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.

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A wide blade, high solidity ratio, axial flow hydrofoil impeller has been developed particularly for gas dispersion when used in the upward-pumping mode. It has a low power number so that a relatively low torque is required when using it with a large impeller to tank diameter ratio, a commonly desired aim of retrofitting. As part of the work characterising these impellers, laser Doppler anemometry has been used to study the single phase flow both down-and uppumping, the latter for the first time. Mean and root-mean-square velocities were measured throughout a fully baffled, flat bottomed cylindrical tank. When down-pumping, the discharge flow was almost axial but when up-pumping, it had a strong radial component. Turbulence energy dissipation rates in the impeller region and the discharge stream when uppumping were found to be higher than those when down-pumping. In both modes, the impeller was found to have a high circulation efficiency. In Part 11, the data presented here are used for obtaining computational fluid dynamic solutions of the flow field. Keywords: up-and down-pumping hydrofoils, LDA data, power, flow patterns, turbulence characteristics.or gas-liquid mixing, the main requirements of agitation F are breakage and dispersion of gas bubbles and bulk mixing of all the phases. Rushton turbines, which have traditionally been used have a number of disadvantages, e.g., a significant decrease in aerated power number as compared to a high unaerated power number, which reduces mass transfer potential due to a decrease in the volumetric mass transfer coefficient (Nienow, 1990). Also, radial flow turbines give poor top to bottom mixing in multiple impeller sy\tems, leading to a large increase in mixing time (Otomo et al., 1995). Liquid pumping and gas handling can be improved by the use of large diameter impellers but, the replacement of standard disc turbines with larger ones is not a simple retrofitting operation (Nienow, 1990). As a result, down-pumping axial hydrofoil impellers of high solidity ratio were developed for gas-liquid systems. McFarlane and Nienow ( 1995) have reviewed their performance and concluded that such impellers can be best used at high impeller to tank diameter ratios, especially to give improved bulk blending in multiple impeller configurations (Otomo et al., 1995). However, they produce rather large gassed power fluctuations and in a later review, Nienow (1996) suggested that further improvements could be made by using such hydrofoils in the up-pumping mode.*Author to whom correspondence should be addressed. E-mail address: A.W.Nienow@bham.ac.uk A new impeller design, APV-B2 (Figure 1 a), with smooth and elongated wide blades to give a solidity ratio of I has therefore been developed at The University of Birmingham where this work was conducted. It is especially for use in the up-pumping mode in gassed reactors. Ozcan-Taskin et al. (1995,1996 reported its gassed power characteristics alongside those of two down-pumping impellers, namely the high solidity ratio Lightnin' A-3 15 and a p...

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