Abstract

In the schlieren method, the deflection of light by the presence of an inhomogeneous medium is proportional to the gradient of its refractive index. In the presence of temperature variations in a fluid flow, the refraction index is related to the gas density by the Gladstone–Dale constant, which depends on the nature of the gas and the wavelength of light propagating in the medium. The deflection of light in a schlieren system is represented by intensity variations on the observation plane. Then, for a digital camera, the intensity level registered in each pixel depends mainly on the refractive index variation of the medium and exposure time. Therefore, if we regulate the intensity value of each pixel by controlling the exposure time, it is possible to adjust the temperature value measurements. In this way, a specific exposure time of a digital camera allows us to measure a determined range of temperature values. For that reason, in this study we determine the range of temperatures that can be measured with a digital camera for different exposure times. By doing this, a wide range of average temperature value fields can be obtained by summing up the temperature contribution of each exposure time. The basic idea in our approach to measure temperature by using a schlieren system 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. Our approach is applied to the measurement of temperature fields of the air convection caused by a heated rectangular metal plate ($7.3\mathrm{cm}\times 12\mathrm{cm}$) and a candle flame. We found that the maximum temperature values obtained for exposure times of 31.3, 15.7, 7.9, 3.9, and 2 ms were 67.3°C, 122.6°C, 217.4°C, 364.3°C, and 524.0°C, respectively.

© 2016 Optical Society of America

Measurement of temperature and velocity fields in a convective fluid flow in air using schlieren images

A. Martínez-González, D. Moreno-Hernández, and J. A. Guerrero-Viramontes
Appl. Opt. 52(22) 5562-5569 (2013)

Temperature and velocity measurement fields of fluids using a schlieren system

Adrian Martínez-González, J. A. Guerrero-Viramontes, and David Moreno-Hernández
Appl. Opt. 51(16) 3519-3525 (2012)

Methodology of designing compact schlieren systems using off-axis parabolic mirrors

Lingzhi Zheng, Adam J. Susa, and Ronald K. Hanson
Appl. Opt. 61(16) 4857-4864 (2022)

Schlieren-based temperature measurement inside the cylinder of an optical spark ignition and homogeneous charge compression ignition engine

Pavlos Aleiferis, Alexandros Charalambides, Yannis Hardalupas, Nikolaos Soulopoulos, A. M. K. P. Taylor, and Yunichi Urata
Appl. Opt. 54(14) 4566-4579 (2015)

Optical tweezer calibration by using a part of the intensity distribution of a trapped particle

Harun Yücel and Nazmi Turan Okumuşoğlu
Appl. Opt. 55(28) 7861-7865 (2016)