Speckle Photography for Nonintrusive Temperature Measurement

Image blurring of the test section boundary in a laser specklegram technique measuring temperature gradients of the compressible medium

Laser Speckle Photography Tenique for Measuring Local and Global Heat Transfer Correlation Coefficients

Study of thermal flows from two-dimensional, upward-facing isothermal surfaces using a laser speckle photography technique

Tomographic Deconvolution of Laser Speckle Photography for Axisymmetric Flame Temperature Measurement

Laser Speckle Photography Technique Applied for Heat and Mass Transfer Problems

Applications of Laser Speckle Photography for Thermal Flow Problems

An extended algebraic reconstruction technique (ART) for density-gradient projections: laser speckle photographic tomography

Image blurring of the test section boundary in a laser specklegram technique
measuring temperature gradients of the compressible medium

K. D. Kihm

Image blurring of the solid boundary of a test section has been investigated for a specklegram technique that nonintrusiuely measures temperature gradients in transparent media

for details, click here [119KB in PDF]

Laser Speckle Photography Technique for Measuring Local and Global Heat Transfer Correlation Coefficients

T. E. Walsh and K. D. Kihm

A laser specklegram technique, or, equivalently, speckle photography, is capable of directly measuring local surface temperature gradients providing an extremely high resolution and a full-field interrogation from a single data taking. A complete specklegram system using a 35 mW power He-Ne laser has been developed at Texas A&M University, and the system has been applied to investigate heat transfer characteristics for a common configuration, but under some dispute in determining the heat transfer correlation. Convective heat transfer from an upward-facing isothermal plate has been studied by measuring the local and glob& Nussell numbers. An aspect ratio (AR) of 1.75 has been considered in the present case. The Rayleigh number, based on the length scale equivalent to the ratio of the surface area to the perimeter, has varied from 8.5 x 10⁴ to 2.0 x 10⁵. The results have been compared with several previously published calculations and data that employed classical and conventional techniques. The present result for the global heat transfer shows a 0.234 power law, i.e., Nu = 0. 46 Ra^0.234, correlates the data more property, whereas previously published predictions and data for infinite or semi-infinite plate exhibit 0.2 power law. For the aspect ratios of order of unity, published correlations indicate that a 0.25power law fit the data well. It is suggested that the band between 0.25 and 0.2 power correlations should contain the information for horizontal heated plains of AR ranging from 1.0 to infinity showing a gradual decrease in Nusselt number with increasing aspect ratio.

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Study of thermal flows from two-dimensional, upward-facing isothermal surfaces using a laser speckle photography technique

K. D. Kihm, S. K. R. Cheeti

A laser specklegram or speckle photography technique allows a direct measurement of surface temperature gradients and provides a full field interrogation with an extremely high resolution from a single data taking. The specklegram technique has been successfully applied to investigate the natural convection heat transfer from an upward facing isothermal plate. For a plate with a large aspect ratio of 15, both local and global Nusselt numbers have been determined from the direct measurement of local temperature gradients. The Rayleigh number, based on the length scale equivalent to the ratio of the surface area to the perimeter, has been varied from 9.0 × 10³ to 4.0 × 10⁴. The present result for the global heat transfer has shown that a 1/5-power law, i.e., Nu =C₁ Ra^1/5, correlates the data more properly whilst previously published results showed a large scatter in the exponent, ranging from 1/8-power to 1/4-power. The proportional constant, C₁ has been determined to be 0.56 which shows a fairly good agreement with previously published theoretical results. The laser specklegram technique has shown a strong potential as a powerful and convenient method for an experimental assessment of natural convection heat transfer problems. The specklegram technique at the same time has eliminated the deficiencies of both the mass transfer analogy technique and the classical heat transfer measurement technique.

for details, click here [381KB in PDF]  

Tomographic Deconvolution of Laser Speckle Photography for Axisymmetric Flame Temperature Measurement

T. E. Walsh and K. D. Kihm

A laser speckle photography technique can nonintrusively measure thermal flow properties such as medium density, index of refraction or temperature. The laser specklegram records a line-of-sight or path-intergrated information on these properties. For varying properties in a medium along the optical path, a mathematical technique called a tomography deconvolves cross-sectional information aou of the projected measurement. the present work will outline the underlying priciples of optical tomography and show how to apply it to the diagnostic technique of laser speckle photography. Comparisons of temperature measurements using a thermocouple probe against the temperature conversion from the specklegram data have been made for laminar flames. the speckle photography technique show good potential as a new nonintrusive temperature measurement tool for various thermal flows.

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Applications of laser speckle photography for thermal flow problems

K. D. Kihm

Laser speckle photography measures projected beam deflection of a phase object. The beam deflection measured at the solid surface will directly determine the wall-temperature gradient. Thus, the laser-speckle photography allows the evaluation of the convection-heat-transfer coefficients without the need to correct for conduction and radiation heat losses, which otherwise would be necessary. Selected results and brief discussions are presented for several natural convection-heat-transfer problems. Second, high-temperature applications of laser speckle photography shows potential as a nonintrusive means of measuring flame temperature. A fairly good agreement is shown in comparison of the laser speckle data with intrusive thermocouple data. Suggestive discussions are made to further improve the accuracy and sensitivity of the laser speckle photography technique in high-temperature applications. Finally, tomographic reconstruction of laser speckle photography data is discussed using density computer-synthesized phantom fields. The conventional algebraic reconstruction technique (ART) has been modified to apply for the laser speckle tomography. The reconstruction accuracy of ART is compared with Fourier convolution (FC) technique particularly under a limited number of projections.

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Laser Speckle Photography Technique Applied for Heat and Mass Transfer Problems

K. D. KIHM

Speckle photography technique is an optical diagnostic method to measure nonintrusively the refractive index gradients of inhomogeneous medium, also called a phase object, based on light ray refraction and deflection. The measured refractive index gradients are converted into the medium temperature and density information using pertinent physical equations. The technique provides highly accurate and quantitative information on the temperature and density fields, with an excellent spatial resolution.
The encyclopedic definition of optical speckle is "a phenomenon in which the scattering of light from a highly coherent source, such as a laser, by a rough surface or inhomogeneous (refractive index) medium generates a random-intensity distribution of light that gives the surface or medium a granular appearance." Here, the random-intensity distribution results from the randomly constructive or destructive interference of the scattered light rays.
Speckle photography is frequently confused with particle image Velocimetry (PIV) under dense seeding particle concentration. However, specklelike images of PIV are the result of overlapping of Mie scattering images from the physically seeded particles and not from optically created speckles. The dislocations of speckle images result from the flow-particle displacement in PIV. In this chapter, speckle photography refers to an optical method that measures the refractive index gradients of a phase object based on the optically created and refractively dislocated speckle patterns.

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An extended algebraic reconstruction technique (ART) for density-gradient projections: laser speckle photographic tomography

H. S. Ko, K. D. Kihm

An extended algebraic reconstruction technique (ART) is presented for tomographic image reconstruction from the density-gradient projections, such as laser speckle photography. The essence of the extended ART is that the density-gradient projection data of speckle photography (Eq. (1)) are first numerically integrated to the algebraic representation of interferometric fringe number data (Eq. (12)), which ART can readily reconstruct into the cross-sectional field. The extended ART is numerically examined by using two computer synthesized phantom fields, and experimentally by using asymmetric single and double helium jets in air. The experimentally reconstructed images were also compared with the direct measurements of helium concentration using an oxygen analyzing probe. The extended ART method shows an improved accuracy and is proposed to use to tomographically reconstruct the density-gradient projections over the previous Fourier convolution (FC) method (Liu et al. 1989).

for details, click here [119KB in PDF]

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