Calibration and Application of Transient Liquid Crystals for Heat Transfer Measurements
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Date
2015-08
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The Ohio State University
Abstract
Gas turbine engines are often subjected to high temperatures required to maximize efficiency. However, these temperatures exceed the melting temperature of the metal and hence turbine blades require effective cooling. Heat transfer experiments are conducted at the OSU Gas Turbine Laboratory to better understand the effects of these cooling flows. The current method of temperature measurement involves using discrete instrumentation such as resistance temperature devices (RTDs), which are limited to extracting measurements only at specific locations. Thermochromic Liquid Crystals (TLCs) provide full coverage temperature measurements that can act as boundary conditions for a conduction model to enable calculation of surface heat transfer. The crystals respond to temperature changes by reflecting light of a particular wavelength, and this apparent color change may be captured using a calibrated digital camera. There are various data available on TLCs, but industry remains cautious about the reliability of the data and requires careful verification of any measurements acquired using this technique. This thesis describes the development of a facility needed to obtain the accurate data that can demonstrate that the TLC methodology employed at OSU provides reliable temperature measurements. To conduct this experiment, a model for the steady-state calibration of the liquid crystals applied to a flat copper plate has been designed and constructed. The hue values of the reflected color are captured by a high-resolution camera and are then compared against known temperatures given by RTDs. Calibration curves for two trials are obtained, which show consistent results. The relationship between color and temperature can be well defined using a seventh degree polynomial fit.
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Keywords
Liquid Crystals, Heat Transfer, Calibration, Temperature measurement