The reversed chemical engine cycle with application to desalination processes

• A new thermodynamic cycle, termed the reversed chemical engine, is proposed.
• It is analogous to the reversed Carnot cycle.
• A new work term based on difference of hydraulic and osmotic pressure is defined.
• Performance ratio at reversible limit and for minimum power requirement is found.
• Hybrids of RO with FO and PRO are applications of this cycle.

In this paper, a novel thermodynamic cycle is proposed, termed the reversed chemical engine cycle. In the cycle, a net input of work is used to transfer mass from a low chemical potential reservoir to a high chemical potential reservoir. The cycle has two mass exchangers, a pump and a turbine. The only irreversibility considered in the model is finite-rate mass transfer. Similar to the reversed Carnot cycle, expressions for the performance ratio (analogous to the coefficient of performance) are obtained under the condition of minimized power requirement for the endoreversible and, in turn, the reversible case. The reversed mass engine cycle is shown to be a special case of the reversed chemical engine. An equipartitioned hybrid forward osmosis reverse osmosis (FO–RO) system is considered as an example of the cycle.