Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
In the last two decades thermochromic liquid crystal (TLS),
true-color digital image processing and laser anemometry (PIV)
have been successfully used in non-intrusive, technical and heat
and mass transfer studies and applications. The aim of the paper
is to asses the state of the art in the exploration of heat transfer
control by transverse vortex generators. They are able to
increase heat transfer by several hundred percent. Prior to the
use of vortices to influence heat transfer it must be known how
different vortices are generated and controlled and how they
interact with the original or base flow and temperature field.
Liquid crystals were used to determinate the distribution of
surface temperature and then evaluation of heat transfer
coefficient or the Nusselt number. The flow pattern produced
by transverse vortex generators (rib-roughened passages) was
visualized using a planar beam of double-impulse laser tailored
by a cylindrical lens and oil particles. Sequential images of
particles in the cross sectional plane taken with CCD video
camera from the downstream side the flow were stored on a
personal computer to obtain distributions of velocity vectors by
means of the PIV method. Local and average Nusselt numbers,
friction factors and velocity fields are presented for rectangular
channels with an aspect ratio of 6.35 and five types of
transverse vortex generators which were brought to required
temperatures by hot film method. The pitch-to-height-ratio of
the ribs was 11.
