Linear-nonequilibrium thermodynamics theory for coupled heat and mass transport

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.