GRISON results

[Fran Poodry]

I was inspired by the assignment I've given my Physics 2 students: to do
"one evening's internet research" on a topic relating to fluids.  In
particular, as I did one evening of research looking for things for THEM to
research, I came across "degree MacMichael" which is apparently a unit of
viscosity used in the food industry to describe liquid chocolate, and
whether it is appropriate for spray-coating, drip-coating, dunk-coating,
etc.
There are a number of viscosimeters (viscometers) available for purchase
from various places, each named for its inventor, apparently, and using many
different methods.  The "falling sphere" type generally requires a
transparent fluid, however there are also rotating-disk viscometers and cone
viscometers, among others.
It is true that the viscosities of non-Newtonian fluids are interesting to
measure.  In addition to thixotropic and plastic fluids, there are
rhoepectic, pseudo-plastic, and dilatant fluids, each exhibiting their own
characteristic viscosity/shear rate curve.  Shear is sideways force.  For
example, sour cream tends to be fairly glommy (a very scientific term) until
you start stirring it, and then it loosens up.  A cornstarch and water
mixture can be rolled into a ball, and then "melt" into a puddle on your
hand.  Paint flows easily when stirred or pushed around by paint bristles,
but then stiffens up so as not to flow down the wall you've put it on.
The units of viscosity for Newtonian fluids (viscosity does not change with
shear rate) are measured in Pascal-seconds (SI) or centipoise (1/100 Poise)
(pronounced "Pwaz") (named after the French physician Poiseuille who first
developed a theory of viscosity related to blood flow in arteries) by
physicists.
BTW, an intriguing story about something really viscous can be found at
http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml
(those crazy Australians!)

Now you know more than you ever wanted to about viscosity!
-Fran


On 11/7/05 7:07 PM, "eLLioTT morEton" <emoreton at alum.swarthmore.edu> wrote:

> grison (n.) (rheology) -- A unit of viscosity used to describe
> shear-thinning or thixotropic fluids in the food processing industry such
> as ketchup or salad dressing.  See also: Grison viscosimeter, degree
> Grison. Typical values for ketchup are in the range of 40-60 Grison, while
> Bleu cheese dressing can vary from 25 to 70 Grison.  Note that some
> ketchups are "plastic" fluids and their viscosities must be measured using
> a different method.  [Named for Eduardo L. Grison, who invented several
> devices for measuring the viscosity of food liquids while working for
> Analytical Food Laboratories 1979-1983.]
> 
> By FRAN.  2 points + 1 for correct guess = 3 points.
> Hutch:  I don't think that something this new ('79-'83) could have
> made it into Neddie this quickly.
> Jean-Joseph:  Interesting name this fellow has, kind of
> inconsistent in ethnicity, though that does happen (anybosy remember Juan
> Epstein?).  I guess I have to wonder why the units of viscosity (whatever
> they may be) that are used for other liquids (motor oil?) would not
> suffice for food as well.  "Thixotropic" is a real word, and it does refer
> to substances whose viscosities change with shear, but I usually think of
> things that go the other way, that become more viscous with shear.  I
> think I might have been aware of common food products having non-Newtonian
> fluid properties, but maybe not.  No points, though.
> Pierre:  This sounds more like Rowlett's dictionary than Oxford's.
> Two points and the tog award.