Parametric Study of Charging Inlet Diffuser Performance in Stratified Chilled Water Storage Tanks with Radial Diffusers: Part 2–Dimensional Analysis, Parametric Simulations and Simplified Model Development

Abstract

A parametric study of the thermal performance during charging of a full-scale radial inlet diffuser in a cylindrical stratified chilled water storage tank was performed by applying factorial experimental theory to the results of simulations performed with a validated computational fluid dynamics (CFD) model. Part 1 describes the development and validation of the CFD model. Part 2 summarizes the results of the parametric study. Dimensional storage tank and inlet diffuser parameters having the potential to influence inlet thermal performance were identified, then formed into dimensionless groups using Buckingham Pi analysis. These included the inlet Richardson number (Ri), inlet Reynolds number (Re i ), ratio of diffuser radius to tank radius (R D /R w ) and ratio of diffuser radius to diffuser inlet height (R D /h i ). Thermal performance was measured in terms of thermocline thickness and equivalent lost tank height. Sixteen simulations comprising a full 2 k factorial experiment were completed and analyzed. Parameter ranges considered were as follows: Ri from 1.0 to 11.1, Re i from 1,000 to 12,000, R D /R w from 0.2 to 0.4 and R D /h i from 5 to 10. Within these ranges, Ri, R D /R w and R D /h i were found to be of first-order significance while Re i was not. Regression models of thermal performance metrics as functions of Ri, R D /R w and R D /h i that are sufficiently simple to be useful for design were developed. These models agreed well with CFD simulations from which they were derived and with field data. INTRODUCTIONNaturally stratified chilled water storage tanks are widely used in large chilled water systems for load shifting. In a naturally stratified tank, cooler, denser water is stored beneath warmer, less dense water. The two bodies of water are prevented from mixing by buoyancy forces. A relatively thin thermal transition layer called a thermocline forms at the interface between warm and cool water.In order to create and maintain good stratification, cool water must always enter and leave a stratified tank at the bottom and warm water must enter and leave at the top. Diffusers at the top and bottom of the tank reduce inlet velocity and promote stratification. The characteristics of the diffuser have a significant effect on thermal performance because of their influence on thermocline formation.The radial parallel plate design is one of two types commonly used in cylindrical tanks. A radial diffuser consists of a plate located near a spreading surface, which is the floor of the tank in the case of a lower diffuser and the water free surface in the case of an upper diffuser ( Figure 52 HVAC&R RESEARCH 1). Inlet flow from a radial parallel plate diffuser enters a cylindrical tank as a horizontal current that flows outward radially from the perimeter of the gap formed by the diffuser disk and spreading surface. During charging, cool water enters the tank through the lower diffuser as warm water is withdrawn through the upper diffuser. During discharging, flow reverses and cool water is withdrawn through...

Parametric Study of Single-Pipe Diffusers in Stratified Chilled Water Storage Tanks (RP-1185)

“…They concluded that Re i is not of first-order importance for this diffuser type within typical full-scale tank operating parameter ranges that included Re i as large as 12,000. They also demonstrated that effects attributed to Re i could be explained to some extent by other parameters that are not represented in the current design methodology (Musser and Bahnfleth 2001b). The most significant parameters influencing radial diffuser performance were found to be Ri, R D /R W , and R D /h i , where Ri is the Richardson number, defined as in Equation 2, R D is the radius of the diffuser disk, and R W is the tank radius.…”

Προσομοίωση Τυρβωδών Ροών Φυσικής Και Μικτής Συναγωγής Σε Ηλιακά Και Ενεργειακά Συστήματα

“…Από τις κύριες κατηγορίες είναι η γεωμετρία της δεξαμενής. Μπορεί να είναι κυλινδρικής κατακόρυφου προσανατολισμού ( (Shin et al, 2004), (Musser and Bahnfleth, 2001), κ.α. ), κυλινδρικής οριζόντιου προσανατολισμού ( (Young and Baughn, 1981), (Helwa et al, 1995), (Consul et al, 2004), (Aviv et al, 2009)), ορθογωνικής (Nakos (1994), Chung et al (2008), Papanicolaou and Belessiotis (2009), κ.α.)…”