An LDA study of the turbulent flow field in a baffled vessel agitated by an axial, down‐pumping hydrofoil impeller

Abstract

The turbulent flow of water in a cylindrical, baffled vessel with an axial flow hydrofoil impeller, either a Chemineer HE3 (CHE3) or a Prochem Maxflo T (PMT), has been studied using a laser Doppler anemometer. Using ensemble averaging, the mean axial and radial flow and the associated fluctuating components were obtained for the whole of the vessel; plus similar data for the tangential component close to the impeller. Assuming axial symmetry, flow rates were calculated as were flow numbers and circulation flow numbers. Power numbers were also determined. AU the data obtained were used to compare the circulation efficiency of the two hydrofoils plus a pitched blade and a Rushton turbine. This comparison showed that the CHE3 required a power input of about 2/3 of that for the PMT and about 113 of that for the pitched blade and Rushton turbine to obtain the same axial-radial circulation in the tank. On a 6tudiC B I'aide d'un anCmomttre laser Doppler l'ckoulement d'eau turbulent dans un rCservoir cylindrique B chicanes muni d'une cine B patin (hydrofoil) B hulement axial, soit une "Chemineer HE3" (CHE3) ou une "Prochem Maxflo T" (PMT). A l'aide de technique de calcul de moyennes, l'koulement moyen radial et axial et les composantes fluctuantes associks ont 6th obtenus dans tout le rkservoir; des donnks semblables ont Cgalement Cd obtenues pour la composante tangentielle proche de la turbine. En supposant une symktrie axiale, les debits ont Cd calculds tout comme les nombres d'hulement et les nombres de circulation. Les nombres de puissances ont Cgalement Ctd dCterminh. Toutes les donnks obtenues ont 6d utilisks pour comparer I'eficacitC de la circulation des deux turbines B patin ainsi que celle d'une turbine B pale inclink et d'une turbine Rushton. Cette comparaison montre que le CHE3 requiert une alimentation en puissance d'environ 2/3 de celle du PMT et d'environ 113 de la puissance requise pour la pale inclink ou la turbine Rushton, et ce pour la m2me circulation axiale-radiale dans le rtservoir.

Estimation of a characteristic friction velocity in stirred benthic chambers

“…(10) is very similar to a relationship previously reported by Jaworski et al (1991) and Vrábel et al (2000) for axial-flow impellers:…”

Flow Instabilities in Mechanically Agitated Stirred Vessels

“…In particular the discharge angle varied from 7.5° with respect to the horizontal plane for C = T/4 down to 2.5° for C = T/2. Jaworski et al (1991) circulation from the vessel axis towards the walls. For the higher clearance the impeller stream turned upwards before reaching the base of the vessel, generating also a reverse flow directed radially from the walls towards the vessel axis at the base of the vessel.…”

Trailing vortices around a 45° pitched‐blade impeller

“…The results presented indicated that the flow is directed upward over the outer part of the impeller, but, as Kresta and Wood (1993a) point out, this was due to an error in Ranade and Joshi's labeling of coordinates in the article. The bulk-flow patterns with 45" PBTs were reported to be different for low and high off-bottom clearances by Jaworski et al (1991) for six-blade and Kresta and Wood (1993a) for four-blade turbines. Hockey and Nouri (1996) employed a six-blade 60" PBT and measured mean and rms velocities in the bulk flow and around the turbine using ensemble-averaged and angle-resolved LDA techniques, respectively, and reported a peak velocity of 0.55 Ali et al (1981) observed that only a single trailing vortex was formed at the trailing edge of a four-blade 45" PBT, while Kresta and Wood (1993a) reported that a trailing vortex extending over approximately 20% of the blade was formed at the lower tip of the blade and a smaller one at the top corner of the blade.…”