Temperature measurement of the air convection using a Schlieren system

The determination of density gradients is an important task in several branches of science. Several full field techniques such as Laser Induced Fluorescence (LIF), Holography Interferometry, Laser Speckle and Schlieren have been developed to face this important task. Schlieren technique was developed as a visualization technique in the eighteenth century. Its success is due to its relative easy implementation, low cost, use of conventional light sources, and high and variable sensitivity. In this work, we have developed a procedure for the measurement of temperature in a fluid flow by the schlieren technique. The z-type configuration schlieren system is used in this research, which include two similar spherical mirrors (D = 0.15 m,f = 1.54 m), a white LED, a knife edge that can be translated in the x or y direction by a 2D micrometer. The basic idea of the procedure to measure temperature is to relate the gray level values of a schlieren image to the corresponding knife position at the exit focal plane of the system. The technique was applied to measure temperature fields of the air convection caused by a heated metal rectangular plate (7.3X12 cm) controlled by a calibrated Peltier cell. Our tests were carried out at temperatures of 50 and 80 deg C. The results were compared with temperature measurements done with a thermocouple, both result show a good matching between them.