Papers Published

1. Bejan, A. and Lage, J.L., Prandtl number effect on the transition in natural convection along a vertical surface, Journal of Heat Transfer, Transactions ASME, vol. 112 no. 3 (1990), pp. 787 - 790 .
   (last updated on 2007/04/08)

   Abstract:
   The present study was motivated by certain observations and the apparent suggestion that in low-Pr fluids the laminar flow expires at unexpectedly low Rayleigh numbers. This idea is particularly interesting if we think of the natural convection boundary layer near a vertical wall, for which the textbook teaches us to associate the constant Ra approximately equals 10⁹ with the height of transition to the turbulent flow, regardless of the Prandtl number. In order to test this idea, we re-examined the experimental record of observations on transition in vertical natural convection boundary layer flow. Indeed, the empirical data described show that the Prandtl number has a strong influence on the transition Rayleigh number. In low-Pr fluids the transition occurs at Rayleigh numbers much lower than the often-mentioned Ra approximately equals 10⁹, while in high-Pr fluids the transition Rayleigh number is higher than 10⁹. It appears that the constant Grashof number Gr approximately equals 10⁹ (i.e., not Ra approximately equals 10⁹) marks the transition in the wide Pr range 0.001-1000.

   Keywords:
   Flow of Fluids--Boundary Layer;