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ABSTRACT
Jet-mixing and residence time in a rectangular water storage tank with a constant water level are investigated using the tools of Computational Fluid Dynamics (CFD). A set of Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations using a realisable k-ε model for different inlet configurations has been used. Numerical simulations were validated by means of experimental measurements. A saline inflow was simulated and the computed salinity in the outflow was compared with the measured values, with the aim of improving the tank performance based only on simple modifications of the inlet position and inflow rate. The results show that the URANS technique is able to adequately capture the experimental dilution curve measured at the outlet of the tank. The residence time is mainly influenced by advective transport. Modifications of the horizontal angle and Reynolds number of the inflow jet produce changes in the mixing characteristics when different performance indexes are compared.
Acknowledgements
This work has been conducted within the framework of the research project “Línea Multidisciplinar para Aplicación de las técnicas de la Mecánica de Fluidos Computacional a la modelación de movimiento de flujos ambientales (2614)” from Vicerrectorado de Investigación, Universidat Politècnica de València, Spain.
Notation
| CFD | = | computational fluid dynamics |
| COV | = | coefficient of variation |
| CSalt | = | salt concentration (g l–1) |
| Dm | = | coefficient of molecular diffusion (m2 s–1) |
| Fd | = | densimetric Froude number |
| G | = | velocity gradient (s–1) |
| H | = | vertical dimension of the tested tank (m) |
| KIT | = | Karlsruhe Institute of Technology |
| l | = | characteristic length scale (m) |
| L | = | longitudinal dimension of the tested tank (m) |
| M | = | momentum flux of the inflowing jet (m4 s–4) |
| P | = | mixing power (W) |
| Pe | = | Peclet number (–) |
| Qin | = | inflow tank (m3 s–1) |
| RANS | = | Reynolds-average Navier-Stokes |
| RTD | = | Residence time distribution |
| Rjet | = | Reynolds number in the jet nozzle section (–) |
| Tr | = | theoretical residence time (s) |
| t | = | time (s) |
| t10 | = | 10% arrival time (s) |
| tm | = | mixing time (s) |
| URANS | = | unsteady Reynolds-average Navier-Stokes |
| U | = | characteristic velocity (m s–1) |
| Uin | = | inlet velocity (m s–1) |
| Ujet | = | jet nozzle velocity (ms−1) |
| = | mean velocity magnitude (m s–1) | |
| = | longitudinal mean velocity module (m s–1) | |
| Vt | = | volume of the tank (m3) |
| = | transverse mean velocity vector module (m s–1) | |
| = | vertical mean velocity module (m s–1) | |
| W | = | transverse dimension of the tested tank (m) |
| WDS | = | water distribution system |
| X | = | longitudinal direction of the model (m) |
| Y | = | transverse direction of the model (m) |
| y+ | = | dimensionless wall distance (–) |
| Z | = | vertical direction of the model (m) |
| Δp | = | pressure drop (Pa) |
| ϕ | = | vertical inlet angle (°) |
| µ | = | dynamic viscosity (m2 s–1) |
| θ | = | horizontal inlet angle (°) |
| θ10 | = | short-circuit index (–) |
| τ | = | dimensionless time (–) |
| τm | = | dimensionless mixing time (–) |