| dc.description.abstract | A two-part experimental investigation is reported on the effects
of transverse square rib roughening on fluid flow and heat transfer
in channels with uniform and non-uniform boundary conditions.
The first part of the experimental programme consisted of providing
detailed measurements of mean and basic turbulent characteristics of
fully developed, flow in two rectangular ducts of aspect ratios 1.63
and 3.0. In each duct only one wall was roughened. In channels having
low aspect ratios secondary flows play an important part in momentum
transfer, and an interpretation of their effect on the measured Reynolds
shear stress distribution has been attempted.
In the second part of the experimental programme mean velocity and
temperature profiles, friction factors and Stanton numbers were measured
in an internally roughened pipe and annuli composed of a rough inner rod
and either a smooth or a rough outer pipe. Heating was always applied
on the outer surface.
In all the geometries the mean velocities near the rough walls were
found to be represented by logarithmic straight lines. The gradients of
these lines were independent of Reynolds number but differed for various
geometries. The mean temperature profiles, measured in the rough pipe
and the fully rough annulus, showed that these could also be represented
by logarithmic straight lines, but the slopes of these profiles were
markedly different from those of the velocity profiles. These results
cast considerable doubt on the validity of the 'universal law of the wall'
and Nikuradse's drag law for ribbed surfaces, as well as on the
correctness of applying Dipprey and Sabersky's heat-momentum analogy to
such surfaces.
Finally, the various transformation methods proposed for the
interpretation of measured pressure drop and heat transfer in channels
with mixed rough and smooth surfaces have been analysed. A new simple
transformation method has been proposed for the overall pressure drop
results. | en_US |
