Comparison of Experimental and Simulation Studies on Thermal Stratification in a Thermal Energy Storage System
Keywords:
Thermal energy storage, Sensible heat storage, thermal stratification, CFD, ANSYS-CFX, Influencing factors, Tank design.Abstract
Renewable energy supplies are steadily gaining increasing importance in all the countries. In particular, solar energy being non-polluting, clean and inexhaustible has received wide attention among scientists and engineers. Though there are many advantages, an important factor is that solar energy is time dependent energy source with an intermittent character. Hence some form of thermal energy storage is necessary for the most effective utilization of this energy source. Most of the thermal energy storage systems in use rely on the specific heat or sensible heat of the storage material, such as water, oil and rock beds and they are known as sensible heat storage systems. Thermal performance of sensible heat storage systems mainly depends on the thermal stratification. Thermal stratification in solar tanks is essential for a better performance of energy systems where these tanks are integrated. The objective of this paper is to study the thermal stratification of energy storage tanks, by means of experiments and computer simulations. The current study is proposed in order to quantify the thermal stratification inside the storage. A special attention is given to the validation of the model considered in this study by using a commercial CFD tool ANSYS WORKBENCH-CFX. Good thermal stratification is vital in order to achieve high thermal performance on solar thermal storages where the tank design is one of the most important elements to accomplish it. As it is known, the best tank design depends on several factors such as the system typology and storage size. In this paper an attempt is made to quantify thermal stratification by considering two such influencing parameters with the help of experiments and computer simulations. With this work, it is possible to conclude what are the important design parameters to build up and best preserve thermal stratification in a solar energy storage tank.
References
2. Shyu, R.J., J.Y. Lin, and L.J. Fang, “Thermal analysis of stratified storage tanks”. ASME J. Solar Energy Eng. 111, 54-61.
3. Lavan, Z. and Y. Thompson, “Experimental study of thermally stratified hot water storage tanks”. Solar Energy 19, 519-524.
4. Cole R.L. and Bellinger F.O., “Thermally stratified tanks”, ASHRAE Transactions 88, 1005-1017.
5. Ismail, K.A.R., Leal, J.F.B., Zanardi, M.A., “Models of Liquid Storage Tanks”, International Journal of Energy Research 22, 805-815.
6. Hahne, E. and Y. Chen, “Numerical study of flow and heat transfer characteristics in hot water stores”, Solar Energy 64, 9-18.
7. Nelson, J.E.B., Balakrishnan, A.R. and Murthy, “Experiments on Stratified Chilled Water Tanks”, International Journal of Refrigeration, Vol. 22, 216-234.
8. Lightstone, M.F., Raithby G.D., and Hollands K.G.T., “Numerical simulation of the charging of liquid storage
tanks: comparison with experiment”, Journal of Solar Energy Engineering 111, 225-231.
9. G. Naga Malleswara Rao, K. Hema Chandra Reddy, “ Effect of Operating Parameters on Thermal Stratification in Sensible Heat Storage Systems- A Simulation Study”, International Journal of Advances in Science and Technology. Volume 1, Number 5, December 2010-11.
10. Robert Huhn, “Correlation of Design, Material, “Flow conditions and the thermodynamic losses in hot water storage tanks”, 10th International Symposium on District Heating and Cool, 3-5 September 2006.
11. G. Naga Malleswara Rao, K. Hema Chandra Reddy, “Simulation of Energy Storage Tank with Mantle Heat Exchanger: Influence of Preheating and Mantle Fluid Entry on Heat Transfer”, Journal of The Institute of Engineers (India), Kolkata, Volume 92, July18, 2011-13.
