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|Type:||Artigo de periódico|
|Title:||Local Measurements In Two-phase Flows Using A Resistivity Double Probe Technique|
|Author:||Mendes de Moura Luiz Felipe|
|Abstract:||Local measurements are of primary importance for the characterization of gas-liquid two-phase flows, both for processes control and numerical modeling validation. It is a very active research field due to the increasing number of applications in the thermohydraulics of heat exchangers, nuclear plants, chemical processes and oil industries. This paper presents the local measurements in a vertical upward air-water flow using the electrical resistivity double probe technique. The test section was a 80 mm i.d. and 160 cm long Plexiglas pipe. Five different gas superficial velocities, ranging from 0.02 to 0.10 m/s, were used in combination with two liquid superficial velocities of 0 and 0.10 m/s. A resistivity double probe was employed for measurements of the radial profiles of void fraction, bubble frequency, bubble interface velocity, interfacial area concentration and Sauter mean diameter. The electrical resistivity probe method consists of a instantaneous measurement of the local electrical resistivity in the two-phase flow by means of a sensor electrode. Since the circuit is opened or closed depending on whether the sensor tip is in contact with gas or liquid, the probe behaves in principle like a switch, yielding a two-stage signal. However, to obtain a true square wave type signals, a proper threshold voltage has to be used as a triggering criterion. Herein the signal conditioning is discussed and the influence of the threshold level is analyzed. With a probe with two sensors displaced axially, the bubble interface velocity could be determined from the time delay which gave maximum correlation between the sensor responses. These values of gas velocity in conjunction with void fractions could be integrated to give average gas superficial velocities. Values determined in this manner were compared to values from the inlet gas flowrate measurements and showed an average deviation of less than 6% for bubbly flow.|
|Editor:||Braz Soc Mech Sci, Rio de Janeiro, Brazil|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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