Liquid flow and mixing investigation inside rotary energy recovery device: A numerical study

Abstract

In the context of reverse osmosis seawater desalination technology, rotary energy recovery devices are most commonly utilized due to their high energy recovery efficiency and simple design route. One significant concern during operation is that the liquid fluid inside the rotor channel is prone to mix, resulting in an increased NaCl concentration at the outlet of high-pressure fresh seawater, which however raises the operational cost in turn. This study presents a three-dimensional numerical model for the rotary energy recovery device and conducts a comprehensive investigation on the flow and mixing characteristics associated with this device. The results indicate that a reduction in the turbulence energy within rotor channel is observed as the inclination angle of liquid-collection groove increases, and the vortex becomes more pronounced. Besides, the displacement of liquid piston determined by the concentration fluctuation within the rotor channel observed at the monitoring point is quantified. It is shown that an increase in the inlet flow rate or a decrease in the rotational speed can lead to the increase of axial displacement of the liquid piston. However, the inclination angle of liquid-collection groove has a minor effect on the axial displacement. Increasing the inclination angle correlates closely with an increase in the length of liquid piston. Moreover, the energy recovery efficiency and mixing rate of the device are discussed in detail regarding the parametric effects of rotational speed, flow rate and inclination angle of liquid-collection groove.