Fourier Moiré Deflectometry For The Measurement Of Mini/Micro Scale Fluid Temperature Distribution

Optical flow visualization and measurement is one of the interesting fields in the experimental researches of heat transfer, especially in the field of mini/micro scale heat transfer. An optical method, Fourier Transform Moiré Deflectometry, applicable to mini/micro scale heat transfer, is proposed in this paper.In this paper, the researches are focused on the improvement of measurement sensitivity, so as to meet the needs of measurement for mini/micro scale fluid temperature distribution. Three approaches are presented. Firstly, physical and mathematical models of Moiré Deflectometry are investigated to make clear the rule of Moiré fringes' generation. Based on the investigation, it is pointed out how to select appropriate optical parameters to measure the teperature of mini/micro scale fluid. Secondly, the image processing method by which the experimental data can be extracted from Moire fringes is proposed based on Fourier Transform. The researches showed that three approaches could be adopted to reduce the fringe processing error: 1) continumm of the fringe's spatial region to an integer multiple of fringe period; 2) selection of appropriate sampling frequency in data processing; 3) adjustment of parameters in the optical set-up to make it possible for the fundamental frequency to be separated from the whole frequency band. The data processing method proposed in this paper could improve the sensitivity by an order to 10-5 degree, which could meet the needs of mini/micro scale fluid temperature measurement. Thirdly, CFI (Computational Flow Imaging) is applied to the analyses of the measured results instead of directly comparing the temperature data extracted from Moiré fringes with those calculated by numerical heat transfer, which can effectively reduce the error in the reconstruction from light deflect angle to fluid temperature. To verify the optical method, temperature distribution for natural convection around a vertical heated thin wire was measured by Fourier Transform Moiré Deflectometry. The small phase variation in moiré fringes, when the thin wire was heated, was obtained successfully. Furthermore, the temperature distribution around the heated thin wire was finally determined. In the experiments, the spatial resolution was about , the measured deflect angle was about 10-4 degree, which was corresponding to the temperature gradient of about for the natural convection around a heated thin wire with the diameter of .The experiment showed that Fourier Transform Moiré Deflectometry proposed in this paper is actually applicable to mini/micro scale fluid temperature measurement. The researches also showed that the three approaches to improve the measurement sensitivity work well. The optical method will be a useful experiment technique for mini/micro scale heat transfer.