Internal Flow Conditions Research Articles

Influence of the channel inclination on the exchange flow and vorticity transport characteristics in a regenerative flow pump

To enhance the overall performance of regenerative flow pump (RFP) to achieve efficient and stable operation over a broad range, this paper employs numerical simulation to study the internal flow conditions of RFP models with three different inclination coefficients (Ic = −0.25, Ic = 0, Ic = 0.25). The analysis focuses on the pressure distribution, energy exchange, velocity variation, and vorticity distribution characteristics within the impeller and channel. The comparison indicates that at Ic = −0.25 with an outward channel, the flow within the pump is stabilized, and the rate of pressure growth and exchange intensity are increased. When Ic = 0 with a semi-circular channel and Ic = 0.25 with an inward channel, there are narrower flow space at the channel's outer diameter, impeding effective fluid motion along the channel and inducing chaotic flow. This condition escalates flow losses and adversely affects the hydraulic performance of the RFP. Additionally, the analysis based on the vorticity transport equation reveals that the Coriolis force term significantly contributes to the generation and transport of vortex in the impeller, while the vortex stretching term dominates the transport of vortex in the channel.

Intensifying interfacial oscillations in falling film flows over rectangular corrugations

Unsteady film flows play an important role in intensifying heat and mass transfer processes, with applications, e.g., in falling film absorbers or reactors. In this context, the influence of surface structure modification on the wave dynamics of falling film flows is experimentally investigated based on localized film thickness time series data. Arrays of rectangular ridges oriented perpendicular to the main flow direction are considered, and an optimum ridge distance is identified, at which particularly strong interfacial oscillations are induced in the falling film. These potentially result from the interaction of the flow with a statically deformed base film under resonance-like conditions. The transient destabilization is amplified in the case of narrow ridge sizes, where inertia-driven flow features are particularly pronounced. With regard to mass transfer applications, the structure-induced increase in gas–liquid interfacial area may be of secondary importance compared to changes in internal flow conditions.

Design and optimization of bionic Nautilus volute for a hydrodynamic retarder

To reduce the energy loss of volute and improve the emergency braking performance of hydrodynamic retarder under design condition, a bionic volute optimization design method is proposed based on the Nautilus shell. First, the accuracy of the numerical method is verified by grid convergence analysis and experiments. Thereafter, the bionic parametric expression is performed based on the cross-section shape of the Nautilus shell. Subsequently, sample points are created using the Optimal Latin Hypercube sampling method and numerically simulated. Radial basis function neural network and multi-objective genetic algorithm are used for optimization. Finally, the flow field inside the volute and the braking performance of the hydrodynamic retarder are compared by numerical calculation and experiment. Results show that the internal flow field of the bionic volute is more uniform, the energy loss is reduced by 78.95%, and the oil flow speed is increased by 40.61%. In addition, the stable flow field can be established faster during braking, the peak torque can be increased by 6.15%, and the onset time can be advanced by 6.58%. The analysis of energy characteristics shows that the improved performance of the bionic volute can be attributed to its improved internal oil flow conditions, thus reducing the energy loss.

Potenential for thermal energy from Tunnels beneath Manchester and Crewe: a case study

potenential for thermal energy from Tunnels beneath Manchester and Crewe: a case study

Research on pumping laws of different-shaped Roots rotors for multi-stage vacuum pump design

Multi-stage Roots dry vacuum pumps are widely used in the semiconductor industry, metallurgy, pharmaceuticals, solar photovoltaic, thin film equipment, and other such fields. There are many combinations of rotors from the inlet to the exhaust of the multi-stage Roots vacuum pump. Depending on the application process of the multi-stage Roots vacuum pump, different rotation and self-combination designs are required. Currently, the pumping characteristics of different rotor types of the multi-stage Roots dry vacuum pump are not clear, and the combined design of the multi-stage pump rotor cannot be supported. In order to realize the applicability analysis of different rotors in different pressure ranges, a vacuum pump test platform and an adjustable rotor Roots experimental pump were designed. The pumping performance and power consumption of two-lobe Roots rotors, three-lobe Roots rotors and five-lobe Roots rotors in different pressure ranges were tested in experiments, and the internal flow conditions of multi-stage pump exhaust stages were numerically simulated. The results demonstrate that considering the ultimate performance and power consumption, the two-lobe Roots rotors and the three-lobe Roots rotors are more suitable for the exhaust pressure range of 1–10,000 Pa. With the increase of the exhaust pressure, the pumping performance of the three-lobe Roots rotors begins to gradually improve, and the pumping performance has obvious advantages. When the exhaust pressure exceeds 50,000 Pa, the advantages of the five-lobe Roots rotors gradually become obvious. The five-lobe Roots rotors can better handle the process of direct exhaust to atmosphere. The research methods and conclusions adopted in this paper can provide a reference for the design of the rotor combination scheme of the multi-stage Roots dry vacuum pump.

Lattice Boltzmann solidification modeling of forced convection internal flows applied to Gen-IV nuclear reactor coolants

Generation-IV nuclear reactors involve novel coolants such as molten salts and lead. One of the issues that must be assessed with these coolants is the risk of solidification during reactor operation owing to their high melting temperature. However, the numerical simulation of solidification problems is computationally demanding. In this work, we assess the applicability of Lattice Boltzmann Method (LBM) to nuclear coolants solidification problems under laminar internal forced flow conditions. The double distribution Total Enthalpy-Partially Saturated Method is implemented in the open-source code OpenLB and compared against more standard Finite-Volume Computational Fluid Dynamics (FV-CFD) results, which uses the enthalpy-porosity Eulerian Multiphase method, in commercial code Star-CCM+. The test cases comprise the solidification of two fluids with significantly different Prandtl numbers, molten salt and lead, in a 3D pipe geometry in laminar flow conditions with an initial Reynolds number of 100. The solid interface advances from the cooled wall towards the bulk of the pipe reducing the area of flow passage as the transient evolves. Results of LBM velocity fields, solid fraction profiles, temperature fields, and pressure fields are in good agreement with FV-CFD results for both coolants. Furthermore, LBM stability and accuracy limits are independently explored for molten salts and lead using Two-Relaxation Time (TRT) and Bhatnagar-Gross-Krook (BGK) collision operators. Simulation time between FV-CFD and LBM is also contrasted for both coolants. In this work, LBM solvers use explicit time schemes with a regular grid, whereas FV-CFD solutions are able to include implicit time schemes and near-wall mesh refinement. For molten salt flows (high Prandtl number) FV-CFD allows for considerably larger timesteps than LBM, which is limited by the maximum lattice Mach number limitation and stability considerations. For lead flows (low Prandtl number), the implicit scheme in FV-CFD is limited in terms of accuracy for large timesteps due to the limiting Fourier-number. On the other hand, LBM does not present notable stability issues for lead and the lattice Mach number limit is not as relevant as for the molten salt case for this Reynolds number, allowing for faster simulation times than FV-CFD.

Time-Averaged Analysis and Numerical Modelling of the Behavior of the Multiphase Flow and Liquid Lamella Thickness Inside an Internal-Mixing ACLR Nozzle

The Air-Core-Liquid-Ring (ACLR) atomizer is an innovative internal-mixing pneumatic atomization technique, suitable for energy-efficient spray drying of highly viscous liquid feeds, with high solid contents. However, pneumatic atomizers such as the ACLR can suffer from unstable internal flow conditions, which may lead to a wide variation in the droplet diameter obtained. Therefore, the internal flow conditions of an ACLR-atomizer needs to be properly studied and comprehended. With that in mind, a computational fluid dynamic (CFD) model was implemented and tested with experimental data collected for different air pressures and liquid feed viscosities. The model used can predict average lamella thickness with a relative error of less than 10%, when compared to experimental results, although some degree of artificial dampening of the flow instabilities occurs at high viscosities and low pressures. These instabilities have to be investigated in more detail from both the numerical side, by further refining the CFD model to capture the moment-to-moment behavior of the flow, as well as on the experimental side, by studying the instability development at higher recording speeds.

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

Effect of Blade Number on the Performance of a Centrifugal Pump Using Commercial Tool ANYS 91.2

Computational fluid dynamics (CFD) is frequently used in centrifugal pump design. The characteristics of the flow fields around turbomachinery can be simulated using tools for numerical computational fluid dynamics in three dimensions. Numerical simulation, which also provides significant information for the hydraulic design of the centrifugal pump, can be used to visualize the internal flow condition of a centrifugal pump. The purpose of this study was to examine the effect of blade number on the hydraulic performance curve using a commercial instrument. ANSYS 91.2. code commercial.The geometric model of the pump was built using CF turbo, and the flow domain was meshed using the commercial programme ICEM. The results demonstrated that an increase in the number of blades significantly improved the hydraulic performance of the centrifugal pump’s head. The findings also revealed that the area of the low-pressure zone at the blade’s input suction grew and that the static pressure distribution homogeneity in the diffusion section was significantly better than that in the spiral section. The design flow of 35 m3 per hour is where the best efficiency point (BEP) is located. At Z = 6 and Z = 7, the head values were 51.58 m and 53.13 m, respectively, while the efficiency values were 50.32% and 53.35%. The comparison of the H-Q curve for estimated head discharge indicates that all impeller efficiency curves share the same fundamental tendency.

Influence of Diffuser Vane Thickness on Centrifugal Compressor Performance

The structure of diffuser vanes has a significant influence on the performance of centrifugal compressors. To research the influence of diffuser vane thickness on the overall performance and internal flow condition of the centrifugal compressor. This paper takes a centrifugal compressor as the research object. By changing the diffuser vane thickness, and using three-dimensional fluid simulation technology to carry out simulation research. The results show that the thinner diffuser vanes can greatly improve the efficiency, flow rate and outlet temperature of the centrifugal compressor. For internal local fluid characteristics, thin diffuser blades have lower internal heat load. However, the local flow of fluid is not consistent with the change of vane thickness.

Numerical Analysis of the Radial Load, Pressure and Velocity Fields of a Single Blade Pump

The centrifugal screw-type pump is a type of pump which, due to its hydraulic and mechanical properties, is used in several areas of the industry (e.g., for sludge and rainwater disposal). To avoid impeller passage clogging, the 3D impeller geometry is designed as a helically curved blade added to a conical hub. The passability through the fluid canal of the modelled impeller is 100 mm. In this paper, the magnitude of the radial force on an impeller blade is investigated as a function of the flow rate. The digital model was designed in Catia V5 and calculated using the commercial Ansys CFX software. A numerical computational fluid dynamics (CFD) method was used to investigate the performance characteristics of the pump, specifically discussing internal flow conditions such as velocity, pressure and the radial force mentioned above.

PIV Measurement of Flow Conditions Near Casing Tongue of Mini Centrifugal Pump

Flow conditions near the casing tongue have a significant impact on the performance and stable operation of the centrifugal pump, so the internal flow conditions have been measured by the experiment and PIV measurement. The internal flow conditions of mini centrifugal pumps especially smaller than 100mm are less measured by PIV measurement and its flow conditions near the casing tongue are not clarified yet. Therefore, PIV measurement was conducted near the casing tongue for the mini centrifugal pump having 55mm impeller diameter. The two-dimensional open impeller with the large blade outlet angle β₂=60° was selected as the test impeller. FlowMaster Stereo-PIV by LaVision was used for the PIV measurement and the whole test section was made of the acrylic resin including the test impeller. Two CCD cameras with its resolution 2048×2048 pixels were used and velocity vector and contour were calculated by the PIV measurement software DaVis(Lavision). The internal flow conditions near the casing tongue were focused in this research. The PIV measurement results at different flow rates were shown and the tongue flow angle was defined to clarify the flow condition near the casing tongue with the impeller rotation. With the increase of the flow rate, the tongue flow angle increases which means the flow near the casing tongue is discharged to the casing throat. In the present paper, the internal flow near the casing tongue is clarified by PIV measurement results and the flow conditions with the impeller rotation are discussed.

PIV Measurement of Flow Conditions near Casing Tongue of Mini Centrifugal Pump

Flow conditions near the casing tongue have a significant impact on the performance and stable operation of the centrifugal pump, so the internal flow conditions have been measured by the experiment and PIV measurement. The internal flow conditions of mini centrifugal pumps especially smaller than 100mm are less measured by PIV measurement and its flow conditions near the casing tongue are not clarified yet. Therefore, PIV measurement was conducted near the casing tongue for the mini centrifugal pump having 55mm impeller diameter. The two-dimensional open impeller with the large blade outlet angle β2=60° was selected as the test impeller. FlowMaster Stereo-PIV by LaVision was used for the PIV measurement and the whole test section was made of the acrylic resin including the test impeller. Two CCD cameras with its resolution 2048×2048 pixels were used and velocity vector and contour were calculated by the PIV measurement software DaVis(Lavision). The internal flow conditions near the casing tongue were focused in this research. The PIV measurement results at different flow rates were shown and the tongue flow angle was defined to clarify the flow condition near the casing tongue with the impeller rotation. With the increase of the flow rate, the tongue flow angle increases which means the flow near the casing tongue is discharged to the casing throat. In the present paper, the internal flow near the casing tongue is clarified by PIV measurement results and the flow conditions with the impeller rotation are discussed.

Pressure fluctuation on casing wall and investigation to tip leakage flow of contra-rotating small hydro-turbine

Renewable energy is strongly recommended to replace the traditional fossil fuels to solve the severe environmental pollution. However, small hydro-turbine performs lower efficiency, and it is also easy to be blocked and impacted. Therefore, the contra-rotating rotors are adopted to overcome the disadvantages of small hydro-turbine. The performance and internal flow condition of contra-rotating small hydro-turbine have been clarified. In this paper, a new transparent casing is manufactured, and pressure fluctuation experiments are conducted. The pressure fluctuation experiments are to clarify the pressure fluctuation during the running of contra-rotating small hydro-turbine. Then the hydraulic stability of contra-rotating small hydro-turbine can be further investigated. According to the experiment results, for the new model, most of the amplitudes of pressure fluctuation are decreased. The maximum decreasing percentage of peak-to-peak value is 74.22%, and it is appeared on the point of Pr3. On frequency domain, the dominant frequencies of pressure fluctuation are rotation frequency and blade passing frequency. The investigation to tip leakage flow of contra-rotating small hydro-turbine is conducted based on the pressure fluctuation experiment and numerical simulation. The tip leakage vortex is identified by Q-criterion. The pressure distributions in tip clearance area show that the tip leakage vortex of new model is suppressed, and this helps to reduce the amplitude of pressure fluctuation in tip clearance area.

Characterisation of Internal Flow Conditions in GDI Injectors by Means of Spray-Hole-Individual Mass Flow Rate and Momentum Flux Measurements

Characterisation of Internal Flow Conditions in GDI Injectors by Means of Spray-Hole-Individual Mass Flow Rate and Momentum Flux Measurements

Analysis of pipe thickness reduction according to pH in FAC facility with In situ ultrasonic measurement real time monitoring

Flow accelerated corrosion (FAC) is a type of pipe corrosion in which the pipe thickness decreases depending on the fluid flow conditions. In nuclear power plants, FAC mainly occurs in the carbon steel pipes of a secondary system. However, because the temperature of a secondary system pipe is over 150 °C, in situ monitoring using a conventional ultrasonic non-destructive testing method is difficult. In our previous study, we developed a waveguide ultrasonic thickness measurement system. In this study, we applied a waveguide ultrasonic thickness measurement system to monitor the thinning of the pipe according to the change in pH.The Korea Atomic Energy Research Institute installed FAC-proof facilities, enabling the monitoring of internal fluid flow conditions, which were fixed for ~1000 h to analyze the effect of the pH. The measurement system operated without failure for ~3000 h and the pipe thickness was found to be reduced by ~10% at pH 9 compared to that at pH 7. The thickness of the pipe was measured using a microscope after the experiment, and the reliability of the system was confirmed with less than 1% error. This technology is expected to also be applicable to the thickness-reduction monitoring of other high-temperature materials.

ANN prediction of particle flow characteristics in a drum based on synthetic acoustic signals from DEM simulations

Rotating drums are widely used in industries for particle mixing, granulation and grinding. Linking internal particle flow condition with externally measured variables is crucial to online process monitoring and control. This work proposed a modelling framework to use an artificial neural network (ANN) model for quick prediction of particle flow based on the acoustic emission (AE) signals generated from the discrete element method (DEM) simulations. In total 131 DEM simulations were conducted under different conditions (i.e., different particle size distributions and filling levels). The AE signals on the drum surface were then obtained based on the simulated particle–wall collisions. Through FFT transformation and principal component analysis (PCA), 5 principal components (PCs) were obtained and, together with power draw, fed into the ANN model to predict to the unmeasurable internal flow conditions, including filling level and the distributions of particle size and internal collision energy. The back propagation neural network was adopted in the model. After being trained with 90 datasets, the ANN model was able to predict those internal variables with reasonable accuracy (R2 > 0.95). Finally, the potentials and limitations of the model to the optimal operation of drums were discussed.

Unsteady flow characteristics of energy conversion in impeller of centrifugal pump as turbine

To study unsteady flow characteristics of energy conversion in impeller of centrifugal pump as turbine (PAT), the overall and sub-section methods are used to calculate the unsteady flow of the PAT under six working conditions. Through numerical calculations, the net input power of the impeller, the time domain change law of the fluid's work on the impeller, the time domain change law of power loss in the impeller, and the time domain change law of energy conversion in different regions of the impeller are analyzed. Results show that: the dynamic and static interference between the impeller blades and the tongue caused the fluctuation of energy conversion; with the increase of area between the head of the impeller blade and the opposite tongue, the power loss in the impeller decreases. And when the blade head completely deviates from the position of the tongue about 10°, the power loss in the impeller is minimized. The power output of the PAT at different flow rates is related to its internal flow conditions and the geometric structure of each region of the impeller. The above research results can provide guidance on how to operate the PAT impeller stably and efficiently.

Influence of Blade Number on Performance and Internal Flow Condition of Centrifugal Pump for Low Viscous Fluid Food

There are many kinds of the fluid food transportation pumps depending on the characteristics of the fluid, i.e. a sanitary pump made from stainless steel, a screw pump and so on. A centrifugal pump was adopted as a fluid food pump in this research because it makes the stable continuous transportation of fluid food and the structure of the pump is simple compared to positive displacement pumps. The purpose of this research is to investigate the influence of the blade number on the pump performance and internal flow to enrich the pump design data for low viscous fluid food. The centrifugal pump with an open impeller was used and six impellers having the different blade number were prepared. Performance test using an experimental apparatus was conducted and the numerical analysis was also carried out. In the numerical analysis, the commercial software ANSYS-CFX16.2 was used. The head, shaft power and efficiency obtained by the numerical analysis, are almost the same with the experimental results. The head and shaft power increase with the increase of the blade number. The shear rate, which is concerned to fluid food quality, is high near the inlet region of the blade-to-blade passage for all types of blades. The shear rate of each type of the blade is discussed based on the numerical analysis results and relations between the blade number and shear rate are clarified.

Research on the Flow Characteristic in a Multi-Stage Multiphase Pump by Numerical Simulations

As a cost-effective option for subsea gas and oil fields development, multiphase pump has been widely used and plays an important role in promoting field production especially for those brownfields. The objective of this research is to study the variations of flow parameters at the inlet of each stage in a five-stage helico-axial pump under design conditions by using commercial CFD packages. The numerical results show that inlet volume flow rate, gas volume fraction (GVF) and flow angle of each stage both decreases from the first stage to the fifth stage because of the compression. The variations of these parameters along the flow direction are susceptible to the effect of rotational speed and initial gas volume fraction at inlet of the first stage. These inlet flow parameters from inlet to outlet of the five-stage pump just change little when the initial inlet GVF is lower than 10% or higher than 90%. While the variation is obvious when inlet GVF is from 20% to 80%. Based on numerical simulation results, the stage-by-stage design method is proposed and geometry parameters such as inlet impeller hub diameter and inlet angle of blade in the second stage are modified according to its inlet flow conditions. The comparison results between the modified pump and original pump show that pressure distribution at leading edge of impeller blades in each stage becomes uniform in the modified multistage pump. The inlet incident flow loss of each stage is diminished and internal flow conditions has been significantly improved. Thus, the pump’s boosting capacity is enhanced. These research results in this paper are instructive for the performance optimization of multistage pumps used in gas oil fields.