A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Standard two-color optical fiber thermometry involves measuring the spectral intensity at the end of the fiber at two wavelengths. The temperature at the sensing tip of the fiber can then be inferred using Planck's law and the ratio of the spectral intensities. If, however, the length of the optical fiber is exposed to elevated temperatures, erroneous temperature measurements will occur due to emission by the fiber. This thesis presents a method to account for emission by the fiber and accurately infer the temperature at the tip of the optical fiber. Additionally, an estimate of the temperature profile along the fiber may be obtained. A mathematical relation for radiation transfer down the optical fiber is developed. The radiation exiting the fiber and the temperature profile along the fiber are related to the detector signal by a signal measurement equation. Since the temperature profile cannot be solved for directly using the signal measurement equation, two inverse minimization techniques are developed to find the temperature profile. Simulated temperature profile reconstructions show the techniques produce valid and unique results. Tip temperatures are reconstructed to within 1.0%. Experimental results are also presented. Due to the limitations of the detection system and the optical fiber probe, the uncertainty in the signal measurement equation is high. Also, due to the limitations of the laboratory furnace and the optical detector, the measurement uncertainty is also high. This leads to reconstructions that are not always accurate. Even though the temperature profiles are not completely accurate, the tip-temperatures are reconstructed to within 1%—a significant improvement over the standard two-color technique under the same conditions. Improvements are recommended that will lead to decreased measurement and signal measurement equation uncertainty. This decreased uncertainty will lead to the development of a reliable and accurate temperature measurement device.

The objective of this work is to apply the method of variation of parameters to various direct and inverse nonlinear, multimode heat transfer problems. An overview of the general method of variation of parameters is presented and applied to a simple example problem. The method is then used to obtain solutions to three specific extended surface heat transfer problems: 1. a radiating annular fin, 2. convective and radiative exchange between the surface of a continuously moving strip and its surroundings, and 3. convection from a fin with temperature-dependent thermal conductivity and variable cross-sectional area. The results for each of these examples are compared to those obtained using other analytical and numerical methods. The method of variation of parameters is also applied to the more complex problem of combined conduction-radiation in a one-dimensional, planar, absorbing, emitting, non-gray medium with non-gray opaque boundaries. Unlike previous solutions to this problem, the solution presented here is exact. The model is verified by comparing the temperature profiles calculated from this work to those found using numerical methods for both gray and non-gray cases. The combined conduction-radiation model is then applied to determine the temperature profile in a ceramic thermal barrier coating designed to protect super alloy turbine blades from large and extended heat loads. Inverse methods are implemented in the development of a non-contact method of measuring the properties and temperatures within the thermal barrier coating. Numerical experiments are performed to assess the effectiveness of this measurement technique. The combined conduction-radiation model is also applied to determine the temperature profile along the fiber of an optical fiber thermometer. An optical fiber thermometer consists of an optical fiber whose sensing tip is coated with an opaque material which emits radiative energy along the fiber to a detector. Inverse methods are used to infer the tip temperature from spectral measurements made by the detector. Numerical experiments are conducted to assess the effectiveness of these methods. Experimental processes are presented in which a coating is applied to the end of an optical fiber and connected to an FTIR spectrometer. The system is calibrated and the inverse analysis is used to infer the tip temperature in various heat sources.

The following work deals with basics of fiber optics, history of fiber optics, and methods of measuring physical quantities with the use of fiber optic sensors. The work includes facts about physics, chemistry and biology - these elements are necessary for a full understanding of the issue. In order to create an optical fiber temperature sensor based on Fabry Perot resonator principle, several methods of manufacturing the optical cavity are investigated. A practical part of paper consist in the manufacturing of the miniature fiber thermometer, its coating and testing.