Osmotic pump, controls not only drug release as a novel drug delivery systems (NDDS) in humans and animals, but also energy release as a novel green energy system (NGES), by mixing fresh water with pressurized salt water through a semi-permeable membrane. SaltPower’s osmotic pump is based on pressure retarded osmosis (PRO) membrane process, utilizing saturated brine at relative high hydraulic pressure. In this process, water molecular migrating through membrane from fresh water side to salt water side is primarily driven by the transmembrane pressure (TMP), which is the difference between osmotic pressure and the hydraulic pressure. The osmotic pressure is dependent on the salt concentration at defined temperature, while the hydraulic pressure applied on salt water side is proportional to work but retards osmotic pressure and eventually adversely affect water migration. In theory, the ideal hydraulic pressure is half of osmotic pressure to obtain the optimum water permeation and the highest energy output. It says 200 bar in case of NaCl solution. Currently, membrane has never been operated at such high pressure, and the corresponding water transport behavior is rarely investigated neither.

Reverse osmosis (RO) membrane is the high pressure type in membrane category, and the thin film composite (TFC) RO membrane is normally selected as the object for PRO researches. In many cases, the thin film (TF) layer is cross-linked polyamide (PA), which has no measurable pores. Therefore, such TF is considered as non-porous polymer, and a solution-diffusion (SD) model is applied to describe mass transfer in TFCPA. It shall be noticed that a solution-friction (SF) model becomes popular recent years which critically challenges SD model by viewing the PA network as water channel with sub-nanometer pores, and water transfer mechanism is hydraulic pressure gradient rather than diffusion. Even though, the water flux expressed in SF model is equivalent to SD model, which is derived from Fick’s Law, in RO process, it is described as...