Abstract
Void fraction and two-phase frictional pressure drop in microchannels were experimentally
investigated. Using air and water, experiments were conducted in transparent circular microchannels
with 1.1 and 1.45 mm inner diameters and in microchannels with semi-triangular (triangular with
one corner smoothed) cross-sections with hydraulic diameters 1.09 and 1.49 mm. Gas and liquid
super®cial velocities were varied in the 0.02±80 m/s and 0.02±8 m/s ranges, respectively, and void
fractions were calculated by analyzing photographs taken from the test sections with circular cross-
section.
Measured void fractions were compared with several correlations. The homogeneous ̄ow model
provided the best prediction of the experimental void fractions in bubbly and slug ̄ow patterns.
The homogeneous ̄ow model and all other tested empirical correlations signi®cantly over predicted
the void fractions in annular ̄ow pattern, however.
A one-dimensional model, based on the numerical solution of mass and momentum
conservation equations was applied for the calculation of test section pressure drops, using various two-phase friction models. For bubbly and slug ̄ow patterns, the two-phase friction factor based on homogeneous mixture assumption provided the best agreement with experimental data. For annular ̄ow the homogeneous mixture model and other widely used correlations significantly over predicted the frictional pressure drop.
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