Design Of Flow Systems Research Articles

Mechanism-guided design of flow systems for multicomponent reactions: conversion of CO2 and olefins to cyclic carbonates

A mechanism-guided design of a multi-step flow system enabled an efficient general process for the synthesis of cyclic carbonates from alkenes and CO2. The flow system proved to be an ideal platform for multicomponent reactions because it was straightforward to introduce reagents at specific stages without their interacting with each other or with reaction intermediates prone to destruction by them. This system exhibited superior reactivity, increased yield, and broader substrate scope relative to conventional batch conditions and suppressed the formation of undesired byproducts, such as, epoxides and 1,2-dibromoalkanes.

Development and experimental results from a 1 kW prototype AMR

A novel rotary magnetic refrigeration device has been designed and constructed following the concepts recently outlined in Bahl et al. (2011). The magnet and flow system design allow for almost continuous usage of both the magnetic field and the magnetocaloric material in 24 cassettes, each containing an active magnetic regenerator (AMR) bed. The prototype design facilitates easy exchange of the 24 cassettes, allowing the testing of different material amounts and compositions. Operating with 2.8 kg of commercial grade Gd spheres a maximum no-span cooling power of 1010 W and a maximum zero load temperature span of 25.4 K have been achieved. For the purpose of actual operation, simultaneous high span and high performance is required. At a heat load of 200 W a high temperature span of 18.9 K has been obtained, dropping to a span of 13.8 K at the higher heat load value of 400 W.

J101035 ロケットターボポンプ内部流れの動的設計(〔J101-03〕回転機械のダイナミック設計(3))

J101035 ロケットターボポンプ内部流れの動的設計(〔J101-03〕回転機械のダイナミック設計(3))

Using dominant modes for optimal feedback control of aerodynamic forces

The problem of active feedback control of fluid flows falls into a class of problems in the area of distributed parameter control, typically defined by partial-differential equations. Physical processes modeled by partial-differential equations are infinite-dimensional systems and are often simulated by numerical methods. However, for complex flows, the degrees of freedom may still be of the order of millions and are not practical for direct use in control design and optimization of fluid flow systems. Consequently, ‘reduce-then-control’ strategy is often employed for flow control of many engineering and industrial applications. In this study, the authors develop a linear quadratic regulator control to suppress fluctuating forces on a circular cylinder using a proper orthogonal decomposition based low-dimensional model. They numerically simulate the flow past a circular cylinder by solving the incompressible Navier–Stokes equations, and record the flow field data over one vortex shedding cycle. Using the data ensemble, they compute the proper orthogonal decomposition basis functions (modes) of the divergence-free velocity and pressure fields. The authors project the Navier–Stokes equations onto these proper orthogonal decomposition modes to develop a reduced-order model. Later, they modify the model by applying suction on the cylinder surface and adding a control function in the velocity expansion. The nonlinear dynamical system thus developed is linearly unstable due to negative damping in the system. They linearize the system about the mean velocity and apply optimal control. The authors seek to minimize the fluctuating forces on the cylinder using a reasonable amount of control effort. The novelty in this control strategy lies in feeding back only the dominant mode to suppress the fluctuating forces. On the contrary, feedback of higher modes fails to control and destabilizes the system.

Loss Coefficients in Laminar Flows: Essential for the Design of Micro Flow Systems

AbstractThe concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has mainly been applied to fully turbulent flows it is extended here to also cover the laminar flow regime which is relevant for micro systems due to the low Reynolds numbers of these flows. Specific numbers of K can be determined by integration of the entropy generation field (second law analysis) obtained from a numerical simulation. It will be shown that a definition of K based on entropy generation is superior to a widely used definition that refers to a pressure drop caused by the conduit component. With the second law analysis details of the physics become available. For example it can be shown that often the main part of the entropy generation occurs downstream of the component. This aspect becomes important when several conduit components are combined in close proximity, like two 90 degree bends that are close to each other. Often in such situations the combination as a whole has to be looked upon as one new complex component. The general approach is discussed and illustrated for various conduit components and combinations of them. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Applications of Computational Fluid Dynamics(CFD) in the Food Industry

The application of computational fluid dynamics(CFD) in the food industry such as drying, thermal sterilization, mixing, refrigeration and humidification of cold storage was reviewed. The results from previous studies have shown that CFD was a powerful numerical tool that is applied to model fluid flow situations and aid in the optimal design of engineering equipment and food process. With the development of computer technology, it is conceivable that CFD will continue to provide more explanations for physical modeling of fluid flow and process system design for the food industry.

A Probabilistic Secondary Flow System Design Process for Gas Turbine Engines

Gas turbine engine secondary flow systems are sensitive to variation in part dimensions, clearances, flow coefficients, swirl ratios, head loss factors, tolerances, boundary conditions, etc. This paper reveals a process and software application, which embodies the process, wherein both offer a measurable contribution to secondary airflow system reliability. The probabilistic methodology is empirically validated by (1) applying it to an engine component that failed in a validation test and (2) demonstrating that a multiple order sensitivity analysis performed during detailed design was unable to detect a failure mode while a probabilistic analysis revealed a small yet significant risk of failure. Therefore, a secondary flow analyst does not have a justifiable reason to be highly confident of a design qualified by a first, second, or higher order sensitivity analysis. The last example empirically demonstrates the compatibility of optimization techniques with probabilistic methods (as part of the process) to quantify the likelihood of failure and reveal an optimized design space of key characteristics, where risk is eliminated and the effects of variation are controlled. Trade study analysis is more valuable if it includes a quantitative evaluation of the effects of variation on alternate designs and the response to failure modes. A key feature of the software application is a relational database with the capability to configure and effectively manage flow networks in many forms including a status model, failure modes of the status model, multiple alternative designs, as well as failure modes specific to an alternative design.

Low-Noise Pulsed Pre-Polarization Magnet Systems for Ultra-Low Field NMR

A liquid cooled, pulsed electromagnet of solenoid configuration suitable for duty in an ultra-low field nuclear magnetic resonance system has been designed, fabricated and successfully operated. The magnet design minimizes Johnson noise, minimizes the hydrogen signal and incorporates minimal metal and no ferromagnetic materials. In addition, an acoustically quiet cooling system permitting 50% duty cycle operation was achieved by designing for single-phase, laminar flow, forced convection cooling. Winding, conductor splicing and epoxy impregnation techniques were successfully developed to produce a coil winding body with integral cooling passageways and adequate structural integrity. Issues of material compatibility, housing, coolant flow system and heat rejection system design will be discussed. Additionally, this pulsed electromagnet design has been extended to produce a boiling liquid cooled version in a paired solenoid configuration suitable for duty in an ultra-low field nuclear magnetic resonance system. This pair of liquid nitrogen cooled coils is currently being tested and commissioned. Issues of material compatibility, thermal insulation, thermal contraction, housing and coolant flow design are discussed.

A Critical Review of Advanced Experimental Techniques to Measure Two-Phase Gas/Liquid Flow

Gas assisted atomization is becoming increasingly important in many industrial applications such as physical, chemical and petroleum processes. In order to achieve proper atomization it is crucial to have proper mixing of gas (air) and liquid (water) in the feeding conduit before it enters into the nozzle. The flow regime, as well as the flow pattern and structure of the flow, are some of the important parameters that describe two-phase gas/liquid flows, and identify two- phase gas/liquid flow regimes. It is also desirable to know under what conditions there is a transition among the different flow regimes (dispersed, stratified, annular, annular-dispersed, slug, wavy-slug, mist-annular). Due to the existence of relative movement in the interfaces and variable interactions between two phases, two-phase gas/liquid flow is a complex transport phenomenon compared to single-phase flow. Still, there is no effective technique to identify the two-phase gas/liquid flow regimes and it is even difficult to capture the accurate flow structures in smaller conduits in turbulent flow cases. Lack of solid and comprehensive theories for predicting and calculating the pressure and void fraction variations in two-phase air/water flow situations has left engineers without essential information for proper design of two-phase flow systems. This review is an effort to explore the state of the present advanced measurement techniques in this field of research. Subsequently, some of the advanced void fraction, photonics and pressure measurement techniques and correlations for identification of two-phase gas/liquid flow regimes and bubble sizes are investigated.

Numerical and experimental studies of mixing characteristics in a T-junction microchannel using residence-time distribution

The mixing behavior in laminar flow in microchannels is investigated using numerical and experimental approaches. The concept of residence-time distribution (RTD) was applied to indirectly characterize flow and mixing in a T-junction microchannel chosen as a model microchannel mixer/reactor. The residence-time distribution used in this study, although a well-known method for characterizing mixing behavior in conventional macro mixers/reactors, is still a novel measure for the characterization of mixing in microchannels. The standard T-junction microchannel and one of its modifications were studied for their mixing characteristics by performing computational fluid dynamics (CFD) simulations of pulse tracer experiments. Experimentally, RTD measure in conjunction with a UV–vis absorption spectroscopy detection technique was used to characterize flow and mixing quality in the microchannels studied. The moments of the RTD and coefficient of variation were used to quantify the mixing behavior. Two flow models, namely the well-known axial dispersion model (ADM) and a semi-empirical model (SEM), were used to obtain model descriptions for the RTD of the microchannel. As expected, the SEM fits better the experimental data than the ADM since the SEM with its characteristic asymmetric distribution predicts better the strong laminar flow behavior in the microchannels than the ADM. The results from the simulations and experiments are in very good agreement thus establishing the validity of the mathematical model and the associated solution algorithm implemented in the CFD simulations. The CFD code in conjunction with the RTD measure can then be used as a predictive tool in the design, evaluation, and optimization of microscale flow systems.

Observation of the fluid pulsation behind a prism in gas-liquid annular flow

The fluid pulsation behind a prism is closely concerned with the design and operation of gas-liquid two-phase flow systems. This paper explored the property of such fluid pulsations in a horizontal pipe using air and water as the tested media. The pressure difference between the upstream and downstream of the prism was adopted to represent the characteristics of the fluid pulsation. Based on the experimental results, it is found that there exit obvious pulsations in the fluid behind the prism in annular flows, and this pulsation is more marked at low gas mass qualities than those at high gas mass qualities. Furthermore, the average pressure basically decreases with the gas mass quality and increases with the gas-liquid total mass flowrate. These findings could be useful for the analysis of flowing characteristics in gas-liquid annular flow across a prism.

Filtration software: Shedding light on fluid flow system design

Design analysis and simulation techniques have come a long way from the days of slide rules and drafting tables. The next step, claims Jim Spann of Blue Ridge Numerics, is putting fluid flow simulation capabilities into the hands of multi-tasking design engineers, potentially saving costs and energy further along in the filtration process.

The value of the shortest loop covering all work centers in a manufacturing facility layout

In this study we develop mathematical models to design circular material flow systems. We first develop a tight formulation to find the shortest loop covering all work centers within a manufacturing facility layout. The shortest loop is an attractive solution for most types of conveyors and power-and-free systems, where the length of the flow path is the major driver of the total cost. We develop a primal as well as a dual graph formulation and discuss their one-to-one correspondence in node-edge as well as in connectivity constraints. Our solution times outperform other optimization models available for the facility layout shortest loop design problem. We then approach trip-based material handling, such as automated guided vehicle systems, where the total loaded and empty trip distance is the major driver of the total cost. The problem in these systems evolves into concurrent design of the loop, pickup and dropoff station, and the empty vehicle dispatching policies. On the foundation of the shortest loop model, we propose a decomposition heuristic for design of trip-based flow systems. Computational results indicate that the heuristic provides high quality and robust solutions.

Improved formulation, branch-and-cut and tabu search heuristic for single loop material flow system design

The single loop material flow system design is a combinatorial optimization problem, arising in material handling system design, which amounts to designing an unidirectional loop flow pattern as well as to locate pickup and delivery stations. The objective is to minimize the time required to carry out all material flow movements between cells. In this paper, we develop valid inequalities for a previously proposed formulation. The valid inequalities are then embedded into a branch-and-cut framework which is shown to solve much larger instances to optimality than those reported in the literature. A tailored tabu search heuristic is also illustrated and computationally assessed.

Towards standards for measuring greenhouse gas fluxes from agricultural fields using instrumented towers

This is a discussion of the available technology for measuring turbulent fluxes using instrumented towers. This review focuses on the flux measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) for agricultural systems and the development of standards and protocols for measuring them. Agroecosystems present unique challenges because they undergo large leaf area index (LAI) and canopy architecture changes in a relatively short period of time (i.e., months) coupled with the fact that many of the greenhouse gas sources are diffuse. This review examines all aspects of the theory and application of the micrometeorological techniques, with focus on the flux gradient, eddy accumulation and eddy covariance techniques. Instrument placement, sens or response and noise characteristics are also explored. Innovative applications of micrometeorological methods are discussed for closed- and open-path trace gas sensors and commonly used meteorological instrumentation. The use of fast response single-pass optical tunable diode laser (i.e., CH4, N2O) and infrared gas analyzers (i.e., CO2, H2O) is described. Consideration is also taken of the trace gas sensors’flow system design, mixing ratio measurement, and data acquisition and reduction requirements for micrometeorological flux measurement. Procedures are outlined for the meteorological instrumentation necessary for eddy covariance-based energy budget measurement including ultrasonic anemometry. Key words: Tower-based greenhouse gas flux measurements, nitrous oxide, methane, carbon dioxide, tunable diode laser

Nonadiabatic and frictional constant area duct flow: A visual software based simulation for compressible systems

AbstractNumerical investigation of compressible flows in constant area ducts becomes substantially complicated when the surface roughness and heat flux conditions simultaneously act as independent and considerable boundary conditions that create significant influences on the flow and heat transfer characteristics. This article presents GAS‐DYN v2.0, a specialized software package, capable of handling nonadiabatic and frictional systems with the contribution of a database, developed also by the author, which involves the real time temperature‐dependent gas properties. Results of the presented computational analysis are in harmony with the available literature, which not only indicates the reliability of the package but also points out its adaptability to MSc and PhD level research studies and for the compressible flow system design projects. © 2006 Wiley Periodicals, Inc. Comput Appl Eng Educ 14: 64–75, 2006; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20068

On The Use of Entropy to Predict Boundary Layer Stability

Boundary layer transition is a critical parameter in the design of fluid flow systems. This situation is due to the dramatic change in both entropy production and heat transfer that accompanies it. It is well recognized that many parameters affect the location of transition onset, however, no models exist which unify all these parameters. This paper presents a new hypothesis that the driving force of boundary layer transition onset is the entropy generation rate alone, with all other parameters being functions of this higher order quantity. At present this hypothesis is speculative, but encouraging since good compatibility is found with more established transition models.

Multiphase Inverse Modeling: Review and iTOUGH2 Applications

Calibration of a numerical process model against laboratory or field data is often referred to as ''inverse modeling''. As the numerical simulation models become more complex, the number of parameters to be estimated generally increases, requiring new testing, modeling, and inversion strategies. The purpose of this survey is to review inverse modeling approaches for unsaturated and multiphase flow models. The discussion focuses on applications rather than theoretical considerations, which have been previously reviewed in the context of saturated flow and transport modeling. We also examine model parameterization issues, specifically the representation of heterogeneity through a limited number of variables that can be subjected to parameter estimation and uncertainty propagation analyses. Different parameterization strategies are illustrated using the multiphase flow simulation-optimization code iTOUGH2 (Finsterle, 1999a,b,c). A comprehensive inverse modeling package (such as iTOUGH2, which includes automatic model calibration followed by an extensive residual, error, and uncertainty propagation analysis) is an essential tool to improve test design and data analysis of complex multiphase flow systems.

Multiphase Inverse Modeling: Review and iTOUGH2 Applications

Calibration of a numerical process model against laboratory or field data is often referred to as “inverse modeling.” As the numerical simulation models become more complex, the number of parameters to be estimated generally increases, requiring new testing, modeling, and inversion strategies. The purpose of this survey is to review inverse modeling approaches for unsaturated and multiphase flow models. The discussion focuses on applications rather than theoretical considerations, which have been previously reviewed in the context of saturated flow and transport modeling. We also examine model parameterization issues, specifically the representation of heterogeneity through a limited number of variables that can be subjected to parameter estimation and uncertainty propagation analyses. Different parameterization strategies are illustrated using the multiphase flow simulation–optimization code iTOUGH2. A comprehensive inverse modeling package (such as iTOUGH2, which includes automatic model calibration followed by an extensive residual, error, and uncertainty propagation analysis) is an essential tool to improve test design and data analysis of complex multiphase flow systems.

A diode laser based gas monitor suitable for measurement of trace gas exchange using micrometeorological techniques

A fast response, sensitive, field-worthy trace gas analyzer (TGA), based on the principle of diode laser absorption spectroscopy has been developed. The TGA is suitable for in situ trace gas flux measurements using micrometeorological techniques, and is capable of achieving total system noise levels of less than 1, 2, or 4 part per billion by volume (ppbv) rms for N 2O, NH 3, and CH 4, respectively, for a 5-s integration period, and less than 50 pptv for 1-h averaging periods. This sensitivity is accomplished using a unique approach to digital signal processing and a single-path sample absorption cell, both of which reduce noise due to optical fringes. The instrument is also capable of rapid sampling rates (10 samples/s) sufficient for eddy correlation (EC) measurements when used with the appropriate flow system design. The TGA software and electronics have been designed to interface directly with micrometeorological instrumentation such as sonic anemometers, facilitating the use with the eddy correlation and gradient techniques. The operation, characteristics, and practical aspects of employing the TGA with micrometeorological techniques are reviewed. Gradient flux data for N 2O and CH 4 from field study measurements is from two plots are presented. The results demonstrate the capabilities of the TGA to make sensitive, continuous measurements of trace gas fluxes using micrometeorological techniques, allowing the assessment of the immediate and long-term impact of treatments or perturbations to natural and agricultural systems.