Abstract
A calculus of discontinuous functions employed in recent models of interfacial flow phenomena is examined. It is found that this calculus is not the calculus of distribution theory as the models suppose. Misapplication of the calculus leads to an incorrect formulation of the energy conservation equation, the entropy production rate and the phenomenological laws at the interface. The appropriate calculus is derived from first principles and applied to the interfacial flow modeL The resulting phenomenological laws at the interface are more physically reasonable than those given in the existing models.
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