Thermal performance of single-pipe diffusers in stratified chilled water storage tanks

Field data from the constant flow rate charging of a stratified chilled water storage tank with double-ring octagonal slotted-pipe diffusers serving a university chilled water system were analyzed. A transient axisymmetric computational fluid dynamics (CFD) model of flow near the lower inlet diffuser was constructed. The simulations were performed using a commercially available software package.; The CFD model was validated by modeling charge processes at flows from 50% to 95% of design. The performance of the CFD model was assessed by direct comparison of temperature profiles and by comparison of common thermal performance metrics. The inlet Richardson number based on the slot hydraulic radius was found to have the strongest effect on model results.; Statistical factorial experimental theory was applied to construct a 2k parametric study on identified dimensionless parameters relevant to the development of thermal stratification. Each identified dimensionless parameter assumed two values representing the high and low operating conditions. The inlet Richardson number based on the slot hydraulic radius and two geometric parameters were found to be of first order significance on the stratification. Linear regression models were developed to predict these effects. The results of the present study allow further assessment of current guidance for the design of lower slotted pipe diffusers.