Q1: Transition from laminar to turbulent zone in free convection heat transfer is governed by the critical value of

ANS:D - Grashoff number & Prandtl number.

The transition from laminar to turbulent flow in free convection heat transfer is primarily governed by the critical value of the Grashof number. The Grashof number (Gr) represents the ratio of buoyancy forces to viscous forces and is defined as: Gr=ν2gβ(Ts​−T∞​)L3​ Where:

• g = acceleration due to gravity
• β = coefficient of thermal expansion
• Ts​ = surface temperature
• T∞​ = ambient fluid temperature
• L = characteristic length scale
• ν = kinematic viscosity

When the Grashof number exceeds a certain critical value, the flow becomes unstable, leading to the onset of turbulence. In free convection, this critical value of the Grashof number varies depending on the geometry and boundary conditions of the flow. While the Reynolds number (Re) also plays a role in determining flow behavior, particularly in forced convection, it is the Grashof number that primarily governs the transition from laminar to turbulent flow in free convection heat transfer. Therefore, the correct answer is: Grashof number.