Pyrometry second Draft version 2

Pyrometry second Draft version 2 - PYROMETRY Ehsan...

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P YROMETRY Ehsan Noursalehi enoursa2@illinois.edu Co-worker John Michel Section AB2 Group C Date Due 9/16/2009 Date Received revision
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MSE 307 Fall 2009 Ehsan Noursalehi 1. Abstract When using a pyroelectric detector to measure radiation heat, the source must be demagnified on to the detector. The detector must operate in conjunction with a chopper which creates an alternating current. The graphite well sample behaves like a black body, with an emissivity assumed to be 1. In comparison, it is expected for a smooth surface of aluminum to have a low emissivity because, it is not good at absorbing and emitting photons. However, the rough surface of aluminum is expected to have an emissivity more similar to a black body because the surface randomly scatters light. At a temperature of 200°C, it was experimentally found that the emissivity for the rough surface of aluminum is 0.418, and the smooth side is 0.180. The window for the detector has a significant effect on the voltage output of the pyroelectric material. A silica window does not transmit as large a bandwidth of light as glass, and accordingly the voltage readings with a silica window are substantially of lesser magnitude for the same temperature.
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MSE 307 Fall 2009 Ehsan Noursalehi 2. Introduction Many materials science processes are required to occur at temperatures of 1,700 O C, or higher. Therefore, it is important to have a reliable and accurate method for taking temperature measurements at such elevated temperatures. A thermocouple would not work well at 1,700 O C or higher because, the thermocouple itself will heat up substantially, and be unable to give accurate results. Therefore, other methods are required. In this lab, we specifically look at the thermometry method of pyrometry. There are three mechanisms of heat transfer: conduction, convection, and radiation. For high temperature thermometry, we want to measure infrared radiation. Radiation is the transfer of heat by an electromagnetic wave; which can be used for non-contact temperature measurement. Emissivity is the measure of a material's capability to radiate and absorb quanta of light. There is a theoretical material which has perfect absorption and emission. This material is called a black body, and has an emissivity of one. On the other hand, a theoretical material which has no absorption or emission capabilities, has an emissivity of zero. Real materials have an emissivity between zero and one. In order to measure thermal radiation and emission, we need to make use of a pyroelectric material such as, KTaO 3 . Due to the characteristic nature of a pyroelectric detector which creates a surface charge, it must be operated with alternating current in order to take measurements. In this pyrometry lab, samples are heated in a Carbonite MTF 10 furnace, and the emitted
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This note was uploaded on 03/02/2010 for the course ITAL 102 taught by Professor Hill during the Spring '10 term at Zane State.

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Pyrometry second Draft version 2 - PYROMETRY Ehsan...

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