This study presents the measurements of R-134a two-phase frictional pressure gradient subject to vertical and horizontal arrangements of a U-type wavy tube with inner diameter of 5.07 mm and a curvature ratio of 5. The ratio between two-phase pressure gradients of U-bend and straight tube is about 2.5 - 3.5. For the straight tube, the frictional two-phase pressure gradient ratio between the vertical and horizontal arrangements is marginally higher (1.0 - 1.2) for annular flow pattern at x > 0.5, and is 1.0 - 1.4 for the U-bend in the wavy tube. The higher resistance in the vertical arrangement is due to the buoyancy force against the flow inertia. However, for x < 0.5, this ratio is gradually increased due to the difference of flow pattern. The ratio is increased to 1.8 in the straight tube. For the U-bend, the ratio is 2.1 for flow entering the upper tube and is 1.5 for flow entering the lower tube at x = 0.1 and G = 200 kg/m2·s. For the vertical wavy tube, additional effects like the flow pattern transition, liquid flow reversal, and freezing slug may cause additional pressure drops.
Frictional Pressure Drops of Two-Phase R-134A Flow in Horizontal and Vertical U-Type Wavy and Straight Tubes
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Chen, IY, Wu, Y, Chang, Y, & Wang, C. "Frictional Pressure Drops of Two-Phase R-134A Flow in Horizontal and Vertical U-Type Wavy and Straight Tubes." Proceedings of the ASME 2006 International Mechanical Engineering Congress and Exposition. Fluids Engineering. Chicago, Illinois, USA. November 5–10, 2006. pp. 803-809. ASME. https://doi.org/10.1115/IMECE2006-13247
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