Schlieren Imaging
Overview: Schlieren works by imaging deflected rays of light in a transparent medium. By deflecting the rays of light it enables us to see the flow of warm air around objects.
Supplies: Schlieren mirror, pinhole light source, knife edge such as a razor blade, stand for the knife edge, camera with a lens, computer with software for the camera, TV for larger audience projection of the camera image, various heat sources such as a candle or a hair dryer
Objectives: Demonstrate how we can see the changes in an area of air that is heated in various ways when using this unique setup.
Setup:
- Place the light source and camera side by side at one end of the table
- Place the Schlieren mirror at the opposite end of the table at the prescribed distance. If the focal length of the mirror is not labeled the FL will need to be determined
- Place the knife edge in front of the camera
- Turn on the light source
- Adjust the light source, mirror and knife edge so the light spot is in focus at the knife edge and bisected by the knife edge
- Hook up the camera to the laptop and open the camera software
How to run the demo:
- Place various heat sources in front of the mirror (NOT TOO CLOSE!!)
- Items that can be used are a hair dryer, a candle, even rubbing your hands together to create heat and placing your hand face up in front of the mirror
- Bottles of isoporpyl alcohol can be gently squeezed to expel the alcohol vapor (not the liquid)
What’s Happening?
Light rays bend when they pass through different densities of air. Warmer air has a different density than cooler air. When we put a heat source through a path of parallel light, the light rays encountering the warmer section will bend, or refract. Because the knife edge is at the focal point of the mirror the refracted rays of light hit the knife edge instead of continuing through to the camera. The resulting image shows dark areas where the density gradients are present.
Image courtesy of https://www.instructables.com/Schlieren-Imaging-How-to-see-air-flow/
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