Niedzielska and Kuncewicz [6] discussed experimental in- vestigations and model calculations of power consumption and heat transfer coefficients from a vessel wall to mixed liquid for ribbon impellers operating in a laminar regime. Kuncewicz et al. [7] studied the liquid flow in a tank equipped with a screw impeller operating in the laminar regime. They used a two-dimensional model describing the liquid flow to determine the velocity fields, the fluid used here is Newtonian.

By CFD method, Iranshahi et al. [8] compared the viscous mixing characteristics of the Ekato Paravisc with those of an anchor and a double helical ribbon. They found that the Paravisc mixer characteristics lie between that of the other impellers at low Reynolds number.

Delaplace et al. [9] developed an approximate analytical model to predict power consumption for the mixing of shear- thinning fluids with helical ribbon and helical screw ribbon impellers in the laminar flow regime.

Masiuk and Rakoczy [10] showed that the theory of in- formation can be used to describe the random process of mixing of granular materials in a multi-ribbon blender. A new form of the entropy criterion estimating the current state of a mixture is proposed, a mathematical model to

describe the variations of the informational entropy during

the process is developed, and the experimental validation of the model is done for the blending process duration. Anne-Archard et al. [11] investigated the hydrodynamics and power consumption in laminar stirred vessel flow using numerical computation. The Metzner-Otto correlation was established for mixing in power-law fluids. Distributions of shear rates and their link to power consumption for helical and anchor agitators are discussed. Depending on the fluid model, the concept is valid or constitutes a satisfactory approximation for fully sheared flows.

Zhang et al. [12] have simulated the three-dimensional non-Newtonian flow field generated by a double helical rib- bon (DHR) impeller. They developed three computational fluid dynamic (CFD) methods to compute the Metzner constant ks .

Maingonnat et al. [13] have studied the power consumption

of a double ribbon impeller (Ekato-Paravisc) as a function of the operating conditions and the rheological behavior of the experimental fluids.

Estelle and Lanos [14] studied rheological behavior of fluids in mixing systems using a simplified approach in shear rate calculation. The efficiency of this approach is investigated from Newtonian and non-Newtonian fluids, exploring also the geometry of mixing systems. Results are favourably compared with those obtained from previous published works. With helical ribbon, they have considered the virtual radius of the probe obtained by Roos et al. [15]. The use of the real radius leads to an error in calculated shear stress. This means that the fluid is mainly sheared at the inner periphery of the helical ribbon as the virtual radius is closed to the inner radius of this geometry.

Seyssiecq et al. [16] devoted to the triphasic in situ rheo- logical characterization of an activated sludge, with total suspended solid and operated in a bioreactor under dif- ferent stirring and aeration rates. The bioreactor is a Plexiglas vessel of diameter 0.15 m. It is equipped with a double helical ribbon impeller rotating rather close to the wall. In this work, the flow properties are directly measured inside the bioreactor.

Muzzio et al. [17] investigated the effects of processing and equipment parameters of a ribbon blender on magnesium separate homogeneity. A core sampling technique is used to obtain at least one hundred samples per sampling event, which are extracted throughout the blender and yield a thorough characterization of the entire bed.

Riveraa et al. [18] studied the macromixing mechanisms of the Super blend coaxial mixer consisting of a Maxblend impeller and a double helical ribbon agitator mounted on two independent coaxial shafts rotating at different speeds. To model the rotation of agitators a hybrid approach based on a novel finite element sliding mesh and fictitious domain method is used. The power consumption, the flow patterns,