Other fluids education resources II – online videos

There are far too many videos out there to list here. Below is a list of some that I use in class. Obviously FYFD! has links to others. I apologize if some of the links die. I have mixed opinions about using videos in class. They can provide a break, show interesting phenomena, and surprise students, but they also are hard to directly, quantitatively re-connect to the class material, that is, they are often hard to analyze.

Shear thickening fluids – this is a fun video of people running over or settling into a paddling pool filled with water and corn starch. I used to make up a batch in a pain can for students to stir, but only very few students bothered. I think this is one case where the video is more effective for demonstrating a shear thickening fluid.

Surface tension and bouncing droplets – I know that I do not understand all the physics going on here, but my students always love watching the tiny droplets re-bound.

Momentum and jet packs (see also jet pack fail and the cheaper version) – This is one case where you can do some analysis. If you look around online (mainly on the manufacturer’s website) you can find the weight of the pack. If you add to that an estimate of the weight of the person then you can find the force required by the jet pack to keep the person airborne. The nice thing about this jetpack is that it is a steady flow. There is no fluid stored in the pack so the weight does not change with time. If you estimate the diameter of the intake hose and the outlet nozzles you can use the momentum equation to estimate the required flow rate. It is then possible to estimate the power required to operate the pack (that data is also available on their website). Of course you could always buy one for ~$70,000 and demonstrate it yourself.

Drag and rowing – I use this to discuss drag and the power required to overcome drag. Some level of analysis is possible here. The simple version is to write down the drag equation and explain that the power required is the velocity multiplied by the drag and therefore the power scales on the cube of the velocity. This result can be used to explain why races are often very close as a 1% increase in speed requires a 3% increase in power. It is possible to go into a little more depth if you estimate the surface area of a rowing shell and the frontal area of the rowers. Treat the shell as a smooth flat plate boundary layer drag problem and the rowers as a bluff body drag problem. You will need a velocity estimate (about 6 minutes for 2,000 m is decent for a good crew). From there you can estimate the power required per rower.  A more humorous rowing video is here.

Drag and ember flight – Ember flight from wild fires is a major cause of home destruction. The embers are lofted and transported downwind by aerodynamic drag forces. There is not a whole lot of analysis to do here, but it is a nice video put out by IBHS and is another example of the application of the drag.

Drag and wind loading on houses – This is another IBHS video. It is a lot more dramatic than the ember flight video. IBHS has a very big wind tunnel in South Carolina and they use it to look at building safety in strong winds. Here they show two houses built to slightly different standards. The video is a lot of fun, but there are also some nice details. For example, in one version of the video there is a moment when the front door blows in. almost immediately the side door blows out and the roof lifts off (due to the internal pressurization of the house). After that it is all over and the house collapses.

For those of you who teach stormwater classes there are videos of

A culvert failure – The video shows the gradual failure of a culvert and resulting road collapse during a storm. The culvert is in trouble right from the start of the video, but the major problem is when a tree is swept into it. It is a fun video to watch, but is also good for discussing failure. I pose the question to the class “is this is a design failure?” It is often a good discussion and the answer is always that there is not enough information. Was the storm in excess of the design event? Was the culvert designed correctly but not maintained? Was the culvert designed correctly but upstream development increased the risk of higher flow rates?

A highway storm sewer failure – Like the culvert video, this is a lot of fun to watch. It is also very dramatic when the 6’-8’ access hole cover gets lifted up into the air and lands on some ones truck. It is a good lead in to discussing HGL analysis of storm sewers. Unfortunately the resolution is quite poor.

The Toowoomba floods from 2010 – I mainly show this because I like listening to the Australian accents on the voiceover. It shows a very dramatic flash flood in Toowoomba, Australia that came from a thunderstorm. It is not clear if the thunderstorm was a design event, but it did occur a day or two after a cyclone (hurricane) came through the region so the soil was saturated and everything ran off. It is a nice video to start off a stormwater class, or to lead into a discussion of the differences between event and continuous modeling of stormwater events.

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Other fluids education resources I – websites, books, and DVDs

No new demonstration this week. However, there are a lot of other resources available for people teaching fluid mechanics classes. These include websites, books, DVDs, and online videos. I have put together a list of some of them. They are very briefly described below.

Websites:

Efluids has been around for a while and has an education section that includes links to a lot of materials including videos, class notes, etc. It also has a section on experiments with write ups of simple demonstrations and experiments that can be used as part of a fluids course.

FYFD! is a blog that posts videos, images, and news stories about fluid dynamics. The videos come with simple explanations of the flow physics and are often very dramatic. I have used many of them in class (usually on Friday as a little end of the week entertainment) to give students a sense of the breadth of the role of fluid dynamics in the world.

Fluids Education Google group is a community for sharing information and resources about teaching fluid mechanics and other fluids education information (such as REU opportunities).

www.learncheme.com out of the University of Colorado is a resource for Chemical engineering faculty, but also contains a lot of resources in the area of fluid mechanics including concept test questions, clicker questions, and interactive simulations.

Oklahoma University list of brief descriptions of fluid dynamics demonstrations: There are a lot of good ideas here but somewhat limited descriptions.

U.C. Berkeley demonstrations from their physics department: Again, lots of ideas, but little in the way of descriptions of how to run the demonstrations or do the analysis.

http://www.onlineconversion.com/ A very useful site for doing every imaginable unit conversion.

Books and DVDs:

Cambridge University Press has a DVD of Multimedia Fluid Mechanics that includes hundreds of videos with very brief descriptions of the flow.

H2Oh! is an new ASCE publication that documents a broad range of in class activities and demonstrations for use in introductory fluid mechanics and water resources classes. Each demonstration contains a list of objectives, equipment (sometimes including a rough budget), and a detailed step-by-step set of instructions.

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Video of Pipe networks and head loss

Here is a video of the “Pipe networks and head loss” demonstration. The full video is here. Sorry that it is sideways.

Video Feb 10, 9 51 27 AM 00_00_00-00_00_10

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Pipe networks and head loss

I find that students often find pipe networks difficult because they have difficulty visualizing that the head change along two different paths that are connected at each end must be the same. One way to demonstrate this is to drain a tank through two different length pipes. You can do this with the same equipment as the siphoning experiment though you will need an extra length of tube. I use a tank with pneumatic tubing connectors in it so that you don’t have to hold the tubes at both ends.

Equipment

  1. A large tank and a table to put it on
  2. Two tubes or pipes of substantially different (known) lengths
  3. Two measuring cups
  4. A stop watch.

Photo Feb 10, 9 45 05 AM

In the example in the photos there is a press-to-connect fitting in the base of the tank which I connect to a T-junction and then have the two pipes connected to that.

Photo Feb 10, 9 45 12 AM

Demonstration

  1. Fill the tank with water and flood the tubes.
  2. Place the measuring cups on the floor so that there is a substantial head difference between the top of the water in the tank and the top of the measuring cups
  3. Lower the outlet of the tubes to the top of each measuring cup and start the water flowing
  4. Record the time taken for each cup to fill. The longer tube should take a longer time

Analysis

The analysis is very similar to the siphoning demonstration so I will only summarize it here.

The total head (H) is the distance from the water surface in the tank to the top of the measuring cups. The head is balanced by the entrance head loss (hen), the head loss in the junction (hj), the head loss in the pipe (hp1 or hp2) and the exit loss from each pipe (hex1 and hex2). That is,

H = hen +hj + hp1 + hex1 = hen +hj + hp2 + hex2.

The first two loss terms cancel. Using the Darcy Weisbach equation we can re-write the remaining terms as

U12/2g (1+f1L1/d1)=U22/2g(1+f2L2/d2)

The ratio of the flow rates is given by

Q2/Q1=((1+f1L1/d1)/(1+f2L2/d2))1/2

Here is where it gets messy and, as a result, you won’t get a nice neat ratio of flow rates. In the example that I show in the video the tubes are 1/4” in diameter and 256” and 64” long respectively. Therefore, if the exit velocity head is negligible, the flow rate in the long tube should be roughly half that in the shorter tube. In the test I ran the ratio was 2.5:1. There are various explanations for this difference. First, the exit velocity head may not have been negligible (though accounting for that would have reduced the predicted flow rate ratio). Second, the friction factors for the tubes would be different due to the different Reynolds number (though again, accounting for that would have reduced the predicted flow rate ratio). The most likely explanation for the difference between the predicted and measured flow rate ratio is that the longer tube was curled up in a series of loops whereas the shorter tube was straight. There are additional measurement errors in the tube lengths, and the time for each cup to fill. For example, the times we measured were 25 seconds and 63. It does not take much of an error to get a substantial change in ratio. For example, there is a parallax error in reading the water level in the cups, and There can also be a delay between the person watching the cup calling out ans the timer registering the time. If the recorded times were each out by say plus or minus 3 seconds then the flow rate ratio would vary from  2.1 to 3.  Clearly the demonstration provides a great opportunity to talk about experimental error and uncertainty.

Thank you to Kate and Austin for helping out with the video.

An index of all the demonstrations posted on this blog can be found on my website here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Video of Control volumes and conservation of ping-pong balls

Here are the videos of the “Control volumes and conservation of ping-pong balls” demonstration. The full videos are linked from the GIF titles.

part one: a simple pipe with ping pong balls flowing from right to left.

cpb1

 

Part two: a pipe with a junction in the middle with 1/3rd of the balls going in the middle bucket.

cpb2

Part three: the same as part two but with ping pong balls flowing out of the down stream pond (the bucket on the far left).  

cpb3 00_00_00-00_00_07

 

Thank to (from right to left) Tanjina, Aws, Derek, Kakan, Austin, and Nasim for helping with the videos.

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.