Correct option is B
In free convection (natural convection), the transition from laminar to turbulent flow is primarily determined by the Rayleigh number (Ra).
The Rayleigh number is defined as the product of the Grashof number (Gr) and the Prandtl number (Pr):
Ra = Gr⋅Pr
The Grashof number (Gr) represents the ratio of buoyancy forces to viscous forces.
The Prandtl number (Pr) represents the ratio of momentum diffusivity to thermal diffusivity.
The critical Rayleigh number (approximately Ra_c≈10^9) is commonly used to predict the transition from laminar to turbulent flow in free convection.
