What is the significance of a Grashof number?

In forced convection, the Reynolds number provides the information about the fluid is laminar or turbulent. Like this in natural convection, grashof numbers provide information about whether the flow regime is laminar or turbulent.

Grashof number natural convection heat transfer

Where,

• g = gravitational acceleration, m/s^2
• β = coefficient of volume expansion, 1/K (β = 1/T for ideal gases)
• Ts = Surface temperature, °C
• T∞ = Temperature of the fluid sufficiently far from the surface, °C
• L = characteristics length of the geometry, m
• ν = kinematic viscosity of the fluid, m^2/s

Like Reynolds number, grashof number is the ratio of buoyancy force to viscous force which governs the flow regime in natural convection.

For a flow regime on a vertical plate, the critical grashof number is observed around 10^9. Therefore the flow regime is laminar at grashof number less than 10^9 and it becomes turbulent at grashof number greater than 10^9.

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