Flow Rate Distribution Research Articles

Experimental Investigation on Water Seepage through Transparent Synthetic Rough-Walled Fractures

One of the impacts of climate changes nowadays is the increase in the frequency of high-intensity rainfall events alternating with extreme dry periods, which affect the components of the hydrologic cycle, such as runoff, infiltration, and aquifer recharge. Several experimental investigations and theoretical studies have demonstrated that infiltration flow in fractured media can develop along preferential pathways. However, the prediction of infiltration phenomena in fractured media still remains an open issue. This, together with erratic rainfall patterns due to climate changes, affects the prediction of aquifer recharge and contaminant transport in fractured aquifers. The present work contributes to reducing this research gap by means of experimental investigation and forecast analysis, with a focus on the geometrical properties of single fractures and their influence on flow patterns. Several fracture surfaces based on different fractal dimensions, standard deviations, and mismatch lengths were designed using the SynFrac model and were generated by 3D printing technology. The results revealed that the fracture’s fractal dimension has a significant impact on the number of flow paths, while the fracture inclination only increases the number of intermediate preferential channels, and, hence, modifies the flow rate distribution over the fracture outlet. Additionally, the change in the inclination angle of the dry fracture from 55 to 65 degrees resulted in an 8% reduction in the mean width of first flow path. A sensitivity analysis using an M5 tree indicates that there is a linear relationship between flow rate and the exponential form of the fractal dimension. The location of flow channels is a function of fracture fractal dimension, and the influence of mismatch length on their location is negligible. Finally, an accurate prediction algorithm with a Nash value of 0.81 was developed using Wavelet transform in order to estimate the time series of periodic flow rates over the fracture outlet.

An Innovative Approach to Design and Optimize Flow Field Pattern of Polymer Electrolyte Membrane Fuel Cell

To increase power density of polymer electrolyte membrane fuel cells (PEMFCs), further optimization and downsizing of cell and stack design are necessary.To support cell and stack design, we have been developing a three-dimensional (3D) PEMFC simulator P-Stack [1]. P-Stack can estimate power generation performance in good agreement with experimental results, and can clarify relationships between the performance and internal states depending on cell designs, operation conditions, and material properties [1]. Although 3D PEMFC simulations are powerful means, preparing 3D model is very time consuming, thus it was difficult to explore various cell designs.In the present study, we have developed a new modeling technology for PEMFC flow fields. In this technology (Figure (a)), flow fields of anode and cathode gases are drawn by lines in 2D canvas. Properties of the lines such as width, depth and wall angle are given, then it automatically generate 3D model for anode/cathode flow fields and bipolar plates, coolant flow field, seal, gasket and MEA. Power generation performance of the 3D model can be estimated by P-Stack continuously. In addition, the line properties, vertex positions, and the number of repeat can be parametrized, enabling the parametric study of cell design.In this technology, pressure and flow rate distributions can be calculated by a network model based on Darcy’s law [1], without generating 3D model. As shown in Figure (b), the result is in good agreement with computational fluid dynamics (CFD) calculation of 3D model. Although the CFD calculation takes several hours using 32 parallel processes, the calculation of the network model is finished within several seconds using single process. In similar manner, it can calculate flow rate distribution of cells in the stacking axis. Since the execution time per one case is very short, it can be combined with optimization by genetic algorithm (GA).In the presentation, we will talk about a result of the parametric study and optimization for more practical cell design. Influence of flow field design on power generation performance and internal states will be discussed.

Математична модель роботи системи різномасштабних двокомпонентних реактивних двигунів малої тяги

The aim of this work is to modify a comprehensive mathematical model of a system of two-component low-thrust jet engines using the numerical method of characteristics in the propellant pipeline system with account for different sound speeds in the oxidizer and the fuel employing a unified method of pipeline discretization. This paper presents a unified approach to a numerical implementation of the method of characteristics for both fuel components and for regular computational cross-sections (internal for structural sections with constant geometrical and elastic parameters) and terminal cross-sections at the pipeline system inlets, the section joints, and the engine inlets for each propellant components. The approach accounts for the hydraulic resistances of the propellant injectors and electric propellant valves and the actual pressures in the engine combustion chambers. The performance of the mathematical model is illustrated by the example of the predesigning of a system of different-scale low-thrust engines to control the motion of a spacecraft relative to its center of mass in pitch, yaw, and roll and transfer the spacecraft to a new orbit (higher of lower) for maneuvering and docking with another spacecraft. The computed results show the possibility of determining the key hydraulic and gas-dynamic parameters of the system in transient conditions: the pressure and propellant component flow rate distribution at the inlet of any of the engines, the combustion chamber pressure and thrust characteristics of each engine, and the mutual effect of the engines on their thrust characteristics by the example of varying the flow areas of the propellant manifolds in the steady (continuous) and unsteady pulsed operation of all engines or some of them. The proposed mathematical model may be used in the computational justification of design parameters and operating conditions in the preparation of a draft proposal or in the predesign determination of an engine system configuration. Detailed information on the hydraulic and gas-dynamic performance parameters of an engine system is an important complement to the results of a ground tryout of both single engines and an engine system in conditions that simulate the flight environment.

Performance Improvement of Glass Microfiber Based Thermal Transpiration Pump Using TPMS.

The Knudsen pump, known as a thermal transpiration membrane, is an air inducer that has been mostly studied for small-scale power generation devices. It is a porous medium that does not require any mechanically moving component, but rather uses the temperature gradient across two surfaces of the membrane to induce air from the colder side to the hotter side. If the temperature on the colder side of the membrane is reduced by a thermal guard, the pumping performance of the membrane seems to be improved. Therefore, the membrane integrating with TPMS structures as thermal guards for both experiment and simulation were conducted in this study. The results of flow rate and temperature distribution on the membrane surface were compared. Three characteristic parameters of the membrane, i.e., area factor, pore radius and permeability, were found and can be used in an equation to estimate the air flow rate through the membrane. Diamond was found to be the highest flow improvement while Primitive was the lowest flow improvement. The simulation results with varying %RD also supported that the contact area between the TPMS structure and the membrane inlet surface made Diamond conduct more heat out from the membrane surface than other TPMS structures.

Influence of Flow Rate Distribution on Combustion Instability of Hypergolic Propellant

Combustion instability is the biggest threat to the reliability of liquid rocket engines, whose prediction and suppression are of great significance for engineering applications. To predict the stability of a combustion chamber with a hypergolic propellant, this work used the method of decoupling unsteady combustion and acoustic system. The turbulence is described by the Reynolds-averaged Navier–Stokes technique, and the interaction of turbulence and chemistry interaction is described by the eddy-dissipation model. By extracting the flame transfer function of the combustion field, the eigenvalues of each acoustic mode were obtained by solving the Helmholtz equation, thereby predicting the combustion stability for the combustion chamber. By predictions of the combustion chamber instability with different flow rate distributions, it was found that the increasing of inlet flow rate amplitude will improve the stability or instability of combustion. The combustion stability of the chamber was optimized when the flow rate distribution for the oxidant was set more uniform in the radial direction. The heterogeneity of the flow rate distribution in the circumferential direction is not recommended, considering that a homogeneous flow rate distribution in the circumferential direction is beneficial to the combustion stability of the chamber.

Numerical investigation on conjugate cooling performance of double swirl cooling at vane leading edge

Numerical investigations are conducted on the conjugate cooling performance of leading edge double swirl cooling (DSC) method coupled with simplified film cooling. The target channel of DSC method is composed of two partially overlapping swirl channels. As a reference, a semicircular target channel (Imp) is also established. One row of 10 jet holes with the average jet Reynolds number of 15,000 and one row of 10 film holes at the stagnation region with an inclination angle of 30° are employed. Numerical simulations are conducted with five blowing ratios range from 1.0–3.0 under both adiabatic and conductive vane conditions to reflect the contribution of internal cooling on conjugate cooling performance. The basic flow features are illustrated. The coolant mass flow rate distribution, the internal mechanical energy losses and overall performance are compared. The film cooling performance is also compared and analyzed. Results show that, compared with Imp cases, the area average Nusselt number increases 44–49%, the mechanical energy losses increase 7–24% and the target channel overall performance increases 35–38% in DSC cases. Also compared with Imp cases, the area average conjugate film cooling effectiveness increases 5–12% and the area average contribution on the conjugate cooling performance increases 10–23% in DSC cases.

Effects of stator and rotor geometry on inline high shear mixers: Residence time distribution, flow, and energy consumption

Using high shear mixers (HSMs) as the vessel to intensify chemical processes requires knowledge of the residence time distribution (RTD) characteristic. Considering the numerous structural characteristics of HSMs, a series of pilot-scale HSMs was developed to investigate the RTD characteristics through pulse tracing and deconvolution. A number of structural parameters were included here, including tooth height, tooth thickness, and the number of rotor-stator tooth rows, slots, and stages. Meanwhile, by using CFD simulations with the large-eddy simulation model coupled with the sliding mesh method, the flow rate, power consumption, and energy dissipation rate distribution, as well as RTD of HSM were examined. It is illustrated that adding a distributor or increasing rotor speed improves the local energy dissipation, reducing short-circuits and dead zone. The RTD curves become smoother and closer to plug flow with increasing stator-rotor stages. Typical first/second-order reactions are favored by higher or thicker rotor-stator teeth, and HSM is better suited when kR1 > 1 s−1 or kR2cA0 > 5 s−1. Furthermore, the correlations of E(t), tR, σθ2, Potot, and qave, 1+ were obtained, which would provide useful guidance on the scale-up design and optimization of HSMs.

Multi-physics modeling of a symmetric flat-tube solid oxide fuel cell with internal methane steam reforming

Methane is regarded as one of the ideal fuels for solid oxide fuel cells (SOFCs) due to its huge reserves and transportation properties. In this study, a 3D numerical model coupling with chemical reaction, electrochemical reaction, mass transfer, charge transfer, and heat transfer is developed to understand the heat and mass transfer processes of methane steam direct internal reforming based on double-sided cathodes (DSC) SOFC. After the model verification, the parametric simulations are performed to study the effects of operating voltage, inlet temperature, and steam to carbon (S/C) ratio on the performance of a DSC. It is found that the non-uniform distribution of flow rate among channels results in the non-uniform distribution of each physical field. Increasing the inlet temperature significantly enhances the performance of DSC, however, when the temperature is above 1073 K, the concentration loss and the temperature gradient of DSC increase, which is not conducive to the long-term operation of the DSC. In addition, we revealed the effect of the S/C ratios on the heat and mass transfer process. This study provides an insight into the heat and mass transfer process of SOFC with a mixture of steam and methane and operating conditions for enhancing the performance.

Effect of Cooling Header on the Hydrocarbon Fuel Flow Distribution in a Regenerative Cooling Channel

Regenerative cooling technology is the most widely used cooling technology in liquid rocket engines, and flow distribution is very important for regenerative cooling heat transfer. In this work, the flow distribution characteristics of Z -type parallel channels were studied through numerical simulation, and the effects of flow area ratio, inlet header shape, and inlet aspect ratio were analyzed. Results showed that changing the inlet cooling header can improve the uniform distribution of flow rate effectively. The nonuniformity coefficient and fuel temperature varied with change in the flow area ratio, inlet header shape, and inlet aspect ratio. The maximum temperature of the wall decreased from 1334.52 K to 1220.61 K when the flow area ratio was changed from 1 to 0.25. An appropriate decrement in the inlet header shape was beneficial to the uniform flow distribution. The inlet aspect ratio should be reduced properly to ensure that each channel experiences similar pressure drop. This research has a certain reference value for the structural design of regenerative cooling channels.

Dynamic moist air monitor in a micro area with extremely high figure-of-merit.

In the rapidly changing moisture air, conventional relative humidity (RH) sensors are often difficult to respond in time and accurately due to the limitation of flow rate and non-uniform airflow distribution. In this study, we numerically demonstrate that humidity changes on micro-zones can be monitored in real time using a Bloch surface wave (BSW) ubiquitous in one-dimensional photonic crystals (1DPC). This phenomenon can be observed by leakage radiation microscope (LRM). After theoretically deriving the angular resolution limit of LRM, we obtained the minimum BSW angular change on a practical scheme that can be observed in the momentum space to complete the detection, and realized the dynamic real-time monitoring of small-scale humidity change in experiment for the first time. This monitoring method has extremely high figure of merit (FOM) without hysteresis, which can be used in humidity sensing and refractive index sensing as well as the research on turbulence.

Analysis of interpolar air motion coherence and heat transfer under different asymmetric rotor yoke ventilation duct structures of the pumped storage power machine

Large-capacity per pole and high current density in the rotor lead to the high heat load per unit volume of the excitation winding. In order to improve cooling efficiency on the heat exchange surface and the axial uniformity of the rotor excitation winding temperature, the asymmetric yoke ventilation duct structures with four different widths are proposed along both sides of the pole axis. However, the structure of yoke ventilation duct with different width not only affect motion coherence of interpolar air at different axial positions, but also produce two adjacent interpolar air motion difference. Consequently, it is essential to study the flow rate distribution, motion law and motion difference of interpolar air for the accurate temperature field analysis of the rotor excitation winding. Taking a Xiangshuijian pumped storage machine with rated capacity of 277.8MVA (generator condition)/ 286.4MVA (motor condition) and rated speed of 250 rpm as an example, based on the multiple frames of reference model, the fluid-structure coupling analysis is performed in the solution domain by the finite volume method. The obtained numerical results of excitation winding average temperature are validated using the temperature measured data under the operation conditions of rated power generation, 80% power generation and rated pumping.

A novel, fast and clean 3D permeability measurement method for multi-layer textiles and fabrics

Permeability quantifies flow conductance of textile reinforcements, is required for process simulations, and can be used for a range of materials and process monitoring by industry. Current permeability measurement techniques are destructive, either because a liquid penetrates the sample or the sample must be cut from products to a specific size. A non-destructive measurement concept is introduced based on air flow established between flat circular patterns containing flow rate and pressure sensors. The presented experimental studies show that from flow rate and pressure distribution data, the technique clearly distinguishes changes in volume fraction and layup while being applicable to a range of woven and non-crimp textiles. The concept interprets permeability from a neural network trained using a large set of air flow simulations. A preliminary set of 250,000 simulated cases was applied to train seven different neural network types. Limited predictive accuracy has been achieved, utilizing a CGB neural net structure.

Velocity Measurements in Highly Aerated Flow on a Stepped Chute without Sidewall Constraint Using a BIV Technique

The lack of sidewalls in a spillway leads to lateral expansion of the flow and, consequently, a non-uniform transversal flow rate distribution along the chute. The present work shows the velocity field measured in a physical model of a 1 V:0.8 H steeply sloping stepped spillway without sidewalls. An application of a Bubble Image Velocimetry (BIV) technique in the self-aerated region is shown, using air bubbles entrained into the flow downstream of the inception point as tracers. The results indicate that, for small dimensionless discharges and sufficiently downstream of the point of inception, the free-surface velocity compares relatively well with the corresponding air–water interfacial velocity previously obtained with a double-tip fiber optical probe in the same facility. In turn, the velocity profiles along the normal to the pseudo-bottom, far downstream of the inception point, are reasonably in agreement with the air–water interfacial velocity profiles in the inner part of the skimming flow, with the largest differences being verified in the upper skimming flow region near the free-surface.

Refrigerant flow distribution research for battery cooling coupled with cabin comfort based on dual-evaporator heat pump system for electric vehicle acceleration

Abstract The heat pump system employed with a dual evaporator for battery cooling coupled with cabin comfort is an innovative thermal management method. It can be inferred that the refrigerant thermal load distribution can trigger temperature fluctuations for thermal performance of both battery and cabin. To trade-off between the thermal management demands of battery and cabin, this study proposed a strategy to promote the decreasing of battery temperature and to ensure battery thermal uniformity with a higher priority. Hence a transient refrigerant flow rate distribution scheme with a minimum flow rate to satisfy battery thermal demands was designed. The results showed a significant reduction in the temperature fluctuations for cabin thermal comfort and BTM thermal controlling. It offers a satisfactory reference for refrigerant thermal load distribution strategy applied with the heat pump system connected to the battery and cabin by the dual evaporator.

3D Fracture Propagation Simulation and Pressure Decline Analysis Research for I-Shaped Fracture of Coalbed

After hydraulic fracturing, some treatments intended for production enhancement fail to yield predetermined effects. The main reason is the insufficient research about the fracture propagation mechanism. There is compelling evidence that I-shaped fracture, two horizontal fractures at the junction of coalbed and cover/bottom layer, and one vertical fracture in the coalbed have formed in part of the coalbed after hydraulic fracturing. Therefore, this paper aims at I-shaped fracture propagation simulation. A novel propagation model is derived on the basis of a three-dimensional (3D) model, and the coupling conditions of vertical fracture and horizontal fractures are established based on the flow rate distribution and the bottom-hole pressure equality, respectively. Moreover, an associated PDA (pressure decline analysis of post-fracturing) model is established. Both models complement with each other and work together to guide fracturing treatment. Finally, a field case is studied to show that the proposed models can effectively investigate and simulate fracture initiation/propagation and pressure decline.

Computation of thermal energy in a rectangular cavity with a heated top wall

A heat exchanger is a device that transmits heat energy from one object to another, or within the same object. Examples of heat exchanger include a boiler, an oven and a cooker. Experimental techniques for testing these devices make it more costly and time-consuming. Consequently, computational fluid dynamics (CFD) can manage heat exchanger systems and their performance with ease. The actual impacts of what is being examined may then be predicted computationally which yields a precise output with approximate results. The designed geometry includes a rectangular duct with an inlet, outlet and two obstacles of equal height. The Navier–Stokes equations for the fluid flow are used. During the meshing process, the continuous geometric space of an item is divided into thousands or more forms, which helps to correctly identify the object’s physical shape. The desired model is computed numerically. Finite volume method (FVM) is used to study the results at a low Reynolds number (around [Formula: see text]. The goal is to theoretically analyze the transmission of heat and fluid resistance to the flow. The CFD findings with experimental data are compared to confirm the model predictions. A CFD model based on the FVM and experimental data from a flow cell is used to study how fluid moves through ducts. This study focuses on the pressure, velocity and temperature fields of a fluid moving through a rectangular duct. As the top wall fluid temperature rises, the temperature distribution changes. Increasing fluid flow declines the temperature distribution. Temperature distribution grows with duct heat flow. As the flow rate rises, so does dispersion. Furthermore, as flow rate and velocity distribution drop, pressure distribution rises.

Application of machine learning in predicting blood flow and red cell distribution in capillary vessel networks.

Capillary blood vessels in the body partake in the exchange of gas and nutrients with tissues. They are interconnected via multiple vascular junctions forming the microvascular network. Distributions of blood flow and red cells (RBCs) in such networks are spatially uneven and vary in time. Since they dictate the pathophysiology of tissues, their knowledge is important. Theoretical models used to obtain flow and RBC distribution in large networks have limitations as they treat each vessel as a one-dimensional segment and do not explicitly consider cell-cell and cell-vessel interactions. High-fidelity computational models that accurately model each individual RBC are computationally too expensive to predict haemodynamics in large vascular networks and over a long time. Here we investigate the applicability of machine learning (ML) techniques to predict blood flow and RBC distributions in physiologically realistic vascular networks. We acquire data from high-fidelity simulations of deformable RBC suspension flowing in the networks. With the flow and haematocrit specified at an inlet of vasculature, the ML models predict the time-averaged flow rate and RBC distributions in the entire network, time-dependent flow rate and haematocrit in each vessel and vascular bifurcation in isolation over a long time, and finally, simultaneous spatially and temporally evolving quantities through the vessel hierarchy in the networks.

Modeling of abrasive waterjet generated kerf on the top layer of a multi-layered structure

Abrasive waterjet (AWJ) is an effective tool for manufacturing parts from multi-layered structures (MLSs) due to its capability in machining a wide range of materials. However, the challenge in employing AWJ in producing the desired kerf geometry in MLS can be attributed to the complex nature of the jet's interaction with multiple layers that possess different material properties. Hence, a model that captures the interaction of the jet with MLS, and predicts the whole kerf geometry is required to gain control over the kerf quality. On the other hand, the kerf generated in a layer is affected by the presence of preceding-/following- layers. In this context, it is essential to develop a comprehensive model for the prediction of kerf profile during the penetration of the jet in each layer. Although, several models exist to predict the process response (erosion depth, top ( w t ), and bottom kerf width ( w b ), kerf taper), very limited models available on kerf profile prediction. Further, neglecting the actual jet characteristics limits their ability to predict accurately. By considering the above, this work proposes a model for the prediction of the kerf geometry (profile and characteristics) in a single layer of MLS along with its kerf characteristics apart from considering the non-linearities, such as jet characteristics and the effects of AWJ process parameters . A discretized form of the jet, abrasives mass flow distribution, and their velocity in the jet plume to realize a more realistic model for predicting kerf geometry. Further, a new parameter, ' depth of damaged region ’ was defined towards realizing the w t . The model was evaluated by comparing the kerf geometry formed on mild steel (MS) and aluminum (Al) materials by using root mean square and mean absolute error. The proposed model was found to predict the kerf geometry accurately. • First model to predict AWJ generated kerf profile considering abrasive particle velocity profile and mass flow rate distribution. • Development of analytical model to accurately predict the complete kerf profile in a single layer cut by AWJs. • Erosion theories combined with discretization approach in the development of model. • Effective representation of the top kerf width in different materials based on depth of damaged region.

On the Relation Between Active Network Length and Catchment Discharge.

The ever‐changing hydroclimatic conditions of the landscape induce ceaseless variations in the wet channel length (L) and the streamflow (Q) of a catchment. Here we use a perceptual model to analyze the links among (and the drivers of) four descriptors commonly used to characterize discharge and active length dynamics in streams, namely the L(Q) relationship and the cumulative distributions of local persistency, flowrate and active length. The model demonstrates that the shape of the L(Q) law is defined by the cumulative distribution of the specific subsurface discharge capacity along the network, a finding which provides a clue for the parametrization of L(Q) relations in dynamic streams. Furthermore, we show that L(Q) laws can be constructed combining the streamflow distribution with disjoint active length data. Our framework links previously unconnected formulations for characterizing stream network dynamics, and offers a novel perspective to describe the scaling between wet length and discharge in rivers.

Process design and economic analysis of membrane-integrated absorption processes for CO2 capture

This study proposes a design and optimization framework for a membrane-integrated absorption CO2 capture process for a coal-fired power plant. A modeling framework was developed for the hybrid capture process. The design was made by considering different flow-rate distributions between the combustion and sweep air for the membrane, as well as series and parallel configurations in an integrated manner. Sensitivity analysis was performed to understand the impact of the ratio of the combustion air being fed to the membrane on the capture performance and its economics under a hybrid configuration. As a case study, a coal-fired power plant was selected to implement the membrane-integrated absorption CO2 capture process, which was simulated with Unisim® and MATLAB®. A techno-economic assessment was used to understand the capital investment and operating expenditure related to the capture process. Compared to a stand-alone absorption process, 4.73% energy savings could be identified with a hybrid series configuration, whereas the parallel configuration offered 6.11% savings in capital cost from the reduction in equipment size. Although economic benefits can be obtained from hybrid processes through the development of membrane performance, the hybrid processes considered in this work are marginally more expensive than a stand-alone absorption process.