What is the significance of 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 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 is Bernard cell?
Rayleigh-Bénard convection is a type of natural convection, occurring in a planar horizontal layer of fluid heated from below, in which the fluid develops a regular pattern of convection cells known as Bénard cells. This upwelling spontaneously organizes into a regular pattern of cells.
What is Rayleigh number formula?
The Rayleigh number is simply defined as the product of the Grashof number, which describes the relationship between buoyancy and viscosity within a fluid, and the Prandtl number, which describes the relationship between momentum diffusivity and thermal diffusivity. Rax = Grx .
What are the examples of convection?
Everyday Examples of Convection radiator – A radiator puts warm air out at the top and draws in cooler air at the bottom. steaming cup of hot tea – The steam you see when drinking a cup of hot tea indicates that heat is being transferred into the air. ice melting – Ice melts because heat moves to the ice from the air.
What causes convection?
Convection currents are the result of differential heating. Lighter (less dense), warm material rises while heavier (more dense) cool material sinks. It is this movement that creates circulation patterns known as convection currents in the atmosphere, in water, and in the mantle of Earth.
What is convection definition and example?
Convection is the transfer of heat by circulating it through air or liquids. A heat source at the bottom of the balloon heats the air molecules around the flame, and those molecules rise. Warmer air is less dense than cold air, so as the warm air rises the molecules spread out.
What is the definition of Rayleigh-Benard convection?
Rayleigh–Benard convection is the coordinated movement of a fluid which is confined between two thermally conducting plates, and is heated from below to produce a temperature difference.
When does instability occur in a Rayleigh convection?
Rayleigh showed that instability occurs when the temperature gradient T is large enough to make the non-dimensional Rayleigh number, Ra, exceed a certain critical alue.v The Rayleigh number is de\ned as Ra = Tgh3
How is the Rayleigh-Benard ( RB ) problem modified?
Low concentration Carbopol® 940 samples were employed to explore how the development of thermal convection, in particular the Rayleigh-Bénard (RB) problem, is modified when the fluid is non-Newtonian ( Balmforth and Rust, 2009 ).
How does convection allow energy transfer between plates?
An uncoordinated movement of fluid particles which allows energy transfer between lower and upper plates is substituted by a coordinated movement above a certain temperature gradient. Rayleigh–Benard convection forms convection rolls (see Fig. 1) and allows a much more efficient energy transport between the plates.