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Understanding rheological properties – did they do it better in the Sixties??

20 September 2012 2 Comments

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Prior to coming to Malvern, I spent my time at Bristol University as a researcher looking at rheological properties of non-Newtonian fluids in microfluidic channels. Part of my role was also to give an introductory lecture course on Rheology to undergraduate students, and I clearly recall every year making up polymer solutions and getting together a series of props to try and illustrate some rheological phenomena shown by complex fluids. Rod climbing up a Black and Decker drill was always messier in practice than it looked when illustrated in rheology text books though…..

If only I had access to this video at the time – Rheological Behavior of Fluids – presented by Hershel Markovitz from the Mellon Institute (now Carnegie Mellon University), and made in 1964 by the US National Committee for Fluid Mechanics Films. For me, it’s an absolute gem, and highlights rheological properties with such clarity, using beautifully conceived and engineered demonstrations, that I really don’t think we could do any better today with all the advances in computing power and multimedia presentations at our disposal!

Beyond the first two minutes of background to Euler’s and Navier-Stokes equations, there’s twenty minutes on non-linear, non-Newtonian flow effects in fluids – with elastic snap-back, time dependence and viscoelasticity, importance of strain history, yield stress, shear thinning, shear thickening, creep and recovery, and normal stresses all covered.

A few things that I noted from the film – include the forgotten art of impeccable writing on a blackboard and the ability to draw arrow straight lines with a piece of chalk freehand! The use of the term ‘memory fluid’ tends to be uncommon nowadays, and the design of today’s rheometers has certainly changed from those early models (see from 7:30 onwards on the running time). There are also some very familiar names to rheologists on the Advisory Committee credit listing at the end of the film. A National Science Foundation grant was surely well spent on the production of this one!  Massachusetts Institute of Technology are also hosting all the printed notes that go along with the film – an excellent resource.

It’s well worth watching, and shows me some lessons that I could have picked up for my rheology lectures. Obviously one is to use a ‘50s Sunbeam Mixmaster (truly a design classic!) for the most impressive rod climbing demonstration. And maybe I should have worn a bow tie……