Are you one of those persons who love to see the droplets wandering around in a very hot frying pan when cooking? Well, you might not be alone.
More than 260 years ago, Dr. Johann Gottlab Leidenfrost described what today is known as the Leidenfrost effect: If you place a liquid droplet on a very hot surface, a vapor cushion is formed underneath the droplet, which gives the impression that the droplet levitates. Because the vapor acts like a thermal insulator, the heat from the surface is not being transfered to the liquid droplet – and then the droplet wanders over the surface for several seconds until it evaporates completely.
Cooling electronic devices
The temperature at which this phenomenon occurs is very important in a large number of applications. In the case of the cooling applications, for example computers or electronic devices, if the surface reaches the Leidenfrost temperature, the device can be damaged, because the heat cannot be transferred from the surface to the liquid droplet.
In the recent years the drive to understand the physics of this phenomenon has motivated significant research, in particular in the influence of the surface properties on the Leidenfrost effect.
Fabricating new surfaces in the Nano lab
During the past two years, we have been designing and fabricating new surfaces at the NTNU Nanolab, that can control the Leidenfrost effect.
One of these surfaces are Silicium nano wires, at the scanning electron microscope the surface looks like a carpet but this structure no visible to the naked eye is capable of increasing the Leidenfrost temperature more than 200oC. This result implies that a surface with this Silicium nano wires can remove heat efficiently even at 200 oC higher than the bare Si (Silicium) surface. Why this is happening is one of the questions our research group is looking to answer.
More details from the study are available in this publication: International Journal of Heat and Mass Transfer .
Illustration above: Comparison between the plain Si and the Si nano wires.
This blog post was written by PhD candidate Manuel Auliano, at Department of Energy and Process Engineering, NTNU. He belongs to the thermal two-phase flow laboratory. The surface fabrication and characterization has been done at the NTNU Nanolab