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Discs placed across the flow of electrolyte in the tube generate wakes and
eddies whereas, twisted tapes generate swirling action in a circular conduit. The swirl
in turn would influence attractive shear forces near the wall region, which in
turn would reduce the thickness of the concentration of boundary layer,
thereby augmenting the mass transfer rates. Swirl flow devices can be used for
electrowinning of metals, combustion chambers, turbo machinery, fusion reactors and
pollution control devices. The heat and mass transfer
enhancement can be obtained using swirl flow devices. Earlier, the
effect of roughness on friction factor and velocity distribution was done by Nikuradse (1933) for sand grain roughness.
Cope (1941) studied heat and momentum transfer for roughness of the
elements. Nunner (1956) studied heat and momentum transfer in rough pipes.
Friction and heat transfer
measurements for repeated rib roughness in tube flow
was done by Sams (1956), Koch (1958), and Burgoyne et al. (1964). Webb et al. (1971) conducted experiments using a tube with
internal pins and correlated their data in terms
of roughness Reynolds number (Re+) and roughness momentum transfer
function R(h+). Dipprey and Sabersky (1963) analyzed their data in
terms of roughness function for their experimental study.
Sethumadhavan and Raja Rao (1983)
conducted experiments for heat and momentum transfer for the tubes with tightly fitted helical wire coils.
Most of the works mentioned above utilized wall similarity concept and correlated their data in terms of roughness
function and roughness Re + by assuming two regions namely: viscous region close to the wall of the tube, and turbulent region which existed in the turbulent core away from the surface of the
tube. The same two-region flow is
assumed in this study. The range of variables covered
in this study are presented in Table 1. |
