Different kinds of probes have been proposed for the measurement of void fraction, bubble dimension and velocity in two phase flows. All these probes require the interaction between the bubbles and a solid sensing element so that flow disturbance and bubble deformation occurs. In this paper a new non-contact sensing element is described. This new sensing element is based on the interaction between the bubble and two focalized laser beams. The measurement principle is that known as transit-time technique used, for example, in laser dual focus velocimetry or cross-correlation based measuring systems. The object measurement system is based on optical fiber components. The probe is designed for measurements on two-phase flows with minimal disturbance to the flow, since no contact between the bubble and the probe tip is achieved. The probe has been tested in an hydraulic test rig circulated by a vertical two-phase air-water flow at different velocities. The test section that was used is a 100 mm in diameter vertical plexiglass tube. Nitrogen gas was injected upstream the probe in order to obtain small spherical bubbles, with variable bubble concentration, shape and dimensions, to better characterize the probe. The reference bubble velocity was measured independently using photographic techniques and by means of an LDV system.

New non-contact fiber optic sensor for measurement of bubble velocity in two-phase flow

ROSSI, Gianluca;
1994

Abstract

Different kinds of probes have been proposed for the measurement of void fraction, bubble dimension and velocity in two phase flows. All these probes require the interaction between the bubbles and a solid sensing element so that flow disturbance and bubble deformation occurs. In this paper a new non-contact sensing element is described. This new sensing element is based on the interaction between the bubble and two focalized laser beams. The measurement principle is that known as transit-time technique used, for example, in laser dual focus velocimetry or cross-correlation based measuring systems. The object measurement system is based on optical fiber components. The probe is designed for measurements on two-phase flows with minimal disturbance to the flow, since no contact between the bubble and the probe tip is achieved. The probe has been tested in an hydraulic test rig circulated by a vertical two-phase air-water flow at different velocities. The test section that was used is a 100 mm in diameter vertical plexiglass tube. Nitrogen gas was injected upstream the probe in order to obtain small spherical bubbles, with variable bubble concentration, shape and dimensions, to better characterize the probe. The reference bubble velocity was measured independently using photographic techniques and by means of an LDV system.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1118068
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