Application Note

Using Viscosity Profiles And Rheological Models To Benchmark Your Products

Source: AMETEK Brookfield
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Looking for a quick and easy way to benchmark your products and compare them to those of your competitors? Well, a single point viscosity test is a start. But, for a shear-thinning fluid it doesn't give you the whole picture, i.e. how the viscosities of products compare over a range of spindle speeds or shear rates. This Application Note will explain how to use a single point viscosity test to benchmark your food products.

Often two products that give similar single-point viscosity readings - say 1200 mPa.s (1200 cP) with spindle 3 at 10 rpm - will exhibit differing flow properties in the "real world". If you've ever over-ruled the results of a viscosity test because the appearance of the sample contradicted what the viscometer was telling you then you'll know what I mean; the visual assessment - what it's "really" like when you swirl, pour or spoon it, for example - may impose completely different degrees of shear to the sample than those applied in the viscometer test spec. A multi-point flow curve, over a range of speeds or shear rates, will often reveal any rheological differences between products that are not immediately apparent in a single-point test.

Once we can do this we can then quantify those differences with a simple rheological model. One such is the Power Law (or Ostwald) Model. This will fit a typical viscosity vs shear rate or stress vs shear rate curve within the range of about one to a few hundred reciprocal seconds.

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