Showing papers by "Raymond Viskanta published in 1975"
TL;DR: In this paper, the authors present an overview of the background information needed to formulate and analyze heat transfer in semitransparent materials systematically and then review the literature in some specific problem areas.
Abstract: Publisher Summary The chapter presents an overview of the background information needed to formulate and analyze heat transfer in semitransparent materials systematically and then reviews the literature in some specific problem areas Primary emphasis is placed on semitransparent solids, although the principles presented are general and apply to any phase The chapter also discusses the wide variety of applications and involves nature of heat transfer phenomena in semitransparent condensed phases The radiation characteristics of semitransparent materials are not only dependent on surface but also volume phenomenon since some of the emitted radiation originates at considerable depths In short, the radiation characteristics depend on the spectral absorption coefficient and index of refraction, thickness, boundary conditions, and temperature distribution The transient heating of semitransparent materials under idealized conditions in which the emission of radiation from the material is neglected is also discussed This implies that the body is cold and the rate of emission of radiation per unit volume is negligible compared to absorption This simplification limits the applicability of analysis and results to those early stages of heating during which temperatures have not raised high enough to render the assumption invalid The chapter also presents an analysis to show the influence of physical parameters on the temperature field in a semitransparent solid irradiated from a high temperature source such as the sun The results intend to aid the designer of solar collectors in selecting the optimum material by indicating physical parameters, which determine maximum efficiency of solar energy conversion in different semitransparent solids
157 citations
TL;DR: An analytical model that relates the emerging spectral intensity from a plane layer of solid heated by an external radiation source to the temperature distribution, spectral radiation properties, radiation characteristics of the interfaces of the solid, and the source is formulated.
Abstract: A spectral remote sensing method for recovering the temperature distribution in semitransparent solids from remotely sensed spectral emission data is studied. An analytical model that relates the emerging spectral intensity from a plane layer of solid heated by an external radiation source to the temperature distribution, spectral radiation properties, radiation characteristics of the interfaces of the solid, and the source is formulated. The temperature profile is expressed in the form of a finite series of Legendre polynomials; and the coefficients are obtained using an optimization scheme that, by iteratively solving the expressions for emerging intensity, reconstructs the distribution that best fits the spectral emission data. The validity and accuracy of the remote sensing method is evaluated by comparing the recovered temperature with independent measurements in two different experiments; one using surface thermocouples only and the other a Mach-Zehnder interferometer. Experimental results are reported for PPG clear float glass and Corning Code 7940 fused silica using a Perkin-Elmer spectrometer and Barnes Spectralmaster radiometer to measure the emerging spectral radiant energy. For clear float glass, the recovered temperatures were a maximum of 1.5% higher than those measured with surface thermocouples. For fused silica, the linear recovered and interferometrically measured temperature profiles agreed well, with the maximum deviation never exceeding approximately 2% up to about 1000 K.
20 citations
TL;DR: In this paper, a method for recovering the temperature distribution in glass from remotely sensed spectral emission data is studied, which is related analytically to the spectral emerging intensity, was determined by an optimization technique that minimizes the difference between measured and calculated emissions.
Abstract: A method for recovering the temperature distribution in glass from remotely sensed spectral emission data was studied. The temperature distribution, which was related analytically to the spectral emerging intensity, was determined by an optimization technique that minimizes the difference between measured and calculated emissions. The method was evaluated by measuring spectral emission from heated glass using both a spectrometer and a spectroradiometer. Data were taken from 600 to 900 K for window glass samples with different back-surface boundary conditions. The recovered temperature profiles obtained using data from both measuring instruments were compared with each other and with temperature profiles predicted from a combined conduction-radiation heat-transfer analysis. When only 2 unknown coefficients were used to represent the temperature distribution, the recovered and predicted profiles agreed within 1%.
9 citations
TL;DR: In this paper, a numerical method is developed for recovering the temperature distribution in glass from spectral radiation emission data, which is obtained using an optimization scheme that determines the best temperature profile from the data in a form of discrete points or Legendre polynomials.
Abstract: A numerical method is developed for recovering the temperature distribution in glass from spectral radiation emission data. The desired temperature distribution is obtained using an optimization scheme that determines the best temperature profile from the data in a form of discrete points or Legendre polynomials. In order to evaluate the accuracy and validity of the spectral remote sensing method, the recovered temperatures are compared with independent measurements in two different experiments, one of which uses a Mach-Zehnder interferometer. Experimental results are reported for Corning Code 7940 fused silica using a Perkin-Eimer spectrometer to measure the spectral radiant energy emerging from the glass. The recovered and interferometrically measured temperatures are found to be in good agreement, i.e., within about 1 ? percent at temperatures up to about 800 K.
9 citations
TL;DR: Approximate methods for calculating the error introduced by the deflection of the light beam or refractive error in schlieren, shadowgraph, interferometric, and holographic measurements of transport phenomena are investigated and a new first-order approximation in both a linear and nonlinear refractive index field is reported.
Abstract: Approximate methods for calculating the error introduced by the deflection of the light beam or refractive error in schlieren, shadowgraph, interferometric, and holographic measurements of transport phenomena are investigated. Relative error is reported for the well-known correction parabola and paraxial approximations as well as for a new first-order approximation in both a linear and nonlinear refractive index field. The first-order approximation is exact in a linear field but is in about the same error as the other approximations in the nonlinear field of a boundary layer. In many cases, actual optical data can be corrected for refractive errors by using the results presented.
8 citations
TL;DR: In this paper, a method for recovering the temperature distribution in glass from remotely sensed spectral emission data is studied, which is related analytically to the spectral emerging intensity, was determined by an optimization technique that minimizes the difference between measured and calculated emissions.
Abstract: A method for recovering the temperature distribution in glass from remotely sensed spectral emission data was studied. The temperature distribution, which was related analytically to the spectral emerging intensity, was determined by an optimization technique that minimizes the difference between measured and calculated emissions. The method was evaluated by measuring spectral emission from heated glass using both a spectrometer and a spectroradiometer. Data were taken from 600 to 900 K for window glass samples with different back-surface boundary conditions. The recovered temperature profiles obtained using data from both measuring instruments were compared with each other and with temperature profiles predicted from a combined conduction-radiation heat-transfer analysis. When only 2 unknown coefficients were used to represent the temperature distribution, the recovered and predicted profiles agreed within 1%.
2 citations