AN EXPERIMENTAL-STUDY OF THE SUITABILITY OF USING A GAMMA DENSITOMETER FOR VOID FRACTION MEASUREMENTS IN GAS-LIQUID FLOW IN A SMALL DIAMETER TUBE

The design of a single-beam gamma densitometer operated in the count m ode is briefly described. The design is simple and reasonably compact and is suitable for two-phase flow void fraction measurement in small diameter tubes. The influence of the various parameters and test condi tions on the gamma densitometer has also been thoroughly examined. The void fraction results were calibrated against the readings from a set of quick-closing valves. The present test results show that the perfo rmance of the gamma densitometer is good, and that the measurement alg ebraic error is within +5% (the rms deviation is less than 7%). It als o shows that a good average void fraction could be obtained by measuri ng the volumetric void fraction for the small pipe size. The typical d esign of such a gamma densitometer is summarized in this paper. Void f raction measurements were taken during adiabatic upward and downward t wo-phase gas-liquid flow in a vertical tube with inside diameter 9.525 mm. The present void fraction data were compared with data available in the literature for measurements of the void fraction for upward flo w in vertical pipes with inside diameters of 100 mm and 25.4 mm. The r esults of this comparison shows that there is no significant influence of the tube diameter on the measuring technique using the gamma radia tion method. The results from the gamma densitometer show good agreeme nt with the literature for upward flow. The downward void fraction dat a appeared to be generally higher than correlations published previous ly.