2C40.50 - Laminar and Turbulent Flow Demos

Code Number:
2C40.50
Demo Title:
Laminar and Turbulent Flow Demos
Condition:
Fair
Principle:
Flow Rates of Liquids, Viscosities
Area of Study:
Heat & Fluids
Equipment:
5 Gallon Bucket with Holes in Bottom, Stainless Steel Tubes with Stoppers, Meter Stick, Stop Watch, Large Plastic Beakers, Graduated Cylinders, Large Plexiglas Splash Tank, Tube Assembly (Two Tubes Whose Ratio of Diameters is 1 to 2), Rheoscopic Fluid, Fish Tank and Fluorescein Dyed Water, Funnel and Tygon Tube with Eyedropper Nozzle, Pinpoint Light Source with Power Supply, Dewar Flask, Insulated Gloves, and Fish Tank Accessory Mount for Nozzle.
Procedure:

A very visual demonstration of laminar or turbulent flow can be done using the pin point light source and the lighters.  Place the light about 10 feet from the screen and turn it on.  With the lighter about 2 or 3 feet from the screen, turn it on and see the shadow on the screen that is created by the different indexes of refraction in the heated air.  Observe the regions of laminar and turbulent flow.

Basically this method uses changes in refractive index to cast a shadow on the screen of the laminar and turbulent flow regions.  Shine the pinpoint light source through the tank, at the nozzle and onto a screen behind the tank.  Pointing the light upward through the tank will allow you to see the shadowgraph above tank height on the screen.  A piece of masking tape along the top water level of the tank will eliminate the internal reflection from the top surface.  The height difference between the funnel and the nozzle determines flow velocity.  Using water that is hotter or colder than the tank water temperature determines whether the turbulent regions flow upward or sink.  The Dewar is for carrying the hot or cold water.  A VERY DRAMATIC DEMO!!

Laminar Flow: Insert the desired tubes into the 5 gallon bucket.  Fill the bucket to a measure water height.  While timing with a stopwatch unplug the ends of the tubes and catch the water from each tube in a separate graduated cylinder.  At a desired time interval remove the graduated cylinders from each tube and measure the amount of water in each.  The results from one of these experiments is enclosed with the calculations and a calculation of the errors as they deviate from theoretical.

Set the splash tank on the lecture bench with the drain hole over the lecture bench sink.  Raise the tubes to a height where the water flow drops straight down when set at a certain flow rate.  As the diameters of the tubes are a ratio of 1 to 2, the distance each water jet falls from the end of the tubes should be in a ratio of 1 to 4 (Increase the diameter by 2 and increase the flow rate by 4).

The Rheoscopic fluid will very easily show planes of shear fluid dynamics.  Hand soap that has glycerol stearate in it will also show nice flow patterns when mixed with water.  Glycerol di-stearate does not work as well.

References:
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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.