Pump Mode Research Articles

Instability characteristics regarding the saddle-shaped region in a reversible mixed-flow pump applied to the low-head pumped storage

The expanding renewable energy has eased the energy crisis but hampers grid stability, which can be offset by scaling up pumped hydro storage. Low-head hydropower resources can be utilized efficiently and economically by a reversible mixed-flow pump (RMFP). However, the saddle-shaped region, a representative unstable feature in the pump mode, severely limits the flexibility and reliability of the RMFP. In this study, external characteristics of the RMFP were experimentally investigated based on a bidirectional test rig. A saddle-shaped region was discovered in the pump head curve formed by the near-rated discharge hump (0.92Qd), valley (0.88Qd), and low-discharge hump (0.71Qd). Transient flows under these feature conditions were simulated using CFD method and compared with the rated discharge condition (1.0Qd). The flow under 0.92Qd was as stable as 1.0Qd but worsened with decreasing discharge. When the discharge decreased to 0.88Qd, the pre-swirl emerged, and the rotating stall occurred and adhered to the blade suction side near the runner shroud. The inflow was blocked by stall vortices, which increased the hydraulic loss and triggered the head drop. When the discharge decreased to 0.71Qd, the inflow collided with stall vortices at the leading edge. This interaction led to the recirculation around the runner inlet, which endowed the inflow with extra energy and triggered the head rise. Overall, this study unveils flow instabilities in the RMFP, which explain the formation of the saddle-shaped region.

Vortex structure and pressure fluctuation of a pump-turbine in pump mode using large Eddy simulation

Pump-turbines are usually used to ensure the stability of power system frequency and make up for the shortcomings of the intermittent nature of new energy such as wind energy. They are an important part of modern power systems. The Large Eddy Simulation (LES) method is used to study the vortex characteristics and pressure fluctuation intensity of the model pump-turbine working in pump mode. Results show that the wake vortex of the impeller has a great influence on the internal flow field of the pump-turbine, which is developed from the vortex structure near the suction surface of the blade. The distribution of trailing edge shedding vortex of guide vanes and shock vortex around tongue is closely related to the wake vortex of impeller. The wake vortex is divided into α and β according to the distribution range along the blade height. Their motion law and dissipation rate are different, and the influence of the α vortex on the flow field is greater. The distribution of pressure fluctuation intensity near the wall corresponds to the vortex structure, which indicated that the vortex is an important factor in pressure fluctuation. It is of great significance to improve the vortex structure inside the pump-turbine for safe and stable operation. The research in this paper can provide reference for the stable operation of the pump-turbine.

All-optical control of topological valley transport in graphene metasurfaces.

We demonstrate that the influence of Kerr effect on valley-Hall topological transport in graphene metasurfaces can be used to implement an all-optical switch. In particular, by taking advantage of the large Kerr coefficient of graphene, the index of refraction of a topologically-protected graphene metasurface can be tuned via a pump beam, which results in an optically controllable frequency shift of the photonic bands of the metasurface. This spectral variation can in turn be readily employed to control and switch the propagation of an optical signal in certain waveguide modes of the graphene metasurface. Importantly, our theoretical and computational analysis reveals that the threshold pump power needed to optically switch ON/OFF the signal is strongly dependent on the group velocity of the pump mode, especially when the device is operated in the slow-light regime. This study could open up new routes towards active photonic nanodevices whose underlying functionality stems from their topological characteristics.

Optimization of Setting Angle Distribution to Suppress Hump Characteristic in Pump Turbine

Pump turbines play a quite important role of peak-valley shifting in the grid, and the hump margin is a critical criterion related to the safety and stability of operation in pump mode. Aiming at investigating the influence of runner outlet setting angle distribution on hump performance of a pump turbine, three runners with different linear distributions of setting angle at outlet were proposed, and the corresponding hump performance comparison was analyzed numerically through the SST k-ω turbulent model. The numerical result shows that, compared to the experiment, the relative errors of all simulated performances (energy characteristic, torque characteristic, and efficiency) were within 3%. Moreover, it was found that setting angle distribution modes could lead to a remarkably different performance in the hump region and, for the runner whose setting angle at shroud was 10° larger than that at hub, the hump safety margin could be increased from 4% to 4.5%. Thereafter, the corresponding mechanisms including energy input and hydraulic loss were investigated through the Euler head theory and the entropy method, respectively. It was found that hydraulic loss distribution played a more important role than the input energy on controlling hump performance. Moreover, for the runner with the largest hump margin, the hydraulic loss was distributed more evenly in the decreasing discharge direction, contributing to the elimination of hump performance. In addition, hydraulic loss distribution was calculated through local entropy production rate (LEPR) method. For all proposed runners, when the pump turbine entered the hump region from a normal operation point, the hydraulic loss was mainly concentrated in vaneless areas and guide/stay vane channels, while the runner with a large setting angle at shroud could better control the hydraulic loss distribution in both the spatial location and the discharge varying direction, increasing the hump margin. The design method presented in our paper is more likely to be applied in engineering applications.

Broadening the operating range of pump-turbine to deep-part load by runner optimization

To cooperate with new energy sources such as wind and solar, pumped storage units are required to frequently change conditions and operate under part loads, leading to the problem of violent pressure fluctuation and unit vibration. To meet this challenge, the next generation of pump-turbine runners will therefore have to be designed differently. The goal of this article is to construct a framework for broadening the operating range of pump-turbine to deep-part loads. In this study, a multi-objective optimization strategy for the runner with wider output range is suggested, wherein the blade control parameters, specifically the blade loading and blade lean angle, are optimized to enhance the efficiency, anti-cavitation, and stability of the pump-turbine runner. A runner with turbine output range of 40%–100% is optimized for a specific power station. Next, the impact of runner control parameters on runner performance is evaluated, and the runner geometric characteristics for different optimizing priorities such as the pump peak efficiency, cavitation performance, turbine rated efficiency, and turbine partial load efficiency, are concluded. The mutual restriction mechanism between the pump peak efficiency and cavitation performance of pump mode, as well as the turbine-rated efficiency and partial load efficiency of turbine mode, is revealed. The main contributions of this paper include putting forward an effective optimization design process for wide output pump-turbine, and pointing out the relationship between runner geometric characteristics and performance. The results indicate that the present approach can significantly improve the efficiency and stability of runners operating in deep-part loads. The blade loading pattern with hub section aft-loaded and shroud section fore-loaded, combined with negative blade lean angle, is recommended for such runners. Blades with a smaller wrap angle and lower arch are conducive to improving the pump peak efficiency and turbine-rated efficiency, while the opposite geometrical features are advantageous for improving the runner cavitation performance and efficiency performance under part load conditions. These findings can serve as an important guide for the development of runners with a wider output range.

Method for preliminary estimation of the crankshaft rotational speed of a reciprocating hybrid power machine with regenerative heat exchange when operating in compressor and pump modes

The determination of the crankshaft rotational speed of a reciprocating hybrid power machine with regenerative heat exchange when operating in the pump mode at a known angular velocity of the crankshaft and when operating in the compressor mode is considered. Based on the analysis of the working processes of injection and suction and assuming equal maximum pressure losses in these processes, the analytical expressions for determining the angular velocity of the crankshaft when operating in the pump mode with a known angular velocity of the crankshaft when operating in the compressor mode are obtained. In addition, based on the equality of work losses in the processes of injection and suction when operating in the compressor and pump modes, the angular velocity of the crankshaft in the pump mode is determined with a known angular velocity of the crankshaft when operating in the compressor mode. Based on the numerical analysis for the air-water working bodies, the dependences of the rotational speed of the crankshaft when operating in the pump mode on the rotational speed of the crankshaft when operating in the compressor mode and on the discharge pressure were obtained. It is shown that the rotational speed of the crankshaft is 100150 min–1 at the rotational speed of the crankshaft in the compressor mode from 2000 to 3000 min–1. Keywords: reciprocating hybrid power machine, regenerative heat exchange, reciprocating compressor, reciprocating pump, crankshaft rotational speed, discharge pressure. Scherba_V_E@list.ru

Modelling and complementary analysis of a small hybrid hydro-photovoltaic power system

Renewable energy sources, especially solar power combined with pumped hydro storage generation (PHSG), have emerged as a remedy to conventional power generation, providing important opportunities for the safe operation of electricity. However, renewable energy is intermittent and random due to unreliable solar radiation. In view of these considerations, this paper focuses on the flexible complementary regulation of the PHSG responding to the fluctuation of solar power generation. To implement the analysis, a mathematical model of the small hybrid hydro-photovoltaic power system is established. Based on the established model, the complementary characteristic between these two renewable energies is simulated at the second scale. The results show that the PHSG has the ability to respond to the disturbance of solar power due to the flexible transition between generator mode and pump mode. The implemented model and obtained conclusions help promote the efficient use of renewable energy systems and reduce power failure accidents.

Effect of stationary diffuser size on performance and pressure field characteristics of an axial-flow pump in pump mode

Effect of stationary diffuser size on performance and pressure field characteristics of an axial-flow pump in pump mode

CFD as a Decision Tool for Pumped Storage Hydropower Plant Flow Measurement Method

Suitable and accurate flow measurement in pumped storage hydropower plants (PSP) is a challenging task due to the entirely different hydraulic behaviour of the penstock. This study presents a novel approach to choosing a suitable flow measurement method and position. The focus is on the flow measurement in a specific short penstock of the largest peak-load hydropower plant, Orlík, after its transformation to a PSP. Our approach is based on three main pillars: numerical modelling of fluid flow (ANSYS CFX), standards, and scientific literature. First, the steady-state numerical model output for the current state is compared to historical measurements of point velocities using current meters and measured hydraulic losses in the penstock. Subsequently, for the planned conversion to the reversible Francis turbine, including shape modifications of the flow paths, a steady numerical simulation of the flow in the penstock was performed in both turbine and pump modes. By analysing the resulting pressure and velocity fields and comparing them to standards and scientific literature, the values of the uncertainty in the flow measurement were calculated. The outcome is a straightforward evaluation and comparison of three main flow measurement methods: current meter, pressure–time, and ultrasonic transit time.

Mode pumping in photonic lattices using a single tailored auxiliary waveguide

In this work, we propose a completely general method to pump the gapped topological modes of a lattice of optical waveguides by controlling the propagation constant of an auxiliary waveguide and its coupling to the main lattice. In this way, we can transform a single-waveguide excitation on the auxiliary waveguide into a specific mode of the lattice. We also demonstrate the possibility of transferring supermodes between two waveguide lattices using the same method. We illustrate the results by pumping and transferring the topological modes of Su-Schrieffer-Heeger lattices. For both scenarios, we show that purities above 99% can be achieved with parameter values within experimental reach. Additionally, we demonstrate how the technique can be used to pump the bulk modes of the lattice for low number of waveguides or enable mode conversion between waveguide lattices.

Flow Evolution and Energy Loss Mechanism in Accidental Shutdown Process of a Large Submersible Mixed-Flow Pump System

To investigate the accidental shutdown process for a large vertical and submersible mixed-flow pump unit in a drainage pumping station, a three-dimensional numerical method for this transition process was proposed according to the angular momentum balance theorem and rigid body rotation technology. We obtained the transient performance curves of the unit and the internal flow characteristics of the full flow channel. In addition, we also analyzed the energy loss distribution of the through-flow components during this progress based on the entropy production theory. The results show that the whole runaway process needs to go through four stages: the pump mode, the pump braking mode, the turbine mode, and the stable runaway mode. The pressure amplitude changes greatly in impeller and guide vanes, and the main fluctuation frequency is the blade frequency. There are higher harmonic frequencies in the dynamic rotor-stator interface. As the rotating speed increases in turbine mode, the negative pressure area near the impeller blade’s trailing edge gradually increases. The entropy production method can be used to determine the location, intensity of energy loss during the transient process. If the rotating speed exceeds the allowed value in the runaway turbine mode, the interaction between blade tip vortex and hub vortex rope may cause loss of stability.

Internal Flow Phenomena of Two-Way Contra-Rotating Axial Flow Pump-Turbine in Pump Mode under Variable Speed

This paper investigated the variable speed operation of a two-way contra-rotating axial flow pump–turbine in pump mode. When counter-rotating impellers operate at the same speed, a significant difference exists in the shaft power of the two impellers, thereby causing difficulties in motor selection. However, the same motor is required for both impellers in two-way pump–turbines. To solve this problem, this paper aims to determine the appropriate speed at which the two impellers operate with a similar shaft power. Accordingly, improving the performance of the tidal unit while enabling the basic functions of the pump–turbine is of considerable engineering and academic significance. An analysis of performance variations of the front and rear impellers in the pump mode reveals the law of power variation for each impeller at different speeds of the rear impeller. Under different flow conditions, shaft power of the rear impeller is found to be at least 31% higher compared with that of the front impeller. This result provides practical reference for further research on the operation of counter-rotating axial flow pump–turbine.

Study of the efficiency of the climate control system of an electric bus in the cold season

In this paper, a one-dimensional mathematical model of a vapor-compression climate system was created, taking into account the characteristics of real equipment, and a study was made of the thermodynamic efficiency of the cycles of a vapor-compression climate system of an electric bus in a stationary and non-stationary setting in the cold season using freons R134a, R290, R407c, R410a, R404a, R507a, R600a and R1234yf. The heat output of the vapor-compression climate system in the heat pump mode is significantly reduced compared to the chiller mode, due to the large temperature difference in the evaporator and condenser. The air conditioner showed the highest heat output when using freons R290, R407c, R410a and R507a. Keywords: air conditioning, heating, vapor compression refrigeration, HVAC, efficiency, freon, electric heavy duty vehicle, electric bus

Wideband multimode optical parametric oscillation in a Kerr microresonator.

Parametric oscillation in Kerr microresonators provides an attractive pathway for the generation of new optical frequencies in a low-power, small-footprint device. The frequency shift of the newly generated parametric sidebands is set by the phasematching of the underlying four-wave-mixing process, with the generation of large frequency shift sidebands typically placing exacting requirements on a resonator's dispersion profile. In practice, this limits the range of viable pump wavelengths, and ultimately the range of output frequencies. In this paper, we consider a multimode four-wave-mixing process in which the pump and sidebands propagate in different mode families of the resonator. We show that this multimode configuration yields a considerable relaxation in the phasematching requirements needed to generate large frequency shift parametric sidebands, allowing their formation even in resonators with strong second-order dispersion. Experimentally we use a magnesium-fluoride micro-disk resonator to demonstrate this multimode phasematching. By accessing different pump and sideband modes, four distinct multimode parametric processes generating frequency shifts between 118 and 216 THz are reported. The resulting separation between the two sidebands is almost three octaves.

Tuning of nuclear spectroscopic telescope array application specific integrated circuits to improve low energy threshold of future hard x-ray imaging detectors

Detector commanding, processing and readout of spaceborne instrumentation is often accomplished with application specific integrated circuits (ASICs). The ASIC designed for the nuclear spectroscopic telescope array (NuSTAR) mission enables future tiled CdZnTe (CZT) detector array readout for x-ray detectors, such as the high resolution energetic x-ray imager (HREXI). Modified NuSTAR ASIC (NuASIC) gain settings have been implemented for HREXI’s broader targeted imaging energy range (3 to 300 keV) compared with NuSTAR (2 to 79 keV), which may require updated NuASIC internal parameters for optimal energy resolution. To reach HREXI’s targeted low energy threshold, we have also enabled the NuASIC’s “charge pump mode,” which introduces an additional tuning parameter. We describe the mechanics of the NuASIC’s adjustable parameters and use our recently developed ASIC test stand to probe a “bare” NuASIC using its internal test pulser. We record the effects of parameter tuning on the device’s electronics noise and low energy threshold and report the optimal set of parameters for HREXI’s updated gain setting. We detail a semiautomated procedure to derive the optimal parameters for each of HREXI’s large area closely tiled NuASIC/CZT detectors to expedite instrument integration.

Intensified gas-liquid mixing in bioreactors equipped with a dual coaxial mixer containing biopolymer solutions

One of the significant challenges in the efficient operation of bioreactors is uniform gas dispersion in very viscous non-Newtonian fluids because of the complex rheology exhibited by these fluids. The uneven gas distribution is more pronounced when large-scale aerated bioreactors with aspect ratios of higher than one are utilized. Prior studies have shown that using a close clearance anchor and two centrally positioned impellers in gas-liquid coaxial mixers can improve gas dispersion in pseudoplastic fluids. Nonetheless, despite the extensive applications of yield-pseudoplastic fluids in many industries, no research has been conducted on the gas dispersion in yield-pseudoplastic fluids within a dual coaxial bioreactor with a greater-than-one aspect ratio. In this regard, electrical resistance tomography (ERT) and computational fluid dynamics (CFD) were employed to assess the effect of operating parameters, namely central impeller speed, anchor speed, aeration rate, rotating mode, and pumping mode of central impeller on the aeration efficiency in yield-pseudoplastic fluids. The experimental measurement of the overall gas hold-up affirmed the profound impact of using a close clearance anchor. Even though the down-pumping and co-rotational mode at Na = 30 rpm provided the highest aeration efficiency, more uniform gas dispersion was observed at Na = 10 rpm owing to a greater axial velocity in the downward direction and more effective circulation loops. Compared to the downward pumping direction, lower gas hold-up values were obtained for the up-pumping configurations. Finally, the superiority of the down-pumping and co-rotational mode was demonstrated by comparing the aeration efficiency of various mixing configurations.

Amplification and Transmission System With Matching Multi-Layer Ion-Doped FM-EDFA

System stability and robustness are highly desired in a mode division multiplexing (MDM) transmission system. The matching of the active fiber and transmission FMF effectively reduces the transmission impairments and is conducive to transmission stability. In this paper, we proposed and fabricated a well-matched triple-layered-core few-mode erbium-doped fiber (FM-EDF) for low differential modal gain (DMG) with multilayer ions doping adjustment. Based on the fabricated FM-EDF, the amplifier is constructed experimentally. By a simple LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> pump mode, the modal gains are higher than 24 dB, and meanwhile, the DMG of 1.6 dB is obtained. The compatibility between the FM-EDF and the passive transmission FMF is verified in an MDM transmission system with a matching degree higher than 83%. Results show that after long-haul FMF transmission and single-stage amplification, the difference in the output signal power is lower than 1.8 dB at the receiver. The fabricated FM-EDF is beneficial for practical MDM systems with high mode stability, excellent fiber linkage integration, and signal channel equalization, which shows much potential for long-haul MDM transmission and multistage amplification.

Physical Modeling of the Drying Process Using Thermoelectric Heat Pump

A functional and technological scheme and a physical model of a convective thermoelectric dryer for vegetables, fruits, mushrooms, seeds, medicinal plants and other household materials have been developed. A laboratory bench has been prepared and studies of the thermal and electrical parameters of a thermoelectric dryer operating in a heat pump mode have been carried out. Experimental studies of the operating sample of the thermoelectric dryer have shown the high energy efficiency of the plant being developed.

Функціональний портрет шестеренної гідравлічної машини

Increasing the efficiency of the functional performance of various mechanisms, including hydraulic gear pumps and motors, is one of the most important issues in the development of mechanical engineering. Special attention should be paid to the indicators of the volume flow rate and the torque. One of the ways is to study the mutual influence of the output parameters of the hydraulic gear machine. Some of the main parameters that determine the functional performance of a gear hydraulic machine are volume flow, power and torque, which in turn form the overall efficiency. It is necessary to create a functional portrait in order to determine the influence of these indicators on the overall efficiency and to improve the efficiency of the gear hydraulic machine. The resulting functional portrait will make it possible to determine the indicator for optimizing the operation of a gear hydraulic machine, both in pump mode and in motor mode. In turn, it will allow us to combine correlations with each other. In order to obtain the optimal indicators for building a functional portrait, a scheme for diagnosing a gear hydraulic machine in the pump-motor mode has been developed. An algorithm for its operation has been presented. As a result of the construction of a functional diagram of a gear hydraulic machine in pump mode, it was found that its operation has no inertia and its parameters are stable and dependent on the dimensional diagram. The orientation of the end bearings occurs during operation in pumping mode under frictional, sliding and dynamic conditions, which ensures improved sealing. On the other hand, the functional portrait of a gear hydraulic machine in motor mode has a zone of inertia, which can be stable or not, depending on the starting moment. Also, on the basis of the obtained functional portrait, it can be assumed that the probable cause of the failure of the gear pump and the motor during the acceptance tests may be the insufficient study of their interdependencies at the stage of development of the design documentation.

Energy performance evaluation of an axial-flow pump as turbine under conventional and reverse operating modes based on an energy loss intensity model

As a low-cost scheme for small-scale hydropower generation, pump as turbines (PATs) are used at different hydrosites around the world. Nevertheless, a big number of recently conducted studies on PAT performance have mainly focused on the centrifugal type, despite the fact that the axial-flow type has a comparatively large flow capacity, thus disposing of higher power density. Therefore, this article seeks to investigate the flow dynamics of an axial-flow PAT and associated energy loss characteristics, under both pump and turbine operating modes. It adopts the numerical simulation method and uses entropy production theory to propose an energy loss intensity model in the cylindrical coordinate system, which quantitatively gives the spatial variation pattern for energy losses in pump and turbine operating modes. In addition, the correlation between energy loss and flow instability is deeply analyzed, where the energy characteristics in pump and turbine modes are quantitatively evaluated. It is shown that the energy loss within the impeller and the guide vane flow fields, for both operating modes, is mainly because of the turbulent entropy production. The proportion of direct entropy production and wall entropy production is found to be relatively small. The velocity gradient, flow vorticity, turbulence intensity, and energy losses within the flow passages of the axial-flow PAT have been closely related. However, owing to the difference in PAT operating modes, there is a significant difference in the location of energy losses. The unstable flow phenomena, such as the impact at the blade inlet, flow deviation at the blade outlet, flow separation, back-flow, and vortex, are the main reasons for entropy production. This study serves as a reference for the design, optimization, and application of axial-flow PATs.