James Bomber and I are studying the phenomenon of liquid jet bouncing as part of his Blugold Fellow project. Apparently, any sufficiently viscous newtonian liquid will bounce (without splashing) off a pool of the same liquid for the flow speeds and angles of impact withing restricted ranges. For other angle and speed combinations, the jet does what one would expect: it merges with the bath. Here is a picture of James producing a bouncing jet (using paraffin oil in this case) by hand:
Click the image to view a video (wmv) of the jet bounce, and a special treat: a double bounce.
A nice bounce in a canola oil jet. Note that the jet maintains its integrity within the dimple during the bounce.
Click here (or on the image) to see a video (wmv format) showing what happens when the stream is stopped while a jet is bouncing - notice the slingshot effect of the jet on the right due to the thin liquid bridge breaking - the trailing end of the jet gets thrown farther than the continuous jet did by about 30%. This video uses our new high-speed camera and a more elaborate experimental setup. The frame rate is 300 fps. The frames have been color-coded: the original jump is in red and the later positions are cyan (where the images are identical, the coloring is white).!
Click here or on image to see a video (600 fps, in Quicktime format) of an unstable jet in canola oil. Note that every time an air bubble passes through the jet, an instability develops which causes the jet to pinch off and fall down. The first pinchoff creates a little oil droplet that gets pushed across the oil bath surface by the falling jet.
Our poster at the 2009 UW-Eau Claire Research Day was awarded 2nd place in the Physical and Mathematical Sciences category. View a pdf of the poster. We were able to determine the fraction of energy lost in a bounce as a function of angle as measured from the bath surface:
We have successfully incorporated a laser beam which can travel along the jet similar to the way light is trapped in fiber optics. This picture shows that the jet liquid and the bath liquid do not mix during the bounce (note the difference between the first time the jet hits the bath when it rebounds and the second time where the jet and bath merge - the thin tracks at the merge point are made by small air bubbles in the bath and jet). The image was taken with the camera focused on the jet while below the average level of the bath liquid. The liquid is canola oil.
Students James Bomber and Nick Brewer worked together to produce the 4th place poster at the 2010 UW-Eau Claire Research Day which further explored the air film surrounding the jet. Click here to view the poster.
Using the same apparatus, Nick Brewer and Thomas Nevins (a Blugold Fellow) moved on the study antibubbles (an air film enclosing an oil droplet, all surrounded by oil) using the same apparatus and the high speed camera:
(The image shows antibubble about to detach from the submerged jet with a free antibubble on the right..)
The air film surrounding the inner oil droplet imaged in sodium light shows interference fringes similar to Newton's rings:
More antibubble results coming soon!