Temperature diagnostic with

Fig. 8.4. Comparison of the electron temperature measured in the plasma center by the X-ray spectrometer and the ECE diagnostics with hydrogen (solid points) and deuterium (open points) as working gas. The squares and triangles correspond to discharges with neutral beam injection [3]...

Another type of thermotropic liquid crystals is called cholesteric liquid crystals. The color of cholesteric liquid crystals changes with temperature and therefore they are suitable for use as sensitive thermometers. In metallurgy, for example, they are used to detect metal stress, heat sources, and conduction paths. Medically, the temperature of the body at specific sites can be determined with the aid of liquid crystals. This technique has become an important diagnostic tool in treating infection and mmor growth (for example, breast tumors). Because locahzed infections and tumors increase metabolic rate and hence temperature in the affected tissues, a thin film of liquid crystal can help a physician see whether an infection or tumor is present by responding to a temperature difference with a change of color. 

Laser techniques have a great potential for studies of microscopic as well as macroscopic combustion in flames and engines. Combustion diagnostics with lasers was discussed in several reviews [10.8-13]. We will here give examples of measurements of concentrations and temperature (flame kinetics) using fluorescence, Raman and coherent Raman techniques. In practical combustion systems turbulence is extremely important and we will also briefly discuss laser techniques for flow and turbulence measurements. 

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

The color development of photochromic compounds can also be utili2ed as a diagnostic tool. The temperature dependence of the fa ding of 6-nitroindolinospiropyran served as the basis for a nondestmctive inspection technique for honeycomb aerospace stmctures (43). One surface of the stmcture to be exarnined was covered with a paint containing the photochromic compound and activated to a violet color with ultraviolet light. The other side of the stmcture was then heated. The transfer of heat through the honeycomb stmcture caused bleaching of the temperature-dependent photochromic compound. Defects in the honeycomb where heat transfer was inhibited could be detected as darker areas. 

Heat transfer in micro-channels occurs under superposition of hydrodynamic and thermal effects, determining the main characteristics of this process. Experimental study of the heat transfer in micro-channels is problematic because of their small size, which makes a direct diagnostics of temperature field in the fluid and the wall difficult. Certain information on mechanisms of this phenomenon can be obtained by analysis of the experimental data, in particular, by comparison of measurements with predictions that are based on several models of heat transfer in circular, rectangular and trapezoidal micro-channels. This approach makes it possible to estimate the applicability of the conventional theory, and the correctness of several hypotheses related to the mechanism of heat transfer. It is possible to reveal the effects of the Reynolds number, axial conduction, energy dissipation, heat losses to the environment, etc., on the heat transfer. 

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