A comparative study of phase Doppler and laser diffraction techniques to investigate drop sizes in annular two-phase flow

Abstract

Drop size information is a common requirement in many parts of industry. Phase Doppler anemometry and laser diffraction techniques are usually employed for this purpose. Both measuring techniques give the drop size whereas the phase Doppler anemometry also provides additional information on the drop velocities. In the present work an inclinable two-phase flow facility has been constructed and the impact of inclination on the drop sizes has been investigated. This paper describes the drop size results obtained from two laser techniques and identifies the difference in drop sizes obtained from two laser systems when measurements were made under similar flow conditions. Possible reasons for this discrepancy have been discussed and a technique has been suggested to modify the new data obtained from the phase Doppler anemometry. The modified data have then been compared with those obtained from the laser diffraction technique. Results from both laser systems reveal similar trends in the measurements made under identical flow conditions. It has been found that the drop sizes are affected by the flow orientation and the effect is more pronounced at angles greater than 50° from the vertical. The effect of liquid mass flux has also been recorded. General problems and common sources of error while employing these two laser techniques have also been identified and necessary steps required to obtain laser results have been discussed in detail.