Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.
Fields of vector speed have been measured by the method of
laser visualisation (PIV) in the case of a vertical heat exchanger
in co current in mixed convection. The reversal zones have
been given prominence for different numbers of Grashof and
Reynolds. Where the internal and external flows are weak(in
the region of 51/h) and the differences of internal and external
temperature are in the region of 20°C ,we see reversal zones
appear in the two places simultaneously. These results show the
importance of studying the thermal exchange of a heat
exchanger in its totality and call into question the traditional
methods of proportionality of a heat exchanger.