Which of these statements hold true?
(a) Diffusive flux is always positive
(b) Diffusive flux is positive in the direction of the positive gradient of fluid property
(c) Diffusive flux is positive in the direction of the negative gradient of fluid property
(d) Diffusive flux is always negative
This question was posed to me by my school teacher while I was bunking the class.
This interesting question is from General Transport Equation topic in portion Governing Equations of Fluid Dynamics of Computational Fluid Dynamics