Miniature rainbow schlieren deflectometry system for quantitative measurements in microjets and flames

Recent interest in small-scale flow devices has created the need for miniature instruments capable of measuring scalar flow properties with high spatial resolution. We present a miniature rainbow schlieren deflectometry system to nonintrusively obtain quantitative species concentration and temperature data across the whole field. The optical layout of the miniature system is similar to that of a macroscale system, although the field of view is smaller by an order of magnitude. Employing achromatic lenses and a CCD array together with a camera lens and extension tubes, we achieved spatial resolution down to 4 mum. Quantitative measurements required a careful evaluation of the optical components. The capability of the system is demonstrated by obtaining concentration measurements in a helium microjet (diameter, d=650 microm) and temperature and concentration measurements in a hydrogen jet diffusion flame from a microinjector (d=50 microm). Further, the flow field of underexpanded nitrogen jets is visualized to reveal details of the shock structures existing downstream of the jet exit.