Rotary Energy Recovery Device Research Articles

A system-level CFD simulation model for investigating the energy dissipation mechanism of seawater pump and rotary energy recovery device in SWRO desalination system

Seawater reverse osmosis (SWRO) technology has been universally adopted because of its high efficiency, economic benefits, easy maintenance, and high-pressure seawater pump (HPSP) and energy recovery device (ERD) are essential components, which determine the specific energy consumption of SWRO system. However, it is still unclear about energy dissipation mechanism and mixing characteristics from the perspective of system. For that, this thesis proposes a novel system-level Computational Fluid Dynamics (CFD) model considering all interfaces in HPSP and integrated energy recovery and pressure boost device (IERPBD). To profoundly investigate the system performance under various operating conditions, the pressure and composition distribution, power loss of each interface and mixing rate are numerically calculated and analyzed. Additionally, experiment of the effect of temperature on SWRO system performance is conducted to practically verify the proposed model, which indicates that the presented model could precisely reflect the energy dissipation and mixing characteristics. Besides, it is advised that the rotating speed of HPSP and IERPBD should not be set too high which could increase the mixing rate and energy consumption, and higher temperature might lower the quality of produced freshwater. This study offers a feasible way to reveal the energy dissipation mechanism of SWRO desalination system.

Research on the Influence of Lateral Force and Pressure Fluctuation on the Stability of a Rotary Energy Recovery Device in the Desalination System

The rotary energy recovery device (RERD) plays an important role in reverse osmosis (RO) desalination; however, few investigations on the formation and influence of lateral force on the RERD rotor have been published. The transient characteristics of lateral force and its relationship with pressure distribution and fluctuation in the clearance were analyzed via computational fluid dynamics (CFD) simulation. The clearance pressure distribution and lateral force were quantified under different working conditions. The eccentricity of the rotor, resistance torque and decrease in the rotary speed due to the lateral force were simulated and they were found to change with flow rate and pressure of high-pressure outlet (PHO). A new rotary speed prediction method including the effect of PHO was developed. With the increasing flow rate or PHO, the stability of RERD declined. A design optimization direction was proposed. The variation trends of rotary speed, pressure in the clearance and its fluctuation were verified through experiment. This research provides an explanation why in practice the rotary speed decreases with increasing pressure. The conclusions obtained herein can be of great significance for future research on improving the stability and lifespan and reducing the maintenance consumption of RERD.

Numerical Investigation of the Influence of a Splitter Plate on Mixing Transfer in the Ducts of a Rotary Energy Recovery Device

The rotary energy recovery device (RERD) is integral in reducing energy consumption in desalination processes. The absence of a physical piston in RERD ducts allows salinity transfer from the brine to the seawater stream, which reduces RERD efficiency. To address this challenge, this study investigates the potential of utilizing splitter plates as a flow control technique to decrease the mixing degree within RERDs. Numerical simulations were performed to examine five different splitter plate configurations in RERD ducts in order to identify optimal designs for reducing the mixing degree. The analysis of internal streamlines and vortex distributions revealed that horizontal splitter plates positioned at the duct inlet effectively suppressed swirling flows, while splitter plates positioned at the center of the duct suppressed the formation of flow-induced vortices. This resulted in a more uniform salinity distribution and a reduction in the mass transfer rate between brine and seawater streams. The most significant reduction in the volumetric mixing rate was observed when employing cross-spread splitter plates positioned at the center of the duct. This paper presents an innovative method to reduce the mixing degree in the RERD.

Investigation of the Mixing Rate and Channel Volume Efficiency of a Self-Driven Rotary Energy Recovery Device in the Reverse Osmosis System

Investigation of the Mixing Rate and Channel Volume Efficiency of a Self-Driven Rotary Energy Recovery Device in the Reverse Osmosis System

Investigations on the energy conversion and dissipation in hydraulic-driven rotary energy recovery device from a designer's perspective: Simulation and validation

Hydraulic-driven rotary energy recovery device (HD-RERD) has attracted considerable attention in membrane desalination for energy conservation. Plentiful studies have typically aimed at the operating performance in specific working conditions which fail to evaluate the energy flows holistically. This paper focuses on the revelation of energy conversion and dissipation in HD-RERD by exploring the operating performances under multiple conditions, which pays close attention to the hydraulic driven, internal leakage, salinity mixing and energy efficiency. The results indicate that the rotor speed follows the cubic function and varies from 0 rpm to 742 rpm within the flowrate range of 70 m3/h. A linear function appears in internal leakage within the pressure scope of 7.00 MPa. The salinity mixing leads to the extra energy consumption in HD-RERD which is about 10.71 kJ/(m3/h) at the flowrate of 70 m3/h. In addition, the ratios of dissipation energy to total energy conversion are about 0.46 % 1.53 % and 1.46 % for hydraulic driven, internal leakage and pressure losses respectively at the pressure and flowrate of 7.00 MPa and 70 m3/h. This study provides an in-depth understanding of the energy conversion in HD-RERD for researchers and engineers.

CFD supported thermodynamic analysis of a CO2 pressure exchanger based refrigeration system for supermarkets

This manuscript presents a method to thermodynamically model a pressure exchanger device. CFD-based model of a rotary energy recovery device used in desalination process is developed and validated with published experimental data with a maximum deviation of 5.19%. The dimensionality of the validated model was reduced to investigate the potential of the pressure exchanger device operating with CO2 as the working fluid. Based on the data obtained from several numerical experiments, two correlations were developed, by means of non-linear regression analysis, for estimating the pressure lift generated by the device as a function of inlet velocity of high pressure fluid (0.5 – 3 m/s), rotor speed (500 – 3000 rpm), receiver pressure (25 – 40 bar) and gas-cooler pressure (90 – 120 bar). The correlations were found to be within acceptable error margin. The pressure lift generated by the pressure exchanger was found to be directly proportional to the inlet velocity of the high pressure fluid and inverse proportionality to the rotor speed. The developed correlations are used to evaluate the thermodynamic performance of a multi evaporator supermarket refrigeration system integrated with pressure exchanger to a conventional parallel compression system and a published multi-ejector system in the ambient temperature range of 30 to 40 °C. The pressure exchanger based system was found to outperform the parallel compression as well as the multi-ejector system and demonstrate significant energy savings.

Influence of structural and operating factors on mixing transfer of rotary energy recovery device through CFD simulation

The rotary energy recovery device (RERD) is an essential component in seawater desalination for decreasing the energy consumption of reverse osmosis plants. To research the complex flow fields and mixing motion in ducts of a rotary energy recovery device, a 3D numerical simulation was studied in this work. Three-dimensional vortex structures were visualized and identified based on the Q criterion. The effects of the operating condition and the structure parameter on the flow fields and the mixing motion had been discussed. Simulation results indicated that the interaction between vortices in the mixing zone and vortices in the duct entrance led to a high level of turbulence intensity and mixing degree. The mixing process could be controlled by the operating condition and the structure parameter. This paper provides a new approach to researching structural and operating factors on the mixing process of the rotary energy recovery device.

Adopting inclined channel to decline the salinity mixing for rotary energy recovery device: Simulation and optimization

After years of research, the energy efficiency of energy recovery device has been raised to a high level, but the salinity mixing has not been effectively improved. Mixing will lead to a rise of high-pressure seawater salinity, which will increase the operating cost. In this paper, the computational fluid dynamics (CFD) simulation of the rotary energy recovery device (RERD) is carried out. It is found that the unstable flow caused by the non-parallel between the channel and the flow direction of fluid is an important reason for mixing. After the inclined channel structure is adopted, the non-parallel problem is improved. The formation of unstable flow is effectively controlled. Under the commercial product operating conditions, the volumetric mixing of the optimized device is reduced from 3.34% to 1.29%, showing the effectiveness of the structure.

Simulation Investigation on the Flow and Mixing in Ducts of the Rotary Energy Recovery Device

The rotary energy recovery device (RERD) is widely equipped in desalination to reduce the system energy consumption. In this study, the fluid dynamics and mixing performance of a typical structure RERD and a visualization apparatus of a RERD (V-RERD) had been compared by simulation. The effects of rotating components on fluid dynamics and mixing had been researched. Simulation results indicated that a swirling flow can be observed from flow fields in the device duct. In the RERD case, the swirling flow changed its rotating direction in the center of the duct, while in the V-RERD case, its rotating direction was unchanged. Then, a swirling number Sn was applied to characterize the degree of swirl intensity, and its formation mechanism in RERD had been discussed. In addition, the Q criterion was adopted to visualize the three-dimensional flow structures and identify vortex structures in the duct. The evolution of vortices in the working process had been investigated. It was found that vortices significantly affected the mixing performance, and the detached vortex could lead to high turbulence and mixing in the duct. Suppressing the vortex shedding may reduce the flow turbulence and gain a lower volumetric mixing rate.

Comparing brine-seawater mixing between two-port and four-port rotary energy recovery device

Comparing brine-seawater mixing between two-port and four-port rotary energy recovery device

Research on Rotational Resistance Moment of Rotary Energy Recovery Device

The effects of operational conditions on the resistance moment of a rotary energy recovery device have been systematically investigated through the computational fluid dynamics in this paper. Based on the structural characteristics of the rotary energy recovery device, the hydro-static bearing was established on both sides of the rotor. Simulation results indicate that for the rotation resistance moment generated by the rotor internal flow path, the rotation speed is linearly positive with the rotational resistance moment. For the rotation resistance moment generated by the clearance flow, the rotation speed is also positively correlated with the rotational resistance moment. The circular clearance size is negatively correlated with the rotation resistance moment, and the endcover fluid film size is negatively correlated with the rotation resistance moment. The boundary speed between laminar flow and turbulent flow was found by comparing the changing trend of rotational resistance moment. The obtained relation between clearance, the speed of the rotor and resistance moment provides a simple way to predict the resistance moment of the device, which will be beneficial to design the energy-efficient rotary energy recovery device

Theoretical analysis and auxiliary experiment of the optimization of energy recovery efficiency of a rotary energy recovery device

A rotary energy recovery device (RERD), as the energy saving equipment of seawater desalination system, has a great significance on reducing the energy consumption and permeate cost of the system. The high or low energy recovery efficiency directly determines whether the engineering application of the RERD can be widely used. In this paper, firstly, based on the calculation formula of energy recovery efficiency, the main impact factors of efficiency were analyzed theoretically, including processing capacity, the high and low pressure differentials, and the leakage of the device. Secondly, in order to carry out some required auxiliary tests smoothly, a new RERD was designed and manufactured, and a complete SWRO desalination system was also established. The results depicted that the energy recovery efficiency reached the maximum and the corresponding optimal processing capacity was about 12.15m3/h when the pressure of the low pressure seawater was 1.0bar, that of the high pressure brine was 60.0bar, and leakage of the device was 0.6m3/h. Furthermore, when processing capacity was kept 13m3/h constant and the efficiency was required to exceed 94%, under the existing operating conditions, the maximal leakage of the device was needed no more than 0.43m3/h.

Introducing pre-pressurization/depressurization grooves to diminish flow fluctuations of a rotary energy recovery device: Numerical simulation and validating experiment

In order to diminish the flow fluctuations of the rotary energy recovery device (RERD), the pre-pressurization and pre-depressurization grooves were introduced and typically slotted on the surface of the RERD's endcovers. Effects of the grooves on performance fluctuations of the RERD were researched by means of computational fluid dynamics (CFD) simulations and validating experiments. Simulative results indicated that when compared with the un-slotted RERD under flow rate of 12m3/h, rotary speed of 400rpm, and operating pressure of 6.0MPa, the flow fluctuation amplitudes of the slotted RERD were reduced about 75.3% for high pressure outlet and 77.2% for low pressure outlet respectively. Similarly, the pressure fluctuation amplitudes of the slotted RERD were dramatically reduced about 92.5% for high pressure outlet and 90.7% for low pressure outlet. In addition, the validating experiments were conducted under the same operating conditions. The results showed that flow fluctuation amplitudes of experiments were in good agreement with that of the simulations, and the difference between them were about 2.76–7.55%, verifying the simulation model was reasonable. Thus, it provides a feasible and effective way to use the pre-pressurization and pre-depressurization grooves to diminish the flow fluctuations of the RERD.

Theoretical investigations on rotor speed of the self-driven rotary energy recovery device through CFD simulation

The theory about how to calculate the rotor speed for a self-driven rotary energy recovery device has been investigated by methods of computational fluid dynamics simulation and validating experiments in this paper. Rotor speed can be obtained according to impulse torque of the rotor and its frictional resistance. Impulse torque was simulated at different flow rates and oblique ramp angles, and the frictional resistance can be calculated according to the Newton's law of viscosity. Simulative rotor speed was in agreement with the experimental rotor speed, indicating that the simulation model was reasonable. Based on the simulation results, a theoretical formula was established between rotor speed and key dimensions of the self-driven device, which provides a simple way to calculate and predict the rotor speed in the designing of an eligible device.

Investigations on the applicability of hydrostatic bearing technology in a rotary energy recovery device through CFD simulation and validating experiment

Based on the structural characteristics of the rotary energy recovery device, the hydrostatic bearing was established on both sides of the rotor. Effects of the hydrostatic bearing on the resultant force and fluid film thickness were investigated by the methods of computational fluid dynamics simulation and validating experiments. Simulation results indicate that resultant force rises linearly with the increase of both operating pressure and thickness difference between the upper and lower fluid films, indicating that there exists a cooperative function between the upper and lower fluid films which favors for the self-adjustment of film thickness and resuming the rotor to a stable lubrication state when the pressure changes. The circular clearance regarded as fluid restrictor was optimized in order to adjust the fluid film thickness rapidly and the best circular clearance is about 0.03mm. The experimental results indicate that the practical resistance of the rotor can well be reflected by the changing trend of the experimental rotor speed at operating pressure from 0.1MPa to 6.0MPa, and is in good accordance with the theoretical resistance calculated by using the simulation results, verifying that the simulation model was reliable. This study provides an applied structure for improving the frictional state of the rotor and prolonging the working life of the device.

Employing groove-textured surface to improve operational performance of rotary energy recovery device in membrane desalination system

A rotary energy recovery device (RERD) is widely used in a reverse osmosis desalination system. In order to maintain the device running in an available torque and obtaining a long service life, a portion of high pressure seawater is usually sacrificed to work as lubrication to reduce the friction torque of the device. However, when using such method, a certain amount of energy recovery efficiency will be lost due to the lubrication or leakage. This paper focuses on improving operating performance of a rotary energy recovery device by making textured grooves on the surfaces of two end covers of the RERD. The experimental results show that compared to the un-textured RERD, the textured RERD reduces the device's torque by half, and successfully improved the efficiency by 40% under the mating clearance of 0.035mm, operating pressure of 6.0MPa and rotary speed of 500rpm. In addition, thanks to the groove textured surface which dramatically reduces the RERD's torque and permits the mating clearance to be minimized. Under the small clearance of 0.025mm, the energy recovery efficiency of the textured RERD can be increased up to 96.3% at an operating pressure of 6.0MPa which can well satisfy the requirement of the industry application.

Computational Fluid Dynamics Simulation of Brine–Seawater Mixing in a Rotary Energy Recovery Device

The effects of operational conditions on the mixing behavior of a rotary energy recovery device have been systematically investigated through the combined methods of computational fluid dynamics and validating experiments in this paper. The sliding mesh technique and species transport equations were applied in the simulation process. An innovative parameter of inflow length was defined to express the moving distance of a mixing section in rotor ducts. A theoretical formula between the inflow length and operational conditions was first established on the basis of the mass balance and computational fluid dynamics analysis. Simulation results revealed that the mixing has a polynomial relation with dimensionless inflow length, which was in good agreement with the experimental results. The obtained formulas between mixing and dimensionless flow length provide a simple way to calculate and predict the mixing behavior of the device, which will be beneficial to design and operate the rotary energy recovery device...