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There are five factors which can be considered when trying to decide which flowmeter to use. These are
the type of fluid to be metered, process conditions, installation conditions, performance requirements, and
economic factors. Information required when considering the fluid to be metered are, whether it is a single
phase fluid or whether it contains a second component such as gas or solids, the fluid viscosity and density,
whether the fluid is corrosive, and if it is a gas whether it is dry or wet. Factors to be considered under
process conditions include the pipeline temperature and pressure, and the ambient conditions outside of
the pipeline. Installation conditions covers information such as the pipe diameter, the pipe Reynolds
number, the orientation of pipework at the measurement point, the length of straight pipework available,
whether the flow is pulsating, the need for any flow conditioning, whether an external power source is
available, and if the measurement is being made in a hazardous environment. Performance requirements
cover the accuracy, repeatability, range, and dynamic response required by the flowmeter. Finally, economic
factors cover issues such as the initial cost of the flowmeter, installation cost, maintenance cost, and the
type of training required.
Most flow measurement textbooks also contain flowmeter selection charts (for example, [3, 4, 6]),
and an international standard is now available on the selection and application of flowmeters [12].

References
1. Flow Measurement and Instrumentation, Oxford: Elsevier Science.
2. Grant, D. M., Open channel flow measurement, in D. W. Spitzer (Ed.), Flow Measurement: Practical
Guides for Measurement and Control, 2nd ed., Research Triangle Park, NC: ISA, 2001.
3. Miller, R. W., Flow Measurement Engineering Handbook, 3rd ed., New York: McGraw Hill, 1996.
4. Baker, R. C., Flow Measurement Handbook, Cambridge: Cambridge University Press, 2000.
5. Webster, J. G. (Ed.), Mechanical Variables Measurement: Solid, Fluid, and Thermal, Boca Raton: CRC
Press, 2000.
6. Spitzer, D. W. (Ed.), Flow Measurement: Practical Guides for Measurement and Control, 2nd ed., Research
Triangle Park, NC: ISA, 2001.
7. International Organisation for Standardization, ISO5167-1, Measurement of Fluid Flow by Means
of Pressure Differential Devices—Part 1: Orifice plates, nozzles and Venturi tubes inserted in circular
cross-section conduits running full, Geneva, Switzerland, 1991.
8. American Petroleum Institute, API 2530, Manual of Petroleum Measurement Standards Chapter 14—
Natural Gas Fluids Measurement, Section 3—Orifice Metering of Natural Gas and Other Related
Hydrocarbon Fluids, Washington, 1985.
9. Lynnworth, L. C., Ultrasonic Measurements for Process Control: Theory, Techniques, Applications, Boston:
Academic Press, 1989.
10. National Engineering Laboratory, UK, Effects of Two-Phase Flow on Single-Phase Flowmeters, Flow
Measurement Guidance Note No. 3, 1997.
11. Rajan, V. S. V., Ridley, R. K., and Rafa, K. G., Multiphase flow measurement techniques—a review,
Journal of Energy Resource Technology, 115, 151–161, 1993.
12. British Standards Institution, BS7405, Guide to the Selection and Application of Flowmeters for
Measurement of Fluid Flow in Closed Conduits, London, 1991.

19.6 Temperature Measurements

Pamela M. Norris and Bouvard Hosticka

Introduction
Temperature is often cited as the most widely monitored parameter in science and industry, yet the exact
definition of temperature is elusive. The simplest definition would relate temperature to the average kinetic
energy of the individual molecules that comprise the system. As the temperature increases, the molecular
activity also increases, and thus the average kinetic energy increases. This is an adequate definition for

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