Pump Mode Research Articles

Comparative numerical studies for the flow energy dissipation features in a pump-turbine in pump mode and turbine mode

Reduction of flow energy dissipation (FED) in pump-turbine is important in improving the energy conversion efficiency of pumped storage power station. By eliminating obvious undesirable flow regimes, the efficiency of modern pump-turbines is higher than 90% in both pump and turbine modes. However, the further efficiency improvement is difficult because it is hard to visualizing, locating and quantifying FED. Based on Computational Fluid Dynamics (CFD) and thermodynamics evaluation, the irreversible FED features in a reversible pump-turbine is comparatively analyzed in pump mode and turbine mode. By analyzing different off-wall distance zones, the near-wall (<2 mm) and far-away (>10 mm) regions are found with high FED. By comparing different components, runner is found as the main FED source (proportion >50%). The stators downstream to runner (vanes in pump mode and draft tube in turbine mode) has also high FED due to local vortical flow. FED in pump-turbine is found with different sub-types. The viscosity-dominated type is found with local increasing of turbulence kinetic energy and temperature. The striking-dominated type is found with local sudden velocity reduction. Targeted elimination of vortical flow, reduction of surface-roughness and improvement of geometry-flow adaptability will be effective in the future high-efficiency design of reversible pump-turbines.

Концепція енергоефективності й перспективи реалізації принципу струминної термокомпресії в малій теплоенергетиці

The expediency of the implementation of the principle of steam thermal compression to improve the energy efficiency of sources of electricity and heat supply of small heat power engineering is substantiated. The results of thermodynamic analysis and numerical optimization of the parameters of the compressor steam-turbine cycle of a small cogeneration power plant are presented. A jet step-down thermotransformer has been tested - as an alternative to traditional boiler heating. On the basis of the conducted thermodynamic analysis, a new combined cycle of a step-down thermotransformer has been developed, which ensures efficient conversion of the supplied energy (mainly in the form of fuel heat) into the heat carrier flow of the heat supply system with the required temperature level 50 ... 90 °C). The fundamental difference between the considered thermal transformer and steam compressor heat pumps is the replacement of a mechanical compressor with a steam thermocompressor module (STC-unit). The working process in the STK-module is realized by using the liquid phase of the refrigerant, which boils up during expiration, subcooled to saturation, as an active medium of a jet compressor. Injection of steam from the evaporator is provided due to the fine-dispersed vapor-droplet structure formed in the outlet section of the active flow nozzle. A program for the numerical study of the working process of a step-down thermal transformer was prepared and tested, on the basis of which multivariate calculations were carried out. On the basis of computational studies, the area of achievable indicators of the proposed heat supply system has been established; the area of initial operating parameters corresponding to the maximum values of the conversion coefficient and exergy efficiency was determined; comparative indicators of the main parameters of the investigated thermal transformer on various working substances in the range of operating modes as a heat pump or a refrigerating machine were obtained. Key words: workflow, steam thermocompressor, step-down thermotransformer, energy efficiency, heat pump mode

Analysis of Control Characteristics and Design of Control System Based on Internal Parameters in Doubly Fed Variable-Speed Pumped Storage Unit

In this paper, the control strategies and their characteristics when applied to the doubly-fed variable-speed pumped storage unit in generating mode and pump mode are discussed. The composition of doubly fed variable-speed pumped storage unit is introduced, and the mathematical model of every component is proposed. Two control strategies of the unit are introduced. One is the power priority control strategy and the other is the speed priority control strategy. Then, the control block diagrams of the two control strategies in the generating mode and the pump mode are established, and the parameters of the unit in each control strategy are designed. The two control strategies are simulated in power generation and pumping conditions. Finally, the conclusion that power priority strategy has a better effect on power control is obtained.

Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine

Pumped Hydropower Storage (PHS) is the maturest and most economically viable technology for storing energy and regulating the electrical grid on a large scale. Due to the growing amount of intermittent renewable energy sources, the necessity of maintaining grid stability increases. Most PHS facilities today require a geographical topology with large differences in elevation. The ALPHEUS H2020 EU project has the aim to develop PHS for flat geographical topologies. The present study was concerned with the initial design of a low-head model counter-rotating pump-turbine. The machine was numerically analysed during the shutdown and startup sequences using computational fluid dynamics. The rotational speed of the individual runners was decreased from the design point to stand-still and increased back to the design point, in both pump and turbine modes. As the rotational speeds were close to zero, the flow field was chaotic, and a large flow separation occurred by the blades of the runners. Rapid load variations on the runner blades and reverse flow were encountered in pump mode as the machine lost the ability to produce head. The loads were less severe in the turbine mode sequence. Frequency analyses revealed that the blade passing frequencies and their linear combinations yielded the strongest pulsations in the system.

Experimental studies of unsteady cavitation at the tongue of a pump-turbine in pump mode

The paper deals with the cavitation at tongue of a pump-turbine in pump mode, including the typical patterns, unsteady behaviors, and the influence on pump performance and fluid-borne noise. Visualization experiments were conducted under different flow rates and rotational speeds for variation cavity regimes. The results show the patterns can be divided into three regimes with cavitation development: bubble cavitation, cloud cavitation, and lock cavitation for the gas-lock phenomenon and performance plummet. The rotor-stator interaction and jet-wake flow could affect the cavitation generation. The blade passing effect is the leading cause of bubble clusters periodic collapsing or shedding at the early stages of cavitation, while playing a small role as cavities become thick and evaporation rate rises. The combined action of the attached vortex (re-entrant jet) and the depression by pressure gradient outside cavity surface account for the shedding at the developed cloud cavitation stage. Based on the noise measurement by hydrophone at the outlet, the broadband sound in the range of 1000 HZ-2000 Hz can be used for cavitation detection since it can be rarely influenced by operating conditions under non-cavitation.

Mutual cooperative effects between the mode components of two-photon and Raman induced cavity lasing processes

The paper proposes to unify the two-photon laser and induced cooperative scattering Raman lasing in which the flying ensemble of two-level excited radiators are coupled with the bimodal cavity field in nonlinear two-photon and scattering interactions. It discusses the situation in which the induced two-quantum lasing takes place together with the cooperative scattering conversion of photons between the pump, Stokes, and anti-Stokes cavity modes. The proposed master equation describes cooperative energy exchanges between Raman and two-photon lasing processes by portions of energies multiple to the energy of the entangled photon pair.The generators of such emission and absorption processes belonging to the symmetries of Raman conversion and two-photon cooperative generation are unified. The first symmetry belongs to su(2) algebra connected to the scattering conversion in the Stokes, pump, and anti-Stokes modes of cavity (Opt. Commun.,285(5) (2012) 686–692). The second one belongs to multi-mode su(1,1) symmetry which quantifies the cooperative process belonging to two-photon emission in cavity/fiber mode components of field (see Opt. Commun. 247(4–6) (2005) 381–392). The bimodal collective photon operators are introduced describing the emission or absorption acts of the fixed portion of energy from the cavity equal to the transition energy between the states of each excited atom. A key impact of the study focuses on the statistical properties of the bimodal field and their detection possibilities are proposed for the description of the time evolution of quantum correlations between the field components of Raman conversion and two-photon emission.

Characteristic Curve Prediction of a Commercial Centrifugal Pump Operating as a Turbine Through Numerical Simulations

In this work, we seek to predict the characteristic curve of a commercial centrifugal radial flow pump operating as a turbine, applying a novel methodology based on the state of the art. Initially, the characteristic curve in pump mode is validated through numerical simulations. The results obtained are approximate to the points awarded by the manufacturer, with an error of less than 7% at the best efficiency point. Subsequently, the characteristic curve is generated in turbine mode, obtaining an error of less than 10% respect to mathematical model. Then, velocity and pressure contours are evaluated to validate the fluid dynamic behavior. Finally, the site operating conditions for electricity generation are obtained. With this, it is proposing a methodology for the selection of these turbomachines, applying an economic technology for zones that do not have access to the electrical energy, since it was not found a method that is being applied for its correct election in the hydroelectric generation at low scale.

Analysis of Transient Force Performances of Pump-Turbine during Stop Process in Pump Mode

The stop process occurs frequently for pump turbine due to the requirement of switching from pump mode to turbine mode. During stop process, the operating parameters such as the axial thrust, radial thrust and torque of the runner change rapidly, causing vibration of runner. In some cases, the rotating part can be lifted. In this paper, the unbalanced force acting on a pump-turbine during stop process in pump mode was studied using numerical simulation method. The CFD analysis was based on Reynolds averaged equation and the SST model was used to predict the transient flow characteristics. The clearance flow was also taken into consideration. Results show that the axial thrust was in opposite direction of gravity and changed with the variation of the head and torque. The axial thrust reached the maximum value in no-load condition.

Numerical and experimental study of pump as turbine for sediment affected micro hydropower project in Nepal

Designing and manufacturing site-specific turbines for small hydropower is not economical. Using abundantly available Pump, from the market, as Turbine (PAT) instead of designing a completely different turbine can be much more economical for small-scale hydropower. Lot of research have been going throughout the world on this and has already proven its effectiveness. In Nepalese hydropower, including the ones already developed and the ones that will be developed in the future, Francis turbines are supposedly the suitable turbine of choice. However, designing and manufacturing Francis turbine is a tedious task and the local manufacturers, who are expert in manufacturing Cross-flow turbines; do not have the technology and competence to manufacture the modern Francis turbines. Sediment in Himalayan rivers are the major hurdles of operation as they reduce the lifetime of the turbine by a very large factor, shooting up the maintenance cost of the hydropower. The operational region of Francis turbine and PAT overlaps quite a lot, thus indicating that PAT can be used in many of the hydropower in Nepal. The Chinese and Indian pump manufacturers are already renowned in developing a wide range of pumps and supplying them in Nepal. Despite having such great opportunity, pumps have never been used in turbine mode in Nepalese hydropower. In addition to that, no research has been done, in Nepal, regarding the effects of sediment on pumps being operated as pump or turbine. This paper describes performance of pump in erosive environment using Computational Fluid Dynamics (CFD). It also compares the results obtained from the CFD analysis of sediment erosion in pump operated in pump mode as well as turbine mode with other researchers work. Finally, it compares the results obtained from the CFD with the results obtained from the experiment.

Transient TEHD Analysis of a Thrust Bearing Based on Two-Way Fluid-Solid-Thermal Interaction

Thrust bearing is a key component of hydroelectric generator and bears the axial load of the unit. During transient processes, such as start and stop of the unit, thrust bearing usually occurs wear phenomenon at pad surface, which affects the stable operation of the unit and reduces service life of the bearing. Based on two-way fluid-solid-thermal interaction, this paper did transient thermal-elastic-hydrodynamic (TEHD) analysis of a tilting pad thrust bearing under the pump mode. For the fluid region, the Reynolds equation and the viscosity-temperature equation are solved. For the solid region, transient heat conduction equation and basic thermal-elasticity equation are considered. The data transferred in the fluid-solid interface satisfy the fluid-solid-thermal interaction equation. The variation of the lubricant oil temperature, the oil film force, the pad surface inclination angle and axial velocity of pad and mirror plate are analysed, which provide theoretical basis for the design of bearing and the safe operation of the unit.

CFD simulations of a Y-junction for the implementation of hydraulic short-circuit operating mode

In the framework of the XFLEX HYDRO H2020 European Project, one of the demonstrators focuses on the implementation of the hydraulic short-circuit on the pump storage power plant of Grand-Maison owned by Electricité De France (EDF). The Grand-Maison power plant is a two-level plant production with one plant located above the downstream reservoir and equipped with four Pelton turbines; a second plant located downstream the reservoir and equipped with eight reversible pump-turbines. Hydraulic short circuit consists in running pumps and turbines in the meantime to balance the energy consumption of the pumps compared to the grid. Such an operating mode allows increasing the flexibility of the power plant and targeting the requirement of balancing the intermittent production due to the growing of new renewable energies such as wind and solar power plants. The hydraulic short-circuit operating mode leads to a change in the flow paths in the penstocks and junctions compared to the normal turbine or pump modes. Indeed, compared to the pump mode, this mode will lead to a flow derivation at the junction between the penstocks directed to the Pelton units and the penstocks directed to the upper reservoir. As this mode have not been scheduled at the beginning of the power plant construction, it is necessary to quantitatively assess the singular head losses generated at the junction to be able to simulate the complete behaviour of the power plant by means of a 1D model. CFD simulations are carried out with the Fluent software for several configurations of hydraulic short-circuit defined by the ratio of flow rate deviated to the Pelton turbines.

Numerical analysis of an initial design of a counter-rotating pump-turbine

Renewable sources of energy are on the rise and will continue to increase the coming decades [1]. A common problem with the renewable energy sources is that they rely on effects which cannot be controlled, for instance the strength of the wind or the intensity of the sunlight. The ALPHEUS Horizon 2020 EU project has the aim to develop a low-head hydraulic pump-turbine which can work as a grid stabilising unit. This work presents numerical results of an initial hub-driven counter-rotating pump-turbine design within ALPHEUS. Computational fluid dynamics simulations are carried out in both prototype and model scale, for pump and turbine modes, and under steady-state and unsteady conditions. The results indicate that the initial design have a hydraulic efficiency of roughly 90 % in both modes and for a wide range of operating conditions. The unsteady simulations reveal a complex flow pattern downstream the two runners and frequency analysis show that the dominating pressure pulsations originates from the rotor dynamics. Given the promising high efficiency, this initial design makes an ideal platform to continue the work to optimise efficiency and transient operations further.

Numerical study of hydraulic axial force of prototype pump-turbine pump mode’s stop with power down

Pumped storage power station is regarded as a key component in modern social power system. It usually requires pump-turbine start and stop frequently. The hydraulic axial thrust is one of the most essential effects on the stable operation during start and stop. The hydraulic axial thrusts of pump-turbine pump mode’s stop with power down based on 1D transient flow simulation and 3D CFD simulation were carried out in this paper. The hydraulic axial thrusts of two operation conditions show different trends in early stage. In later stage, results show similar characteristics with load-rejection process of turbine mode. The components of Fz including the crown, band and blade reach an obvious peak value with unit operation status change. This study provides the reference for the safety and stable operation of pump storage power stations.

Numerical Analysis of reactor coolant pump performance under reverse conditions

Since no anti-reverse device is equipped in the system of the third generation AP 1000 of nuclear power plant, the reactor coolant pump (RCP) might operate in the reverse condition. However, it is hard to carry out the experiments of RCP in reverse condition due to its high temperature and special thrust bearing (their thrust bearing may not afford the reverse condition either). Hence, CFX with unsteady RANS turbulence model is employed to thoroughly study the characteristics of the reactor coolant pump in reverse pump mode as well as the normal pump condition. Their different flow patterns between the normal case and the reverse case are compared. It is found that a beat frequency captured in the impeller in the reverse case is suggested to be the diagnostic signal of the generation of reverse condition.

Seven-Rod Pumping Approach for the Most Efficient Production of TEM00 Mode Solar Laser Power by a Fresnel Lens

Abstract A seven-rod/seven-TEM00 mode beam Fresnel lens solar laser pumping approach is here proposed. The Fresnel lens with 4.0 m2 collection area was used as the primary solar concentrator to pump seven 2.5 mm diameter, 15 mm length Nd:YAG rods within a conical pump cavity through a secondary fused silica aspheric concentrator. Within the pump cavity, solar pump rays not completely absorbed by one of the seven rods were furtherly absorbed by other rods, ensuring hence a high absorption efficiency and avoiding the serious thermal lensing and thermal stress issues associated with classical large rod solar lasers. Seven individual plane-concave large-mode resonators were adopted to enable a good overlap between solar pump mode and TEM00 laser oscillating mode. By using both zemax® and lascad® software, the maximum total TEM00 mode solar laser power of 54.65 W was numerically calculated by optimizing the radius parameter of the Fresnel lens, the diameter of the laser rod, and the radius of curvature of the laser resonator output mirror. TEM00 mode solar laser collection efficiency of 13.66 W/m2 and solar power-to-TEM00 mode laser power conversion efficiency of 1.44% were calculated, representing substantial enhancements of 4.66 times and 4.38 times, respectively, as compared with previous experimental records of the TEM00 mode solar laser pumped through a Fresnel lens with 0.785 m2 collection area. The feasibility of TEM00 mode solar laser power delivery by hollow-core photonic crystal fibers was finally studied.

Разработка и исследование осушителя и подогревателя воздуха на базе элементов Пельтье

A functional flow diagram of an energy-saving dehumidifier and an air heater based on Peltier elements has been developed. A method for calculating the heat-power and design parameters of a thermoelectric assembly is presented. Physical modeling of the process of dehumidification and heating of air in a thermoelectric installation has been carried out. The results of tests of a working model of the thermoelectric dehumidifier and air heater are presented. Rational operating modes of the installation have been substantiated, and its energy efficiency in the heat pump mode has been shown.

Hydraulic interaction of two parallel pump-turbines in constant-speed oscillation: Measurement, simulation, and sensitivity analysis

The S-shaped characteristic of a pump-turbine poses a latent risk to problems such as failure to start the unit, excessive water hammer pressure after load rejection, severe pressure pulsation, and intense vibration. However, S-shaped characteristics of a pump-turbine are usually investigated by static model tests, while the scope of this method is relatively limited. In a previous study exploring the S-shaped characteristic curve of pump-turbines, the constant-speed oscillation (CSO) was experimentally discovered. This transient process can be utilized to acquire the dynamic trajectory of the unit at a fixed rotational speed in the turbine mode, turbine brake mode, and reverse pump mode. On this basis, this study investigated the hydraulic oscillations between two pump-turbines after the net flow of the system was reduced to zero when the two units were operated in parallel. It was found that the two pump-turbines had an equal oscillation cycle, but their transient trajectories were significantly different. One of the runners oscillated only in the reverse pump mode, whereas the other runner oscillated in the turbine, turbine brake, and reverse pump modes. This process was termed the CSO interaction (CSOI). Subsequently, a one-dimensional rigid column simulation and a sensitivity analysis were performed to analyze the CSOI further, thereby verifying that the S-shaped characteristic curve was the root cause of the oscillation period and amplitude variation of the unit in the CSOI. The runner with the more prominent S-shaped characteristic curve tends to operate in the reverse pump mode during oscillation. The novelty of the work is that a new hydraulic interaction between pump-turbines, CSOI, was discovered. CSOI provides a metric for comparing the intensities of the S-shaped characteristic curves of two pump-turbines experimentally or theoretically.

Optical Parametric Oscillation with Ultra-Low Power Threshold in a Dimer of Active-Passive Cavities

Optical parametric oscillation can convert the input laser into a couple of coherent optical output with signal and idler frequencies. It is an important method for the realization of the broadband middle infrared tunable lasers. The optical parametric oscillation process depends on the ultra-fast non-linear response of matter to light with a certain pump power. Therefore, reducing the pump threshold of the optical parametric oscillation process and improving the energy conversion efficiency are of great significance to the study of non-linear optics. In this paper, we construct a dimer system that couples a passive non-linear resonator to an active resonator. Based on the dimer system, an ultra-low threshold optical parametric oscillation generation method is proposed. By coupling the gain pump mode, the non-linear effect is effectively enhanced, the pump power threshold is reduced to half of when there is no gain, and the energy conversion efficiency is increased. We believe this research provides a feasible method for a low-threshold tunable and easy-to-integrate optical parametric oscillation laser source.

Entanglement and Photon Anti-Bunching in Coupled Non-Degenerate Parametric Oscillators.

We analytically and numerically show that the Hillery-Zubairy’s entanglement criterion is satisfied both below and above the threshold of coupled non-degenerate optical parametric oscillators (NOPOs) with strong nonlinear gain saturation and dissipative linear coupling. We investigated two cases: for large pump mode dissipation, below-threshold entanglement is possible only when the parametric interaction has an enough detuning among the signal, idler, and pump photon modes. On the other hand, for a large dissipative coupling, below-threshold entanglement is possible even when there is no detuning in the parametric interaction. In both cases, a non-Gaussian state entanglement criterion is satisfied even at the threshold. Recent progress in nano-photonic devices might make it possible to experimentally demonstrate this phase transition in a coherent XY machine with quantum correlations.

Research progress on effects of different ankle pump exercises on venous drainage of the lower limb

The incidence of venous thromboembolism (VTE) is increasing year by year in Asian population, and has become a major cause of seriously affecting patients' quality of life and hospital death. Therefore, effective prevention and treatment of VTE are very important. Ankle pump exercise is widely used as a safe, economical and accessible measure for thrombosis prevention. However, there is no unified standard for ankle pump movement in different medical units in clinical practice, thus it's unable to achieve the desired effect. In this study, we reviewed the movement modes of the ankle pump from aspects of movement autonomy, form, angle and frequency. In addition, we also had a review in the ankle pump auxiliary devices and promotion measures, aiming to provide a basis for the correct clinical implementation of ankle pump movement and to give full play to the thrombosis prevention effect of ankle pump exercise.