Question

Which of these terms need a surface integral?

(a) Diffusion and rate of change terms

(b) Convection and source terms

(c) Convection and diffusion terms

(d) Diffusion and source terms

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This is a very interesting question from Finite Volume Method in portion Finite Volume Methods of Computational Fluid Dynamics

Answer 1

Right answer is (c) Convection and diffusion terms

Explanation: The convection and diffusion terms have fluxes flowing along the surfaces of the control volume. So, they have to be integrated over the faces of the control volume. So, the convection and diffusion terms need a surface integral.