domain, as well as phase change behavior in both axial and radial directions as a function of the Reynolds and Stefan numbers.