Abstract
The fully developed laminar mixed convection flow in inclined tubes subject to axially and circumferentially uniform heat flux has been studied numerically for a Boussinesq fluid. Dual solutions characterized by a two and a fourvortex secondary flow structure in a crosssection normal to the tubes longitudinal axis have been found for different combinations of the Grashof number Gr and of the tube inclination for all Prandtl numbers between 0.7 and 7. In the twoparameter space defined by Gr and dual solutions occur at a given , if the Grashof number exceeds a critical value Gr for horizontal tubes Gr is approximately 5.5 105, 1.7 105 and 1.7 104 respectively for Pr 0.7, 7 and 70 at a given Gr, if the tube inclination is below a critical value c for Gr 106 this critical angle is approximately 62.5 and 83.5 respectively for Pr 0.7 and 7. Numerical experiments carried out for developing flows indicate that the twovortex solution is the only stable flow structure.