Temperature measurement of air convection using a Schlieren system

In this work, we have developed a procedure for full-field measurement of temperature of a fluid flow by using the schlieren technique. The basic idea is to relate the intensity level of each pixel in a schlieren image to the corresponding knife-edge position measured at the exit focal plane of the system. The method is applied in the measurement of temperature fields of the air convection caused by a heated rectangular metal plate (7.3 cm×12 cm). Our tests are carried out at plate temperatures of 50 °C and 80 °C. To validate the proposed method, the schlieren temperature results are compared to those obtained by a thermocouple. Thermocouple data are obtained along two mutually perpendicular directions (one direction along the optical axis, z-direction, and other direction along the x-axis, which is perpendicular to the optical axis) at points located on a 9×9 grid with a variable spacing. The thermocouple measurements were integrated along the z-axis in order to be compared with the measurements obtained by the schlieren technique. The results from the two methods show good agreement between them.