Large Flow Conditions Research Articles

Analysis of Unsteady Flow and Interstage Interference of Pressure Pulsation of Two-Stage Pump as Turbine Under Turbine Model

The process pump as turbine (PPAT) serves as a crucial component for recovering high-pressure energy from mediums used in chemical and refining processes. Ensuring the long-term safe and stable operation of PPAT in high-temperature and high-pressure environments is essential, with pressure pulsation being one of its most significant external characteristic indicators. This study investigates the evolution of vortex structure distribution and the generation and propagation mechanisms of pressure pulsation in a two-stage PPAT operating in turbine mode. Results indicate that the uniformity of the pressure coefficient (Cp) gradient distribution is poorer in the first stage runner compared to the second stage, with a larger distribution area of high-strength vortices. In the draft tube, vortex strength increases with rising flow rates, and the flow around the circular cylinder on one side gradually develops to both sides. In the two-stage diffusers, the primary source of pressure pulsation is the dynamic and static interference effect between the two impellers and the corresponding diffuser tongue. The interstage interference with a frequency of n*15fn is most pronounced in the inflow runner, gradually weakening along the flow direction, and ultimately disappearing in the draft tube. In addition, more low-frequency signals with a frequency of 0.5fn are captured in the draft tube under large flow conditions, which is mainly generated by the vortex band in the draft tube. The low-frequency pulsation energy is high and the attenuation is slow, which has a great destructive effect on the energy recovery system of the PPAT.

Numerical Simulation and Model Test on Pressure Fluctuation and Structural Characteristics of Lightweight Axial Flow Pump

In order to explore the relationship between the hydraulic performance, pressure pulsation, and structural characteristics of lightweight axial flow pumps, this paper takes the axial flow pump as the research object and analyzes pressure pulsation and structural characteristics by changing the blade length and thickness to realize the lightweight design of the axial flow pump impeller. Compared with the initial scheme (Scheme 1), the mass of the impeller is reduced by 17.2% (Scheme 2) and 29.9% (Scheme 3), respectively. The lightweight axial flow pump (Scheme 2 and Scheme 3) has a lower pressure pulsation amplitude at the impeller outlet monitoring point under large flow conditions. After the lightweight design of the axial flow pump impeller, the blade becomes shorter, the mass becomes lighter, and the cavitation performance will become worse. The maximum equivalent stress of Scheme 2 and Scheme 3 is increased by 2.8% and 31.9%, respectively, compared to Scheme 1. The maximum deformation of Scheme 3 increased by 27% compared to Scheme 1. This research can provide guidance for the lightweight optimization design of the axial flow pump.

Heat transfer characterization of SCO2 in non-uniformly heated rectangular cooling tubes under large mass flow and heat flux conditions

A Thermoelectric Conversion System (TECS) with SCO2 as the circulating mass can effectively mitigate the fuel heat sink and electrical energy shortage problems of hypersonic vehicles. However, there is still a lack of research on the use of SCO2 in the harsh thermal conditions in scramjet. In this paper, the heat transfer mechanism of SCO2 in rectangular cooling tubes are numerically analyzed for the first time based on the actual working environment of scramjet. The effects of uneven heat flux (q) axial and circumferential allocations and circumferential and axial tilting of the tube are innovatively considered. Meanwhile, we analyze the heat transfer mechanism of SCO2 under different operating parameters. The results show that the uneven allocation of axial q can suppress the heat transfer deterioration (HTD), and the overall heat transfer coefficient (HTC) can be increased by 11.68 % when the q allocation is Gaussian. The increase of the tube inclination angle can improve its heat transfer performance, and the local HTC can be increased by up to 5.64 % when θ2 = 180°.Increasing the mass flow rate (G) and inlet temperature (Tin) can increase the overall HTC of the tube. This paper can provide guidance for the design and improvement of TECS.

Experimental and numerical study on wet steam flow metering overreading characteristics in venturi tube

The precise measurement of wet-steam flow is of great importance in various industrial systems, including nuclear reactors, oil and gas transportation, and cogeneration systems. However, the measurement accuracy of wet-steam flow can be affected by overreading (OR) when using venturi meters. This paper presents a systematic numerical simulation using the DPM model and an experimental study on the characteristics of overreading in wet-steam flow metering. The experiments are carried out on a two-phase flow liquid and steam platform. Firstly, the OR characteristics of a venturi structure with fixed dimensions (a throttling ratio of 0.6, a divergence angle of 15°, and a venturi diameter of 20 mm) are quantitatively analyzed at different flow rates (0.14-0.32 kg/s) and qualities (ranging from 0.14 to 0.90). It is found that the Lockhart-Martinelli parameter (XLM) plays a more significant role than the gas Froude number (Frg) in determining the overreading (OR) characteristics of a venturi under a given temperature, pressure, and venturi structure. Secondly, a venturi overreading prediction model based on XLM is proposed, and its ability to predict overreading for larger mass flow rates and venturi diameters is verified by numerical simulation data. As evaluated through numerical simulation data, the proposed model’s maximum relative error and average deviation are below 15% and 10%, respectively. This study provides valuable insights into developing an overreading model for industrial applications under large flow and venturi diameter conditions.

An Impeller Optimization Method for the High Specific Speed Mixed-Flow Reactor Coolant Pump Applied to Marine Nuclear Power

The reactor coolant pump (RCP) is the only rotating equipment in the primary circuit system of a nuclear power plant and the “heart” of the nuclear reactor. The L formula is defined, and the L/himp is introduced to study the influence of impeller blade type on the performance of the RCP. Twenty groups of models are designed, the concept of arc height ratio is proposed from the perspective of himp and L, and the distribution of internal entropy production within the impeller of the RCP under different Ls and himps of the impeller blade type is analyzed. The results show that when himp remains un-changed and L increases, the low-pressure area at the inlet of the impeller expands while the high-pressure area at the outlet decreases under the design flow or large flow conditions. The smoother blade profile reduces the occurrence of secondary flow phenomena and makes the RCP pressure distribution more uniform. Under design flow and large flow conditions, smaller L/himp and higher himp lead to higher efficiency and head performance. However, higher efficiency and lower head performance can be achieved under small flow conditions with larger L/himp and lower himp.

Recent Advances in Optimization Design and Performance Analysis of Vortex Pumps

Background: The vortex pump is a type of sewage pump renowned for its non-clogging performance. As the vortex pump has a special structure type, there are many vortex structures in the volute and impeller flow channel, which reduce the efficiency of the vortex pump. Reducing the energy loss and improving the efficiency of the vortex pump has been one of the main research objectives of designers. In this paper, the research progress of vortex pumps is summarized from the two aspects of transporting solid medium and low efficiency, which can provide a reference for future research. Methods: The latest patents and papers on vortex pumps were collected. The solid-liquid flow characteristics from the experimental and numerical perspectives, the influence of geometric parameters on external characteristics, and optimization design methods of the vortex pump were studied. Results: The particles, fibers, and cloth in the vortex pump will become trapped and blocked in the cavity. And the geometric parameters have an obvious effect on the pump. By using the intelligent optimization algorithm to optimize the impeller parameters, the pump efficiency can be increased by 10.25% under large flow conditions and the effective blade shear stress. Conclusion: The concentration and diameter of particles could change the performance of the pump. The retention and plugging of the solid medium in the vortex pump are related to flow structure and backflow. Appropriate geometric parameters should be selected when designing a vortex pump. Too large or too small a structure design will lead to poor performance of the vortex pump. This can be combined with intelligent optimization algorithms for pump design, which is a very effective method.

Design, Preparation, and Performance Study of a Miniaturized High-Temperature Thick-Film Heat Flux Sensor

Solving heat transfer problems in high-temperature and temperature-changing environments is critical in a variety of applications, including modern turbines, aerospace, and nuclear power plants. However, most current thin-film-type heat flow sensors operate at approximately 1000 °C. Thus, we fabricated a kind of platinum–platinum/rhodium thick-film thermopile-type heat flux sensor which can work stably at 1200 °C based on an alumina ceramic substrate. The entire electrode layer was prepared by screen printing process. The surface morphology of the Pt electrode and the material in thermal resistance layer at different stages were investigated using scanning electron microscopy. The steady-state characteristics of the sensor were evaluated by using a high-temperature test platform. The experiments show that the peak voltage of the sensor is 1.4126 mV at the temperature of 1200 °C and the heat flow density of 283.3 kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Moreover, the repeatability of sensor at 1200 °C and high temperature holding for 4 h experiments were performed, verifying that the sensor has good consistency and durability. Therefore, we infer that the designed sensor can be applied for a long time under high temperature and large heat flow conditions, such as aerospace, mechanical metallurgy and energy construction fields.

Numerical investigation of splitter blades on the performance of a forward-curved impeller used in a pump as turbine

As a type of economical energy recovery device, pump as turbine (PAT) is generally used in micro-hydropower plants and energy recovery. To study the influence of the splitter blade on a special impeller used in PAT, impellers without and with splitter blades are designed in this paper. The influences of splitter blade on the energy loss, external characteristics and internal flow field distribution of a PAT were simulated via a verified computational fluid dynamics (CFD) method. The consequences present that the shaft power, efficiency, and head corresponding to the BEP of the PAT with splitter blades are 16.4%, 1.3%, and 8.8% better than those of the PAT without splitter blades. The total entropy production of the PAT without splitter blade is higher than that of the PAT with splitter blades at the same flow rate. Adding splitter blade increased the number of effective blades, made the fluid flow more evenly along the impeller flow passage, and reduced the flow separation inside the impeller. This paper displays that adding splitter blades not only obviously increases hydraulic performance under large flow conditions but also significantly widens the high-efficiency range of PATs.

Internal Flow Characteristics of High-Specific-Speed Centrifugal Pumps with Different Number of Impeller Blades under Large Flow Conditions

As compared with a conventional centrifugal pump, a high-specific-speed centrifugal pump mostly operates under large flow conditions. In this paper, a typical high-specific-speed centrifugal pump is examined, and the effect of the blade number on the internal flow condition is investigated numerically. The numerical predictions have been verified through measurement. It was found that the predictions and the measurements are in good agreement of discrepancy. Serious cavitation could be observed within the pump when the flow rate reached 1300 m3/h. Meanwhile, the effect of the blade number on the cavitation intensity was extremely obvious. The cavitation area at the inlet edge of the blades significantly reduced when the blade number increased from three to six. In addition, the turbulent kinetic energy within the pump was more uniformly distributed. This demonstrates that the blade number can be reasonably chosen to improve the internal flow pattern within the pump, which could provide a theoretical basis for the practical application of high-specific-speed centrifugal pumps

Study on the Performance of an Electric-Field-Enhanced Oil–Water Separator in Treating Heavy Oil with High Water Cut

As most offshore oilfields come to the middle- and late-exploitation period, and with the popularization of tertiary enhanced oil recovery (EOR) technology, the physical properties of produced fluids become more complex, bringing new challenges to oil-water separation. Conventional solutions, such as increasing the input of chemicals, enlarging the volume of the separator equipment, and extending the processing, are usually uneconomical and space-wasting. Electric-field-enhanced oil-water separation equipment was developed in this paper, and a mine field test was carried out. With the average water cut of different sampling ports and the overall dehydration rate taken as indicators, the effects of electric field frequency, inlet flow, chemical type, and addition upon the separation of the device were evaluated. The experimental results showed that for the ABJ mixed liquid, the optimal operating frequency of the electric field is above 3500 Hz. Compared with traditional separation equipment, the advantages of the electric-field-enhanced oil–water separation equipment are more significant in large flow conditions. When the water cut of the platform inlet fluctuates between 78% and 97%, and without the addition of chemicals, the average water cut was reduced to 7% and the average dehydration rate reached 90%, an improvement of about 15%.

Influence of rotational speed on performance of low specific speed hydraulic turbine in turbine mode

To study the influence of rotational speed on the performance of hydraulic turbine in turbine mode (T-type turbine), the performance of turbine at different rotational speed was predicted through theoretical analysis, based on the Navier-Stokes equation and standard k-ε turbulence model, numerical simulation was used to study the performance of turbine at different rotational speed. The head loss, pressure distribution, turbulence kinetic energy, and unsteady pressure pulsation were also clarified. The results shows that with the increase of rotational speed, the high efficiency area of turbine gradually becomes wider, and there is little difference of the maximum efficiency at different rotational speeds. Under the optimal working condition, the pressure difference between inlet and outlet increase gradually, and turbulent kinetic energy of runner also increase. The inlet circulation increases with the increase of rotational speed, the outlet circulation increases with the increase of speed under small flow conditions, and decreases with the increase of rotational speed under large flow conditions. The study of pressure pulsation shows that the increase of rotating speed can effectively reduce the pressure pulsation in the runner. When the rotating speed is 2100 r/min, the amplitude of pressure pulsation at P7 is 10.39% lower than that at 900 r/min. Considering the hydraulic characteristics and the pulsation characteristics, it is recommended that the hydraulic turbine operates at or above the rated speed as far as possible.

Influence of Blade Angle Deviation on the Hydraulic Performance and Structural Characteristics of S-Type Front Shaft Extension Tubular Pump Device

When the axial-flow pump is running, the blade angle is not fully adjusted or there are errors in the manufacture of the blades, which will lead to inconsistent blade placement angles during operation, and which will reduce the efficiency of the axial-flow pump. This paper uses the research methods of numerical simulation and model experiments to analyze the hydraulic performance and impeller structure characteristics of each flow components under different schemes when the angles of each blade of the S-type front shaft extension tubular pump device are inconsistent. The research phenomenon is that the guide vane greatly recovers the flow velocity circulation at the impeller outlet, reduces the hydraulic loss of guide vane, and widens the best efficiency range with an increase in guide vane blade angle. When the blade angle deviation occurs, the flow field of each blade channel affects each other, and the maximum decrease in the best efficiency is up to 7.78%, mainly due to the increased hydraulic loss in the outlet channel. The blade angle deviation will also affect the maximum equivalent stress and maximum deformation of the impeller, which is more obvious in large flow conditions. Inconsistent blade angles seriously affect the operating efficiency of the water pump and water pump device, and make the structural characteristics of the impeller worse.

Modeling and Dynamic Characteristics of a Novel High-Pressure and Large-Flow Water Hydraulic Proportional Valve

In the field of fully mechanized coal mining equipment, the hydraulic valve used in the hydraulic support is an on/off directional valve. There are many problems caused by the valve such as large pressure shock and discontinuous flow control. Therefore, a novel two-position three-way hydraulic proportional valve suitable for high-pressure and large-flow conditions is proposed to overcome the above problems. The novel valve utilizes a two-stage structure and the displacement follow-up principle is adopted between the pilot stage and the main stage to meet proportional control. In this paper, a simulation model of the novel proportional valve was established after a simplified analysis of the structural principle. Its reliability and the feasibility of the design were verified by the test results under different working conditions. Then, the step response characteristics of the proportional valve under different strokes were predicted and analyzed. Nonlinear characteristics were presented, and the closing time was shorter than the opening time because of the influence of nonlinear flow force. Under different ramp signals, the displacement of the main inlet spool was always approximately equal to the displacement of the pilot stage. Then, the motion relationship between the pilot stage and the main stage was studied, and the influence of the structural parameters on the stability was analyzed.

Research on cooperative optimization of multiphase pump impeller and diffuser based on adaptive refined response surface method

Multiphase pumps play an important role in the exploitation of natural gas hydrate. Compared with ordinary pumps, they can handle fluids with higher gas volume fraction (GVF). Therefore, it is important to improve the performance of the pump under high GVF. A model pump is designed based on the design theory of axial flow pump and centrifugal pump inducer. The hydraulic performance of the model pump is verified by numerical simulation and experiment. The Sparse Grid method is applied to the design of experiment (DOE), and three different adaptive refined response surface methods (RSM) are applied to the build the approximate model. Refinement points and verification points are used to improve and verify the precision of the response surface, respectively. The model with high precision and high computational efficiency is obtained through comparison and analysis. The multi-objective optimization of the optimal response surface model is carried out by MOGA (Multi-Objective Genetic Algorithm) method. The pressure increment of the optimized model is increased by 38 kPa. The efficiency is significantly improved under large mass flow conditions. The hydraulic performance of the optimized model is compared with that of the basic model. And the reasons that affect the performance of the multiphase pump are analyzed.

Analysis of the Influence of Inlet Guide Vanes on the Performance of Shaft Tubular Pumps

To study the influence of inlet guide vanes (IGVs) on the pressure pulsation of a shaft tubular pump, this paper first conducts an experiment to study IGVs. Then, numerical calculations of the shaft tubular pump with and without IGVs are performed to analyze the hydraulic performance and pressure fluctuation characteristics. Finally, the reliability and accuracy of the data are verified by a model test. Numerical simulation results show that with additional IGVs, the pressure pulsation amplitude at the impeller inlet first decreases and then increases under small-flow and design conditions but gradually increases under large-flow conditions. When the IGVs are added to the impeller inlet of the shaft tubular pump, the hydraulic loss in front of the impeller inlet increases, resulting in a significant drop in the head and efficiency of the pump device when the flow rate is less than 1.12 Qd; when the flow rate is greater than 1.12Qd, the head and efficiency of the pump device do not change significantly. IGVs can improve the condition of impeller water inflow and reduce pressure fluctuation on the blade surface.

Theoretical Analysis of Entropy Generation at the Blade Interface of a Tubular Turbine Under Cooperative Conditions

To study the influence of the blade entropy production range on the efficiency of a tubular turbine under coassociated conditions, the renormalization group K–ε turbulence model was used to simulate the full flow passage of the tubular turbine based on the Navier–Stokes equation, and the blade interface was analyzed using the eddy analysis method and entropy production theory. The results reveal that there is a strong correlation between the size of the high-entropy production area and the level of association. If the level of association is high, the size of the high-entropy production is small, and the turbine efficiency is high. Furthermore, if the level of association is low, the size of the high-entropy production area is large, and the turbine efficiency is low. Under small opening and small flow conditions, the blade entropy generation is due to the sharp change in the velocity gradient caused by the vortex on the blade. Under large opening and large flow conditions, the blade entropy production is mainly due to the friction loss caused by the impact of high-speed water flow.

DEM–FEM Coupling Simulation of the Transfer Chute Wear with the Dynamic Calibration DEM Parameters

Transfer chutes for bulk material conveying systems have significant importance in ship loading and unloading and are ‘worn’ from large mass flow and fast granular material flow conditions. In this investigation, the impact forces of different granular materials on the transfer chute wear process are considered; the DEM–FEM (Discrete Element Method–Finite Element Method) coupling method was used to calculate the wear and the deformation of the transfer chute. The stress–strain and cumulative contact energy from three different granular materials were analyzed under different working conditions. The results show that the wear, stress–strain, and cumulative contact energy of the transfer chute are closely related to the belt speed, the chute inclination angle, and the types of granular materials; the impact force and the stress–strain on the transfer chute achieves maximum value under a 4 m/s belt speed condition; meanwhile, with the increase of belt speed by 0.5 m/s, the wear of the transfer chute increases 25% and the deformation increases 20%; the shape variable, wear area, and normal cumulative contact capacity of the transfer chute are the smallest with a transfer chute inclination angle from 40° to 45°.

Study on the influence of the number of guide vane blades on the flow characteristics of axial flow pump

Axial flow pump is widely used in energy, agriculture, urban water supply and drainage, water conservancy engineering, ships and other fields. As one of the important flow passage parts of axial flow pump, guide vane can be used to smooth the rotation of fluid after passing through the impeller, change it into axial motion, and change the kinetic energy of rotation into pressure energy. In this paper, the hydraulic performance and pressure pulsation of axial flow pump with three different guide vane numbers are analyzed by numerical simulation. Under rated flow and large flow conditions, increasing the number of guide vanes is more conducive to suppress the pressure pulsation.

Analysis of Dynamic Characteristics of Pressure-Regulating and Pressure-Limiting Combined Relief Valve

Aiming at the problem of the lack of a cooperation mechanism of combined relief valves, this paper proposes a new pressure-regulating and pressure-limiting combined relief valve. Combined with the ordinary relief valve dynamic characteristic analysis method, the dynamic model of the combined relief valve under normal working conditions was established, and its dynamic characteristics were simulated using Simulink. The results showed that the multi-pressure stabilization design of the combined relief valve improves its usability and stability. Under the same structural parameters, the overshoot of the combined relief valve was 5.7%, and the response time was 12 ms, which is better than the ordinary relief valve. Besides, it effectively improves the instability problems, such as the vibration and the large pressure fluctuation of the ordinary relief valve under high pressure and large flow conditions. When the sum of the effective force area on the upper side of the flange of the pressure-regulating valve core and the area of the tail vertebra is equal to the effective force area of the lower side of the flange of the pressure-regulating valve core, the dynamic performance of the relief valve is optimal. For example, if the effective force area under the flange is 1.8 cm2, then the inlet pressure overshoot is 2.8%, and the response time is 10 ms. An appropriate volume of the sensitive cavity, the quality of the valve core, and the fluid resistance of the pressure relief valve are factors that can effectively improve the dynamic performance of the pressure-regulating and pressure-limiting combined relief valve.

The Research of Velocity Factors Sensitivity in Turbine Stages under Off-design Conditions

Velocity factors are important parameters to determine the efficiency of turbine stages, and it is necessary to systematically study the effect of decline in velocity factors on stages efficiency under off-design conditions. In this paper the definition of the sensitivity of the velocity factors is proposed and effect of each parameter on the sensitivity is analysed. A simplified off-design model was also established to study the change of sensitivity of a governing-stage and pressure stage under the varying mass flow conditions. The results show that for the calculated turbine, the nozzle sensitivity of the governing stage is always greater than the blade for off-design conditions, and the efficiency of the nozzle in the governing stage should be emphasized. While the sensitivity of the pressure stage is related to the flow rate, it is more meaningful to improve the blade velocity factors in large mass flow conditions and it is reverse for low mass flow conditions. These findings will be meaningful in the optimization of turbine operation and design