This paper reports the results of research involving observations of flow patterns during air-oil-water three-phase flow through a vertical pipe with an internal diameter of 0.03 m and a length of 3 m. The conductometric method based on the measurement of electrical conductivity of the gas-liquid-liquid system was used to evaluate the flow patterns. In the studies, a set of eight probes spaced concentrically in two tube sections (four probes per each) with a spacing of 0.015 m were used. The paper presents a theoretical description of the test method and the analysis of the measurement results for air-oil-water multiphase flow system. Results of this study indicate that the developed method of characterizing the voltage of the gas-liquid-liquid system can be an important tool supporting other methods to identify flow patterns, including visual observation.

This research explored different types of two-phase flow patterns that influenced heat transfer rate by assessing rectangular two-phase closed thermosyphon (RTPCT) made from glass with the sides of equal length of 25.2 mm, aspect ratio 5 and 20, evaporation temperature of 50, 70, and 90 °C, working substance addition rate of 50% by volume of evaporator, and water inlet temperature at condensation of 20 °C. Upon testing with aspect ratios 5, three flow patterns emerged which were: bubble flow, slug flow and churn flow respectively. As per the aspect ratio 20, four flow patterns were discovered which were: bubble flow, slug flow, churn flow and annular flow, respectively. Aspect ratio 5 pertains characteristic which resulted in a shorter evaporation rate of the RTPCT than that of the aspect ratio 20, thus, a shorter flow distance from the evaporator section to heat releaser was observed. Therefore, flow patterns at aspect ratio 5 exhibited a faster flow velocity than that of the aspect ratio 20. Furthermore, changes of flow pattern to the one that is important for heat transfer rate can be easily achieved. Churn flow was the most important type of the flow for heat transfer, followed by slug flow. Moreover, with aspect ratio 20, annular flow was the most important flow for the heat transfer, followed by churn flow, respectively. Throughout the test, average heat flux as obtained from the aspect ratio 5 were 1.51 and 0.74 kW/m2 which were higher than those of the aspect ratio 20. The highest heat flux at the operating temperature of the evaporator section was 90 °C, which was equivalent to 2.60 and 1.52 kW/m2, respectively.