Measurement of temperature profile of a gaseous flame with a Lau phase interferometer that has circular gratings

We have investigated the utility of a Lau phase interferometer with circular gratings and a white-light source to measure the temperature and temperature profile of an axisymmetric flame. The temperature measured with a Lau phase interferometer is in good agreement with the temperature measured with a thermocouple and multilogger. Detailed theoretical analysis and experimental investigation are presented.     

Digital holographic interferometry for measurement of temperature in axisymmetric flames

In this paper, experimental investigations and analysis is presented to measure the temperature and temperature profile of gaseous flames using lensless Fourier transform digital holographic interferometry. The evaluations of the experimental results give the accuracy, sensitivity, spatial resolution, and range of measurements to be well within the experimental limits. Details of the experimental results and analysis are presented.     

Curved elastic beam with opposed fiber-Bragg gratings for measurement of large displacements with temperature compensation

In this paper, a temperature-compensated configuration for extending the working range of fiber-Bragg grating (FBG) strain sensors has been proposed. This technique consists of the application of two FBGs to the opposite surfaces of a straight elastic beam which was bent in a horizontal direction. The difference of the two FBGs' wavelengths depends on the beam curvature, while the mean value is taken in order to compensate for the temperature effects. The sensor proposed is less fragile than the bare fiber and seems particularly suited as large displacement sensor, and for structures in which it is impossible to affix the bare fiber, such as breaks or separate elements.     

Measurement of gas-phase temperatures in flames with a point-diffraction interferometer

Experiments were performed to evaluate the performance of a point-diffraction interferometry (PDI) system to measure gas-phase temperatures in flames. PDI is an interferometric technique that creates the reference beam after the laser beam passes through the test section and directly provides the index of refraction in two dimensions. PDI-based temperature measurements were compared with thermocouple measurements of two-dimensional and axisymmetric thermal boundary layers, as well as two-dimensional and axisymmetric diffusion flames. The PDI system provided excellent agreement in the measurement of thermal profiles in the boundary layers and was within the uncertainties that are due to the radiation corrections for the thermocouple-based flame temperature measurements.     

Talbot interferometry in measurements of the parameters of an axisymmetric turbulent jet

The Talbot effect has been adapted to measurement of the parameters of mixing in an axisymmetric turbulent helium jet flowing out into a submerged air space. A two-dimensional array of angles of refraction of light has been determined from the displacement of the image of unit Talbot elements in the reproduction plane of the time-averaged talbogram. The distribution of the average refractive index of a medium and the concentration of helium in the flow field have been calculated by means of the Abel transformation. Based on an analysis of the intensity distribution at the maxima of the Talbot image, it has been shown that the turbulence of this jet is locally inhomogeneous and anisotropic. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 94–99, September–October, 2006.     

Multi-pass interferometer for quantitative investigation of axisymmetric inhomogeneities in rarefied gases

A multi-pass interferometer method has been used for visualization and determination of certain flow parameters of a rarefied gas in the slip flow regime over axisymmetric blunt models. An experimental determination has been made of the density distribution in the region of the forward stagnation point ahead of a sphere and of the shock wave profile ahead of a disk at M = 3.85 and Re = 75.     

Efficient generation of large diffraction gratings with a grating interferometer

The advantages of a grating interferometer for the generation of large diffraction gratings are demonstrated. In a one- and a two-stage process, high-quality gratings of 120 and 200 mm, respectively, were made with optics no larger than 50 mm together with an argon-ion laser with no line narrowing or beam stabilization and a rotating diffuser for improved beam uniformity.     

Concurrent measurement of temperature and soot concentration of pulverized coal flames

This paper presents a novel instrumentation system for the concurrent measurement of temperature and soot concentration of pulverized coal flames. The system operates on the two-color principle, combining CCD camera optical sensing and digital image processing techniques. The temperature and its distribution in a flame are calculated from the ratio between the grey-levels of corresponding pixels within two images captured at two carefully selected wavelengths. The soot concentration distribution of the flame is represented and estimated using the KL factor that is derived from intermediate information obtained during the temperature measurement. The system is calibrated using a tungsten lamp as a standard temperature source. The maximum relative error in the temperature measurement is 1.83%. Experimental results obtained on a 0.5 MW/sub th/ combustion test facility show that the temperature distribution of a coal-fired flame ranged from 1380 to 1700/spl deg/C, while the KL factor ranged from 0.18 to 0.33.     

Calibration method for high-accuracy measurement of long focal length with Talbot interferometry

In this paper, a new calibration method for accurate long focal-length measurements, based on Talbot interferometry, is presented. Error analysis is derived in detail by the numerical method, and an effective way to improve the accuracy is proposed. By this method, the systematic errors that are the main factors effecting accuracy are calibrated and reduced. Both simulation and experiments have been carried out to prove the effectiveness and advantages of the proposed method as compared to conventional approaches. The experimental results reveal that the relative error is lower than 0.02%, and the repeatability is better than 0.05%. This method is especially useful for measuring long focal-length lenses.     

Perturbed Talbot patterns for the measurement of low particle concentrations in fluids

Behind periodic amplitude or phase objects, the object transmittance is repeated at the so-called Talbot distances. In these planes perpendicular to the propagation direction, Talbot self-images are formed. In the case of plane wave illumination, the distances between the self-images are equally spaced. A periodic pattern called optical carpet or Talbot carpet is formed along the propagation direction. We show theoretically how the presence of spherical particles (10 to 100 μm in diameter) behind gratings of 20 and 50 μm period affects the formation of Talbot carpets and Talbot self-images at 633 nm illumination wavelength. The scattering of the particles is modeled by the Fresnel diffraction of its geometrical shadow. We analytically calculate the interference of the diffraction orders of rectangular and sinusoidal amplitude gratings disturbed by the presence of particles. To verify our model, we present measurements of Talbot carpets perturbed with both opaque disks and transparent spheres, and discuss the effects for various size parameters. We present an approach to simulate the movement of particles within the Talbot pattern in real time. We simulate and measure axial and lateral particle movements within a probe volume and evaluate the effect on the signal formation in a Talbot interferometric setup. We evaluate the best system parameters in terms of grating period and particle-detector-distance for a prospective measuring setup to determine characteristics of flowing suspensions, such as particle volume concentration or particle size distribution.     

Simultaneous measurement for strain and temperature using fiber Bragg gratings and multimode fibers

An all-fiber sensor capable of simultaneous measurement of temperature and strain is newly presented. The sensing head is formed by a fiber Bragg grating combined with a section of multimode fiber that acts as a Mach-Zehnder interferometer for temperature and strain discrimination. The strain and temperature coefficients of multimode fibers vary with the core sizes and materials. This feature can be used to improve the strain and temperature resolution by suitably choosing the multimode fiber. For a 10 pm wavelength resolution, a resolution of 9.21 mu epsilon in strain and 0.26 degrees C in temperature can be achieved.     

Three-dimensional temperature measurement of combustion flames using a single monochromatic CCD camera

This paper presents an imaging-based instrumentation system for three-dimensional (3-D) temperature measurement of a combustion flame. A combination of image-processing techniques and two-color radiation thermometry is used to first reconstruct band-limited grayscale representations of the flame and then to determine its temperature distribution. The reconstruction process assumes rotational symmetry in the structure of the flame. A series of experiments has been conducted on a laboratory-scale combustion rig to evaluate the performance of the system. The results obtained demonstrate the capability of the system to determine flame temperature on a 3-D basis.     

Axial eigenfunctions for the axisymmetric problem of an elastic circular cylinder

Constructing a biorthogonality relation it is shown how solutions can be obtained for the stress, displacement and mixed problems associated with the axisymmetric deformations in a cylinder whose plane faces are either stress-free or displacement-free. Numerical results are presented for the reproduction of the boundary stresses when a self-equilibrating load is prescribed on the circular boundary of the cylinder whose plane faces are stress-free.     

Simultaneous measurement of temperature and chemical species concentrations with a holographic interferometer and infrared absorption

What is believed to be a new technique that allows for the simultaneous measurement of 2D temperature and chemical species concentration profiles with high spatial resolution and fast time response was developed and tested successfully by measuring a thin layer of fuel vapor created over a volatile fuel surface. Normal propanol was placed in an open-top rectangular container, and n-propanol fuel vapor was formed over the propanol surface in a quiescent laboratory environment. An IR beam with a wavelength of 8-13 mum emitted from a heated plate and a He-Ne laser beam with a wavelength of 632 nm were combined and passed through the n-propanol vapor layer, and both beams were absorbed by the vapor layer. The absorption of the IR beam was recorded by an IR camera, and the He-Ne laser was used to form a holographic interferogram. Two-dimensional temperature and propanol vapor concentration profiles were, respectively, determined by the IR absorption and the fringe pattern associated with the holographic interferogram. This new measurement technique is a significant improvement over the dual wavelength holographic interferometry that has been used previously to measure temperature and fuel concentration, and it is ready for application under different types of fire and flame conditions.     

Double-grating interferometer for measurement of cylinder diameters

We describe a double-grating interferometer for the measurement of cylinder diameters. The unique characteristic of this interferometer is that one can freely change the period of the interference fringes by turning the grating, which permits the measurement range of the interferometer also to be changed freely according to the cylinder diameter to be measured. A clear image of the cylinder can be obtained because the aperture diaphragm blocks the beams diffracted from the edge of the cylinder. The outside and inside diameters of the M4 x 0.7 mm hand tap are measured with this double-grating interferometer.     

An axisymmetric elastic analysis for circular sandwich panels with functionally graded cores

This paper presents an analytical solution in the framework of the elasticity theory, which is useful in describing the elastic bending response of axisymmetric circular sandwich panels with functionally graded material cores and homogeneous face-sheets. The Young’s modulus of the core is assumed to be exponentially dependant on the transverse direction and the Poisson’s ratio as well as uniform and equal to the face-sheets ratio. The elastic solution is obtained using a Plevako representation, which reduces the problem to the search of potential functions satisfying linear fourth-order partial differential equations. We explicitly obtain the analytical solution by writing the potential functions as Fourier Bessel expansions with respect to the radial coordinate. A comparative study of functionally graded versus a homogeneous sandwich core is presented by considering the first term of the expansion as the loading condition. In this way, the solution is written in a closed form and furnishes a benchmark to accurately investigate the agreement with the structural theory results.     

Design of circular Dammann gratings by employing the circular spot rotation method

A new concept based on the theory of Dammann gratings is proposed for the generation of circular optical beams. This grating shows that it can achieve equal intensity and equal spacing with acceptable efficiency that is controlled by set of transition points. A numerical solution is also presented together with the fabrication of 4-order circular Dammann grating by e-beam lithography. Experimental results agree well with the scalar diffraction theory. This grating has the potential to be further developed into practical applications.