| Summary: | 碩士 === 雲林科技大學 === 機械工程系碩士班 === 96 === This study investigates the pressure change and flow pattern subject to the
influence of sudden contraction and sudden expansion. The air and water mixture flows from small rectangular channels (2×4 mm, 2×6 mm, 4×4 mm and 4×6 mm, respectively) connect to a 2 mm diameter tube and rectangular channels (3×6 mm, 3×9 mm, respectively) connect to a 3 mm diameter tube. The total mass flux (G) ranges from 100 to 700 kg/m2·s with gas quality (x) being varied from 0.001 to 0.8.
In general the contraction pressure change increases with the rise of mass
flux, and vapor quality but an unique deflection of contraction pressure
change pertaining to liquid vena contracta at a very low gas quality is
encountered at a very low gas quality in the 4×6 mm and 3×9 mm test section.
It is found that the influence of surface tension and tube size, or quivalently
the Bond number plays a major role for the departure of various
models/correlations. Hence by taking account the influences of Bond number,
Weber number and area contraction ratio into the homogeneous model, a
modified homogeneous correlation is proposed. The mean deviation is 29.3%
to the present data and the available literature data.
For the expansion pressure change, an unique deflection of contraction
pressure change at a very low gas quality is also observed. The phenomenal
observation is related to the liquid jet-like flow pattern. By contrast, an
appreciable increase of pressure difference is seen when the liquid jet-like
flow pattern is completely gone. Finally, the predictions of the available
literature correlations are compared to all literature and the present data. The lowest mean deviation is Richardson’s prediction with the mean deviation of 71.80%.
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