Hot-Film Anemometry

Thermal hot-wire and hot-film anemometers (HFA) have been available for measuring instantaneous single phase fluid velocity for about a century. The small size of the sensor and good frequency response makes them especially suitable for turbulence investigations. These techniques are thus commonly used in many engineering disciplines. 

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Delhaye, J. M., 1969b, Hot-Film Anemometry in Two-Phase Flow, ASME Symp. on Two-Phase Flow Instrumentation, Chicago, pp. 58 69. (3)... 

For experimental determination the flow pattern produced by the stirrer was initially visualized using different photographic methods (e.g. [574, 497]), but hydraulic probes were also used to determine the pressure distribution (e.g. [135]) and velocity distribution (e.g. [437]). Also, convection probes (spherical probes) and pressure probes (Prandtl s Pitot tube) were used. Later constant temperature hotwire/hot-film anemometry was used. Currently contactless laser doppler velocim-ctry (LDV)/anemometry (LDA) is exclusively utilized. 

It is noteworthy that the use of Pitot tubes and hot-film anemometry, which are applicable to newtonian fluids, is questionable for drag-reducing viscoelastic fluids. The anomalous behavior of Pitot tubes and hot-film probes in these fluids has been observed by many investigators [87-92]. 

Measurements have been made of turbulence structure by a number of workers using laser-Doppler methods and using hot-film anemometry Application of computational fluid dynamics to turbulent flow in stirred tanks is developing rapidly and involves using assumptions inherent in Kolmogoroff s theory and turbulence measurements to supply boundary conditions. 

FIGURE 55.3 Velocity profiles measured 2 cm downstream of the aortic valve with hot film anemometry in dogs [Paulsen and Hasenkam, 1983]. The timing of the measurements during the cardiac cycle is shown by the marker on the aortic flow curve. 

Liquid velocity may also be determined using hot film anemometry (Boyer et al., 2002 Magaud et al., 2001). One advantage of this technique is that it is fairly inexpensive, accurate, and relatively easy to implement. However, proper implementation requires a uniform temperature in the bioreactor as well as a limited... 

The concept of hot-wire or hot-film anemometry was first conceived in the early 1900s [1]. Due to the technical difficulty in developing and testing hot-wire anemometers, published experimental data have remained scarce. Boussinesq was one of the first to have validated the theory of hot-wire anemometry [2], followed by other... 

Traditionally, hot-wire or hot-film anemometry has been developed to directly measure the fluid velocities under unsteady state or in the presence of turbulent flow [11]. 

Fig. 13.1 The Hot Film Anemometry (HFA) method [54, 199]. a The HFA measuring system, b Hot-film sensors, c Flow-direction measurements. The figures b and c are reproduced from Doebelin [54] (pp. 608-609) with permission from McGraw-Hill Education...

Reviews of the HFA method, considering setups, strengths, limitations, and comparisons with other velocimeters can be found in the books of Goldstein [73] and Doebelin [54]. More practical aspects of the application of hot-film anemometry characterizing liquid flows has been outlined by Bnum [29]. 

Bruun HH (1996) Hot-film anemometry in liquid flows. Meas Sci Technol 7 1301-1312 Burgess JM, Calderbank PH (1975) The measurement of bubble parameters in two-phase dispersions-1 the development of an improved probe technique. Chem Eng Sci 30 743-750 Cao Z, Xu L, Fan W, Wang H (2010) Electrical capacitance tomography with a non-circular sensor using the dbar method. Meas Sci Techn 21(1-6) 015502... 

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