Mar 20th 2017, 03:20 PM
Join Date: Mar 2017
Natural convection: turbulent or laminar?
I am modelling an inclined rectangular cavity and got confused with Grashof and Rayleigh number. I've reviewed many research papers - some researchers use Rayleigh, some Grashof number to determine the type of flow.
This is probably very simple but I can't find where my mistake lies...
I get 10^6 for Rayleigh which indicates Laminar flow and I also get 10^12 for Grashof which indicates Turbulent flow. This got me confused.
My problem involves upper wall exposed to a heat flux, bottom wall and side walls adiabatic. Heat flux warms up the upper wall and the fluid inside. The conditions become:
Tupper = 306 K (average)
Tbottom = 303 K (average)
Tfluid = 300 K (average)
Dimensions: L=2m, W=1m, H=0.007m (space between plates)
From literature and texbooks, I use the following formulas:
Ra=( g*B* (Tu-Tf)*L^3 ) / (v*a)
Gr = (g*B (Tu-Tf)*H^3) / (v^2)
where Tu - upper plate temperature
Tf - fluid temperature
L - Length of the cavity
g - 9.81m/s
B - thermal expansion coeff for WATER @ 20C (0.0033 [1/K])
v - kinematic viscosity 1x10e-7 m/s2
a - thermal diffusivity 1x10e-7 mē/s
Thank you for you help.
Last edited by Artis; Mar 20th 2017 at 03:27 PM.
Reason: added values for v and a