ABSTRACT
Measurement techniques and special instrumentation are developed to obtain quantitative information on parameters that are deemed important for the understanding and prediction of fluid flow processes. One tries to measure, as directly as possible, the quantities that one is interested in. Frequently, however, this cannot be done, and one has to make use of some basic physical laws to obtain the required parameter. In determining the velocity of a fluid, for instance, with a Pitot tube, one has to use Bernoulli’s equation or, if a hot-wire instrument is the sensor, the velocity is obtained from the electric signal by a heat transfer relation. One also has to have a good understanding of the flow situation to ensure, by an order of magnitude estimate of the possible error, that no extraneous effect influences the desired result of the measurement.
