An experimental two-phase flow study was conducted on a series of Lucite rectangular channels-with aspect ratios of 2 to 16 using an air-water system at atmospbcric pressure. The objectives of the study were: (1) to determine the effect of sudden changes of flow area on the density of two-phase fluids; (2) to investigate the effect of mass flow rate on the two-phase friction factor multipliers and (3) to develop a sound method of measuring the density of a twophase fluid in large conduits. The density of the air-water mixture changed during either an expansion or contraction of flow area; however, the magnitude of the change was not great and was readily predicted by a semi-theoretical equation. A sizeable effect of mass flow rate on the twophase friction factor multiplier was found which was not accounted for in the widely used Martinelli correlation. A traversing technique was developed for measuring the density of a two-phase fluid which also gave a continuous trace of the phase distribution. The method was tried on Lucite mockups of simulated two-phase flow patterns, and excellent agreement was obtained between the measured and calculated voids. (auth)