The frictional pressure drops of single-phase and two-phase flows in mini-pipes and mini-rectangular channels were investigated experimentally. The friction factors and the critical Reynolds number were measured by using water single-phase and gas-water two-phase flows through circular and rectangular channels respectively. Diameter of the circular pipes was 0.5, 0.25 and 0.17 mm, respectively; dimension of the rectangular channels was 0.2 × 20 mm, 0.2 × 10 mm, 0.2 × 5 mm and 0.2 × 2 mm, respectively. The experimental results for water single-phase flow in the circular tubes show that the measured friction factor agreed well with the conventional Poiseuille’s equation (λ = 64/Re) in laminar flow regime; the laminar-turbulent transition Reynolds number was approximately 2300 in a range of the present experimental conditions for each diameter. On the other hand, the experimental results for water flow in the rectangular channels slightly differed from the conventional equation (λ = 96/Re). For the two-phase flow experiments, pressure drops and flow patterns were collected over 0.01 < jG < 15 m/s for the superficial gas velocity and 0.01 < jL < 2 m/s for the superficial liquid velocity. Test gas was pressurized argon; test liquid was water. The argon gas was mixed with water through a coaxial annular nozzle to make two-phase flow. The observed flow patterns were slug, churn and annular flows; bubbly flow pattern was not observed in a range of the present experimental conditions. Time-averaged void fraction and two-phase friction pressure drops were also obtained. The two-phase friction multipliers were shown to be in good agreement with a correlation presented by Mishima-Hibiki in the experimental range considered in the present report.

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