Enthalpy-controlled phenomenon

It has been shown recently (1) that the transfer of urea from water to water-rich water-tetrahydrofuran (THF) mixtures is an entropy-controlled phenomenon (T AS°t > AH°t ), but from water to water-THF mixtures of mole fraction Z2 > 0.20 it is an enthalpy-controlled phenomenon ( AH°t > T AS°t ) moreover, the transfer is energetically favorable in the former case and unfavorable in the latter. A minimum in the standard free energy transfer... 

In general, for an alloy AB, the phenomenon of segregation is controlled by a range of parameters including the differences in bond strengths A-A, B-B and A-B, atomic size, enthalpies of sublimation and surface energies, temperature, the exposed crystal plane, and metal particle size. 

Convection. When a current or macroscopic particle of fluid crosses a specific surface, such as the boundary of a control volume, it carries with it a definite quantity of enthalpy. Such a flow of enthalpy is called a convective flow of heat or simply convection. Since convection is a macroscopic phenomenon, it can occur only when forces act on the particle or stream of fluid and maintain its motion against the forces of friction. Convection is closely associated with fluid mechanics. In fact, thermodynamically, convection is not considered as heat flow but as flux of enthalpy. The identification of convection with heat flow is a matter of convenience, because in practice it is difficult to separate convection from true conduction when both are lumped together under the name convection. Examples of convection are the transfer of enthalpy by the eddies of turbulent flow and by the current of warm air from a household furnace flowing across a room. 

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