Linear-nonequilibrium thermodynamics (LNET) has been used to express the en
tropy generation and dissipation functions representing the true forces and
flows for heat and mass transport in a multicomponent fluid. These forces
and flows are introduced into the phenomenological equations to formulate t
he coupling phenomenon between heat and mass flows. The degree of the coupl
ing is also discussed. In the literature such coupling has been formulated
incompletely and sometimes in a confusing manner. The reason for this is th
e lack of a proper combination of LNET theory with the phenomenological the
ory. The LNET theory involves identifying the conjugated flows and forces t
hat are related to each other with the phenomenological coefficients that o
bey the Onsager relations. In doing so, the theory utilizes the dissipation
function or the entropy generation equation derived from the Gibbs relatio
n. This derivation assumes that local thermodynamic equilibrium holds for p
rocesses not far away from the equilibrium. With this assumption we have us
ed the phenomenological equations relating the conjugated flows and forces
defined by the dissipation function of the irreversible transport and rate
process. We have expressed the phenomenological equations with the resistan
ce coefficients that are capable of reflecting the extent of the interactio
ns between heat and mass flows. We call this the dissipation-phenomenologic
al equation (DPE) approach, which leads to correct expression for coupled p
rocesses, and for the second law analysis. (C) 2001 Elsevier Science Ltd. A
ll rights reserved.