Helical ribbon mixers

Laminar regime (Re < 102). For stirrers with very small wall clearances, such as the anchor or helical ribbon mixer, the laminar regime prevails for Rc < 100. In this regime, the viscous force dominates. The effect of inertial forces (density) is negligible, and thus the baffles are unnecessary. In this regime,... 

Based on the above relation, for most practical operations, this reactor behaves much hke the plug-flow reactor, where ReF = pdtL/pOT, ReM = pdiNjp. Here, 0T is the average residence time. The relationship between power consumption and mixing time reveals the similarity of this vessel to the double helical-ribbon mixer. The fraction of dead space in this apparatus appears to be small. The relationships described above are valid for the fluids in the viscosity range of 50-5000 poises. 

Helical Ribbon Mixers Helical ribbon mixers (Fig. 18-44), or simply helix mixers, have major advantages over the anchor mixer, because they force strong top-to-bottom motion even with viscous... 

Helical ribbon mixers can also be formed to fit in conical bottom tanks. While not as effective at mixing as in a cylindrical tank, the conical bottom mixer can force material to the bottom discharge. By more effectively discharging, a higher yield of the product can be obtained. 

Shamlou P.A., Edwards M.F., Power consumption of helical ribbon mixers in viscous Neurtonian and non-Newtonian fluids, Chem. Eng. Sci. 40 (1985) 9,... 

As with open impellers, elastic fluids are apparently more difficult to process in helical ribbon mixers. To quantify this effect, the mixing efficiency of a highly elastic Separan solution is only 20 to 40% that of glycerol, which is Newtonian. 

For very viscous liquids the helical-ribbon mixer gives a much smaller mixing time than a turbine for the same power/unit volume (M5). For nonviscous liquids, however, it gives longer times. 

The power number for helical ribbon mixers depends on Reynolds number blade/wall clearance, e height, h pitch of the helix, p (height of one turn around the helix) blade width, w and number of helical flights, n. The relationship is... 

With very viscous mixers, the time to empty the vessel may also be an important consideration. Significant degradation may occur if fluid remains stuck to the tank walls and internals. Again, the helical ribbon mixer would be the preferred option for fixed installations. 

The second process is a continuous fluidized bed reactor. In an Idemitsu Petrochemical patent [7], a helical ribbon mixer is adopted. High power consumption and high SPS conversion are important to avoid adhesions. In this process, the polymerization heat is removed by the evaporation heat of styrene and by the jacket coolant. 

Fresh styrene and catalyst components are fed to the fluidized bed reactor (V-300). In the reactor, styrene is polymerized to SPS in the presence of catalysts. The SPS powder is fluidized in the jacketed vessel with a helical ribbon mixer. The polymerization conditions are 70 °C and 225 mmHg under nitrogen flow. Unreacted styrene is taken out from the reactor by a nitrogen flow. Polymerization heat is removed by the evaporation heat of styrene and the jacket coolant. 

Styrene is polymerized in two reactors. The first one is a self-cleaning reactor (Q-300) and the second one is a stirred tank reactor with a helical ribbon mixer (V-300) [11]. 

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