Void fraction measurement by X-ray absorption

An X-ray tube and scintillation detectors were mounted on test pipes containing static voids of air–water mixture. Due to fluctuations in the X-ray tube output, void fraction measurements were carried out by using two detectors, one as a reference and the other as a void monitor. The intensity of a narrow (30–100 kV) X-ray beam transmitted through test pipes of different I.D. was measured to obtain the void fraction. The uncertainty in measuring static void fraction, was found to decrease as the void fraction increases, and to increase as X-ray energy increases. It was found that for a certain test-section pipe diameter, there exist an optimum X-ray energy that gives a minimum uncertainty in void fraction measurement.