How do I know whether the convection is laminar or turbulent?

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

Comments

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

  • prajputprajput Member

    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

Sign In or Register to comment.