Flow and Transfer Processes at Abrupt Expansions

Abstract

Variations in wall static pressure immediately
downstream of abrupt expansions were determined for a
range of expansion ratios (D,/D, < 7/1) in order to
ascertain the rate of development of enclosed jets.

Theoretical expressions for the recovery of static
head from velocity head and the loss of pressure energy
due to eddy turbulence were examined initially.
Experimental data showed only slight deviations from
predicted values. This discrepancy was not attributable
to non-flat velocity profiles, but was shown to arise
from the inherent approximations in the theory.

At a given expansion ratio the static pressure
distribution pattern could be represented by a single
curve independent of velocity. The separate curves for
each expansion ratio would not, however, reduce to a
universal curve.

The parameters of principal interest were the
locations of the eye of the recirculating eddy and the
point of reattachment of the jet. The position of each
of these features was deduced from the changes in gradient
of the pressure distribution curve.

Local mass transfer coefficients downstream of
abrupt expansions were determined by electrolysis of
acidified copper sulphate solution under diffusioncontrolled
conditions. Results were presented in the
form of the dimensionless transfer factor JD: thus
giving heat transfer factors by analogy.

Peak local values were correlated in terms of the
fully developed value <FORMULA>

Recorded data were 10 - 25 per cent higher than
values obtained by other researchers, and occurred closer
to the plane of enlargement.

Comparison of the results of each series of
experiments suggested that peak transfer coefficients
correspond to the eye of the recirculation eddy.

Date of Award	1969
Original language	English