Journal of Mechanical Science and Technology 26 (5) (2012) 1523~1530 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-012-0337-3 Hydrodynamic study involving a maxblend impeller with yield stress fluids † Houari Ameur * , Mohamed Bouzit and Mustapha Helmaoui Faculté de Génie Mécanique, USTO-MB, 1505 El M’nouar, Oran, Algérie (Manuscript Received August 11, 2011; Revised January 1, 2012; Accepted January 20, 2012) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract In the present study, the hydrodynamic characteristics of the Maxblend impeller have been investigated. A commercial CFD package (CFX 12.0) was used to solve the 3D hydrodynamics and to characterize the flow patterns at every point. A shear thinning fluid with yield stress was modeled in the laminar regime and transition regime. The study focused on the effect of fluid rheology, agitator speed, impeller clearance from the tank bottom and blade size on the fluid flow and power consumption. Predictions have been compared with literature data and a satisfactory agreement has been found. Keywords: Hydrodynamic; Maxblend impeller; Power consumption; Stirred vessel; Yield stress fluid ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Mechanically agitated vessels are widely used for various operations within a wide range of industries including the chemical, pharmaceutical, food and petroleum industries. They are used for liquid blending, solid–liquid mixing, gas dispersion in liquids, heat/mass transfer enhancement and chemical reaction. The general practice for the evaluation of stirred vessels has been done over the years through the experimental investiga- tion for a number of different impellers, vessel geometries, and fluid rheology. Such an approach is usually costly and sometimes is not an easy task. With computational fluid dy- namics (CFD), we can examine various parameters contribut- ing to the process with less time and expense, a task otherwise difficult in experimental techniques. During the last two dec- ades, CFD has become an important tool for understanding the flow phenomena [1], developing new processes, and optimiz- ing existing processes [2]. The capability of CFD tools to forecast the mixing behavior in terms of mixing time, power consumption, flow pattern and velocity profiles is considered as a successful achievement of these methods and acceptable results have been obtained. A review of the state-of-the-art in CFD simulations of stirred vessels can be found in Ref. [3]. There is a wide range of mixing geometries available for viscous Newtonian and non-Newtonian fluids, and the selec- tion of an appropriate design for a given application is not an easy task. Several criteria may be used depending on the proc- ess requirements, such as specific power consumption, mixing time, pumping efficiency, shear rate distribution and flow field characteristics. The absence of dead zones is of foremost im- portance for good homogenization. A new impeller design called Maxblend, the geometry of which is shown in Fig. 1, is one of the most promising new generation wide impellers coming from Japan due to its good mixing performance, lower dissipation and simple geometry, which makes it easy to clean. The Maxblend impeller com- bines in a single system a paddle surmounted by a grid. The paddle was designed to generate the flow circulation and the grid to provide capacity for dispersing a second liquid, a gas or a solid. According to the manufacturer [4], the impeller’s main ad- vantages are a precise control of the mixing flow in the vessel and the generation of a relatively uniform shear contrary to open turbines, where high shears are located in the vicinity of the turbine. However, detailed information regarding the Maxblend per- formance is limited. Kouda et al. [5] and Hiruta et al. [6] have employed Maxblend in fermentation processes in aerated con- ditions showing very competitive mass transfer coefficients while keeping the broth culture very well mixed. Sumi and Kamiwano [7] have investigated some mixing characteristics of Maxblend with highly viscous fluids and compared it with multistage impellers. A numerical investigation on dispersive mixing of the Maxblend and a comparison with helical rib- bons impellers has also been carried out [8]. They concluded that in deep laminar regime, the Maxblend cannot reach an effective dispersive mixing. The Maxblend power consump- * Corresponding author. Tel.: +213 770343722 E-mail address: houari_ameur@yahoo.fr † Recommended by Associate Editor Byeong Rog Shin. © KSME & Springer 2012