Optimum Dimensions of an Obstacle Placed in a Hot Water Tank for Thermal Stratification

Abstract

Dimension of an obstacle placed in a hot water tank for thermal stratification is optimized numerically. Numerical method is validated using both experimental and numerical results. A cylindrical tank used to store heat for solar collector applications is considered. A cylindrical obstacle with a hole in the middle is placed in the tank and various f/H and g/D ratios of the obstacle geometry are considered. Here H and D are the height and diameter of the tank, respectively, where f is the distance from the bottom surface of the tank to the cold-water inlet channel and g is the diameter of the hole in the obstacle. Temperature distribution in the tank, water temperature supplied by the tank, and temperature differences at various tank inlet and outlets are obtained for various f/H and g/D ratios. The results show that placing obstacle in the tank improves thermal stratification, and thus it increases the temperature of water supplied by the tank compared with no obstacle case and that the best thermal stratification is obtained for obstacle dimensions corresponding to g/D ratio of 0.2 and f/H ratio of 0.13. I. INTRODUCTIONPerhaps, the most commonly use of solar energy is the solar collector used for water heating. A hot water tank is used for storing part of the solar energy collected by the solar collector for later use. As soon as hot water is drawn from the tank, cold tap water flows into the tank mixing with the remaining hot water, and therefore lowering the water temperature in the tank. This is an undesirable result. In this study, a solar hot water storage tank with an obstacle placed inside is considered and the optimum obstacle dimensions are searched to minimize the mixing of hot and cold water so that water may be supplied at higher temperatures.Thermal energy storage methods, thermal stratification and heat transfer in sensible heat storage and thermodynamic optimization of thermal energy storage systems are given in detail by Dincer andRosen (2002) andDincer (1999). Dincer and Dost (1997) investigated the selection of sensible and latent heat storage techniques in solar energy applications. They explained that water, sand, rock, and phase change materials could

Optimization of the coefficient of performance of a heat pump with an integrated storage tank – A computational fluid dynamics study

“…Other researchers investigated the effect of obstacles placed inside the tank on thermal stratification and concluded that the presence of an obstacle enhanced stratification. An optimal position for an obstacle was found to be 20-30 cm from the tank inlet (Arslan et al, 2006;Erdemir and Altuntop, 2016). In addition, some suggested that the obstacle types having a gap in the center appeared to cause better thermal stratification than those having a gap near the tank wall (Altuntop et al, 2005).…”