Consider an isothermal flat plate which a uniform binary fluid (for example salt water) with constant temperature of T_inf is flowing over it. Now assume that there are some slip mechanisms (for example Brownian motion effect and thermophoresis effect) acts on the salt in the water.
Therefore, the governing PDEs are: continuity, momentum, heat and concentration.
The boundary conditions for heat and flow are clear. The temperature of the plate is constant and the no slip boundary condition and impermeability of the plates is valid.
The question is what is the boundary condition for the concentration equation?
In some papers, it is assumed that the concentration on the wall is constant (often maximum). Is this a valid assumption? why?
What is the realistic boundary condition in this problem?
After a very long time, as the flow tries to reach steady state, the change in momentum, energy, CONCENTRATION will be close to zero. So u can give the SATURATED CONCENTRATION level at the wall. moreover the flow very close to wall is at low speed so concentration near wall shall not be disturbed Hence u can give saturated concentration level at wall
Thank you Verma for your replay.
If we assume a constant concentration for the wall then the gradient of concentration on the wall could not be zero. I conclude that therefore the rate of mass transfer (partial part which here is salt) is not zero.
I see in such papers that one of the parameters of interest is the Sherwood number which is defined by the concentration gradient on the wall.
Can you help me to understand the physic of this assumption? How it is possible to have the mass transfer rate from an impermeable wall?
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