Small scale model for CFD validation in DAF application

Abstract

A laboratory model is used to measure the generic flow patterns in dissolved air flotation (DAF). The Perspex model used in this study allows the use of laser Doppler velocimetry (LDV), a non-invasive, high-resolution (+/- 2 mm s-1) laser technique of flow velocity measurement. Measurement of flow velocity in the single-phase situation was first carried out. Air-saturated water was then supplied to the tank and measurements of bubble velocity in the two-phase system were made. Vertical flow re-circulation was observed in the flotation zone. In the bottom of the flotation zone (near the riser) secondary flow re-circulation was observed, but only in the two-phase system. Another phenomenon was the apparent movement of flow across the tank width, which may be due to lateral dispersion of the bubble cloud. Data from preliminary computational fluid dynamics (CFD) models were compared against this measured data in the case of the single-phase system. The CFD model incorporating a k-epsilon model of turbulence was found to give closer agreement with the measured data than the corresponding laminar flow model. The measured velocity data will be used to verify two-phase computational fluid dynamics (CFD) models of DAF.

A Two-Phase Computational Fluid Dynamics Model for Ozone Tank Design and Troubleshooting in Water Treatment

“…The model is laboratory scale allowing as much freedom as possible with regard to the types of flow measurement and visualization techniques (Hague et al, 1999). In addition to the chemical tracer technique, optical techniques included dye tracer testing, laser Doppler velocimetry (LDV), and particle imaging velocimetry (PIV).…”

“…The distribution of gas and/or water flow through this system is difficult to visualize. In the dissolved air system, air bubbles are small 10-50 µm; they tend to follow the water flow (Hague et al, 2001a(Hague et al, , 2001bTa et al, 2001). In an ozone system, the gas bubbles are larger (200-1000 µm) and they induce greater effect to the water flow.…”

Application of CFD methods to an anaerobic digester: The case of Ontinyent WWTP, Valencia, Spain

“…However, their solution to problems with complex geometries and boundary conditions required the development of efficient numerical solution techniques and the ability to implement these techniques on computers. The development of both numerical techniques and digital machines with increased computational power allowed for the wide application of CFD methods to many areas of fluid dynamics during the last few decades, including water and wastewater engineering [20,17,33,24,14,22,35,41,40,12,49,42,16,38,26,30] . Recently, CFD methods were also applied to study flows inside anaerobic digesters.…”

Avaliação da influência da distribuição de tamanho de partículas e do binômio velocidade/tempo de detenção na zona de reação no desempenho da flotação com emprego de sonda ultra-sônica e de técnica de análise por imagem

“…Alguns dos trabalhos BECKLEY;EADES, 2001;HAGUE, et al, 2001) apresentam resultados extraídos de modelos de dinâmica computacional dos fluídos (CFD). Outros, tais como: Ayman et al (1998), Leppinen, Dalziel Linden (2000) e Lundh, Jönsson e Dahlquist (2001, apresentam resultados de investigações em unidades de laboratório e em escala piloto.…”