Pump Mode Research Articles

Optimization on high-pressure side of pump-turbine runner based on high efficiency and stability criterion via multi-objective genetic algorithm method

Pumped storage power plants are doomed to play a more important role in peak-valley shifting hence the demand for operation stability is gradually regarded as an equal important criterion as high efficiency. In our paper, new concepts, namely “swept,” “bowed (lean),” and “twisted” are introduced to systematic innovative design the geometry of high-pressure side (HPS) of a pump-turbine runner. Thereafter, a multi-objective optimization process, which consists of design of experiment (DoE), meta model generation, multi-objective genetic algorithm (MOGA), self-organization map (SOM) and takes both high efficiency and stability discipline into account is produced. The final optimization plan is selected and testified numerically. Compared to the original runner, the efficiency is improved from 91.7% to 91.9% at pump mode and improved from 92.3% to 92.8% at turbine mode. Moreover, the S margin is increased from 89.34° to 90.23° at small GVO and increased from 79.56° to 80.29° at large GVO. Besides, hump unsteady region is completely eliminated. Moreover, the flow characteristic comparation is conducted based on local hydraulic loss rate (LHLR) method. For design points, the optimized runner obviously decreases the hydraulic loss in hub and middle part of runner domain for turbine mode and slightly decrease the hydraulic loss in stay vane region for pump mode. For unsteady characteristics, HPS can better adjust the hydraulic loss distribution in corresponding discharge operating points, largely decreasing S unsteady characteristic in turbine mode and eliminating hump unsteady characteristic in pump mode. We believe that the methods proposed in our paper can bring the design of hydraulic machinery to a new level.

Hydrodynamic and experimental characterization of pumps as turbines

To estimate the performance, efficacy, modes of operation, hydrodynamic instabilities, and methodologies for harnessing energy from the pump as turbine (PAT), it is necessary to characterize these hydraulic turbomachines in all their modes of operation using an experimental test rig that simulates actual operating conditions. In this process, the characteristic curve of four quadrants of a turbomachine is constructed, especially its five modes: pump mode, brake pump mode, turbine mode, brake turbine mode, and reverse pump mode. In addition, with dynamic sensors installed in the pump volute, it is possible to know the hydrodynamic phenomena within PAT, finding its average behavior and frequency response, which is a tool for diagnosing the machine’s condition.

Coalescence characteristics of vibrated drops on a wettability gradient surface

The coalescence characteristics of two vibrated droplets at a certain distance on a microstructured surface with gradient wettability are investigated using a high-speed camera in this work. The results show that the volume ratio of the two droplets has a significant effect on the vibration modes. With the change in the volume ratio, the droplet exhibits different vibration modes, such as the pumping mode (PM), the rocking mode (RM) or the pumping–rocking mixed mode (PRM). In addition, the coalescence time of the two droplets varies with the volume ratio. When the volume ratio is close to 1, the two vibrated droplets are in synchronous PM and the coalescence time is the shortest. When the volume ratio is far from 1, the two droplets may show the RM, the asynchronous PM or the PRM. At this point, the coalescence time is increased, particularly for small volume ratios. Finally, the movement characteristics of three-phase contact lines are discussed, and a theoretical model is proposed to analyze the coalescence process. This work provides a new method to remove droplets rapidly, which is essential to enhance the heat-transfer performance of dropwise condensation.

Analysis of a solar-assisted heat pump system with hybrid energy storage for space heating

Insufficient heating capacity and low coefficient of performance have always been obstacles that inhibit the application of air source heat pump systems in cold regions. This study proposes an indirect expansion solar-assisted air source heat pump system to improve the heating performance of the air source heat pump. The indirect expansion solar-assisted air source heat pump system consists of solar collectors, a hybrid thermal energy storage tank, and a dual-source heat pump. An optimized control method is proposed to tackle the refrigerant redistribution problem for the dual-source heat pump. An experiment is carried out to study the thermodynamic performance of the indirect expansion solar-assisted air source heat pump. The experimental results indicate that the average coefficient of performance of the solar heat pump mode is increased by 50.0% compared to the air source heat pump mode due to the higher evaporating temperature. Based on the experimental results, a techno-economic and environmental analysis of the indirect expansion solar-assisted air source heat pump system for space heating is conducted in six northern cities in China. The indirect expansion solar-assisted air source heat pump system has the highest annual average coefficient of performance of 2.53 in Jinan, which is increased by 18.8% compared to Harbin. The payback period of the indirect expansion solar-assisted air source heat pump system is shortest in Xining and is reduced by 53.45% compared to Jinan. Applying the IX-SAASHP system in the northwest region is suitable for improving its energy and economic performance. The analysis results indicate that the IX-SAASHP system is beneficial for reducing carbon emissions from space heating systems in the northeast region.

Influence of Leading and Trailing Edge Angle on Impeller Blades of a Pump as Turbine

A pump as turbine (PAT) is a turbomachine that converts hydraulic energy into electricity. One of the study topics in PAT is the efficiency due to centrifugal pumps are not designed to operate in reverse mode. Geometric variations of the impeller have been studied in the literature. However, it was not possible to evidence the influence of the inclination of the blade leading and trailing edge. Therefore, the objective of this work is to analyze numerically and fluid dynamically the inclination angle of the blade leading and trailing edge of a centrifugal pump, in pump and turbine mode. First, the characteristic curve was validated. Then, the inclination of the leading and the trailing edge was modified, in a range of 25° to 90°, obtaining head, efficiency, and power graph. As a result, in pump mode was evidenced that an angle close to 90° on the blade trailing edge provides a higher efficiency of 50.26% and decreases until 40.77% when the angle approaches 30°, reducing the head to around 20%, while power remained constant. In turbine mode, an inverse effect was obtained, where the maximum efficiency was 60.9% and the generated power increased up to 4.76 kW in the blade leading edge. Therefore, the angular variation of the leading and the trailing edge is adequate in turbine mode, while in pump mode there is a loss of capacity.

Determining the angular velocity areas of a reciprocating hybrid power machine for operation in compressor and pump modes

A methodic for determining the angular velocity of a reciprocating compressor with regenerative heat exchange in the pump mode is considered for a known angular velocity of the machine in the compressor mode. The methodic is based on the use of mathematical models of the working processes of a reciprocating compressor and a reciprocating pump. The developed mathematical models are based on the fundamental laws of conservation of energy, mass, motion and equations of state. As the main condition in determining the angular velocity of the machine in the pump mode, the equality of the maximum pressure losses in the injection process when the machine is operating in the compressor and pump modes, as well as the equality of the relative energy losses in this process, is considered. Keywords: reciprocating compressor, reciprocating hybrid power machine, reciprocating pump, regenerative heat transfer, angular velocity. Scherba_V_E@list.ru

Surrogate based optimisation of a pump mode startup sequence for a contra-rotating pump-turbine using a genetic algorithm and computational fluid dynamics

Surrogate based optimisation of a pump mode startup sequence for a contra-rotating pump-turbine using a genetic algorithm and computational fluid dynamics

Light-Shining-Through-Wall Cavity Setups for Probing Axion-Like Particles

We discuss the aspects of axion-like-particles searches with Light-Shining-through-Wall experimental setups consisted of two radio-frequency cavities. We compare the efficiencies of four setups which involve the cavity pump modes and external magnetic fields. Additionally, we discuss the sensitivity dependence both on the relative position of two cylindrical cavities and on their radius-to-length ratio.

Study on pump mode cavitation characteristic of variable speed pump turbine

The continuous variable speed technology is a key technology in the development of pumped storage units. When the operating range of the rotation speed is widened, the unit's stable and safe operation range will be constrained by conditions, such as cavitation, hump, and power limit. This paper uses a traditional fixed-speed pumped storage station as the research object. Based on the complete characteristic curves of the unit, the modification hypothesis after the application of variable speed technology is carried out, and the preferred operation curve of the pump working condition is obtained. The improvement of the cavitation characteristics of the fixed speed unit by the variable speed technology is studied in this paper, and the problems in the prediction of cavitation of prototypes based on model tests are also analyzed. In this paper, the cavitation characteristics of the model and prototype of a pump turbine are analyzed using computational fluid dynamics simulation, with the initial cavitation coefficient as the basis for judging the cavitation. This paper points out that there is a deviation in the direct prediction of the cavitation characteristics of the prototype through the model test and provides a more accurate method to predict the cavitation limit range of variable speed units, which provides a reference for practical engineering.

Optimizing the Pump Storage System for Hot Water Showering at Swimming Pools

Previous studies have demonstrated the energy- and water-saving potentials of showering facilities in residential buildings. However, the prospect of public showering places where multiple showerheads usually worked together according to their opening hours has often been overlooked and rarely investigated. This study measured the water flow rate in a water supply pipe to understand the water-use patterns and water consumption of showering facilities in a swimming pool. The measurements were carried out on typical cold and warm days. The results showed that the average water consumption was 50.5 L/person in December (T = 19.7 °C) and 38.6 L/person in April (T = 24.5 °C). The fluctuation of the water flow rate demonstrated a water demand pattern for the showering facilities, where the maximum water flow rate was more than twice the average level, indicating inefficient working modes of the water supply pump. To improve the current situation, an appropriately sized water tank was suggested to be installed, which could ensure a more stable water flow rate in the main supply pipe, enhancing the water supply system efficiency and saving energy for the water pump. These results contribute to establishing the design data for optimizing water tank design in swimming pools or similar buildings with public showering demand and illustrate the energy-saving potential of water supply systems in showering facilities. Nevertheless, the results of this study are only based on theoretical calculations. More comprehensive field studies with a water tank are required to confirm these findings and better elucidate the effects.

The Suppression of Hump Instability inside a Pump Turbine in Pump Mode Using Water Injection Control

The occurrence of hump instability in pump mode within a pump turbine poses a significant challenge to the safe and stable operation of Pumped Storage Power Plants (PSPP). To achieve more precise numerical simulations, this paper establishes a weakly compressible model of water based on the Tait equation. Using this model, it is discovered that the onset of hump instability is closely linked to an increase in hydraulic losses induced by stalled rotation within the diffuser. Then, a flow control approach employing water injection into the guide vanes of a pump turbine is proposed in order to suppress flow instabilities and optimize the hump region. The findings reveal that the water injection approach can mitigate hydraulic losses, suppress unstable structures, and diminish the pulsation amplitude within the diffuser, ultimately delaying the emergence of the hump region to lower flow mass conditions. This study is helpful in widening the range of the safe and stable operation of pump turbines in pump mode.

Correction to “Experimental and numerical investigations on pressure pulsation in a pump mode operation of a pump as turbine”

Correction to “Experimental and numerical investigations on pressure pulsation in a pump mode operation of a pump as turbine”

Transient simulation of reversible pump turbine during pump mode's starting up

A pumped storage power station is an electric power system that utilizes low-peak electricity to pump water into a high-altitude reservoir and releases water to generate electricity during high-peak electricity demand. The pump mode's starting up impacts the operational stability and lifespan of the reversible pump turbine (RPT). Especially, the pressure pulsation signal during the pump mode's starting up is a typical non-stationary signal in RPT, which is an important basis for judging the operation status of the unit. In this study, the time-varying boundary conditions are used to calculate the pressure fluctuation and flow pattern evolution for a prototype RPT. This paper analyzed and compared the time-frequency characteristics of pressure fluctuations by continuous wavelet transform (CWT) and by variational mode decomposition (VMD). And the internal flow of RPT was also visualized using entropy generation theory. In this study, the effect of the penalty coefficient on the VMD algorithm is investigated in the form of a signal-noise ratio (SNR). With the increase of the penalty coefficient, the SNR of the signal gradually decreases and tends to be stable. Several modal components with strong physical significance and center frequency separation are obtained. Influenced by the boundary conditions that change with time, the pressure fluctuation presents a five-stage trend of “descending - ascending - descending - ascending - descending”. There are three main types of high-flow energy dissipation (FED) areas during this process of the RPT. The research and analysis in this paper will provide a good reference for the stable and safe operation of RPT and pumped storage power stations.

Numerical investigation on the transient gas–liquid flow in the rapid switching process of pump turbine

AbstractThe frequent switching of pump mode and turbine mode of the pump turbine leads to frequent transient phenomena. To ensure the safe and stable operation of the unit, a detailed study on the exhaust and pressurization process when the unit switches from turbine mode to the pump mode has been carried out. Based on the Shear Stress Transfer model (SST) k–ω turbulent model, the numerical simulations are processed both in a steady and unsteady state. The visualization results of gas–liquid two phases distribution in the dynamic process of exhaust and pressurization are given, and the characteristic references of each stage are also carried out. The transient characteristics of the torque, axial, and radial force of the runner and guide vane are analyzed by combining the short‐time Fourier transform. The results show that the main frequencies in this transient process are the blade passing frequency and its harmonic frequency. This process also presents a high amplitude band at all frequency values, which may be caused by the entrainment and centrifugal action of the runner on the free liquid surface.

Analysis of flow characteristics and cavitation in the vanes of a reversible pump-turbine in pump mode

In reversible pump-turbines, cavitation erosion can be found at the leading edge of stay vanes (SVs), which is generally considered related to the undesirable flow regime in the double radial vanes in pump mode. In this study, the flow characteristics in the vanes were studied at small guide vane (GV) openings in pump mode to evaluate the easily-ignored stay vane (SV) cavitation. Numerical simulations for three-dimensional (3D) flow passages of pump-turbine revealed that a large pressure drop was induced at SV leading edge in the situation of large velocity magnitude in the GV-SV vaneless space with a backflow flow pattern in the SV channel. Since a quasi-two-dimensional characteristic was confirmed for the flow regime in the vanes, refined simulations for GV-SV region with a two-dimensional (2D) approach were conducted to analyze the evolution of flow regime and the influence of flow rate coefficient. A low-frequency pressure fluctuation was found at SV leading edge, in which the minimum pressure appeared when the flow separation occurred near SV inlet in the situation with backflow in SV channel. This special flow pattern transferred to the adjacent SV channel in the direction of runner rotation. Moreover, the increase of flow rate coefficient resulted in a larger pressure drop at SV leading edge and accelerated the evolution of the flow regime in the vanes. This implies that a high cavitation risk at SV leading edge appears when operating at small GV opening angles with large flow rate coefficients. The outcomes of this study may help researchers to focus on the SV cavitation and improve the start-up and shutdown processes in pump mode.

Construction of Nitrogen Content Observer for Fuel Cell Hydrogen Circuit Based on Anode Recirculation Mode

The anode recirculation mode is increasingly being adopted in today’s fuel cell systems. The recycling of hydrogen gas can effectively improve fuel utilization and the wider economy. However, using the purge strategy for the recirculation exhaust has a significant impact on the operational performance and economic efficiency of fuel cell systems.Experiments have shown that, when the purge interval increases from 6 s to 10 s, the recirculation pump power increases by about 20%, the nitrogen content in the exhaust gas increases, and the stack voltage shows a 10 V attenuation. The accumulation of nitrogen permeation in the anode circuit leads to the degradation of the fuel cell performance. Therefore, it is necessary to discharge the accumulated nitrogen through the purge valve in a timely manner. However, opening the exhaust valve with excessively high frequency can result in the unreacted hydrogen being discharged, which reduces the economic efficiency of the fuel cell. This paper is based on the principle of mass conservation and models each subsystem of the anode circuit in the recirculation pump mode of the fuel cell separately, including the proportional valve model, the hydrogen consumption model of the fuel cell, the nitrogen permeation model of the fuel cell, the neural network model of the circulating pump, and the purge valve model. These submodels are integrated to construct a nitrogen content observer for the hydrogen circuit, which can estimate the nitrogen content. The accuracy of the model is validated through experimental data. The estimation error is less than 5.5%. The nitrogen content in the anode circuit can be effectively estimated, providing a model reference for purge operations and improving hydrogen utilization.

Research on Two-Way Contra-Rotating Axial-Flow Pump–Turbine with Various Blade Angles in Pump Mode

In tidal two-way contra-rotating units, significant differences in performance often occur when arranging the front and rear impellers, which requires an optimized design of the impellers. To solve this problem, by reducing the blade inlet and outlet angles, the impact of different blade angles on the performance of two-way pump–turbines and the internal flow was explored, and the effects of the blade inlet angle of the impellers on the performance of the counter-rotating pump were obtained. Afterward, the streamline and vorticity of the two-stage impeller at different angles were analyzed. The results show that different blade angles will have a certain impact on the internal flow of the two-way pump–turbine. Different blade outlet angles have a significant impact. The variation in different inlet blade angles is not significant for the vorticity changes in the front impeller and rear impeller. In addition, changes in the outlet blade angle will have an impact on the location of LE impact water of the rear impeller, which in turn affects the contours of vorticity of the rear impeller near LE, which also means that the vorticity in this area is mainly dominated by the vortex stretching term.

Optimal hydraulic energy harvesting strategy for PaT installation in Water Distribution Networks

Water Distribution Networks (WDNs) represent a noteworthy field for possible implementation of Small Hydropower (SHP), by replacing Pressure Reduction Valves (PRV) with turbomachines, in particular Pump as Turbines (PaTs), to control and regulate the pressure, while harvesting energy otherwise wasted. Different models were developed to predict the performance and select the positioning of the PaTs for the maximum energy recovery but most of them neglect practical aspect such as: power grid limitations and optimal harvesting strategy. In this framework, we intend to propose a new method to select a PaT, defining its optimal working point, by introducing an energy exploitation coefficient. The proposed methodology is based on the experimental results of a real PaT tested in the high capacity hydraulic laboratory at Polytechnic University of Bari. Firstly, the selected commercial centrifugal pump was tested in both pump and turbine modes. Then, three different approaches, for the Best Efficiency Point (BEP) selection, are described and compared in terms of energy exploitation and capacity factor for a WDN. The first consists of selecting the BEP at the average flow rate, the second one considers the probability distribution of the flow rate and the corresponding available hydraulic energy, whereas the latter is based on the highest energy harvesting. By applying energy production, economic and environmental analyses, the new proposed methodology, based on the third approach, shows a remarkable advantage in terms of exploited energy. Indeed a remarkable 60% energy recovery is achieved with 334 ton CO2/year avoided. Furthermore, the impact of the electrical motor on the maximum power generation (cut-off) is considered. Eventually, useful insights for the future PaT selection and installation are discussed.

Analysis on the Mechanism of Rotating Stall Inner a Pump Turbine in Pump Mode Based on the Proper Orthogonal Decomposition

Abstract An in-depth understanding of stall behavior is essential to improve the safe and stable operation of the pump turbine. In this research, the detached eddy simulation (DES) is used to investigate the various characteristics and propagation mechanism of the rotating stall of the hump instability region. The frequency characteristics and spatial intensity distribution of the stall cells are studied by adopting the proper orthogonal decomposition (POD) method. The results indicate that the energy loss at 0.80QDES and 0.75QDES are induced by the rotating stall with three cells that occur in the diffuser flow channel, and the corresponding high amplitude frequencies are St0.0074 and St0.0111, respectively. The effect of the stall cells is particularly severe near the hub. When the flow rate is further reduced to 0.68QDES, the three rotating stall cells develop into two symmetrically distributed stable stall cells with no definite characteristic frequencies, and the blocking phenomenon is concentrated near the shroud. With the stall cells losing their rotational characteristics, they have less impact on the flow field and contribute less energy. This paper also reveals that the energy loss in the diffuser contributes significantly to the hump formation on the performance curve.

ATHEROMA PROGRESSION: PHYSICAL MODELING IN EXPERIMENTAL CARDIOLOGY

Prototype models of intra-arterial circulation is one of the priority aims of experimental cardiology, as well as for the study of atherosclerosis. Purpose: To study the features of intra-arterial hemodynamics in the area of​​atheroma of the artery in physical modeling. Materials and methods: We used an original "Device for modeling intra-arterial circulation". The main parts of the model: glass rotameter tube in the form of a truncated cylinder, inlet and outlet ends of which are fixed with elastic plastic tubes connected to an electric water pump immersed in a container with glycerol solution. Inside the rotameter, using a fitting from the inlet, it is possible to install a pressure sensor that transfers data to the oscilloscope; indicators - a silk thread or dye - ink. The variable pump mode allowed us to simulate a regular heart rhythm, extrasystole (ES) and atrial fibrillation (AF). Results: In the first post-extrasystolic wave, a turbulent fluid flow formed after the plaque, standing waves and waves reflected from the walls of the rotameter were observed; the sensor registered an increase in pressure 1,6 times more compared with a regular heart rate wave. The marginal plaque zones along and against the fluid flow, especially the areas bordering the intact part of the arterial vessel, underwent the main mechanical impact. The same patterns were observed in AF with a maximum duration of a pause between pulse waves of ≥1,5 s. Conclusions: Heart arrhythmias play an important role in the intra-arterial hemodynamics changes and are the part of the pathophysiological changes in the arteries in atherosclerosis. The main danger is not the ES itself, but by the first post-extrasystolic contraction or the first pulse wave after a long pause between ventricular contractions in AF.