Two-phase flow on the shell side of a shell and tube heat exchanger
Two-phase flow on the shell side of a shell and tube heat exchanger is complex. Several studies have produced flow pattern maps that show surprising differences in flow regime boundaries for data sets that contain relatively small variations in fluid and flow properties. Despite this, correlations f...
| Main Authors: | , , |
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| Format: | Conference or Workshop Item |
| Published: |
2010
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| Subjects: | |
| Online Access: | doi:10.1115/IHTC14-22790 doi:10.1115/IHTC14-22790 |
| Summary: | Two-phase flow on the shell side of a shell and tube
heat exchanger is complex. Several studies have
produced flow pattern maps that show surprising
differences in flow regime boundaries for data sets that
contain relatively small variations in fluid and flow
properties. Despite this, correlations for void fraction
and pressure drop are sufficiently accurate to allow the
thermal-fluid design of heat exchangers to be
completed. However, these correlations are based on
experimental data taken from tube bundles containing
tubes with diameters less than 20 mm. This study
examines their applicability to tube bundles containing
tubes with a diameter of 38 mm.
Results for void fraction and pressure drop are
presented for air-water flows near atmospheric
pressure. The results were obtained for flows through
a thin-slice, in-line tube bundle containing 10 rows. The
tube bundle contained a central column of tubes with
half tubes placed on the shell wall to simulate the
presence of other columns. The tubes were 38 mm in
diameter and 50 mm long with a pitch to diameter ratio
of 1.32.
Previous studies have shown that the void fraction in a
shell-side, gas-liquid flow becomes constant after only
a few rows. Thus, the void fraction was only measured
at one location. A single-beam, gamma-ray
densitometer was used to measure void fractions near
row 7 in the maximum gap between the rows.
Corresponding pressure drops were obtained between
rows 3 and 10. Data are presented for a mass flux
range of 25-688 kg/m2s and a gas mass fraction range
of 0.0005-0.6. The measurements are shown to
compare reasonably well with predictions from
correlations available in the open literature. This shows
that these methods can be used for tube-bundles
containing larger diameter tubes.
Some elements of a heat-exchanger design require a
more complex analysis. For example, tube vibration
calculations require the distribution of void and phase
velocity along the tube length. Such analysis can be
provided by multiphase computational fluid dynamic
(CFD) simulations. CFD approaches to modelling
these flows require empirical inputs for the drag
coefficient and the force on the fluid by the tubes.
These are deduced from the measured data. The wall
forces are shown to scale well with increased tube
diameter, however, caution is required when selecting
the drag coefficients. |
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