Velocity measurement transducers, table

Table 4-1 Transducer Comparison of Commonly Used Velocity Measurement Diagnostics...

Ultrasonic techniques are an obvious choice for measuring the wall thickness. In the pulse-echo method times between echoes from the outer and inner surface of the tube can be measured and the wall thickness may be calculated, when the ultrasonic velocity of the material is known. In the prototype a computer should capture the measuring data as well as calculate and pre.sent the results. First some fundamental questions was considered and verified by experiments concerning ultrasonic technique (Table I), equipment, transducers and demands for guidance of the tube. 

Pandit and King (1982) and Bathe et al. (1984) presented measurements using transducer techniques, which are somewhat different from the accepted values of Kiefte et al. (1985). The reason for the discrepancy of the sonic velocity values from those in Table 2.8 and above is not fully understood. It should be noted that compressional velocity values can vary significantly depending on the hydrate composition and occupancy. This has been demonstrated by lattice-dynamics calculations, which showed that the adiabatic elastic moduli of methane hydrate is larger than that of a hypothetical empty hydrate lattice (Shpakov et al., 1998). 

Hot wire anemometry (HWA) or constant temperature anemometry (CTA), laser Doppler anemometry (LDA) or laser Doppler velocimetry (LDV), and particle image velocimetry (PIV) are currently the most commonly used and commercially available diagnostic techniques to measure fluid flow velocity. The great majority of the HWA systems in use employ the constant temperature anemometry (CTA) implementation. A quick comparison of the key transducer properties of each technique is shown in Table 4-1, with expanded details on spatial resolution, temporal resolution, and calibration provided in the following sections. 

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