Thermal convection thresholds in viscoelastic solutions

The threshold for oscillatory convection in Rayleigh-Benard experiments wit h viscoelastic binary fluids is explicitly determined as a function of sepa ration ratio and rheological parameters. In particular, it is shown that th e critical oscillation frequency may differ by several orders of magnitude on varying separation ratio and Deborah number. The results suggest that bi nary fluid aspects may not be discarded when studying thermal convection in polymeric solutions. (C) 2000 Elsevier Science B.V. All rights reserved.