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ramé-hart instrument co. October 2014 Newsletter
|How to Boil Water without Bubbles|
Today's cool science trick first requires
a review of the Leidenfrost effect1
which is named after Johann Gottlob Leidenfrost who discovered the
phenomenon in 1756. He observed that a drop of water on a hot surface
will dance around and quickly evaporate. However, if the temperature of
the surface is increased beyond a certain point (around 193° C but it
can vary depending on the properties of the surface), the drop produces
an insulating layer of vapor underneath it. This keeps it from boiling
and from evaporating as quickly as the same drop on the same surface at
a lower temperature. Researchers have been able to use the Leidenfrost
effect to make water drops climb uphill as illustrated in the video
below and do other interesting tricks.
Researchers at Northwestern University2 and elsewhere have treated small steel balls with a superhydrophobic coating. The balls are then heated to 400° C and dropped in water that is at room temperature. The Leidenfrost effect kicks in and a small layer of vapor forms between the ball and the water preventing bubbles from forming on the ball. Even as the ball cools to below the critical temperature, no bubbles form as the Leidenfrost effect is stablized by the superhydrophobic surface. Watch the ball on the right in the video below. You will see that the bubble phase is completely eliminated.
Another set of balls were made hydrophilic and again heated up and dropped into room temperature water. As you can see from the ball on the left in the video below, bubbles form as expected.
This unique phenomenon can be used to develop new and more efficient heat transfer technologies, improve water-based cooling systems (e.g., car radiator), and reduce drag in a variety of mechanical systems through the use of hydrophobic coatings and surfaces.
DROPimage Advanced Single and Two-Window Modes
Some of our more recent videos come at the request of our customers. One seemingly confusing topic is the issue of one image window or two in DROPimage Advanced and how to switch between modes. As it turns out, this has been a recurring question lately with several new users. So, we created the video below to help explain. The default mode for DROPimage Advanced is two-window mode. In this case, there is a smaller live video window and a larger static image window. The live video window is updating constantly at many frames per second. As you dispense a liquid and form a sessile drop, you can watch this activity real-time in the live video window. The larger image window (shown on left below) is the static image window. When you click on the camera icon on the tool bar (or Ctrl-T on the keyboard), you can take a picture - or grab a frame from the live video and see it in the larger static image window (on left below) where measurements are actually made. This two-window arrangement is really the optimal way to use DROPimage Advanced although it may take some getting used to. Some users prefer to work in a single window. This can be done by going to the View pull-down menu, stopping pass-thru, and then changing pass-thru to the main window and then restarting pass-thru. Watch the video to see these steps in action.
In single-window mode, all measurements are taken in the main window with live video always on. This is how DROPimage Standard and CA work by default. For static contact angle work, it does not matter so much whether you choose to use DROPimage Advanced in single window or two-window mode. However, for time-dependant studies including high-speed dynamic measurements, the software works more efficiently in two-window mode and it's also much easier to monitor simultaneously the measurements and the activity in the live video window.
If you have a request for a particular video please contact us and we'll add it to our list if we have not made one already that covers the requested task or topic.