Learning Forum

[Karthik Remella]

I have a static heater warming up a room how do I know whether the convection is laminar or turbulent?

[prajput]

I am assuming that your case is purely natural convection. In that case the Rayleigh Number would probably be your answer. However, the Rayleigh Number would inform you whether the boundary layer that forms on the heater would be laminar or turbulent. Typically transition happens when Ra = 10^9.

[Karthik Remella]

Oh, I see. I found that the Rayleigh number is Ra = Gr*Pr. What are Gr and Pr?

[prajput]

The Grashof number is the ratio of the buoyancy forces to the viscous forces:

Gr = [g*beta*(T_s - T_infinity)*L^3]/nu^2

where

g is the gravitational acceleration

beta is the thermal expansion coefficient

T_s is the surface temperature

T_infinity is the free-stream temperature

L is the characteristic length

nu is the kinematic viscosity

and the Prandtl number is the ratio of the momentum diffusivity to the thermal diffusivity:

Pr = nu/ alpha

where

nu is the kinematic viscosity

alpha is the thermal diffusivity