In our previous study, we derived a correlation for countercurrent flow limitation (CCFL) at the sharp-edged upper end in vertical pipes, where the dimensionless velocity was the Kutateladze parameter with the characteristic length of the Laplace capillary length, by using air-water experimental data reported by Richter (1981) with the diameters of D = 19–140 mm and Doi et al. (2012) with D = 30, 45, and 60 mm. In this study, we reevaluated effects of the diameter on CCFL in detail for small diameters by using those data by Richter and Doi et al. The dimensionless velocity for CCFL data by Richter was the Kutateladze parameter for D = 44–140 mm but was the Wallis parameter (where the characteristic length is the diameter) for D = 19–51 mm (data for D = 44 and 51 mm could be expressed by both of the Wallis and Kutateladze parameters). The difference of the CCFL constants in the Wallis CCFL correlation for D = 30 mm by Doi et al. and D = 32 mm by Richter was a little larger than the uncertainty bands. This means that it is needed to measure reliable CCFL data in the small diameters of D < 30 mm in order to make effects of the diameter clear.

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