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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 [Fi [91 Lin 8.2 —— No PgE [91 CHAPTER 12 Experimental Methods JOS ´ E L. LAGE Mechanical Engineering Department Southern Methodist University Dallas, Texas 12.1 Fundamentals 12.1.1 Measurement 12.1.2 Sensing 12.1.3 Calibration 12.1.4 Readability 12.2 Measurement error 12.2.1 Uncertainty: bias and precision errors 12.2.2 Mean and deviation 12.2.3 Error distribution 12.2.4 Chauvenet’s criterion and the chi-square test 12.3 Calculation error 12.4 Curve fitting 12.5 Equipment 12.5.1 Glass thermometers 12.5.2 Thermocouples 12.5.3 Resistance temperature detectors 12.5.4 Liquid crystals 12.5.5 Pyrometers 12.5.6 Heat flow meters Nomenclature References 12.1 FUNDAMENTALS 12.1.1 Measurement Measurement is one of the most important activities in science and engineering. Validation of new theories, determination of material property values, classification of new materials, performance evaluation of new and existing devices, and monitoring and control of existing and new processes are activities that depend on measurements. 913
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914 EXPERIMENTAL METHODS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 [914 Lin 0.0 —— Nor PgE [914 Measurement, or measuring, is also the most important part of an experiment. Measuring is not absolute, as it does not define a quantity (standard) to be measured. Measuring is a relative effort and is made to compare and to evaluate. To be indepen- dent, a comparison requires a measure, a standard unit. The art of measuring is at least as old as humanity itself. The human body performs measurements all the time. One of the most basic quantities continuously measured by the human body is the environment temperature. Feeling hot or cold is a consequence of this measuring. Although not descriptive (not quantified with a parameter such as temperature), the natural measuring of the environmental temperature by the human body is nevertheless a relative process. This process is based on a comparison of the environmental temperature with a certain standard, in this case the temperature at which the body feels neither hot nor cold—the null point of human thermal control. In heat transfer, temperature and heat flow are unquestionably the most important quantities to be measured. Other quantities of interest to heat transfer include fluid speed, pressure (force), mechanical stress, electric current, voltage, length, surface area, volume, and displacement. In this chapter the focus is on temperature and heat flow measurements. General measuring concepts such as sensitivity, hysteresis, calibration, accuracy, and readability are presented first. Then the discussion turns to statistical concepts such as mean, deviation, standard deviation, normal distribution, Chauvenet’s crite- rion, and the chi-square test, related to the determination of precision, bias error, and measuring uncertainty. The final section of this chapter is devoted to a brief discussion of some common instruments for measuring temperature or heat flow.
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