Post by Twinkle S.

Rayleigh number Significance Rayleigh number is a dimensionless number that represents the ratio of buoyancy and thermal diffusivity. `Ra = (betagL^3ΔT)/(valpha)` where, Ra : Rayleigh number g : Gravitational acceleration [m/s2] β : Termal expansion coefficient [1/K] L : Characteristic length [m] ΔT : Characteristic temperature difference [K] ν: Kinematic viscosity coefficient [m2/s] α : Thermal diffusivity [m2/s] In natural convection, the Reynolds number no longer characterises the flow. The difference between the solid surface temperature and the free stream temperature can be used as the characteristic temperature difference. Rayleigh number is an index that characterises heat transfer in natural convection phenomena. Below the critical Rayleigh number, convection does not occur, and heat is transferred through thermal conduction. Above the critical Rayleigh number, heat is transferred through convection. Take a flat, vertical board as an example. When the Rayleigh number is approximately 109, airflow makes a transition into a turbulent flow. The critical Rayleigh number is around 10^9. Rayleigh number can also be expressed in the following equation using Grashof number Gr and Prandtl number Pr. `Ra = Gr*Pr`   Source: https://lnkd.in/d9tZMyr4  #fluiddynamics #cfd #heattransfer #learningandgrowing #fluidmechanics #fluids #computationalfluiddynamics