Entransy dissipation minimization for a class of one-way isothermal mass transfer processes

Abstract

A class of one-way isothermal mass transfer processes with Fick’s diffusive mass transfer law [g ∝ Δ(c)] is investigated in this paper. Based on the definition of the mass entransy, the entransy dissipation function which reflects the irreversibility of mass transfer ability loss is derived. The optimal concentration allocations of the key components corresponding to the highand low-concentration sides for the minimum entransy dissipation of the mass transfer process are obtained by applying optimal control theory and compared with the strategies of the minimum entropy generation, constant mass transfer flux (constant concentration difference), and constant concentration ratio (constant chemical potential difference). The results are as follows. For the optimal mass transfer strategy of the minimum entransy dissipation, the product of the square of the key component concentration difference between the high- and the low-concentration sides and the inert component concentration at the low-concentration side is a constant, while for that of the minimum entropy generation, the ratio of the square of the key component concentration difference between the high- and the low-concentration sides to the key component concentration at the low-concentration side is a constant; when the mass transfer process is not involved in energy conversion process, the optimization principle should be the minimum entransy dissipation; the mass transfer strategy of constant concentration difference is superior to that of constant concentration ratio. The results obtained in this paper can provide some theoretical guidelines for optimal designs and operations of practical mass transfer processes.