Evaluation of Local Voidage in Two Phase System by Optical Method

One of the important characteristics in predicting the flow of two phases (gas and liquid) in the industrial equipment is the gas percentage in the liquid, which is called voidage. This characteristic can be measured by different methods; the optical method is one of them. In the present work, a He-Ne laser light is employed to measure the voidage. The measurement depends on the principle of laser light attenuation during its passage through a mixture of fluids, which is governed by Beer-Lambert law. The attenuated light is measured using silicon type detector and an oscilloscope with a plotter. The gas phase was air while the liquid phase was contaminated water situated in a vertical column. The experiments were done with different air flow rates in water (1, 2, 3, 4,5and 6 liters per minute) with two spot sizes of laser (5mm dia & 10 mm dia). The results illustrated the possibility of measuring the voidage using laser beam and are compared with another one based on the liquid level variation (level ratio) in the column. Furthermore, the results provide that the 10mm dia spot size of laser beam gives better results.