In the seawater desalination system, the energy recovery system is a crucial part, as it consumes a lot of energy and plays a guiding role in the recovery efficiency. Therefore, in the energy recovery system, the recovery rate and energy consumption are the key factors to guide the system design. In order to make the energy recovery device achieve a high recovery rate under conditions of low energy consumption, the design and selection of each device in the system are particularly important. At the current stage, system matching optimization, device design optimization, and function objective optimization are widely used to improve the energy recovery system. In this paper, the design principle of the energy recovery integration system is analyzed, methods of reducing energy consumption and improving recovery efficiency are presented. The study provides guidance for the design and selection of energy recovery devices under different operating conditions.

In this paper, the effects of modifying the blade pressure side (PS) on unsteady pressure pulsation and flow structures in a low specific speed centrifugal pump are carried out by experimental and computational fluid dynamics (CFD). Seven monitor points are arranged in the circumferential direction of the impeller outlet to capture the pressure signals in the volute at flow rate of 0.2–1.6Q_d. Results show that the blade PS modification introduced here can significantly alleviate the amplitude of pressure pulsation at blade passing frequency (f_BPF) in all concerned operation conditions. To study the effects of blade modification on the internal flow field, the volute domain is replaced by an even outlet region for CFD analysis. The shear stress transfer (SST) turbulence model is adopted for steady-state numerical simulation while the delayed detached eddy simulation (DDES) based on the SST approach is adopted for transient simulation. Results show that local unsteady velocity fluctuation is the dominant reason for pressure pulsation in the volute. After blade PS modification, the relative velocity distribution at the impeller outlet is more uniform and the intensity of shedding vortex at the blade trailing edge (TE) decreases significantly. The change of internal flow structure improves the uniformity of circumferential velocity distribution the downstream of the impeller outlet, which leads to the decrease of pressure fluctuation amplitude in the volute. Meanwhile, the local Euler head (LEH) distribution at the impeller outlet and the blade loading of PS are presented and compared. It can be concluded that the reduction of pressure pulsation attributes to a more uniform energy distribution at the impeller outlet which is achieved by actively unloading the PS of the modified blades.

Double-suction centrifugal pumps have been applied extensively in many areas, and the significance of pressure fluctuations inside these pumps with large power is becoming increasingly important. In this study, a double-suction centrifugal pump with a high-demand for vibration and noise was redesigned by increasing the flow uniformity at the impeller discharge, implemented by combinations of more than two parameters. First, increasing the number of the impeller blades was intended to enhance the bounding effect that the blades imposed on the fluid. Subsequently, increasing the radial gap between the impeller and volute was applied to reduce the rotor-stator interaction. Finally, the staggered arrangement was optimized to weaken the efficacy of the interference superposition. Based on numerical simulation, the steady and unsteady characteristics of the pump models were calculated. From the fluctuation analysis in the frequency domain, the dimensionless pressure fluctuation amplitude at the blade passing frequency and its harmonics, located on the monitoring points in the redesigned pumps (both with larger radial gap), are reduced a lot. Further, in the volute of the model with new impellers staggered at 12°, the average value for the dimensionless pressure fluctuation amplitude decreases to 6% of that in prototype pump. The dimensionless root-mean-square pressure contour on the mid-span of the impeller tends to be more uniform in the redesigned models (both with larger radial gap); similarly, the pressure contour on the mid-section of the volute presents good uniformity in these models, which in turn demonstrating a reduction in the pressure fluctuation intensity. The results reveal the mechanism of pressure fluctuation reduction in a double-suction centrifugal pump, and the results of this study could provide a reference for pressure fluctuation reduction and vibration performance reinforcement of double-suction centrifugal pumps and other pumps.

In this study, three impellers with different blade pressure side (PS) profiles are designed and the influence on the hydraulic and dynamic performance of a low specific speed centrifugal pump is investigated by numerical simulation and experimental research. The results show that blade PS modification introduced in this study can efficiently alleviate the unsteady pressure pulsation of model pump. In order to study the effects of blade modification on the internal flow filed, the volute domain is replaced by an even outlet region for computational fluid dynamic (CFD) analysis. Relative velocity distribution is extracted to visualize the three-dimensional (3D) flow characteristics at the impeller outlet. Results show that the flow at impeller outlet presents a typical jet–wake structure, which is significantly suppressed after the blade modification. The suppression of jet–wake structure, which is attributed to the redistribution of pressure and velocity in the impeller caused by the change of blade work capacity, can directly reduce the intensity of pressure pulsation in the volute by increasing the velocity uniformity at impeller outlet. Given that the existence of jet–wake flow results in large mixing loss and velocity deviation at the impeller outlet, entropy generation rate and slip velocity calculation are introduced here to measure the extent of jet–wake configuration. Results show that both indicators introduced here can be used to quantify the extent of the jet–wake structure at impeller outlet, and thus, indirectly predict the strength of unsteady pressure pulsation in pump volute.

The startup period, one of several transient operations in a centrifugal pump, takes note of some problems with these devices. Sometimes a transient high pressure and high flow rate over a very short period of time are required at the startup process. The pump^’s dynamic response is delayed because of the rotational inertia of the pump and motor. Our research focuses on how to get a large flow in a short time when the pump cannot meet the requirements alone without a large power driver. To achieve a strong response in the startup process, a ball valve is installed downstream of the pump. The pump^’s transient behavior during such transient operations is important and requires investigation. In this study, the external transient hydrodynamic performance and the internal flow of the pump during the transient startup period are studied by experiments and simulations. In order to find an appropriate matching method, different experiments were designed. The content and results of this paper are meaningful for performance prediction during the transient pump-valve startup period.