Flow Rate Distribution Research Articles

Integrated study of flue gas flow and superheating process in a recovery boiler using computational fluid dynamics and 1D-process modeling

Superheaters are the last heat exchangers on the steam side in recovery boilers. They are typically made of expensive materials due to the high steam temperature and risks associated with ash-induced corrosion. Therefore, detailed knowledge about the steam properties and material temperature distribution is essential for improving the energy efficiency, cost efficiency, and safety of recovery boilers. In this work, for the first time, a comprehensive one-dimensional (1D) process model (1D-PM) for a superheated steam cycle is developed and linked with a full-scale three-dimensional (3D) computational fluid dynamics (CFD) model of the superheater region flue gas flow. The results indicate that: (1) the geometries of headers and superheater platens affect platen-wise steam mass flow rate distribution (3%–7%); and (2) the CFD solution of the 3D flue gas flow field and platen heat flux distribution coupled with the 1D-PM affect the platen-wise steam superheating temperature (45%–122%) and material temperature distribution (1%–6%). Moreover, it is also found that the commonly-used uniform heat flux distribution approach for the superheating process is not accurate, as it does not consider the effect of flue gas flow field in the superheater region. These new observations clearly demonstrate the value of the present integrated CFD/1D-PM modeling approach.

Physical Simulation of Dynamic Processes in Hydroeleastic Systems at Nuclear Power Stations

Basic approaches are outlined to solving complex engineering problems arising in the design and operation of power units at nuclear power stations (NPS) and based on large-scale physical simulation of dynamic conditions and parameters of dynamics and structural strength of modern power facilities. A procedure for physical simulation of specific dynamic processes in hydroelastic systems has been developed. Taking into account the identified distributions of pressure pulsations and flow rates on the surfaces of the structures of the investigated reactor plants (RU), hydrodynamic loads in various structures and facilities of modern power-machine buildings were determined considering the found distribution of fluctuations in flow pressure and velocity acting on the structure surfaces. The dynamic response parameters of the main structural members, such as dynamic strains and stresses, were obtained and analyzed. The effect of added masses of liquid, damping, and other factors on the dynamic processes in hydroelastic systems and ways for its reduction to increase the durability and service life of structures, first of all the critical elements of the studied power systems for each commissioned reactor, are determined. This approach is based on a comprehensive investigation of the interaction of a turbulent flow with the multicomponent structure of a reactor unit. The results of investigation confirmed the structure serviceability as to the relative error. The fitness for service of a structure during a specified operation time of the power unit was assessed. The implementation of the proposed approach involving large-scale physical simulation and, in many cases, numerical modeling, confirmed its effectiveness and the validity of the results obtained by the authors.

Determination of local deposition efficiency based on in-flight particle diagnostics in plasma spraying

Increasing the deposition efficiency (DE) and consequently reducing the manufacturing costs has been always one of the central goals in thermal spraying. Hence, the effect of modifying various spraying parameters on DE has been widely investigated in the literature. However, there has not been a methodology so far to correlate the in-flight particle properties with their DE on the substrate locally. In this study, a method is developed to determine the local deposition efficiency (LDE) of the plasma spraying process based on optical particle diagnostics of the in-flight particles. To this end, the entire free-jet transverse section is divided into several non-overlapping focal planes and the size and velocity of the particles are measured at these focal planes. Furthermore, the in-flight particle temperatures are captured in a measurement grid normal to the gun axis. The experiments are conducted with alumina spray powder and a three-cathode plasma gun. The LDE is calculated based on the spatial distribution of the in-flight particle mass flow rate (PMFR) and the local deposited mass on the substrate. Subsequently, the interdependencies between the in-flight particle properties and the calculated LDE are investigated using a nonlinear regression model.

Theoretical and experimental evaluation of the potential-current distribution and the recirculation flow rate effect in the performance of a porous electrode microbial electrolysis cell (MEC)

Microbial electrolysis cells (MECs) are devices employing a biofilm attached on the anode to oxidize organic matter and generate electrons required for thermodynamically unfavorable reactions arising on the cathode. Because of its complexity, factors such as the number of compartments, the presence of the membrane, as well as the position and electrode geometries play an important role in MEC reactor performance. Mathematical modeling is an effective way to describe the phenomenological role of the above-mentioned factors, nevertheless, many models in the literature do not present a complete description of the influence of operational parameters in its general performance. Henceforth, a parametric 2D dynamic mathematical model to describe the current response of a MEC reactor is proposed and experimentally validated in this work. Operational parameters such as the electrode and current collector configurations, flow rate and potential distribution are considered. The results revealed that the flow rate and current collectors hamper the performance when a typical concentric biologic reactor configuration is used. A flow-through configuration is recommended for further tests.

Three-dimensional simulation of performance in through-mask electrochemical micromachining

Through-mask electrochemical micromachining (TMEMM) is a kind of microfabrication. The major feature of through-mask electrochemical micromachining is that the tool is not limited by the shape, and can be processed in various shapes according to the pattern on the mask. This paper uses the finite element method to create a three-dimensional model to discuss the influence of flow direction, voltage, and electrolyte flow rate on the shape of the through-mask electrochemical micromachining. The simulation results show that processing shape is deeply affected by processing parameters, electrolyte flow rate affects processing temperature distribution, and temperature distribution at the bottom of aperture affects processing depth and flatness during processing, which in turn causes the difference in orifice size and roundness. At the same flow rate, the larger voltage, the larger average radius, flatness, and roundness. At the same voltage, the faster flow rate, the lower average depth, flatness, and average radius. Overall, it has best-processed aperture profile at a flow rate of 0.5 m/s. As a whole, the through-mask electrochemical micromachining is indeed suitable for array microfabrication of various shapes. In this study, experiments were added to verify the simulation results. At a fixed electrolyte flow rate, when the voltage, concentration, and mask aperture are changed, it will have an effect on the overall experimental results. From the experimental results, we know that the electrolyte flow rate and temperature distribution will indeed affect the overall processability.

Numerical assessment of the vulnerability to impact erosion of a pump as turbine in a water supply system

Abstract Nowadays, the installation of pumps as turbines (PATs) in water supply systems (WSSs) is considered attractive because it is able to effectively combine the pressure regulation with the small-scale hydropower generation. One critical aspect concerns the behaviour of the PAT in the presence of solid particles in the flow which impinge against the inner surface of the device, producing a loss of material termed impact erosion. In this paper, the numerical assessment of PAT erosion is performed, by referring, as a case study, to an existing pressure control station in Southern Italy. The variable operative strategy (VOS) was applied to derive the frequency distribution of flow rates over the PAT operation, under the hypothesis of performing the hydraulic regulation of the hydropower plant. The commercial computational fluid dynamics (CFD) code Ansys Fluent was employed for simulating the liquid–solid flow inside the PAT and then coupled with an in-house code to estimate the erosion. The vulnerability of the PAT to wear was analysed by varying its flow rate, aiming at characterizing the decay of PAT components at a constant rotational speed. Finally, a detailed characterization of the PAT response to the particle impingement at its best efficiency point (BEP) was developed and discussed.

Numerical and experimental investigation of abrasive flow machining of branching channels

Abrasive flow machining (AFM) is a key internal polishing technology applied to workpieces with difficult-to-reach areas. With the complex viscoelastic responses of abrasive media, the media flow is difficult to predict when the channel geometry is complex. It follows that the process outcome is also difficult to predict. In the present works, we proposed to use both experimental observations and computational fluid dynamics (CFD) simulations to investigate the responses of abrasive media in different branching channels during AFM process. We conducted measurement of media pressure and velocity during AFM for branching channels of different shapes and diameters. These data were used to develop and validate the present numerical model. The CFD simulations were conducted using the viscoelastic solver in OpenFOAM extension version, and we implemented log-conformation tensor representation (LCR) to stabilize the solver for high Weissenberg number problem (HWNP). The benchmark of the present simulations with experiments shows good agreement indicating that the present model is validated. The free-slip phenomenon of the abrasive media on the workpiece was uncovered from experimental observation of media flow in transparent channels and a sudden pressure drop (instead of a linear pressure drop) occurring across the connection between the workpiece and the fixture. Analysis of the numerical data indicates that the first normal stress difference (N1) plays an important role in the mass flow rate distributions of abrasive viscoelastic media in branching channels. Degradation of media properties was also studied and analyzed, suggesting that the flow pattern distribution in the workpieces could be influenced by media property degradation.

CFD simulation on the flow characteristics in the PWR lower plenum with different internal structures

The detailed thermal-hydraulic phenomena inside the lower plenum of Reactor Pressure Vessel (RPV) in Pressurized Water Reactor (PWR) affect the mass flow rate distributions at core inlet significantly, leading to an impact on the operation safety of nuclear reactors. From the engineering point of view, a homogeneous flow rate distribution at the core inlet is expected. Actually, series of design concepts of lower plenum internal structures were proposed for different PWRs in the world. In this paper, the three-dimensional CFD simulations with three types of internal structures in the lower plenum, TYPE 1 (Vortex suppression plate with the secondary supports), TYPE 2 (Flow distribution skirt board with square coolant holes), TYPE 3 (Ellipsoid perforated drums and supports), were performed. The influence of different internal structures on the flow characteristics in the lower plenum were achieved and analyzed. The three types of internal structures were adapted into the same experimental facility “BORA”, which is a 1/5th scale 4-loops mock-up model, to realize the single variable criterion and obtain a uniform standard during the comparison. Results indicate that the mass flow rates in central fuel assemblies are much higher than that in peripheral fuel assemblies at core inlets with TYPE 1 and TYPE 2 internal structures, while the core inlet mass flow rate distribution with TYPE 3 internal structure is more homogeneous. This research has high reference value for the future advanced PWR lower plenum internal structures optimization and design.

Flow Regulation and Heat Transfer Characteristics in a Novel Turbine Shroud with Internal Asymmetric Throttle Chamber

Flow and heat transfer of a novel turbine shroud with throttle chamber under two kinds of orifice arrangements were numerically studied. The original shroud model composed of the impingement holes, film holes and jet channel. The two modified models have identical geometrical spacing except for the number and location of the orifices in the upper plate of the throttle chamber added in the jet channel. Different pressure values were set at the outlets of different row film holes simulating the mainstream favorable pressure gradient. The ratios of inlet total pressures of impingement holes to outlet static pressures of the third row film holes ranged from 1.6 to 3.6. The Nusselt number distributions were validated by the experimental data. The main target of this study was to quantify the impact of the throttle chamber on the flow regulation and internal heat transfer characteristics. The flow factor, relative mass flow rate, the Nusselt number and the heat transfer factors on the target walls were presented. It is found that the mass flow rate distributions in the film hole rows become more reasonable by the modification of location and number of the orifices on the throttle chamber. The throttle chamber decreases the heat transfer on the target walls.

Development of Delayed Equilibrium Model for CO2 convergent-divergent nozzle transonic flashing flow

The one-dimensional implementation of the Delayed Equilibrium Model (DEM) is known as a relatively simple yet accurate approach for prediction of critical mass flow rate, pressure and void fraction distributions for two-phase water transonic flows in ducts of variable geometry. However, the direct application of DEM equipped with original saturation index evolution law and Lockhart-Martinelli approach (the original setup) is incapable of accurate prediction of CO2 transonic flow. Moreover, the Darcy friction factor approach has a significant impact on the simulation results. Consequently, this paper presents a new law of the saturation index evolution and a new frictional pressure gradient approach for CO2 transonic two-phase flows together with experimental validation and discussion of obtained data. A comparative analysis of the developed DEM setup and the referential Homogeneous Equilibrium Model revealed that application of the proposed approaches decreases the mean maximal discrepancy between experimental and calculated static pressure values by a factor of app. 2, with simultaneous decrease of the standard deviation by a factor of app. 4. That proves that both the frictional pressure gradient approach and the proper introduction of the thermal non-equilibrium effects are substantial for accurate modelling of the flashing process in CO2 flows.

Effects of air flowrate distribution and benzene removal in heterogeneous porous media during air sparging remediation

The decrease of remediation effect during air sparging (AS) remediation in heterogeneous porous media has attracted increasing attention. In this study, an improved light transmission visualization method was used to investigate the air accumulation, migration and flowrate distribution in benzene-contaminated heterogeneous porous media during AS. Experimental results indicated that the benzene removal rate in the porous media was mainly controlled by air flowrate distribution which could be used as a major factor to evaluate the remediation effect. Visualization of air migration showed that air accumulation occurred below the geologic heterogeneous interface when ΔPe > 0 kPa (ΔPe: the air entry pressure difference of the media above and below the interface), and the accumulation thickness and length presented exponential decay increases with increasing ΔPe and air injection rates. Air flowrate was monitored by gas flow sensors, and the flowrate distributions were found as Gaussian distribution when ΔPe ≤ 0 kPa, trapezoidal distribution when 0 <ΔPe< 0.3 kPa and fingered distribution when ΔPe ≥ 0.3 kPa. Fingered distribution of air flowrate resulted in extremely nonuniform benzene removal above the interface and reduced the overall benzene removal rate. These findings reveal the reasons for the poor performance of AS remediation in heterogeneous porous media, leading to a better understanding of the remediation mechanisms in heterogeneous aquifer.

Performance of capillary ceiling cooling panel on ceiling surface temperature and indoor thermal environment

A new experimental methodology is presented to show the effect of water supply temperature, mass flow rate and thermal load distribution on the radiant ceiling capacity and thermal comfort conditions. Computerized fluid dynamics simulated vertical temperatures and velocities profiles were validated by a comparison with experimental results and the difference was within 10%. Uniform surface temperature distribution was achieved in a 45.6 m3 test room installed with capillary ceiling radiant cooling panels by an increase in water temperature and air supply velocity. When the ventilation system was turned off, the mean ceiling surface temperature rose from 16.9 ± 0.4°C to 21.5 ± 0.3°C with a rise in the inlet water temperature to 20.1°C. The temperature difference between the head and ankle of an occupant was 2.0°C, which complies with the Chinese standard, GB/T 18049-2017. At a height of 1–1.5 m, the maximum temperature fluctuation was 2°C in the horizontal direction. When the ventilation system was turned on, with the air supply temperature and velocity at 19.8°C and 1.11 m s−1, the ceiling surface temperature was increased by 0.5°C. The indoor air temperature has a positive correlation with the air supply temperature and internal heat load but a negative correlation with air supply velocity.

Buoyancy Effects on Human Skin Tissue Thermoregulation due to Environmental Influence

This paper theoretically examines the impact of thermal buoyancy on human skin tissue’s blood flow, heat exchange and their interaction with the surrounding environment using a two phase mathematical model that relies on continuity, momentum and energy conservation equations in continuum mechanics. The tissue blood flows and heat transfer characteristics are determined numerically based on Darcy’s Brinkman model for a saturated porous medium coupled with modified Pennes bioheat equation while analytical approach is employed to tackle the model of interacting surrounding environmental buoyancy driven air flow with heat sink. The influence of embedded biophysical parameters on the skin tissue’s blood flow rate and temperature distribution together with friction coefficient at skin tissue surface and Nusselt number are display graphically and discussed quantitatively. It is found that a boost in thermal buoyancy enhances skin tissue heat transfer and blood flow rates.

PolySTRAND Model of Flow-Induced Nucleation in Polymers.

We develop a thermodynamic continuum-level model, polySTRAND, for flow-induced nucleation in polymers suitable for use in computational process modeling. The model's molecular origins ensure that it accounts properly for flow and nucleation dynamics of polydisperse systems and can be extended to include effects of exhaustion of highly deformed chains and nucleus roughness. It captures variations with the key processing parameters, flow rate, temperature, and molecular weight distribution. Under strong flow, long chains are over-represented within the nucleus, leading to superexponential nucleation rate growth with shear rate as seen in experiments.

Conceptual design of Super FR for MA transmutation with axially heterogeneous core

Supercritical water cooled Fast Reactor (Super FR) is featured with the large coolant density reduction by almost 1/10 from the core inlet to the outlet. Since Minor Actinides (MAs) not only have large neutron capture cross sections for thermal neutrons, but also can fission with fast neutrons, MA transmutation performance of Super FR may greatly depend on MA loading positions in the core axial direction of Super FR.However, such investigations have never been conducted. Hence, this study aims to design a Super FR transmutation core concept with the axial configuration of multiple layers of Mixed Oxide (MOX) and blanket fuels, with a focus on the influence of the large axial coolant density change on MA transmutation and core characteristics.With the design criteria of the negative Void Reactivity Coefficient (VRC), the Maximum Cladding Surface Temperature (MCST) < 650 ℃ and the Maximum Linear Heat Generation Rate (MLHGR) < 39 kW/m, three-dimensional neutronics and thermal-hydraulics coupled core burnup calculations have been carried out. Assembly-wise coolant flow rate distribution is determined to attain high core average outlet temperature and the core characteristics of different designs have been evaluated for the equilibrium core after the cores have reached equilibrium states with given fuel shuffling schemes. It has been shown that the MA transmutation amount is limited by deterioration of VRC due to increase of Pu enrichment for compensating the reactivity penalty by MA loading. Moreover, such influence has been found to be more significant in the lower region of the core, where the coolant density is relatively high. Hence, the core design with MA loading to the upper MOX layer is favorable for improving the MA transmutation performance. However, the trade-off relationship between the MA transmutation amount and thermal-hydraulics performance (increase of MLHGR and decrease of average outlet temperature) has been revealed. To overcome the issue, the core radial zoning has been applied and it has been found effective to suppress the trade-off relationship.

Fluid Flow Characteristic of EAF Molten Steel with Different Bottom-Blowing Gas Flow Rate Distributions

Fluid Flow Characteristic of EAF Molten Steel with Different Bottom-Blowing Gas Flow Rate Distributions

Onsager-Symmetry Obeyed in Athermal Mesoscopic Systems: Two-Phase Flow in Porous Media

We compute the fluid flow time-correlation functions of incompressible, immiscible two-phase flow in porous media using a 2D network model. Given a properly chosen representative elementary volume, the flow rate distributions are Gaussian and the integrals of time correlation functions of the flows are found to converge to a finite value. The integrated cross-correlations become symmetric, obeying Onsager's reciprocal relations. These findings support the proposal of a non-equilibrium thermodynamic description for two-phase flow in porous media.

Multiphase numerical modeling of a pilot-scale bubble column with a fixed poly-dispersity approach

A three-dimensional numerical study of air/water bubbly flow in a cylindrical large-scale bubble column is performed using Euler-Euler approach. The main objective is to investigate the influence of different boundary conditions such as bubble size distribution (BSD), polydisperse effects (mono and bi-dispersed approach), lift force modelling and flow rate distribution at sparger using a computationally affordable approach. In the bi-dispersed approach the population of bubbles are divided into two groups of small and large bubbles and a mean diameter is considered for each group. The division is based on the critical bubble diameter, for which the lift coefficient changes its sign from positive to negative. For air/water system Tomiyama lift coefficient model is widely used and the critical bubble diameter is equal to 5.8 mm. An alternative critical bubble diameter and lift force coefficient correlation is used in this study and compared with the well-known Tomiyama model. The numerical predictions are compared against the experimental data and the effect of different conditions is assessed on basis of comparison of axial gas fraction (local holdup) and global holdup. Better predictions are obtained by taking into account polydisperse flow with new critical bubble diameter and new lift coefficient model. Also, it was found that mass flow-rate distribution at the sparger does not affect numerical results for global and local holdup, however a different flow pattern is observed near the sparger region.

Effect of leakage on refrigerant distribution in an air conditioned room using propane as working fluid

Propane R-290 as hydrocarbon refrigerant has more benefits from the aspect of thermophysical properties, but the only weakness from this refrigerant is flammable. The distribution prediction of R-290 leakage to an air-conditioned room. The study using numerical simulation of CFD ANSYS FLUENT V.13. The distribution of R-290 with a leakage rate of 0,001kg/s and an airflow of 0,1m/s will run out after 600s, with 0,002kg/s will run out after 300s and with 0,005kg/s and 0,5m/s will run out after 120s. The mass flow rate can influence the refrigerant distribution of leakage effect flowrate. Airflow can increase the dispersion of refrigerant gas and decrease the level of the refrigerant amount at any certain point in the room after the refrigerant charge is empty. This momentum effect was due to the impact of supply air initial velocity. The buoyancy effect was due to R-290 density is greater than the air makes the refrigerant flows downward, accumulated, and stagnant. Make sure that the contactor relays and other electrical tools have the position, x=0 m ≤ x ≤ 1 m on y=0 m ≤ x ≤ 26 m and then y=1 m, x=0 m ≤ x ≤ 4 m.

A Study on the Verification of Inlet Structural Improvement of Side Stream Typed Low Pressure Membrane Module Using PIV Method

Objectives:The purposes of this study are to suggest a method to distribute the flow rate into the overall vessel vertically and evenly by improving the inlet hydraulic structure of the side stream type low pressure membrane module.Methods:For those, particle image velocimetry (PIV) technique was used to measure the evenness of flow rate distribution in both of the existing full scale single baffled inlet structure and the improved membrane module inlet structure (double baffled).Results and Discussion:As a result, it was confirmed that the flow distribution of the double baffled inlet structure is improved in comparison to that of the existing single baffled inlet structure. In the case of double baffled inlet structure, the instantaneous velocity distributions of 3, 4, and 5 seconds showed a velocity distribution close to the mean velocity of 0.03 m/s in the entire flow field. Also, a maximum velocity of 0.06 m/s was about 60% less than that of the single baffled inlet structure case (0.13 m/s). Conclusion:When the horizontal flow was observed, it decreased by about 300%. Those were 0.008 m/s for the double baffled inlet structure and 0.027 m/s for the single baffled, respectively.