A Quantitative Schlieren-Grid Method for Temperature Measurement in a Free Convection Field

摘要

The basic principles of a two dimensional cylindrical schlieren field are developed emphasizing the simplifying assumptions usually found in the literature. The assumption of the straight line path for the light ray in the schliere is replaced by a parabolic path with the index of refraction gradient varying linearly with distance normal to the cylindrical axis. This modification is developed in a form of a correction factor and is evaluated by applying a particular schlieren method to free convection temperature measurements. Results indicate that in regions of high thermal gradients (22000 F/in.) the correction is of the order of 15%. Emphasis is also placed on the particular schlieren method used, that of incorporating a Ronchi grating at the focal point of the second mirror. The corrected average heat transfer coefficient values are compared with shadowgraph and literature interferometer data with agreement being within l% and 5% respectively. (Author)