RSOS-2 RETROREFLECTIVE SHADOWGRAPH
FLOW VISUALIZATION SYSTEM
The RSOS-2 is a laboratory instrument consisting of a retroreflective screen and a tripod –mounted optical transmitting/receiving unit. A compact arc lamp in this unit projects a shadowgram upon the retroreflective screen, which is then imaged by a system camera.
First introduced in 2008 as the RSOS-1, this instrument has seen use primarily in the testing of kitchen ventilation hoods, where it enables the visualization of cooking-effluent spillage around the lip of a ventilation hood. The application of optical methods like this to determine the threshold of cooking-effluent capture and containment for idle and heavy cooking conditions is detailed in
ASTM Standard F 1704-05.
The size of the field-of-view of the RSOS-2 is determined by the size of the retroreflective screen that is provided as a background for shadowgram imaging. For example, a 10x10-foot screen affixed to the wall of a kitchen ventilation laboratory opposite the RSOS-2 transmitter/receiver unit provides a 5x5-foot field-of-view at the midpoint between the two, where the cooking and ventilation equipment are located.
The standard system camera provided with the RSOS-2, for applications such as kitchen ventilation testing, provides high-resolution still images like the one shown above as well as HD video at 30 frames/sec.
FOUCAULT SCHLIEREN SYSTEM
The Foucault test for telescope mirrors forms the basis for a simple but powerful schlieren optical system. As shown in the diagram below, an LED, which is the light source for the schlieren system, illuminates a spherical first-surface mirror at its radius of curvature (equal to twice its focal length). The mirror returns an image of the LED emitter to the radius of curvature, where an adjustable knife-edge cuts off some of the light beam. The remaining light proceeds to a camera and is captured as a schlieren image. If the mirror is perfectly spherical, then a uniform darkening of the schlieren image occurs as the knife-edge is advanced to cut off more light.
Practically, this schlieren instrument consists of two separate assemblies: the Foucault tester with LED, adjustable knife-edge, and provision to mount a camera, and a properly-mounted spherical first-surface mirror.