Non-Newtonian system

Dodge, D.W. and Metzner, A.B., Turbulent flow of non-Newtonian systems, AIChE Journal, 5, pp. 189-204 (1959). 

Non-Newtonian Systems. Although the determination of the required properties is straightforward for liquids, the situation is much more complex for non-Newtonian systems such as gels, emulsions, and slurries. As indicated earlier, there is a significant effort under way to prepare slurries of solids in liquid fuels to increase the volumetric energy of such fuels. These slurries must be stabilized as gels or emulsions to prevent solid separation. It therefore seems worthwhile to discuss the preparation of such slurries as well as the techniques used to measure some of the properties required to characterize these systems. 

The distinguishing feature of non-Newtonian systems is seen to be that the colloidal rather than the molecular properties are of significance. Philippoff (P4) has summarized the properties of the colloidal particles which are relevant in determining their rheological behavior as follows ... 

The completely general case is that of a fluid for which the relationship between shear stress and rate of shear is not linear and may also depend on both the duration of the shear and the extent of the deformation produced. Thus it is possible to divide non-Newtonian systems into three broad categories ... 

It has been pointed out by Weltmann (W4) that the complexity of some non-Newtonian systems leads to unusual changes in fluid properties with temperature. This may occur, for example, if solids tend to go in or out of solution or if the solids are more completely dispersed at the higher temperature. Most non-Newtonian fluids, however, do not show such unusual effects, and the changes in fluid properties with temperature and concentration of material in suspension or solution may be summarized as follows. 

Solution of forced convection problems for flow in non-Newtonian systems. 

We have already devoted a considerable amount of space to our discussion of viscosity without ever venturing beyond Newtonian systems. At least as much —probably more —could be said about non-Newtonian systems. 

Dodge DW, Metzner AB (1959) Turbulent flow of non-Newtonian system AIChE J 5 189... 

In extending the work to non-Newtonian systems, a series of water-in-oil emulsions was used. These were prepared using the following formulations ... 

The non-Newtonian systems used were carboxymethylcellulose (0.5-2.0%) and polyacrylamide (0.5-1.5%) solutions. 

Fumed silica bears the properties of an effective thickener which will not undergo swelling and exhibits chemically inertness. Additionally, thickening by fumed silica results in a non Newtonian system commonly accompanied by a yield point, shear thinning and thixotropy. Thus, fumed silica solves in an excellent manner the requirements of reversible shear thinning under high shear stress but a distinct yield point or high viscosity at lower shear stresses. 

D. W. Dodge and A.B. Metzner, Turbulent flow of non-newtonian systems,... 

Idu/dxl the absolute value of the shear rate, calculated by a modification of the method of Krieger and Elrod (12) which applies to non-Newtonian systems. The apparent viscosity, p, is... 

Like any disperse system, foams produce non-Newtonian systems, and to characterize their rheological properties information must be obtained on the elasticity modulus (the modulus of compressibility and expansion), the shear modulus, yield stress and effective viscosity, and elastic recovery. 

As the power law model [Equation (20.3)] fits the experimental results for many non-Newtonian systems over two or three decades of shear rate, this model is more versatile than the Bingham model, although care should be taken when applying this model outside the range of data used to define it. In addition, the power law fluid model fails at high shear rates, whereby the viscosity must ultimately reach a constant value - that is, the value of n should approach unity. 

When a shear rate is applied to a non-Newtonian system, the resulting stress may not be achieved simultaneously. First, the molecules or particles will undergo spatial rearrangement to follow the applied flow field. Second, the stmcture of the... 

Typically this value ranges from 3.0 for Newtonian systems to up to 1000 for non-Newtonian systems. 

Deviations of liquids from Newtonian behavior are frequently observed for pharmaceutical and biomedical systems. In these, the relationship between stress and the rate of strain is nonlinear, examples of which include pseudoplastic (shear thinning), dilatant (shear thickening), plastic, and Bingham and Ostwald systems (1,17). Such systems are commonly referred to as non-Newtonian systems. 

The calculation of power follows methods described previously, using the estimated weight average density, p, in the expression for Reynolds number and power. The viscosity for a Newtonian system is best measured by using a paddle-type rotating bob viscometer. The Metzner-Otto method is commonly used to determine the Re for a non-Newtonian system, where viscosity is a function of shear rate. This method consists of determining the mean shear rate from y = KN, where N is the stirring speed in rps, K is 10 for a propeller, and y is the mean shear rate is in s. Viscosity will not influence the calculation of power when Re > 200. 

The recovery of bioactive materials from the fermentation broth is generally complicated by the fact that the bio-products are in very low concentration in these often unstable, non-newtonian systems. The downstream processing is a key area for further development of biotechnology. Membrane technologies and particularly UF,MF and RO can be considered as broad core technologies in this industrial segment (1). 

---