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Newton’s Law of Viscosity Demonstration
Chemical Engineering 336
Prof. Besser

1. Get the following materials:
-3 plastic cups; two empty, one half full of water
-stirrer

2. Putapproximately 1 tablespoon of cornstarch in a dry cup. Add small amounts of water with stirring to dissolve. Do not add more than it takes to dissolve or the solution will be too dilute. You will end up withthe cup approximately 1/3 full of solution.

3. Fill a second, empty cup with catsup.

4. Pour out the remainder of the water from the third cup (into the water fountain or sink), and dry itthoroughly with a paper towel. Fill it half full with glycerol.

5. Now, place the three cups side by side, clear your mind, and get your pencil out to jot down notes. Cleaning the stirrer betweenfluids, first stir a fluid very slowly, getting a sense of the force needed to stir. Then slowly increase the rate of stirring, again sensing the stirring force required. If desired, try different stirrershapes (narrow ice-cream stick, wooden ice-cream paddle/spoon, chopstick). Record your observations below. Be careful not to spill the fluids in the classroom!

Cornstarch:

Catsup:

Glycerol:Now answer the following questions. Keep the fluids handy to re-check your observations.

1. Before applying this to the experiment, think about shear rate as a concept. Describe it in words.2. What ways could you increase shear rate in the following situations:

a. In a fluid flowing in a tube:

b. In the fluid between two plates moving in opposite directions:

c. By stirringliquid in a vessel with a stirrer:

3. For case c., draw a sketch illustrating the stirrer near the wall of the vessel. Label: the fluid velocity at the vessel wall, the fluid velocity at the edge of thepaddle, and arrows indicating vector velocity between the paddle and the vessel wall.

4. Repeat the sketch of question 2.c., with two sketches this time, showing: (a) a large shear rate, and (b)...