Tideflex Mixing Systems for water reservoirs: AwwaRF Scale Modeling
Red Valve partnered with the Georgia Institute of Technology on a 2006 AWWA Research Foundation project entitled “Physical Modeling of Mixing in Water Storage Tanks”.
The research consisted of physical scale model experiments of circular reservoirs, rectangular reservoirs, and standpipes utilizing Three-Dimensional Laser-Induced Fluorescense (3DLIF).
Figure 1 shows a schematic and photo of the test setup (click to see larger image). Florescent dye is injected into the inflow during tank filling. A laser sheet is scanned thru the model at 40 frames per second. A digital camera is placed perpendicular to the laser sheets and it captures the fluoresced dye which is directional proportional to concentration. There are timing and data acquisition computers that synchronize the snapshots as the laser sheet scans thru the model and each snapshot is captured. Prior scale modeling techniques used conductivity probes that only provided a limited number of data points. With 3DLIF, the entire flow field is captured and literally millions of data points.
Baseline experiments were run with a single inlet pipe for each tank style. Then, many models were run with varying multiport configurations. The goals of the research were to determine:
1) if multiple ports result in faster mixing,
2) the effect of high and low momentum on mixing,
3) the effect density differences (temperature differences) between inlet water and tank water have on mixing.
The following is a brief listing of results:
- Greater inlet momentum (flow x velocity) results in faster mixing, as expected,
- Standpipes (water depth greater than diameter) take longer to mix than ground level circular reservoirs,
- Multiple ports result in faster mixing, up to 50% faster than a single inlet but is heavily dependent on the manifold configuration and tank style,
- With positive and negative density (buoyancy) conditions, circulation and mixing patterns change drastically and can lead to incomplete mixing with a single inlet, even when the isothermal case achieved complete mixing,
- Multiple ports were able to completely mix tanks, depending on manifold configuration and tank style, with density differences when a single inlet resulted in incomplete mixing and stratification,
- Tanks that simultaneously fill and draw tank longer to mix than fill-then-draw tanks.
Independent scale modeling has been done comparing single inlet/outlet designs to the mutliport Tideflex Mixing System (TMS). Those studies also validated the improved mixing of the TMS.
Based on the extensive scale modeling completed with the AwwaRF project, and the extensive CFD modeling that we have conducted, Red Valve designs TMS manifold configurations for all tank styles that were identified to produce the fastest mixing. The TMS has been field validated in every tank style with sampling and monitoring studies conducted by water utilities.
Tank inlets - see examples of water mixing and stratification in:
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