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.
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.
The effect of three noise reduction methods for rotor-stator interaction in diagonal flow fans was studied. The unsteady flow field and directivity of tonal noise were obtained by numerical ...simulation based on computational fluid dynamics (CFD) and the Ffowcs Williams and Hawkings (FW-H) method; the baseline model was tested in a semi-anechoic chamber. The generation mechanism and location of noise were investigated. In addition, the characteristics of tonal noise at blade-passing frequency (BPF) were studied, along with its harmonics. The results show that the tonal noise at 1 BPF dominates the overall sound pressure level. Proper rotor-stator spacing, a large forward-leaned angle, and a large backward-swept angle are beneficial to reduce tonal noise. Also, the noise reduction effect is related to the low amplitude and to the phase shift caused by the pressure response of the rotor wake impinging on stator surfaces, especially near the leading edge at 1 BPF.
Mixed-flow pumps have been widely used in water jet propulsion field. To ensure reliability and operation efficiency, it is necessary to investigate the characteristics of hydraulic excitation force ...during transient operations. In this paper, the radial force of a water jet mixed-flow pump during rapid startup period was investigated numerically based on improved delayed detached eddy simulation (IDDES) and siding mesh method, the external characteristics were verified by test results. The spatial-temporal evolution of radial force was analyzed. The radial force during rapid startup presents transient and delay phenomenon, which shows disparity compared with quasi-steady state. The flow analysis and blade strip analysis show inlet recirculation significantly affects the radial force’s evolution, the radial force is quite different from blade root to tip and the blade tip contributes most to the radial force delay phenomenon. By applying boundary vorticity flux (BVF) theory and separation vortex formation diagnosis, separation regions caused by the dissipation of inlet recirculation were effectively identified and the change trend is in line with the change of radial force, which explains how inlet recirculation results the delay of radial force on blade tip strip and the whole impeller blade.
The span-wise obstacle on the suction surface of a hydrofoil has been verified to be an effective passive control method for cloud cavitation. The position of obstacle significantly influences the ...performance of cavitation control. In this research, we investigated the effect of obstacle position on attached cavitation control on the suction surface of a NACA0015 hydrofoil through response surface methodology. The cavitation types covered from sheet cavitation to partial and transitional cavity oscillations. We derived regression equations and built response surfaces to illustrate the quantitative relationship between individual factors (obstacle position, cavitation number, and angle of attack) and cavitation dynamic response parameters (cavity length, acoustic intensity, and energy flux). Sheet cavitation was effectively suppressed because the obstacle increased the pressure at the near-wall region. However, the obstacle would induce a shear cavitation when its position was too close to the leading edge of the hydrofoil. Under partial cavity oscillation conditions, the obstacle was consistently performed well in cloud cavitation control. The cavitation dynamic response parameters significantly decreased. Under transitional cavity oscillation conditions, the obstacle cannot suppress the cavitation because the transitional cavity oscillation was likely a system-inherent instability. This research is beneficial for a comprehensive understanding of cavitation control mechanism using an obstacle and for further industrial application of obstacle in hydraulic machinery to control cavitation.
The effect of non-uniform inflow on the spatial and temporal distribution of impeller excitation is investigated. The experiments are first conducted to verify the hydraulic performance of the axial ...flow pump and to provide a reference for the accuracy of the numerical simulations. Subsequently, the effect of non-uniform inflow on the spatial and temporal distribution of the flow field and impeller load is investigated. The results indicate that the non-uniform inflow modifies the velocity distribution at the impeller inlet, resulting in alterations in the attack angle and subsequently affecting the radial and circumferential distribution of the impeller load. The extreme difference in the head between the different blades can reach up to 36 % of the total head. Furthermore, velocity pulsation and attack pulsation exhibit more pronounced fluctuations in the low-speed region, and there exists a strong correlation between the amplitude of unsteady forces and the magnitude of the impeller load.
Low specific speed centrifugal pumps are widely applied in the chemical industry and agricultural irrigation fields. The vibration characteristics are of great importance for centrifugal pumps. Apart ...from rotor installation, fluid-induced vibrations caused by internal flow also play an important role in the vibration performance, and special attention should be paid to low specific speed centrifugal pumps for long and narrow meridian flow channels where secondary flows are easy to generate. In this paper, splitter blades were studied for decreasing the pressure and radial force fluctuations of a low specific speed centrifugal pump at the design point, both numerically and experimentally. Numerical simulations based on the Reynolds averaged Navier-Stokes (RANS) turbulent model were performed for fluid-field analysis. The steady state and unsteady simulations were computed based on ANSYS Fluent. Here, the circumferential location, leading edge location, and the deflection angle of the splitter blades were considered to suppress the secondary flow and to reduce vibration. The experiments show the effectiveness of splitter blades for decreasing fluid-induced vibrations.
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•The high-pressure low temperature sintering method enables the synthesis of highly dense, fine-grained Al2O3-cBN-hBN self-lubricating ceramics with no cBN phase transformation, ...resulting in a Vickers hardness of up to 26.6 GPa, even higher than that of conventional ceramics.•Reinforced phase cBN above 30 vol% tends to form a truss structure, resulting in less efficient pressure transfer during high pressure sintering, which affects the mechanical and thermal properties of the composite.•The large modulus difference between cBN and lubricant facilitates the efficiency of lubricant release, reducing the lubricant content required to obtain excellent lubrication performance by half to 5 vol% and improving mechanical properties of composites.•The wear of self-lubricating ceramics is more sensitive to the lubrication performance, just a 5 vol% increase in the lubricant may result in a lower wear rate than the self-lubricating ceramic with twice mechanical properties.
Al2O3-based self-lubricating ceramics are cutting tool materials that meet the extreme working conditions of dry cutting. However, due to the soft lubricating components, the mechanical properties of composites are dramatically reduced. In this paper, Al2O3-cBN-hBN self-lubricating material was designed. High density, fine grain ceramics were synthesized by high-pressure technology. The influence of thermodynamic condition, cBN/hBN addition on mechanical and thermal properties of sintered composites was analyzed. Friction and wear tests were carried out. It is found that the addition of cBN particles can significantly improve the mechanical and thermal properties of the composites. However, the truss effect caused by excessive volume fraction of cBN can reduce the pressure transfer efficiency, and then affect the properties of sintered composites. The different hBN content can change the wear mechanism of the composites. The release efficiency of hBN particles in composites was enhanced due to the large modulus difference between cBN and hBN. The well-sintered Al2O3-cBN-hBN bulks present an excellent mechanical property. The hardness of the composites is improved at least by 54% compared with the traditional self-lubricating material on the premise of ensuring fracture toughness and lubrication performance.
A sustainable power source is more and more important in modern society. Ocean wave energy is a very promising renewable energy source, and it is widely distributed worldwide. But, it is difficult to ...develop efficiently due to various limitations of the traditional electromagnetic generator. In recent years, the newly developed triboelectric nanogenerator (TENG) provides an excellent way to convert water wave energy into electrical energy, which is mainly based on the coupling between triboelectrification and electrostatic induction. In this paper, a review is given for recent advances in using the TENG technology harvesting water wave energy. We first introduce the four most fundamental modes of TENG, based on which a range of wave energy harvesting devices have been demonstrated. Then, these applications’ structure and performance optimizations are discussed. Besides, the connection methods between TENG units are also summarized. Finally, it also outlines the development prospects and challenges of technology.
For the fault diagnosis of rotating machinery, the demodulation algorithm of the monitoring signals plays a key role in fault feature extraction. Especially for weak fault features extraction, ...existing single narrow band demodulation methods have worse performance under low signal to noise ratio condition. According to the mechanism of rotating machinery, both narrow and broad frequency band modulated signals exist simultaneously. Therefore, weak fault features can be obtained through demodulation of multiple narrow frequency bands rather than only one resonance narrow band. In this study, a novel weak feature extraction method is proposed based on used as a good filtermultiple frequency bands demodulation. The superiority of the proposed method is corroborated by simulation analysis and applications of a centrifugal pump and a propeller. By simulation analysis, the proposed multiple frequency bands demodulation (MFBD) method has better demodulation performance than Fast Kurtogram, Autogram and Fast-SC for weak modulation features. The applications results suggested that the proposed MFBD provided a clearer characteristic frequency identification than Fast Kurtogram, Autogram and Fast-SC, especially in weak modulation condition. Therefore, the proposed MFBD method provides a reliable basis for weak fault signal extraction, which shows good engineering significance for fault diagnosis of rotating machinery and passive detection of propeller.
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