Pump Mode Research Articles

CFD simulations of hydraulic short-circuits in junctions, application to the Grand’Maison power plant

In the framework of the XFLEX HYDRO H2020 European Project, the pumped-storage power plant of Grand’Maison (France), owned by Electricité De France, focuses on the implementation of the hydraulic short-circuit (HSC) operating mode. This mode increases the flexibility in pumping mode, which helps the integration of intermittent energies. Grand’Maison is divided into two power houses: the first features four Pelton turbine units and the second eight reversible pump-turbines units. A trifurcation splits the flow into three penstocks, each is then split into two branches that feed each power house. The HSC operating mode, which consists in operating the pumps and the Pelton turbines simultaneously, changes the flow paths in the junctions compared to the pump mode. The power plant was not designed to operate in HSC mode over a long duration, therefore an assessment of its feasibility is necessary. 151 computational fluid dynamic simulations are carried out for two bifurcations and one trifurcation. The numerical simulation results show that the local head losses in HSC mode represent less than 1% of the gross head. No flow instabilities are observed at the bifurcations contrary to the trifurcation. Additional analyses are required to better understand the flow in the trifurcation.

Pushing the envelope of ancillary services with variable speed technology

Hydropower is the backbone of energy transition thanks to its operational flexibility and ability to provide ancillary services. These grid support capabilities are called upon to play a major role to maintain the grid vulnerability at acceptable levels in view of the increasing penetration of stochastic and intermittent renewable energies. In this context, variable speed reversible pump-turbine technology is a key asset as it can extend the head operating range of a powerplant, enable power network control in pump mode and further increase the flexibility services to the electrical grid. Furthermore, by taking advantage of the so-called flywheel effect, variable speed enables the fast active power injection/absorption in pumping and generating mode. The additional degree of freedom offered by the variable speed opens the door to different control strategies for the hydroelectric plant, as the converter can be used for speed or power control. This can be exploited to maximize either the efficiency or the power reserve dedicated to grid support. In this paper, the strategies to maximize the ancillary service of Frades 2 pumped storage power plant (PSPP) are investigated. The plant features two high-head single-stage reversible variable speed units, coupled with 420 MVA doubly-fed induction motor-generators (DFIM). Using a 1D numerical model to simulate the power plant behavior, it is explored to which extent Frades 2 can deliver frequency containment reserve (FCR) power, while complying with the ENTSO grid code, and speed deviation constrains inherent to DFIM. By choosing a strategy which fully exploits the flywheel effect, it is established that the FCR power band can be equal to the whole operating range of the power plant. Moreover, the fast frequency response capacity (FFR) is also evaluated. It is found that by maximizing the energy stored in the rotating masses, each unit of Frades 2 can deliver up to 110 MW of active power in 1.3 seconds.

Numerical design methodology for reversible Deriaz turbine with high energy performance and reduced fish impacts

The increased interest for further exploitation of hydropower and pumped hydro storage sites of lower head and capacity, and the tightening on the other hand of the environmental terms and restrictions, would require the design of corresponding hydro turbines and reversible machines with improved environmental performance. This work presents a numerical methodology to optimize the design of a Deriaz turbine in order to achieve high energy efficiency and improved fish friendly behaviour in both pump and turbine operation modes. Various numerical simulation and optimization software and tools are used, while the geometry of the machine is fully parameterized to allow for wide design modifications and corresponding numerical tests. At first, the most important design parameters and their variation range limits are identified by a sensitivity study. Next, several multi-objective optimization procedures are carried out, using general quantitative targets for a comparative evaluation of the various machine runner designs. The results show a complex interdependence or competitiveness of the machine efficiency and the various fish impact performance indices that requires careful analysis. The developed and applied methodology can produce one or more candidate designs that satisfactorily meet all the desired objectives.

Analysis of key influencing factors for multi-mode solar heat pump systems

To further improve the stability and renewable energy utilization of the compound heat source heat pump system under complex operating conditions, a multi-mode solar heat pump system was proposed and a mathematical model was established in this paper. The accuracy of the model is verified by the experimental data, with the relative error within ±15%. The effects of the number of solar photovoltaic/thermal (PV/T) collectors (area), environmental parameters, and refrigerant flow rate on system performance are discussed separately for different models by the validated model. The results show that (1) PV/T-water source heat pump mode: the number of PV/T collectors in parallel (area) increases to 3 (3.84 m2), and the system performance improves the most, subsequently weakening; (2) PV/T-water and air composite heat pump model: When the refrigerant distribution ratio in the double-pipe heat exchanger 1 is increased from 55% to 95%, the collector's heat collecting capacity, power generation efficiency, and system coefficient of performance (COP) increase by 8.99%, 1.22%, and 6.4%, respectively. Moreover, the increase in solar irradiance can promote more refrigerant flow into the double-pipe heat exchanger 1 and improve heat pump COP more than the effect of increased ambient temperature. The research results can provide an effective reference for further optimization of solar heat pump systems and full utilization of renewable energy.

Contribution for the roadmap of hydraulic short circuit implementation: Case of Grand-Maison pumped storage power plant

The objectives of the 2050 energy policy based on the decarbonization of the electric power networks generate drastic changes for grid balancing with a massive integration of non-dispatchable Renewable Energy Sources. Hydroelectric power plants already significantly support electricity power system flexibility with innovative solutions such as variable speed units, fast frequency control, fast generating to pumping modes transition, high ramping rate, inertia emulation, etc.For pumped storage power plants (PSP), a quick solution to increase the flexibility without large investment is to operate the power plant in hydraulic short circuit (HSC) mode. This technological solution is simple to implement, but requires an in-depth study of various technical aspects among which the hydraulic transients of the new operating modes is of high importance from the installation’s safety perspective. In the framework of XFLEX HYDRO H2020 European research project, the exploitation of this solution is under implementation at Grand-Maison PSP. Located in the French Alps, Grand-Maison PSP is equipped with 8 reversible multi-stage Francis pump-turbines and 4 Pelton turbines, for a total installed capacity of 1800MW, thus being the largest PSP in Europe and one of the major PSP in the world. The waterway includes a headrace tunnel, a headrace surge tank, 3 parallel penstocks feeding the 12 units operated under a maximum gross head of 955mWC.In this paper, after a description of the general HSC considerations, the 1D model of the Grand Maison PSP and the related validation are presented. Finally, the most critical load cases in HSC operation are described to identify the potential hydraulic transient issues, such as extreme water levels in the upstream surge tank, maximum static pressure along the pressure shaft and minimum static pressure along the tunnels. The analysis performed for Grand Maison PSP is a contribution to the roadmap for the implementation of HSC operation in pumped storage power plant and will be made available as a public deliverable of the XFLEX HYDRO H2020 European research project.

Performance characteristics of an axial‐flow gas induction impeller

AbstractPower number, pressure coefficient, and induced gas flow rate of a novel axial‐flow gas induction impeller with large openings for gas flow are reported. The effects of rotational speed, impeller diameter, submergence, and pumping mode are considered in turbulent operation. The pressure coefficient is measured using the reduction in pressure at speeds below the minimum induction speed as well as from the minimum induction speed. The minimum induction speed approach consistently yields lower pressure coefficient values, indicating the existence of impeller exit losses that are required to force gas from the centre of the impeller into the liquid. The induced gas flow rate is modelled using two approaches. The first approach relates the gas flow rate to the available pressure difference, and in this case, the relation is found to be strongly affected by impeller diameter. The second approach is a literature model that likens the induction process to water jet injection. While this approach appears promising, flow measurement device pressure losses make it difficult to definitively evaluate this method.

Suspended-core fiber with embedded GaSe nanosheets for second harmonic generation.

We report an all-fiber scheme for the second harmonic generation (SHG) by embedding gallium selenide (GaSe) nanosheets into a suspended-core fiber (SCF). Based on modes analysis and theoretical calculations, the phase-matching modes from multiple optional modes in the SHG process and the optimal SCF length are determined by calculating the effective refractive index and balancing the SHG growth and transmission loss. Due to the long-distance interaction between pumped fundamental mode and GaSe nanosheets around the suspended core, an SHG signal is observed under a milliwatt-level pump light, and exhibits a quadratic growth with the increased pump power. The SHG process is also realized in a broad wavelength range by varying the pump in the range of 1420∼1700 nm. The SCF with the large air cladding and suspended core as an excellent platform can therefore be employed to integrate low-dimensional nonlinear materials, which holds great promise for the applications of all-fiber structures in new light source generating, signal processing and fiber sensing.

Generation of counterpropagating and spectrally uncorrelated photon-pair states by spontaneous four-wave mixing in photonic crystal waveguides

In this work, we propose and theoretically analyze a new scheme for generation of counterpropagating photon pairs in photonic crystal waveguides through the process of spontaneous four-wave mixing. Using the fundamental properties of periodic Bloch modes in a standard photonic crystal waveguide, we demonstrate how modal phase-matching can be reached between forward-propagating pump modes and counterpropagating signal and idler modes, for generation of degenerate and non-degenerate photon pairs. We then show how this scheme can be used for generation of photon pairs that are nearly uncorrelated in the spectral degree of freedom. Such a source will be highly interesting as a heralded source of single photons, especially as the spectrally separable signal and idler photons are also spatially separated directly at the source. We conduct our investigation based on a design in silicon, yet our design concept is general and can in principle be applied to any nanostructured material platform.

Ice Melting Performance of Solar-Assisted Cold Water Phase-Change Energy Heat Pump System

The solar-assisted cold water phase-change energy heat pump system is a clean energy heating system which can effectively reduce the ice melting energy consumption of the cold-water phase-change energy heat pump system. In this paper, the operation mode of the solar-assisted cold-water phase-change energy heat pump system is given, three new ice melting methods are proposed, the performance of three ice melting modes using solar energy for thermal ice melting are simulated, and the influence of ice thickness on system operation is analyzed. The results show that among the three ice melting modes, the affected serial dual-source heat pump mode has the largest system COP, and the pure serial dual-source heat pump mode has the smallest annual total cost. Among the solar collector price, glycol price and electricity price, the change in solar collector price has the greatest impact on the total annual cost, and the change in glycol price has the least impact on the total annual cost. When the ice thickness exceeds 8 mm, the increase in the space heating of the solar-assisted cold water phase-change energy heat pump system becomes smaller, and the increase in heat consumption of ice melting becomes larger. The solar-assisted cold-water phase-change energy heat pump system can simultaneously melt ice and heat, and its economic benefits are significant, with good application and promotion value.

Mechanism and performance evaluation of a thermoelectric-chip-based cloak for active regulation of heat flow

In the field of heat manipulation, active thermal cloaks based on thermoelectric chips (TECs) have received much less attention than passive thermal cloaks based on metamaterials. This work focuses on active thermal cloaks and explores in-depth their mechanism of heat flow regulation. For a two-dimensional circular object located in a rectangular background plate with uniform temperature gradient, the theoretical design of an active cloak was realized by analytically solving for the target temperature field. A parameter study was conducted numerically for the designed thermal cloak. The results show that the object-to-background thermal conductivity ratio (m) is the key parameter that determines the working mode of the cloak. When m < 1, the TECs work in a heating mode with less power consumption; when m > 1, the TECs work in a chilling/heat pump mode with higher power consumption. If the change of a certain parameter increases the heat flow regulation, it will also cause performance degradation and an increase of the thermal cloak’s power consumption, especially when m is greater than 1. Improvement can be achieved by increasing the number of TECs (N), but the impact of N diminishes rapidly beyond a certain value. The systematic study in this work reveals the high flexibility and wide adaptability of the TE-chip-based thermal cloak in heat flow regulation.

Investigation on the relationship between hydraulic loss and vortex evolution in pump mode of a pump-turbine

Investigation on the relationship between hydraulic loss and vortex evolution in pump mode of a pump-turbine

Effects of guide vane shape on the performances of pump-turbine: A comparative study in energy storage and power generation

Pumped storage unit is a typical energy storage system in electric power grid system. Flow energy dissipation (FED) is a key factor affecting energy utilization efficiency. Guide vane has an important influence on the hydraulic performance and system stability. This study compares the FED difference of two typical guide vanes in turbine mode and pump mode based on Computational Fluid Dynamics (CFD) and entropy production method. The results show that at the same head, the flow rates in energy storage and power generation are different. In pump mode, FED concentrates in runner, guide vane, stay vane and volute. FED concentrates in runner and draft tube in turbine mode. The sources of FED in pump mode and turbine mode are different, including flow separation, jet wake, wall loss, vortex rope and back-flow. Guide vane with oval leading edge can better enhance the flow rate compared with that with sharp leading edge in turbine mode, which decreases FED at small flow rate condition by improving the matching of blade profiles and flow direction. This paper provides a reference for improving the performance of pump turbine through design.

Angular momentum driven dynamics of stimulated Brillouin scattering in multimode fibers.

The strength of stimulated Brillouin scattering (SBS) in optical fibers is largely governed by the spatial overlap between supported optical and acoustic modes, leading to a complicated amalgamation of photon-phonon interactions in multimode fibers. Here, we study SBS dynamics in ring-core fibers that support modes carrying orbital angular momentum (OAM), which result in distinctive characteristics. We find that the OAM SBS response, as well as modal content, strongly depends on the polarization state of the pump, as OAM modes in fiber have distinct propagation dynamics depending on whether the input is circularly or linearly polarized. This is in contrast to conventionally posited wisdom that SBS strength is independent of the pump's input polarization state in an isotropic material. This increased specificity can lead to interesting effects such as spatial phase conjugation even in the presence of stably transmitted, i.e. non-aberrated, spatial pump modes. More generally, we show that using OAM modes yields additional degrees of control over SBS interactions beyond more conventional parameters, such as effective area, acousto-optic spatial overlaps, and material composition.

Application of a multi-tiered blade system for reversible hydromachines of PSPP

The use of reversible hydraulic machines is often the most cost-effective option in most pumped storage configurations. At the same time, among reversible machines, radial-axial pump-turbines are most often used. This is due to the fact that such hydraulic turbines are capable of operating at high pressures, which are used in pumped storage power plants. The impellers of such reversible machines have a rigid-blade system, that is, they are not able to change their position, like the blades of axial and diagonal rotary-blade hydraulic turbines. What makes the problem in the design of pump-turbines is that, due to the different influence of hydraulic resistances, the optimum in pumping and turbine modes is different. This is taken into account in the design and determines both geometric and operational parameters. As a result, the maximum impeller diameter calculated for the pumping mode does not correspond to the optimal turbine geometry. At the same time, it is the turbine mode that should have the maximum efficiency, since the cost of peak electricity is higher than the cost of energy during the hours of dips in the daily load schedule corresponding to the pumping mode. In order to design the impeller-pump of the turbine optimally for the turbine mode, it is necessary for the same impeller to develop a greater pressure in the pumping mode of operation. To increase the pressure in the pumping mode, multi-tiered paddle grids can be used. This paper discusses the effect of additional tiers of hydrodynamic grids on the turbine regime and the prospects for their modernization in conjunction with other well-known technical solutions to increase the pressure and expand the operating area of HPP hydroelectric units.

Injection locking and breathing soliton microcomb generation dynamics of a nonlinear optical microcavity-laser diode butt-coupled system with pump power much higher than the parametric oscillation threshold

This paper mainly analyzes the injection locking mechanism of pump laser diode and the breathing microcavity optical frequency comb (microcomb) generation dynamics of the nonlinear optical Kerr microcavity-laser diode butt-coupled system with resonant Rayleigh backscattering feedback. The nonlinear dynamics is especially studied under the condition of the laser diode pump power much higher than the parametric oscillation threshold of the four-wave mixing microcomb in nonlinear Kerr microcavity. Further, we find that under the condition of high-power pumping, the exact mechanism for the system to produce the breathing microcomb is not due to the self-injection locking of the lasing frequency of the laser diode main pump mode, but a newly discovered microcavity resonant excitation mechanism through the pump mode modulation sideband (caused by microcavity Rayleigh backscattering feedback), which is closely related to the breathing characteristics of the generated soliton microcomb.

Dynamic Stability Analysis of Isolated Power System

The islanded mode of operation of an electric power system (EPS) that has generation capabilities provided by conventional thermal power plants, by a pumped-storage power station, or from an interlink with a neighboring electric power system through an HVDC BtB converter is addressed in this paper. The risk for electrical power systems to fall into an islanded mode has recently grown, as it is caused not just by technical reasons but by a geopolitical situation as well. The current strains demand the close consideration of problems related to EPS operation in an islanded mode. This paper considers several. The research covers the following issues. The response of the islanded system to a sudden and spasmodic load change is analyzed in cases when the system deals with the disturbance with internal resources alone and with the help of an HVDC BtB converter’s frequency control functionality. Analysis of the impact of the settings of the HVDC BtB converter on the system’s response to disturbances is presented and the optimal set of parameters found. The impact of the system’s extended inertia on the system’s response is evaluated by using an additional unit of the pumped-storage power station in synchronous condenser mode. Transients in the system when switching a unit operating in synchronous condenser mode on and off are analyzed. The capability of the system to withstand major disturbances, such as disconnection of the pumped-storage power station’s unit operating in a pump mode and disconnection of the HVDC BtB converter in emergency modes, if a situation demands, is researched. The research is carried out by numerical simulations using PSS Sincal Electricity Basic software. Updated operating parameters of the isolated power system and the LCC HVDC BtB converter, as well as frequency control automation provided by ABB, were used in the simulations.

Physiologic Data-Driven Iterative Learning Control for Left Ventricular Assist Devices.

Continuous flow ventricular assist devices (cfVADs) constitute a viable and increasingly used therapy for end-stage heart failure patients. However, they are still operating at a fixed-speed mode that precludes physiological cfVAD response and it is often related to adverse events of cfVAD therapy. To ameliorate this, various physiological controllers have been proposed, however, the majority of these controllers do not account for the lack of pulsatility in the cfVAD operation, which is supposed to be beneficial for the physiological function of the cardiovascular system. In this study, we present a physiological data-driven iterative learning controller (PDD-ILC) that accurately tracks predefined pump flow trajectories, aiming to achieve physiological, pulsatile, and treatment-driven response of cfVADs. The controller has been extensively tested in an in-silico environment under various physiological conditions, and compared with a physiologic pump flow proportional-integral-derivative controller (PF-PIDC) developed in this study as well as the constant speed (CS) control that is the current state of the art in clinical practice. Additionally, two treatment objectives were investigated to achieve pulsatility maximization and left ventricular stroke work (LVSW) minimization by implementing copulsation and counterpulsation pump modes, respectively. Under all experimental conditions, the PDD-ILC as well as the PF-PIDC demonstrated highly accurate tracking of the reference pump flow trajectories, outperforming existing model-based iterative learning control approaches. Additionally, the developed controllers achieved the predefined treatment objectives and resulted in improved hemodynamics and preload sensitivities compared to the CS support.

Various pumping modes of high-power double clad fiber laser

As one of the first invented laser categories, fiber laser plays a crucial role in many specific fields, e.g., filed-optic communication, sensing, industrial processing, national defense, military. In order to effectively couple the pump light into the single-mode fiber, double-clad fiber laser was invented, i.e., the power and efficiency of fiber lasers have been significantly improved. There are two mainly categories of pumping mode for double clad fiber laser, named as end smoothing the gain curve pumping and side pumping. This paper will focus on the analysis and comparison of these two pumping modes in terms of the power, efficiency, relative population density, thermal load and feasibility. The experimental procedure will be achieved based on the MATLABR2021b and SFTool. The aim of the paper is to investigate the effects on the forward pumping and backward pumping in the process of side pumping and end pumping. According to the analysis, side pumping and bi-direction pumping smooth the gain curve effectively. Choosing appropriate pumping mode can reduce the loss and save the cost of optical transmission to a large extent. These results shed light on selection of pumping mode for high power fiber laser.

Energy loss mechanisms of transition from pump mode to turbine mode of an axial-flow pump under bidirectional conditions

Pump-as-turbine stations with ultra-low head often face the deterioration risk during load rejection operations when the demands in water delivery and power generation are satisfied. In the course of load rejection, significant energy transfer and hydraulic instability may ensue from the pump-to-turbine transition mode, and vice versa. In order to investigate the variation of energy loss during the transition process of a bidirectional axial-flow pump, the entropy production method is herein utilized for visualization and quantitative analysis of high energy loss regions within key components. In the process of transient simulation, the torque balance equation is applied for calculating the rotational speed of impeller. Two-way transitions are considered with the bidirectional pump for comparing two distinct forms of pumps equipped with front and rear guide vanes. Results show that the simulated external characteristic curves and transition parameters of the pump are in good accordance with the experimental data. The transient process of the transition successively goes through four modes, i.e. pump, braking, turbine and runaway modes. In the process of the direction switch of the main flow and rotation, the different positions of guide vanes also deeply influence the inflow angle and flow pattern in impeller, and then change the distribution of the pressure coefficient, vorticity and entropy production rate. In pump mode, the entropy production rate and pressure coefficient at the impeller inlet edge under backward transition condition (BTC) is higher than that under forward transition condition (FTC), due to the smaller inflow angle caused by the front guide vanes under BTC. In runaway operation, the total entropy production (TEP) under FTC is obviously higher than that under BTC, because the energy loss is reduced by the broken shedding vortices caused by the obstruction of the guide vanes under BTC. This study's results can be referred to while seeking for the operation safety and stability of the pump stations consecutively used to pump and generate power.

Study of operating modes of a double-chamber diaphragm milk pump

Diaphragm (membrane) pumps refer to a class of devices with a reciprocating movement of the working body that are widely used in various industrial technologies and in everyday life. In agricultural production, these pumps are used in the production line of milking installations and for creating a vacuum in individual milking machines. The most important distinguishing feature of a diaphragm pump is the minimum mechanical effect on the pumped product due to the excluded action of centrifugal forces, which in turn excludes mechanical impact and foaming. Therefore, they are mainly used for delicate pumping of products, in particular milk. Another important feature of the pump design is its tightness that serves as a reliable barrier to isolate the working and external environments. A significantly smaller number of rubbing parts in comparison with centrifugal pumps ensures higher reliability and minimum maintenance. Analysis of modern designs of diaphragm pumps showed that their productivity and operational reliability can be improved as follows: two-chamber version; the increased usable volume of the chamber due to the diaphragm structuring; electric drive of the working body. The team of authors substantiated the design of a two-chamber milk pump with an electromagnetic drive, substantiated its supply to ensure stable operation of the milking installation throughout the entire milking time, and calculated the effect of the structured diaphragm diameter on the pump flow. The laboratory bench of the Department of Machines and Technologies of Agro-industrial Complex, Stavropol State Agrarian University, was used for experimental studies, and the estimated payback period for the developed pump design was found not to exceed 1.2...1.5 years.