DOWNHOLE ENTHALPY MEASUREMENT WITH FIBER OPTICS
Studies investigating ways to measure enthalpy down hole have been in progress at Stanford University for the last three years. So far, the void fraction and the dispersed-phase velocity, which are the two essential factors required for calculation of flowing enthalpy, were determined by using resistivity and photosensors. Currently, research efforts have been oriented toward measuring down hole enthalpy by fiber optics. After discussing the applicability of using horizontal or vertical fiber tips, this paper describes the usage of normal reflection probe with the tip surface cut at a right angle to the fiber axis to investigate the void fraction initially in water-air flow then in water-steam flow. The calibration curve was obtained by correlating the void fraction given by the fractional flow ratio detector (FFRD) and the calculated local void fraction. Successful results were obtained for the slow bubble flow case. Future work includes determining the bubble velocity, and testing the device in a model wellbore.
An optical probe for measurements in liquid - liquid two-phase flow
This paper describes a new optical probe system developed for measurements in liquid - liquid two-phase flows with particular reference to kerosene - water flow. The paper gives details of the optical interaction between the probe tip and the kerosene drop front and rear as well as the lay-out of the optical probe system. Static and dynamic interface tests were carried out to determine the theoretical interaction between an approaching flat interface and the probe tip. The modified probe performance in a real bubbly flow was also identified from actual kerosene drop measurements. Finally, the signal analysis procedure used is described and a comparative test of the new optical probe with X hot-wire anemometry for `bubbly' kerosene - water flow in a vertical pipe gave similar results.
Void fraction, bubble velocity and bubble size in two-phase flow
Abstract Experiments were performed in atmosphereic vertical air-water flows, for void fractions between 0.25 and 0.75 (cross-sectional averages) and superficial liquid velocities of 1.3, 1.7 and 2.1 m/s. Local values of void fraction and bubble velocity as well as the bubble diameter were measured by means of a resistivity probe technique. Reliable values were obtained for the local void fraction over the entire range 0 ≤ α ≤ 1 . The void fraction profiles appeared to have a local maximum at the pipe center, local maxima close to the wall were obviously absent. The resistivity probes are shown to measure the velocity of the interface between the conducting and nonconducting phases, which equals the gas velocity only for low void fractions. The measured data for void fraction and bubble velocity were correlated by means of power law distribution functions, with exponents given by a function of the cross-sectionally averaged void fraction. The Sauter mean diameters for the bubble size spectra found, agree reasonably well with diameters predicted by a theoretical model based on the energy dissipation in the flow.