Entry Flow Research Articles

Recoverable Extensional Flow of Polymer Melts and Its Relevance for Processing.

While the uniaxial elongational viscosity is widely investigated, and its relevance for processing is described in the literature, much less has been published on the recoverable extensional flow of polymer melts. This paper presents a short overview of the dependencies of the recoverable elongation on the molecular structure of a polymer, and on some experimental parameters. Its main focus lies on the discussion of processing operations and applications that are largely affected by the elastic components of elongational flow. The recoverable portions of stretched films are considered, and the exploitation of the shrinkage of films, due to the recovery of frozen recoverable deformations, and its role for applications are addressed. The analysis of measurements of velocity fields in the entry region of a slit die and results on the determination of the recoverable elongation from uniaxial experiments, according to the literature, lead to the conclusion of dominant elastic extensions. Considering these facts, the assumptions for Cogswell’s widely used method of determining elongational viscosities under processing conditions from entrance flow are not realistic. As examples of a direct application of extrudate swell from short dies for processing, pelletizing and fused deposition modelling within additive manufacturing are addressed. The special features of extrudate swell from short dies, and uniaxial recoverable elongation for a polymer filled with rigid particles in comparison to an immiscible polymer blend, are presented and discussed.

Short-term traffic prediction model for urban transportation using structure pattern and regression: an Indian context

The paper presents a model for predicting short term traffic flow using structure pattern and regression. The relationship between traffic flow on the current section and upstream stations are used for predicting the short-term traffic flow and is exposed by the traffic flow structure pattern. The structure pattern of the traffic flow can be pinched from freeway toll data based on which, a new prediction model has been proposed. Locally weighted learning is used to predict the next instance’s traffic flow of current section by considering the traffic flow of current section and the next station entrance flow. This learning model deploys both linear and non-linear models to fit the nearby points and then applies those values to forecast the values of the query points. Experimental results illustrates that the short term prediction method based on structure pattern and regression is an effective approach for traffic flow prediction, this is applicable especially during the abnormal traffic states. The proposed system outperforms the conventional systems in terms of accuracy and proves to facilitate in conserving energy. The proposed work benefits the travelers by rerouting and saves fuel consumption.

Filtration efficiency and pressure drop modelling of particulate filters with rear plug damage

A model suitable for wall-flow particulate filters with partial rear plug damage is developed and experimentally validated in this work. A ceramic filter with 16% of the rear plugs mechanically removed is tested at steady-state conditions on the engine bench and transient driving cycle conditions on the chassis dynamometer. After decanning of the monolith, destructive analysis is conducted to identify deposit loading variations and scanning electron microscopy is used to study the deposit structures in the channels. It is shown that channels without rear plugs develop distinct deposit structures in the entry zone. Hence, a local pressure loss coefficient is applied to model the effect of entrance flow constrictions, taking also into account deposit restructuring phenomena at higher flow rates. In addition, a deep-bed filtration submodel is used to capture the effect of non-uniform wall velocities on deposit accumulation in the wall. The modified model is first fitted to the engine bench data and then validated in a wider range of conditions using the driving cycle tests. With the exception of prolonged steady-state loading conditions, good pressure drop and filtration efficiency predictions are obtained throughout the tests in conjunction with correct deposit property profiles. Notably, the cold-start worldwide harmonized light vehicles test cycle shows that the current European on-board diagnosis threshold limit for particulate mass is too relaxed to trigger a malfunction indication for moderate filter faults. In conclusion, the model can be applied in damaged particulate filter studies for the assessment of leaked particulate mass, the specification of more effective legislation limits and the development of rigorous on-board diagnosis systems and algorithms.

Thermophoresis as a technique for separation of nanoparticle species in microfluidic devices

This paper presents numerical studies of thermophoresis approach for separation of nanoparticles in liquid media. We simulated the thermophoresis process to test it as a method of separation of particles in suspension. At the same time, the specific software was appraised to establish whether it would meet the computational challenge. Then, a microfluidic device designed to separate different species of nanoparticles using thermal gradients was conceptualised. We used a theoretical nanoparticle species with diameters ranging between 40 and 250 nm. Different geometrical models, temperature gradients and entry flows were simulated to analyse their effect on the separation of nanoparticle species. On the basis of our results, we formulated a proposal for construction of efficient nanoparticle separation device.

Numerical simulation of 3D magnetohydrodynamic liquid metal flow in a spatially varying solenoidal magnetic field

Abstract Motivated by experiments currently under investigation in the MEKKA laboratory at KIT, numerical simulations have been performed for a liquid metal pipe flow entering a strong magnetic field. Magnetohydrodynamic (MHD) flows in non-uniform magnetic fields are relevant in blanket engineering, in regions where the liquid breeder PbLi enters or exits the magnetic field confining the fusion plasma. Simulations provide insight into 3D phenomena near the non-uniform region of the magnetic field in particular velocity distribution and electric current pattern that cannot be directly observed in the experiments. Moreover, simulations describe the transition from a highly turbulent hydrodynamic entrance flow to a fully established laminar MHD flow. The present work addresses in particular a conservative formulation of the magnetic field, generation and decay of inlet turbulence by means of direct numerical simulation, as well as fluid–wall interaction by electric currents that are exchanged between the liquid metal and the thick electrically conducting pipe wall.

Bi-modal macroscopic traffic dynamics in a single region

Bi-modal or 3D-MFD relates the accumulation of cars, buses to total production at the network level. The current work provides a detailed discussion of extended MFD-based models namely, accumulation-based and trip-based models that accounts for bi-modal flows through 3D-MFD. In addition, delay accumulation-based models, also known as exit-flow models in classical traffic flow theory, are revisited. Fundamental modeling differences between different MFD-based models are illustrated using a benchmark test case. A new FIFO-based entry flow function is also proposed in order to address the inconsistencies of the conventional entry flow function in the context of the 3D-MFD case. A novel weak internal FIFO discipline is proposed to circumnavigate the violation of internal FIFO order during network unloading in the delay accumulation-based model. MFD-based models are verified using the solutions of micro-simulations performed on an idealized grid network. The importance of separating the 3D-MFD into partial car and bus 3D-MFDs is highlighted. Moreover, it is also shown that partial bus 3D-MFD should be further split when dedicated bus lanes are present in the network to account for unequal mean speeds between different bus lanes.

Modeling and Characterization of a Thermally Controlled Iodine Feeding System for Electric Propulsion Applications

Iodine is considered as a feasible alternative to xenon as a propellant for electric propulsion systems, thanks to its good propulsive performance, high availability, and high storage density. However, as iodine is stored in solid state at ambient temperature, current state-of-the-art propellant management systems are not suitable to be used with it. Moreover, due to its high reactivity, iodine imposes requirements on material-compatibility, hindering the use of mass flow measurement and control systems typically used with other propellants. The architecture of a controlled iodine feeding system for low power (200 W class) ion and Hall effect thrusters is presented and the resulting prototype is described. It consists of a sublimation assembly whose temperature is used to control the tank pressure, a normally-closed ON-OFF valve, and a thermal throttle to perform the fine control of the mass flow rate. A 1D thermal-fluid model concerning the vapor generation in the tank, and its evolution along the different components is detailed. The thermal throttle model has been experimentally verified using air as a working fluid. The model results agree with the measurements of the verification tests in the hypothesis of the presence of an extended region at the entrance of the pipe where the laminar flow velocity and temperature profiles are not fully developed (known as entry flow region). Finally, the system is experimentally characterized and the model of the full system is calibrated using experimental measurements. The calibration shows that the thermal throttle flow presents an entry flow region, that the viscosity is correctly modeled, and that there is a difference between the measured tank temperature and the effective sublimation temperature.

Short-Term Passenger Flow Prediction With Decomposition in Urban Railway Systems

Accurate prediction of short-term passenger flow is vital for real-time operations control and management. Identifying passenger demand patterns and selecting appropriate methods are promising to improve prediction accuracy. This paper proposes a hybrid prediction model with time series decomposition and explores its performance for different types of passenger flows with varied characteristics in urban railway systems. The Seasonal and Trend decomposition using Loess (STL) is used to decompose the passenger flow into the seasonal, trend, and residual time series, representing the constant, long-term fluctuant, and stochastic passenger demand patterns. The approximate entropy (ApEn) is utilized to quantify the predictability of each component. After that, the Holt-Winters (HW) method is developed to predict the seasonal and trend components that both with high predictability. The long short-term memory networks (LSTM NN) are proposed to predict the residual with low predictability. The outputs from these models are combined to predict the short-term passenger flow. We assess the model performance with entry, exit, and transfer passenger flows at the target stations, which are selected via the agglomerative hierarchical clustering (AHC) algorithm in the Shanghai Metro. Compared with three representative models, the results show that 1) the decomposition-based hybrid model performs well for both one-step and multi-step predictions in terms of accuracy and robustness; 2) ApEn is useful for choosing appropriate prediction models.

Coupled heat transfer characteristics on gas-solid reacting interface in carbon-oxygen dissociating environment for spacecraft entry flow

Coupled heat transfer characteristics on gas-solid reacting interface in carbon-oxygen dissociating environment for spacecraft entry flow

Aerothermodynamic modelling of meteor entry flows

ABSTRACT Due to their small size and tremendous speeds, meteoroids often burn up at high altitudes above 80 km, where the atmosphere is rarefied. Ground radio stations allow us to detect the concentration of electrons in the meteoroid trail, which are produced by hyperthermal collisions of ablated species with the freestream. The interpretation of these data currently relies on phenomenological methods, derived under the assumption of free molecular flow, that poorly accounts for the detailed chemistry, diffusion in the vapour phase, and rarefied gas effects. In this work, we employ the direct simulation Monte Carlo (DSMC) method to analyse the detailed flowfield structure in the surroundings of a 1 mm meteoroid at different conditions, spanning a broad spectrum of Knudsen and Mach numbers, and we extract resulting ionization efficiencies. For this purpose, we couple the DSMC method with a kinetic boundary condition which models evaporation and condensation processes in a silicate material. Transport properties of the ablated vapour are computed following the Chapman–Enskog theory starting from Lennard–Jones potentials. Semi-empirical inelastic cross-sections for heavy- and electron-impact ionization of metals are computed analytically to obtain steric factors. The ionization of sodium is dominant in the production of free electrons, and hyperthermal air–vapour collisions play the most important role in this process. The ionization of air, classically disregarded, contributes to the electron production as significantly as ionization of magnesium and iron. Finally, we propose that DSMC could be employed as a numerical experiment providing ionization coefficients to be used in synthetic models.

Crossborder tourist mobility in borderland: theoretical and practical aspects

The socio-economic transformations of Russia as well as the change in the functions of state borders in the context of integration processes in the global society, along with the change in the perception of the tourism at the level of government, business and society, served as a prerequisite for the tourist vector of development of border areas. The increasing competition for the financial resources of tourists contributes to a change in the socioeconomic space of the territories, which is most noticeable in the borderlands. The article substantiates the importance of cross-border tourist mobility in the development of the borderland. Depending on the chosen focus of attention (development of the local community, economic and spatial development of the territory), the benefits and risks for the socio-economic development of the territory are different for the both sides of the border. The cross-border tourist mobility is considered on the example of the Russian-Polish and Russian-Finnish borderlands. A significant asymmetry of mutual cross-border tourist flows has been revealed. This tendency will increase thanks to the actively pursued marketing policy of the business of neighboring countries to stimulate the entry flow of Russian citizens with tourist purposes.

Combustion modes periodical transition in a hydrogen-fueled scramjet combustor with rear-wall-expansion cavity flameholder

Cavity-stabilized combustion modes periodical transition in a laboratory hydrogen-fueled scramjet combustor were captured by high speed imaging. Experiments were performed with an isolator entrance Mach number of 2.92, and a sonic transverse fuel jet upstream of the cavity was employed. The reproducibility of the results had been tested in several repeated experiments. It is observed that, under a fixed combustor entry flow parameters and fuel equivalence ratio, after the flame has been fully developed, the flame structure may periodically transform between two different combustion modes. Specifically, under a moderate equivalence ratio, the flame structure switches between the cavity shear-layer stabilized mode and the combined shear-layer/recirculation stabilized mode, which shows an apparent periodicity with a period of about 7.5 ms. The formation mechanism for this novel phenomena is analyzed and some suppositions are given. When increasing the equivalence ratio to a high level, the flame structure shows a quasi-periodic low-frequency oscillation and the combustion mode changes between the combined shear-layer/recirculation stabilized mode and the cavity-assisted jet wake stabilized mode. At last, the formation mechanism and characteristics of the combined shear-layer/recirculation stabilized mode are detailed analyzed.

Mapping Dynamic Exposure: Constructing GIS Models of Spatiotemporal Heterogeneity in Artificial Stream Systems.

In flowing environments, the degree of turbulent flow determines the movement and distribution of chemicals. Variation in flow alters the patchiness of toxicant plumes within a stream ecosystem. This patchiness translates into variability in exposure pulses for organisms encountering the toxic plume. Throughout a stream, the processes that give rise to chemical plume structure will vary as a function of local flow characteristics. This research examines the influence of toxicant mode of entry and stream flow velocity on the spatiotemporal patterning of exposure. Two introduction treatments were evaluated: one mimicking groundwater and the other mimicking runoff. The influence of flow regime was examined through the comparison of models constructed under two stream flow velocities. Concentrations of a tracer molecule were recorded using an electrochemical monitoring system. From these localized, direct measurements, geographic information systems (GIS) were used to model exposure throughout the stream. Conceptualizing exposure as a series of toxicant pulses, exposure can be defined using a variety of chemical peak characteristics. Three-dimensional, layered maps were constructed defining exposure as the integrated area of toxicant peaks, the magnitude of peaks, and peak frequency. Differences in the spatial and temporal patterning of exposure were apparent both within treatments and between treatments. No two definitions of exposure yielded the same exposure distributions for any treatment. These models demonstrate that distribution of chemical exposure throughout a stream ecosystem is linked to both toxicant mode of introduction and stream hydrodynamics. Furthermore, these results demonstrate that optimal exposure modeling relies on first defining exposure.

Metro Passenger Flow Statistics Based on YOLOv3

Passenger flow real-time detection in per train compartment is the basis for realizing metro entrance flow restriction, platform waiting guidance and optimizing train departure interval. In this paper, we collect RGB images as the input of the improved YOLOv3 network, then we can get the statistics of passenger flow by detecting and tracking passengers’ heads. For the head detection part, this paper re-selects the number of anchors by using the k-means++ clustering method and removes the large-scale object detection module in the original YOLOv3 network. For the head tracking part, this paper proposes the probability gradient map, IOU-Max maximum matching algorithm and voting strategy, which make the stability of target tracking greatly enhanced. Compared with the original YOLOv3 network, our research results show that the accuracy of head detecting based on the improved YOLOv3 network increases from 90.1% to 97.84%, the recall rate increases from 85.4% to 94.7%, and the accuracy of the head tracking algorithm is as high as 98.87%, and the accuracy of passenger flow density detecting is as high as 95%. The measured detection speed reaches 47FPS on the TITAN X server, enabling real-time fast detection and tracking of targets.

Theoretical analysis of thermal entrance problem for blood flow: An extension of classical Graetz problem for Casson fluid model using generalized orthogonality relations

An analysis of classical Graetz problem is carried out for the case of fluid obeying the Casson constitutive equation. The considered model physically corresponds to the thermal entry flow of blood in a duct. The governing equation for the premeditated problem is investigated by employing the separation of variables approach in conjunction with the MATLAB built in package bvp4c for the calculation of the eigenvalues and related numerical solution of the eigenvalue problem. The solution is computed for the case of uniform surface temperature boundary condition for both flat and circular geometries. The axial diffusion and viscous dissipation effects on temperature field are also taken into account. The expressions of bulk mean temperature and Nusselt number are presented and discussed in terms of the main effect brought by the yield stress parameter, Peclet number and Brinkman number. It is found that both local and mean Nusselt numbers for blood enhance considerably with the increase of dimensionless plug radius and Brinkman number. In contrast, the thermal entrance length reduces with the rise of Peclet number. The results of present analysis have potential applications in development of nano fluidic, microfluidic and bio-medical devices used in haemodialysis and oxygenation.

Models for estimating the capacity of roundabouts

Roundabouts, as a special form of unsignalised intersections, are an increasingly common choice of designers around the world. Adjusting the capacity of roundabouts with flow requirements is one of the most important steps in order to meet the planned traffic conditions. The capacity of roundabouts can be determined by empirical methods, by the methodology of gap acceptance and by simulation. Each of these methodologies has some limitations, because none of them can independently and fully take into account the complex processes of driver behaviour, as well as the kinematic processes that occur at the entry flows of roundabouts. All of these models require certain semi-empirical or fully-empirical parameters that take into account local conditions that are largely dependent on driver behaviour. Although such calibration allows applicability in similar traffic conditions, it is often restricted by data availability or an incomplete understanding of the relationships between model parameters and capacity.

Transport properties of carbon-phenolic gas mixtures

The development of a new generation of ablative thermal protection systems based on carbon-phenolic composite materials demands the accurate determination of transport properties of pyrolysis gases mixed in various atmospheres. The present work provides recommended collision data for the calculation of the transport properties for Mars and Earth re-entries. A review of available potential data is given for species in the atmospheres of Earth and Mars. Additional data are provided for species formed during the degradation of the theoretical ablative composite for open testing material. Dipole polarizabilities are calculated from ab initio methods and used for the calculation of transport properties of reduced pyrolysis mixtures over a temperature range representative of the boundary layer for atmospheric entry flows.

ECONOMIC SHOCKS, COMPETITION AND MERGER ACTIVITY

This study seeks to understand “how” economic shocks drive industry merger activity. We test whether economic shocks from deregulation and technological change drive industry merger activity by increasing industry competition, controlling for the effect of valuations. We find that these shocks drive merger activity through three channels related to industry competition; deregulation drives merger activity by increasing entry and cash flow volatility; technological change drives merger activity by increasing entry and inter-firm dispersion in the quality of production technology. These findings underscore the role of the competitive mechanism in how managers reallocate assets via mergers and support the view that the industry-level clustering of merger activity is an efficiency-driven restructuring response to increased competition.

Dynamic characteristics of load rejection process in a reversible pump-turbine

The dynamic behavior during load rejection process of a reversible pump-turbine is numerically investigated based on the dynamic grid method. For the dynamic characteristics, the external features like runner rotation speed, torque and flow rate are analyzed. Then the time-frequency characteristics of pressure fluctuations at different positions (like guide vane, vaneless space, runner inlet and draft tube) are discussed in details. During the unsteady process of load rejection, four peculiar frequency bands, are identified and their sources are assessed. These frequency bands are 2 low frequency-high amplitude components, marked as zones a and b, which occur around the zero-torque condition. Another 2 high frequency-high amplitude components, marked as zones c and d, appear near the maximum reversed flow condition. Besides, the rotor-stator interaction plays an important role in the pressure pulsation bands distribution, showing components multiples of runner rotational frequency. They could propagate towards both upstream and downstream. For reversed flow condition, it is also found that the entrance flow from draft tube into runner contributes most energy to the pressure fluctuations.

Three-dimensional electrochemical Bunsen reaction characteristics in the sulfur–iodine water splitting cycle for hydrogen production

Hydrogen production from the sulfur–iodine water splitting cycle integrated with solar or nuclear energy has been proposed as a promising technique. Bunsen reaction is one of the three main steps in the cycle and electrochemical method has been applied to this reaction. In present work, a three-dimensional numerical study of the electrochemical Bunsen reaction was conducted. A three-dimensional, steady state, laminar and isothermal mathematical model of electrolytic cell was developed and verified by experiments. The spatial maldistribution of species concentration was found between electrodes and proton exchange membrane (PEM). The electric power drives most H2SO4 and I2 to the anode and cathode surface, respectively, while the proton attraction contributes to HI enrichment on the surface of PEM. At the high inlet H2SO4 concentration of 50 wt%, the transformation of flow channel from single serpentine to single entry & double serpentine with the same inlet flow rate cannot solve the insufficient problem of SO2. But the increase of the overall inlet flow rate in the double entry & double serpentine flow channel make SO2 sufficient for anode reaction. Further decreasing the inlet H2SO4 concentration to 40 wt% and 30 wt% make the initial SO2 sufficient for overall reactions. The single serpentine channel gives the highest SO2 conversion rate, followed by the single entry & double serpentine and double entry & double serpentine flow channels. The single serpentine flow channel at the H2SO4 inlet concentration of 40 wt% is found optimal for achieving a high electrochemical Bunsen reaction performance.