The experimental and theoretical analysis of pipe contraction flow fields
The accurate prediction of pipe contraction pressure loss is important
in the design of pipe system such as heat exchangers, particularly when
close control of the flow distribution in a network of pipes is required.
The prediction of contraction pressure loss depends heavily on
experimental data. Large discrepancies in these predictions are evident
in the literature. Experimental results giving pres!? re loss
coef fici ents for a range of Reyno 1 ds numbers of 4x 10 -2x 10 and area
ratios of 0.135 - 0.692 are presented and compared with predictions from
a method developed that allows for velocity profile variation through the
contraction. The results show a Reynolds number dependence and good
agreement between predicted and measured values.
It is also important to be able to predict the variation of pressure loss
coefficient with variations in the small-bore inlet geometry, referred
to as the inlet sharpness. There are no know experimental data for the
effects of inlet sharpness on the pipe contraction loss coefficient, but
there are data for intakes set flush in a plane wall which are used as
approximations. Experimental data showing the variation of pressure loss
coefficient with inlet sharpness up to 13.4% are presented and compared
with approximate data. The comparison shows significant differences.
A three beam laser doppler anemmeter has been used to measure the
detailed flow field for an area ratio of 0.332 and a Reynolds number of
153.8 x 10. The mean velocity, turbulent intensity and Reynolds stress
distributions are presented for twenty-two axial stations between four
large-bore diameters upstream to fourteen small-bore diameters downstream
of the contraction. These experimental measurements are compared with
computer predictions using the FLUENT code with the k-e- turbulence model.
The general trends in the flow are predicted, however there are
significant differences in the detailed flow field which are highlighted.