Large Impeller Research Articles

Multidisciplinary Optimization of a Mixed-flow Impeller with 140 Parameters and its Shapley Additive Explanations

Abstract In recent years, we have made several improvements to the geometric parameterization method, the surrogate model method, and the sampling method, with the goal of making the traditional surrogate model-based optimization method applicable to aerodynamic optimization of hundreds of parameters with reasonable computational cost. However, increasing the number of control parameters raises two additional issues. First, the impeller geometry becomes too complex to ensure the required mechanical performance. Second, the optimization mechanism becomes difficult to understand with too many parameters. To address the first issue, this paper builds a multidisciplinary optimization platform to achieve the optimization of a large flow coefficient mixed-flow impeller under 140 control parameters, resulting in a significant improvement in both aerodynamic and mechanical performance. To address the latter, a novel machine learning interpretation tool, Shapley Additive Explanations (SHAP), is introduced in this paper. Using this methodology, the contribution of all 140 parameter values in the final optimal impeller to each aspect of the performance improvement is presented in this paper, providing the first in-depth understanding of the intricate mechanisms involved in the multidisciplinary optimization of hundreds of control parameters.

PIV investigation of stalled flow field near the blade rim region of mixed-flow pump under different tip clearances

In order to further explore the physical mechanism of rotating stall induced by different rim leakage flow intensification, the velocity distribution of the stall flow field of the mixed flow pump under different rim clearance scales was obtained by Particle Image Velocimetry technology. By comparing the flow structure under different shooting sections, different phases and different working conditions, the influence of rim clearance scale on the flow field near the wall of the mixed flow pump was revealed. The results show that under the design flow conditions, there is an obvious reflux phenomenon near the hub of the guide vane inlet of the mixed flow pump under the four kinds of rim clearance, but the intensity is weak, and it does not affect the main flow field in the impeller channel. With the increase of rim clearance scale, the leakage flow intensity also increases, and the main flow area affected by the TLV structure also increases. In the deep stall condition, the reflux vortex at the inlet of the guide vane of the mixed flow pump still exists at each clearance, but the unsteady flow structure begins to appear inside, especially the large secondary vortex structure formed at the guide vane inlet, which seriously blocks the main flow. With the increase of the rim clearance, the flow field at the inlet of the guide vane is also obviously affected, and the secondary vortex core gradually moves towards the end wall area, resulting in an increase in the blocked area in the flow field. At the same time, the unsteady flow intensity of the flow field shows a nonlinear increasing trend. The unsteady strength of flow field increases rapidly with small gap impellers, while the unsteady strength changes slowly with large gap impellers. This study provides a reference for optimizing the rim clearance of mixed-flow pump and improving the efficiency of mixed-flow pump.

Kinetics of hydrate formation by CO2 and mixture of CO2–C3H8 in concentrated NaCl solution: Effect of impellers

Hydrate-based desalination (HBD) can apply directly to high-salinity water produced with crude oils and gases. For HBD technology to be commercialized, the slow kinetics of hydrate formation must be overcome. This study investigates the effects of type, diameter, number and clearance of impellers on kinetics, i.e. nucleation and growth, of hydrates of pure CO2 and mixture of CO2–C3H8 in a stirred vessel. Concentrated saline solution (8 wt%) was applied to form hydrates at constant temperatures (271.15–279.15 K) and pressures (1.73–3.6 MPa). Single pitched blade (PB) and straight blade (SB) impellers and also dual combinations of them were applied. With both SB and PB impellers at single mode, lower clearance improved nucleation rates (lower induction times) and higher clearance improved growth rates. The growth rate with SB was higher than that with PB under similar conditions, showing that radial flow is in favor of growth rate. With dual combination of PB and SB, higher nucleation and growth rates were observed compared to single impellers. The presence of PB in dual configuration influenced only the nucleation rate. Using a large diameter SB impeller, resulted in higher growth rate and gas consumption in dual mode. The results with CO2–C3H8 mixture were the same as pure CO2. Due to the promoting effect of propane on nucleation and growth rates, the effects of variation in propeller characteristics became minor in the presence of propane.

Development and Evaluation of Mixing Performance of New Type Large Paddle Impeller GD220

Development and Evaluation of Mixing Performance of New Type Large Paddle Impeller GD220

Influence of Blade Exit Angle on the Performance and Internal Flow Pattern of a High-Speed Electric Submersible Pump

The impeller vane exit placement angle has a critical role in the flow characteristics of the fluid inside the lobe, thus having a profound effect on the overall pump performance. The purpose of this study is to investigate the effect of the impeller exit angle on the operating characteristics of a high-speed well submersible pump, and the numerical calculation results of the original model are in good agreement with the experimental results. In this paper, five different impeller vane exit angles, namely 10°, 15°, 20°, 25° and 30°, are selected for numerical analysis based on the original model, and the flow conditions of 0.6 Q, 1.0 Q and 1.4 Q are analyzed for each angle. The results show that the impeller vane exit placement angle not only affects the static pressure distribution, velocity distribution and streamline distribution within the impeller and guide vane, but also has a significant effect on the head curve, power curve and efficiency curve of the well submersible pump. As the flow slip inside the impeller of high-speed well submersible pumps intensifies, the large impeller outlet angle will cause the power of the impeller to increase linearly with the flow rate, thus reducing the pump efficiency. In the low-flow and high-flow conditions, a small outlet angle of 10° will make the efficiency of high-speed submersible pumps higher than in other conditions, and these findings can provide some reference for the optimal design of high-speed submersible pumps.

Investigation of continuous stirred tank reactors for improving the mixing in anaerobic digestion: A numerical study

In this paper, mechanical impeller mixing has been analyzed through CFD which has proven to be a useful method for simulating mixing before manufacturing the digester. In this work, simulations were done for five different digester designs for TS level of 12.1%. While the fifth digester was cylindrical, the other four were cubical in design with varying impeller diameters and the number of impellers. The power law model was used to resemble the sewage sludge as a non-Newtonian fluid. The modified versions of dead volume and uniformity index were used along with velocity gradient and mixing energy level to quantify the quality of mixing. An analysis of the temperature distributions during mixing and heating was done using a thermal study. The operating speed of 250 rpm was finalized after testing at continuously increasing speeds from 50 to 600 rpm for a flat blade type impeller. As per the thermal model, a 250-W heater raised the temperature by around 15 °C in just 10 min. It was found that cylindrical vessels worked better than cubical digesters and larger impellers also helped in improving the mixing. The cylindrical digester which achieved about 67% homogeneity at a mixing energy level of around 0.95 W/m3, was the optimum design among the investigated digesters.

CFD and Energy Loss Model Analysis of High-Speed Centrifugal Pump with Low Specific Speed

High-speed centrifugal pumps with low specific speed have the characteristics of a small flowrate, a high head, and being compact and light weight, making them promising candidates for applications in the thermal management of aerospace and electronic devices. The energy loss in the low specific speed pump is critical and complex due to the large impeller diameter, the narrow and long flow channel, and the small outlet width. In this paper, an analysis method based on an energy loss model and computational fluid dynamics simulations (ELM/CFD) is proposed to analyze the performance of the low specific speed pump with a fully sealed structure. Experiments were carried out under variable water flowrates. The results show that the empirical correlation method failed to accurately predict the performance of high-speed centrifugal pumps, because the bearing clearance leakage and motor channel leakage are ignored. Moreover, the volume loss and hydraulic loss are calculated based on the empirical parameters of commonly used pumps that are different from the high-speed pump with the low specific speed in the complex flow channel structure. The ELM/CFD method calculates various loss power based on the simulation results and can predict the head and efficiency with deviations less than 2% and 5%, respectively. ELM/CFD can accurately analyze the optimization direction of the pump. The hydraulic loss and the volume loss of the impeller are the dominant factors that restrict the pump efficiency under the lower flowrates, while the hydraulic loss of subsequent flow channels becomes important under the larger flowrates.

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

AbstractApplication of large blade impellers to turbulent single‐phase and two‐phase mixing is investigated in this work in order to provide a quantitative basis for estimating the possible advantages in industrial mixing operations with respect to fast impeller types. The analysis is based on the discussion of three‐dimensional velocity fields collected in a single‐phase vessel stirred by a Maxblend impeller by stereoscopic particle image velocimetry and of dispersed phase distribution and liquid mixing time obtained in solid–liquid and liquid–liquid systems by electrical resistance tomography. The results highlight that turbulent two‐phase mixing can be efficiently performed in baffled vessels stirred by large blade impellers both in shear‐rate controlled and bulk‐motion controlled processes.

Mixing of Plastic Fluid with Large Paddle Impeller

Mixing of Plastic Fluid with Large Paddle Impeller

Effect of Delay on Control of Direct Resonance of Ships in Beam Waves Using a Proportional–Derivative Controller With Delay

Abstract A harmonically excited, single-degree-of-freedom time-delay system with cubic and quintic nonlinearities is studied. This system describes the direct resonance of a ship with an actively controlled antiroll tank (ART) that is subjected to beam waves. We consider low-, medium-, and high-freeboard ship models. A proportional–derivative (PD) controller with a constant time delay is assumed to operate the pump in the active ART system. The delay originates from the time required to pump fluid from one container to another, the inertia of large impeller blades and linkages, and the measurement and processing time of the roll-sensing unit. The stability boundary of the system, in the parametric space of the control gain and the delay, is derived analytically from the characteristic equation of the linearized system. We show that the area of the zero equilibrium region is inversely related to the derivative time constant of the PD controller; thus, we focus on a strictly proportional-gain controller. The spectral Tau method is used to identify the eigenvalues associated with the zero equilibrium since the rightmost eigenvalues determine the system's robustness to perturbations in the initial conditions. We use the method of multiple scales and harmonic balance to obtain the global bifurcation diagram in the space of the applied frequency and the amplitude of the response. Numerical simulations verify our analytical expressions. Study of the dynamics, stability, and control of the roll motion of ships is critical to avoid dynamic instabilities and capsizing.

The Effect of Inflow Distortion on the Rotordynamic Characteristics of a 1400-MW Reactor Coolant Pump Annular Seal

The annular seal between stator and rotor substantively acts as a bearing that affects the rotordynamic characteristic of the turbomachinery rotor system. The rotor wake turbulence in a canned motor Reactor Coolant Pump (RCP) will lead to inflow pressure distortion at the annular seal entrance, thus further affecting the seal rotordynamic characteristics and threatening the stable operation of RCP. In order to obtain the seal rotordynamic coefficients, a transient numerical method applies the mesh deformation technique to simulate the multiple-frequency elliptical rotor whirling orbit model. The transient solutions were proposed to solve the unsteady reaction forces of annular seals at five excitation frequencies for each case. The inflow pressure distortion patterns were simplified as harmonic functions, including two important influence parameters that are impeller blades number m and pressure fluctuation ratio λ. The numerical results showed that with nonuniform time-averaged pressure distribution at the entrance of the annular seal in Case 2, the inflow distortion significantly affects the seal rotordynamic coefficients, while the rotational spinning speed in Case 3 can weaken the time-averaged nonuniformity and accordingly make a dent in the influence. Increasing impeller blades number m and pressure fluctuation λ both result in a sharp diminution of the negative stiffness Keff, as well as an obvious increase in the effective damping Ceff, which will strengthen rotor misalignment and system stability. In addition, the larger impeller blades number m and higher pressure fluctuation λ will make the effective damping Ceff more independent of the whirling frequency. These results provide theoretical guidance for the operation safety of RCP.

Evaluation of Mixing Performance of Large Paddle Impeller HRX300

Evaluation of Mixing Performance of Large Paddle Impeller HRX300

Thermal modeling in metal additive manufacturing using graph theory – Application to laser powder bed fusion of a large volume impeller

Despite its potential to overcome the design and processing barriers of traditional subtractive and formative manufacturing techniques, the use of laser powder bed fusion (LPBF) metal additive manufacturing is currently limited due to its tendency to create flaws. A multitude of LPBF-related flaws, such as part-level deformation, cracking, and porosity are linked to the spatiotemporal temperature distribution in the part during the process. The temperature distribution, also called the thermal history, is a function of several factors encompassing material properties, part geometry and orientation, processing parameters, placement of supports, among others. These broad range of factors are difficult and expensive to optimize through empirical testing alone. Consequently, fast and accurate models to predict the thermal history are valuable for mitigating flaw formation in LPBF-processed parts. In our prior works, we developed a graph theory-based approach for predicting the temperature distribution in LPBF parts. This mesh-free approach was compared with both non-proprietary and commercial finite element packages, and the thermal history predictions were experimentally validated with in-situ infrared thermal imaging data. It was found that the graph theory-derived thermal history predictions converged within 30–50% of the time of non-proprietary finite element analysis for a similar level of prediction error. However, these prior efforts were based on small prismatic and cylinder-shaped LPBF parts. In this paper, our objective was to scale the graph theory approach to predict the thermal history of large volume, complex geometry LPBF parts. To realize this objective, we developed and applied three computational strategies to predict the thermal history of a stainless steel (SAE 316L) impeller having outside diameter 155 mm and vertical height 35 mm (700 layers). The impeller was processed on a Renishaw AM250 LPBF system and required 16 h to complete. During the process, in-situ layer-by-layer steady state surface temperature measurements for the impeller were obtained using a calibrated longwave infrared thermal camera. As an example of the outcome, on implementing one of the three strategies reported in this work, which did not reduce or simplify the part geometry, the thermal history of the impeller was predicted with approximate mean absolute error of 6% (standard deviation 0.8%) and root mean square error 23 K (standard deviation 3.7 K). Moreover, the thermal history was simulated within 40 min using desktop computing, which is considerably less than the 16 h required to build the impeller part. Furthermore, the graph theory thermal history predictions were compared with a proprietary LPBF thermal modeling software and non-proprietary finite element simulation. For a similar level of root mean square error (28 K), the graph theory approach converged in 17 min, vs. 4.5 h for non-proprietary finite element analysis.

Influence of the Impeller Diameter and Off-Bottom Clearance on the Flow Velocity Distribution Characteristics Near the Bottom inside a Flotation Machine

The solid particle suspension inside a flotation machine is significantly dependent on the flow field, particularly the flow hydrodynamics characteristics near the bottom of the flotation machine. In this study, a laser Doppler anemometer (LDA) was utilized to investigate the influence of the impeller diameter and the impeller off-bottom clearance of a flotation machine on the flow velocity distribution characteristics near its bottom. The results showed that centripetal, centrifugal, and transitional spiral ascending vortexes were generated for different cases of the impeller variables. The impeller diameter and the off-bottom clearance were found to have a significant and interactive influence on the flow pattern, radial and axial velocities, velocity vector distribution, and axial fluctuating root mean square (RMS) velocity characteristics. When the centripetal flow was generated with a large impeller diameter and a small off-bottom clearance, the vortex stability was improved, the low-velocity distribution area was reduced near the bottom center, and the high axial RMS velocity distribution area was extended and became more consistent. The latter provided an advantageous condition for the momentum transfer between the liquid flow and the solid particles, as well as the airflow. However, the axial RMS velocity in the centrifugal flow formed in other cases of the impeller variables was less than that in the centripetal flow. Although the increase in the impeller off-bottom clearance contributed to increasing the velocity magnitude, this is certainly disadvantageous to the service life of the impeller blades, as expected from the high-velocity area extension. These results may provide a reference for the impeller design and optimization of a KYF (Kuang Yuan Flotation) flotation machine, as well as a basis for further investigation on the behavior of the dispersed phases inside a flow field.

Flow, suspension and mixing dynamics in DASGIP bioreactors, Part 2

AbstractThis work aims to characterize the mixing and suspension dynamics occurring within two commercially available DASGIP bioreactor configurations, equipped with a two‐blade paddle impeller with large impeller to tank diameter ratio, D/T = 0.97. Both continuous and intermittent agitation modes were employed to determine the impact that agitation strategy has upon mass transfer and microcarrier settling/suspension. This paper builds upon the flow dynamics data presented in Part 1 for a flat bottom DASGIP bioreactor and shows how intermittent agitation can break‐up regions of slow mixing observed during continuous agitation, therefore substantially increasing the mixing efficiency of the system. Similarly, it was found that microcarrier characteristics might significantly affect the level of suspension when the impeller is in dwell status when intermittent agitation modes are used.

Turbulent blend times with off‐centre v‐mounted agitators

AbstractExperimental measurements in a flat‐bottom tank with narrow‐blade hydrofoil and pitched‐blade impellers are used to develop guidelines for off‐centre, or eccentric, placement of vertical agitators in unbaffled tanks. The guidelines are based on providing a turbulent blend time that is no more than 20% longer than that of the same impeller operating at the same rotational speed on the centreline of a baffled tank. In addition to investigating the effect of impeller type, impeller diameter and off‐bottom clearance are also considered. The results support the commonly noted rule of thumb that as off‐centre distance is increased, performance in an unbaffled vessel approaches that in a baffled tank. A notable exception to this axiom occurs when a large impeller is located close to the tank base (specifically, D/T = 0.40, C/T = 0.10, and O/T = 0.25). In this case, a stable impeller tip vortex forms with both impeller types, with slow exchange of material between the vortex and bulk liquid leading to long blend times. Besides blend time decreasing with increasing off‐centre distance, the uncertainty or run‐to‐run variation in blend time also decreases dramatically. In most cases, the pitched‐blade turbine requires a smaller off‐centre distance than the hydrofoil impeller to approximate the blending performance provided during baffled operation.

Research and development of a permanent-magnet synchronous frequency-convertible centrifugal compressor

Permanent-magnetic Synchronous Frequency-convertible (PSF) compressor as a new technology has been widely used in heating, ventilation and air conditioning. In this paper, a PSF centrifugal compressor was designed and developed. Some key technologies such as large working range 3-Dimensional impeller, 360° circular refrigerant injection port, two-stage impeller directly driven by PSF motor and high-speed inverter were adopted to improve the compressor efficiency. The theoretical comparison of conventional frequency-convertible centrifugal compressor and PSF centrifugal compressor was conducted to show the performance improvement. Then, a comprehensive experimental investigation was carried out to evaluate operating characteristics of the developed compressor. Experimental results showed that the adiabatic efficiency of PSF compressor reached 75.9%~88.5%. The mechanical efficiency, motor efficiency and inverter efficiency of PSF compressor was also greatly improved. Rated COP of PSF centrifugal chiller reached 7.0, and IPLV reached 11.7. The PSF centrifugal chiller has excellent system performances under both rated and partial load conditions.

Scale limitations of gas bearing supported turbocompressors for vapor compression cycles

An analysis of single-stage centrifugal compressors supported on dynamic, gas lubricated bearings for driving vapor compression cycles suggests that the maximum feasible compressor power is limited, primarily by the bearing load capacity, in the range from 80 kW to 250 kW. The analysis further suggests that the maximum feasible compressor power depends significantly on working fluid selection. Low-pressure fluids result in large impellers with good efficiency but heavy machines, the power of which is limited by the bearing load capacity. High-pressure fluids require small machines rotating at high speeds, the power of which is limited by the rotordynamic eigenfrequencies. Consequently, there is a family of fluids that allows maximization of the power range of gas bearing supported turbocompressors. Finally, the analysis suggests that the maximum compressor power can be expressed as a function of the reduced evaporation pressure, regardless of the working fluid choice. Maximum COP is reached at a reduced evaporation pressure decreasing nearly linearly from 0.22 to 0.11 as the temperature lift between the evaporator and the condenser increases from 20 K to 50 K. The feasible maximum compressor power increases with increasing specific compressor speed, bearing tip speed (NDm) and rotordynamic stability safety margin.

Damage mechanism and evaluation model of compressor impeller remanufacturing blanks: A review

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program “Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing” are reviewed in this work. Large centrifugal compressor impeller blanks were used as the study object. The materials of the blanks were FV520B and KMN. The mechanism and evaluation model of ultra-high cycle fatigue, erosion wear, and corrosion damage were studied via theoretical calculation, finite element simulation, and experimentation. For ultra-high cycle fatigue damage, the characteristics of ultra-high cycle fatigue of the impeller material were clarified, and prediction models of ultra-high cycle fatigue strength were established. A residual life evaluation technique based on the “β-HV-N” (where β was the nonlinear parameter, HV was the Vickers hardness, and N was the fatigue life) double criterion method was proposed. For erosion wear, the flow field of gas-solid two-phase flow inside the impeller was simulated, and the erosion wear law was clarified. Two models for erosion rate and erosion depth calculation were established. For corrosion damage, the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated. KISCC (critical stress intensity factor) and da/dt (crack growth rate, where a is the total crack length and t is time) varied with H2S concentration and temperature, and their variation laws were revealed. Through this research, the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multistrength field and cross-scale were solved. The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

Vertical-axis ocean current turbine design research based on separate design concept

Through reasonable structure design, this work made the blades that make up the impeller of turbine automatically opened and closed under the force of ocean current, realizing the capture of ocean current energy in different directions, which greatly improved the power generation efficiency of the turbine. The design of this turbine breaks the traditional integral single-blade design idea, divides the traditional integral blade that constitutes the large impeller into a series of sub-blades and solves the contradiction of the opposite torque caused by the water flow in the left and right blades during the rotation of the impeller. The control system composed of the fan-shaped angle control grooves and the gravity-tilted rotors realized the automatic opening and closing of the blades under the force of ocean current. The blades were designed into fish-shape based on the principle of fluid dynamics to reduce the water flow resistance. The physical model test and numerical simulation of the power generation efficiency of the device were carried out to verify the feasibility of the design model. And the results showed that the energy utilization efficiency of the new vertical-axis ocean current turbine was higher than that of the traditional single-blade turbine.