研究目的
To propose and apply a method for measuring planar temperature fields of fluid flows using a focusing schlieren technique with off-axis circular illumination and a calibration procedure.
研究成果
The focusing schlieren system with off-axis illumination successfully measures planar temperature fields in fluid flows, achieving a narrow depth of focus (~0.4 mm) and agreeing with thermocouple measurements. The method is useful for three-dimensional temperature field exploration and can be improved with high-speed cameras and better lenses for higher sensitivity and larger fields of view.
研究不足
The optical system has specific characteristics that limit the range of temperatures measurable and the type of objects analyzable. Limitations include fluid flow fluctuations, lens aberrations, and errors in measurement process, with relative errors between 0.5% and 13.6%. The field of view is 17.4 x 9.2 mm2, and depth of focus is narrow (~0.4 mm for 12 sources).
1：Experimental Design and Method Selection:
The study uses a focusing schlieren system based on off-axis circular illumination to reduce depth of focus, enabling planar temperature measurements. A calibration procedure relates pixel intensity in schlieren images to cutoff grid positions.
2：Sample Selection and Data Sources:
The fluid flow is hot air from a 10 mm diameter nozzle of a commercial Hot Air Gun Soldering Station Welding, tested at temperatures of 200°C and 400°C.
3：List of Experimental Equipment and Materials:
Includes a source grid with off-axis circular illumination, schlieren lens, cutoff grid, digital camera (Lumenera Lt225), calibration slide, and thermocouple (K-type from Fluke).
4：Experimental Procedures and Operational Workflow:
The optical system is aligned; cutoff grid is displaced for calibration; focused schlieren images are captured with and without flow; temperature is derived from intensity deviations using calibration curves and integration.
5：Data Analysis Methods:
Intensity deviations are converted to cutoff grid displacements; density and temperature are calculated using Gladstone-Dale's equation and ideal gas law; trapezoidal rule for integration is applied; uncertainty is assessed with standard deviation.
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