Chapter 8 Notes

# Chapter 8 Notes - Chapter 8 Temperature Material from...

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1 Chapter 8 Temperature Material from Theory and Design for Mechanical Measurements; Figliola, Third Edition Temperature Standards ± “Temperature can be loosely described as the property of an object that describes its hotness or coldness, concepts that are clearly relative. Our experiences indicate that heat transfer tends to equalize temperature; or more precisely, systems that are in thermal communication will eventually have equal temperatures. The zeroth law of thermodynamics states that two systems in thermal equilibrium with a third system are in thermal equilibrium with each other. Although the zeroth law of thermodynamics essentially provides the definition of equality of temperature, it provides no means for defining a temperature scale.” Temperature Standards ± A temperature scale provides for three essential aspects of temperature measurement: (1) the definition of the size of the scale increment, (2) fixed reference points for establishing known temperatures (3) a means for interpolating between these fixed temperature points.

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2 Temperature Standards ± The calibration of a temperature measurement device entails not only the establishment of fixed temperature points, but the indication of any temperature between fixed points. ± The operation of a mercury-in-glass thermometer is based on the thermal expansion of mercury contained in a glass capillary, where the level of the mercury is read as an indication of the temperature. Temperature Standards ± Submerge the thermometer in water at the ice point, make a mark on the glass at the height of the column of mercury, and label it 0 o C. ± Submerge the thermometer in boiling water, and mark the level of mercury, and label it 100 o C. Figliola, 2000 Temperature Standards ± The process of establishing 50 o C without a fixed- point calibration is called interpolation. ± Theory of the behavior of the mercury in the thermometer, or many fixed points for calibration are necessary. ± Even by the late 18 th century, there was no standard for interpolating between fixed points on the temperature scale; the result was that different thermometers indicated different temperatures away from fixed points, sometimes with surprisingly large errors.
3 Temperature ± Temperature is one of the most commonly measured engineering variables. ± Thermometry is based on thermal expansion. ± Most materials exhibit a change in size as a result of a change on temperature. ± Measure temperature variation through thermal expansion of liquid in glass. ± Difference in thermal expansion between liquid and glass results in a change in level. Temperature ± The modern engineering definition of the temperature scale is provided by a standard called the International Temperature Scale. ± This standard establishes fixed points for

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## This note was uploaded on 11/22/2011 for the course ABE 6031 taught by Professor Burks during the Summer '11 term at University of Florida.

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Chapter 8 Notes - Chapter 8 Temperature Material from...

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