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In meteorology and physical oceanography, advection often refers to the horizontal transport of some property of the atmosphere or ocean, such as heat, humidity or salinity, and convection generally refers to vertical transport (vertical advection).
Advection Equation Let us consider a continuity equation for the one-dimensional drift of incompress-ible fluid. In the case that a particle density u(x,t) changes only due to convection processes one can write u(x,t + t)=u(x−c t,t). If t is sufficient small, the Taylor-expansion of both sides gives u(x,t)+ t ∂u(x,t) ∂t ≃u(x,t)−c t
dimensional advection equation. We will discuss some particular properties of this equation, which are characteristic for advection of fluids. It is difficult, if not impossible, to relate the one-dimensional advection equation to any specific fluid flow situation, but the presence of the advection term gives the equation properties,
Advection and Diffusion of an Instantaneous, Point Source. In this chapter consider the combined transport by advection and diffusion for an instantaneous point release. We neglect source and sink terms. For isotropic and homogeneous diffusion the transport equation reduces to, ∂C ∂C ∂C. (1) + u + v ∂x ∂y ∂C ∂2C ∂2C ∂2C . +w = D ∂x2. ∂y2.
Convection is the collective motion of particles in a fluid and actually encompasses both diffusion and advection. Advection is the motion of particles along the bulk flow. Diffusion is the net movement of particles from high concentration to low concentration.
This chapter incorporates advection into our diffusion equation (deriving the advective diffusion equation) and presents various methods to solve the resulting partial differential equation for different geometries and contaminant conditions.
Both advection and diffusion move the pollutant from one place to another, but each accomplishes this differently. The essential difference is: - Advection goes one way (downstream); - Diffusion goes both ways (regardless of a stream direction). This is seen in the respective mathematical expressions: - Advection u∂c/∂x has a first-order ...
