What does Prandtl number mean?
Prandtl number (Pr) is defined as the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity.
What is Prandtl number used for?
In heat transfer problems, the Prandtl number controls the relative thickness of the momentum and thermal boundary layers. When Pr is small, it means that the heat diffuses quickly compared to the velocity (momentum).
What is the value of Prandtl number for liquid metals?
0.01 to 0.001
Does Prandtl number change with temperature?
The Prandtl number is a fluid property that does not depend on the type of flow or flow geometry. The values of , cp and k are known to change with temperature so the Prandtl number will change with temperature.
Can Nusselt number be less than 1?
The Nusselt number is the ratio of the heat transfer with convection to the original heat transfer with no fluid motion. Since the moving fluid always enhances heat transfer, Nusselt number can only be greater than or equal to 1.
What is meant by Nusselt number?
The Nusselt number is defined as the ratio of convection heat transfer to fluid conduction heat transfer under the same conditions.
How is Nusselt number calculated?
FormulaNusselt Number : Nu = hL/k.Convection Heat Transfer Coefficient : k = Nuk/L.Characteristic Length : L = Nuk/h.Thermal Conductivity of the Fluid : k = hL/Nu.Where, Nu = Nusselt Number, h = Convection Heat Transfer Coefficient, L = Characteristic Length, k = Thermal Conductivity of the Fluid.
What is the value of Prandtl number for highly viscous oils?
Prandtl number is a characteristic of the fluid only. For air at room temperature Pr is 0.71 and most common gases have similar values. The Prandtl number of water at 17°C is 7.56. Liquids in general have high Prandtl numbers, with values as high as 105 for some oils.
What is Reynolds number in heat transfer?
Definition. The Reynolds number is the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities. A region where these forces change behavior is known as a boundary layer, such as the bounding surface in the interior of a pipe.
What is kinematic viscosity?
1 Kinematic Viscosity (ν) The kinematic viscosity is an atmospheric variable defined as the ratio between the dynamic viscosity μ and the density ρ of the fluid, i.e. (7.25) and depends on both air temperature and pressure.
How is Reynolds number calculated?
Reynolds NumberRe = ρ u L / μ = ρ u2 / (μ u / L) = u L / ν (1) where. Re = Reynolds Number (non-dimensional) ρ = density (kg/m3, lbm/ft3) Re = ρ u dh / μ = u dh / ν (2) where. dh = hydraulic diameter (m, ft)Re = 7745.8 u dh / ν (2a) where. Re = Reynolds Number (non dimensional) u = velocity (ft/s) dh = hydraulic diameter (in)
What does the Rayleigh number mean?
The Rayleigh number is 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.