In the fluid movement, the unit time flow through a unit area of a certain amount of property, is that a certain amount of material delivery strength of the physical quantity. In atmospheric science, it contains momentum flux, heat flux, material flux and water flux.
In the fluid movement, the unit time flow through a unit area of a certain amount of property, is that a certain amount of material delivery strength of the physical quantity.Flux
(1) momentum flux
According to Newton's second law, in the absence of external force on the object, the object's speed will not change, the object momentum will not change, its momentum balance. The force acting on the fluid is mainly inertial force, including external force, pressure and adhesion. The physical relationship between fluid momentum and external force, pressure and adhesion is called the equation of motion and is the mathematical basis for the change of fluid momentum. At the bottom of the atmospheric boundary layer, the movement of air under the action of adhesion, between the surface and the atmosphere will form a speed gradient, resulting in shear stress. The process of transmitting momentum from this shear stress is called momentum transmission. The momentum transmitted per unit time through the unit section is called the momentum flux.
(B) sensible heat and latent heat flux
The energy delivered by heat conduction and convection (turbulence) is called sensible heat without changing the phase change of the object and the medium. When two different temperature objects are in contact, the heat is transferred from one side of the temperature to the low temperature, and the heat flow is called the sensible heat flux. The sensible heat flux is proportional to the temperature difference, which is called the sensible heat transfer coefficient or the sensible heat exchange coefficient.Flux
The heat that is absorbed or released by the phase change of matter is called latent heat. Water vapor transmission represents potential transport. The latent heat flux per unit time through an area is called latent heat flux. The latent heat flux is proportional to the difference in the concentration of water vapor on both sides of the section, which is called the latent heat transfer coefficient.Flux
(3) material flux
Diffusion is one of the main mechanisms of physical transport such as matter, heat and momentum. The diffusion of the stationary fluid is mainly the diffusion of molecules driven by the concentration gradient, and in the moving fluid, it is mainly turbulent diffusion. The diffusion phenomenon in the atmosphere is dominated by turbulence in most cases. In the process of diffusion, the amount of diffusion through the plane perpendicular to the diffusion direction is called the material flux.Flux