Sedimentation Tanks for Treating Rainwater: CFD Simulations and PIV Experiments

Abstract

The removal of solids is the most important step when treating rainwater. The article evaluates two designs of sedimentation tanks that can be used for the continuous separation of fine particles from water: OS—standard sedimentation tanks, and OW—swirl sedimentation tanks. The tanks were studied by conducting computational fluid dynamics (CFD) modeling and particle image velocimetry (PIV) experiments. The settling process in sedimentation tank was carried out at varying operating flow rates. A tank with a modified structure was used for the tests, where water was supplied by a nozzle placed at an angle. This solution made it possible to obtain a rotational flow that transported the suspended particles towards its wall, where downward axial velocity resulted in the settling of particles. Based on the research, it was observed that the flow patterns showed inward flow at the bottom of the tank and an upward flow and the lifting of the settled particles near the hatch at the bottom. The presented experimental measurements provided detailed insight into flow patterns, and valuable calibration and verification data for further CFD modeling. Traditional PIV techniques are useful in the case of standard design, whereas CFD is invaluable for supporting this work and for investigating the design of novel sedimentation tanks.

A computational fluid dynamics study on the optimisation of a circular sedimentation tank using perforated inlet baffles

“…To calculate the settling e ciency for a speci c particle class ( ) and the total settling e ciency for a particular case ( ), equations ( 4) and ( 5) are employed, respectively. The speci c equations and their corresponding calculations are as follows: In equations ( 4) and (5), is the number of particles computed as 'trapped' after the end of tracking process for the particle class; is the total number of particles injected for the tracking process, i.e. 21,000 for the present study; is the mass fraction for the particle class.…”

Economic Efficiency of Solar and Rainwater Systems—A Case Study

“…The economic impact of the rainwater system can be positively affected by income, storage capacity, water price, age of rainwater harvesting, and total cost [32]. One of the requirements for the use of rainwater in different applications is also the removal of solids [33], which is usually provided for by the installed system and is not the subject of the presented study.…”