Transient analysis of thermal stratification in chilled water storage tanks

A numerical analysis of thermal stratification in cylindrical chilled water storage tanks is presented. Transient, axisymmetric, natural convection phenomenon is studied using a finite volume based computational code for aspect ratios ranging from 1.5 to 3 and Rayleigh numbers ranging from 109 to 1012. In static mode, the fully charged and the partially charged cases are considered using a conjugate heat transfer model. The transient temperature profiles in the bulk fluid of partially charged tanks reveal increased stratification decay with increasing aspect ratio. In the fully charged storage tanks, on the other hand, higher aspect ratios promote stratification. A Mix Number is defined to represent the decay of stratification in the tank. The results for the partially charged tanks indicate that the convective heat transfer from the ambient to the tank exerts greater influence on the values of Mix Number than the conduction across the thermocline. While the stratification decay is the least for 1/2 charged tank, the tank charged to 3/4 capacity by cold fluid showed less stratification decay compared to that charged to 1/4 only.