Which number is used in free convection?

But, in natural convection the Grashof number is the dimensionless parameter that governs the fluid flow. Using the energy equation and the buoyant force combined with dimensional analysis provides two different ways to derive the Grashof number.

How do I find my Rayleigh number?

Rax = Grx . Pr The Grashof number is defined as the ratio of the buoyant to viscous force acting on a fluid in the velocity boundary layer. Its role in natural convection is much the same as that of the Reynolds number in forced convection.

What is the usefulness of Rayleigh number in free convection?

In fluid mechanics, the Rayleigh number (Ra) for a fluid is a dimensionless number associated with buoyancy-driven flow, also known as free or natural convection. It characterises the fluid’s flow regime: a value in a certain lower range denotes laminar flow; a value in a higher range, turbulent flow.

What does Rayleigh number represent?

The Rayleigh number can be interpreted conceptually as the dimensionless parameter that measures the relative importance between the effects of the buoyancy forces and the effects of the viscosity forces and thermal conduction.

How is the Rayleigh number related to free convection?

Rayleigh number. In fluid mechanics, the Rayleigh number ( Ra) for a fluid is a dimensionless number associated with buoyancy-driven flow, also known as free convection or natural convection. When the Rayleigh number is below a critical value for that fluid, heat transfer is primarily in the form of conduction;

What is the range of the Rayleigh number?

The values of the constants C and n depend on the geometry of the surface and the flow regime, which is characterized by the range of the Rayleigh number. The value of n is usually n = 1/4 for laminar flow and n = 1/3 for turbulent flow. The Rayleigh number is defined as:

How is the Rayleigh number related to Grashof number?

The Rayleigh number is a dimensionless number, named after Lord Rayleigh. The Rayleigh number is closely related to Grashof number and both numbers are used to decribe natural convection (Gr) and heat transfer by natural convection (Ra).

How does the Rayleigh number relate to the flow regime?

It characterises the fluid’s flow regime: a value in a certain lower range denotes laminar flow; a value in a higher range, turbulent flow. Below a certain critical value, there is no fluid motion and heat transfer is by conduction rather than convection.