Direct Simulation Based Model-Predictive Control of Flow Maldistribution in Parallel Microchannels

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Mathieu Martin ◽  
Chris Patton ◽  
John Schmitt ◽  
Sourabh V. Apte
Keyword(s):  
Fluid Flow ◽  
Model Predictive Control ◽  
Numerical Simulations ◽  
Active Control ◽  
Predictive Control ◽  
Nonlinear Flow ◽  
Flow Simulations ◽  
Flow Through ◽  
Parallel Microchannels ◽  
Flow Maldistribution

Flow maldistribution, resulting from bubbles or other particulate matter, can lead to drastic performance degradation in devices that employ parallel microchannels for heat transfer. In this work, direct numerical simulations of fluid flow through a prescribed parallel microchannel geometry are performed and coupled with active control of actuated microvalves to effectively identify and reduce flow maldistribution. Accurate simulation of fluid flow through a set of three parallel microchannels is achieved utilizing a fictitious-domain representation of immersed objects such as microvalves and artificially introduced bubbles. Flow simulations are validated against experimental results obtained for flow through a single high-aspect ratio microchannel, flow around an oscillating cylinder, and flow with a bubble rising in an inclined channel. Results of these simulations compare very well to those obtained experimentally, and validate the use of the solver for the parallel microchannel configuration of this study. System identification techniques are employed on numerical simulations of fluid flow through the geometry to produce a lower dimensional model that captures the essential dynamics of the full nonlinear flow, in terms of a relationship between valve angles and the exit flow rate for each channel. A model-predictive controller is developed, which employs this reduced order model to identify flow maldistribution from exit flow velocities and to prescribe actuation of channel valves to effectively redistribute the flow. Flow simulations with active control are subsequently conducted with artificially introduced bubbles. The model-predictive control methodology is shown to adequately reduce flow maldistribution by quickly varying channel valves to remove bubbles and to equalize flow rates in each channel.

Direct Simulation Based Model-Predictive Control of Flow Maldistribution in Parallel Microchannels

2009 ◽  
Author(s):  
Mathieu Martin ◽  
Chris Patton ◽  
John Schmitt ◽  
Sourabh V. Apte
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Nonlinear Flow ◽  
Flow Simulations ◽  
Control Scheme ◽  
Simulation Based ◽  
Flow Through ◽  
Parallel Microchannels ◽  
Identification Techniques ◽  
Flow Maldistribution

The goal of this investigation is to develop a simulation-based control strategy to eliminate flow-maldistribution in parallel microchannels. An accurate simulation of fluid flow through parallel microchannels is achieved by utilizing a fictitious domain representation of immersed objects, such as microvalves and bubbles. System identification techniques are employed to produce a lower dimensional model that captures the essential dynamics of the full nonlinear flow, in terms of a relationship between the valve angles and the exit flow rate for each channel. The resulting linear model is incorporated into a model predictive control scheme to identify flow maldistribution from exit flow velocities and prescribe actuation of channel valves to effectively redistribute the flow. Flow simulations in a three parallel microchannel geometry including bubbles illustrates the effectiveness of the control design, which quickly and efficiently varies channel valves to remove the bubble and equalize the flow rates in each channel.

Experimental Validation of Graph-Based Hierarchical Control for Thermal Management

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Herschel C. Pangborn ◽  
Justin P. Koeln ◽  
Matthew A. Williams ◽  
Andrew G. Alleyne
Keyword(s):  
Fluid Flow ◽  
Model Predictive Control ◽  
Thermal Management ◽  
Predictive Control ◽  
Experimental Validation ◽  
Hierarchical Control ◽  
Electrical Energy ◽  
Management Systems ◽  
Conservation Of Mass ◽  
Control Framework

This paper proposes and experimentally validates a hierarchical control framework for fluid flow systems performing thermal management in mobile energy platforms. A graph-based modeling approach derived from the conservation of mass and energy inherently captures coupling within and between physical domains. Hydrodynamic and thermodynamic graph-based models are experimentally validated on a thermal-fluid testbed. A scalable hierarchical control framework using the graph-based models with model predictive control (MPC) is proposed to manage the multidomain and multi-timescale dynamics of thermal management systems. The proposed hierarchical control framework is compared to decentralized and centralized benchmark controllers and found to maintain temperature bounds better while using less electrical energy for actuation.

scholarly journals Combined numerical and experimental study of microstructure and permeability in porous granular media

2020 ◽  
Author(s):  
Philipp Eichheimer ◽  
Marcel Thielmann ◽  
Wakana Fujita ◽  
Gregor J. Golabek ◽  
Michihiko Nakamura ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Numerical Simulations ◽  
Granular Media ◽  
Large Scale ◽  
Earth Science ◽  
Numerical Models ◽  
Effective Porosity ◽  
Flow Properties ◽  
Wide Range ◽  
Flow Through

Abstract. Fluid flow on different scales is of interest for several Earth science disciplines like petrophysics, hydrogeology and volcanology. To parameterize fluid flow in large-scale numerical simulations (e.g. groundwater and volcanic systems), flow properties on the microscale need to be considered. For this purpose experimental and numerical investigations of flow through porous media over a wide range of porosities are necessary. In the present study we sinter glass bead media with various porosities. The microstructure, namely effective porosity and effective specific surface, is investigated using image processing. We determine flow properties like hydraulic tortuosity and permeability using both experimental measurements and numerical simulations. By fitting microstructural and flow properties to porosity, we obtain a modified Kozeny-Carman equation for isotropic low-porosity media, that can be used to simulate permeability in large-scale numerical models. To verify the modified Kozeny-Carman equation we compare it to the computed and measured permeability values.

scholarly journals Microtomography-based numerical simulations of heat transfer and fluid flow through β -SiC open-cell foams for catalysis

2016 ◽  
Vol 278 ◽  
pp. 350-360 ◽  
Author(s):  
Xiaolei Fan ◽  
Xiaoxia Ou ◽  
Fei Xing ◽  
Glen A. Turley ◽  
Petr Denissenko ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Numerical Simulations ◽  
Open Cell ◽  
Flow Through ◽  
Open Cell Foams

Linking direct and continuum fluid flow models for fractured media: The intersection problem

2020 ◽  
Author(s):  
Maximilian O. Kottwitz ◽  
Anton A. Popov ◽  
Steffen Abe ◽  
Boris J. P. Kaus
Keyword(s):  
Fluid Flow ◽  
Numerical Simulations ◽  
Rock Masses ◽  
Fracture Networks ◽  
Direct Flow ◽  
Flow Models ◽  
Flow Simulations ◽  
Hydraulic Aperture ◽  
Continuum Flow ◽  
Equivalent Continuum

<p>Finding an adequate bridge between direct and continuum modeling approaches has been the fundamental issue of upscaling fluid flow in rock masses. Typically, numerical simulations of direct fluid flow (e.g. Stokes or Lattice-Boltzmann) in fractured or porous media serve as small-scale building blocks for larger-scale continuum flow simulations (e.g. Darcy). For fractured rock masses, the discrete-fracture-network (DFN) modeling approach is often used as an initial step to upscale flow properties by parameterizing the permeability of each fracture with its hydraulic aperture and solving steady-state flow equations within the fracture system. However, numerical simulations of Stokes flow in small fracture networks (FN) indicate that, depending on the orientation of the applied pressure gradient, fluid flow tends to localize at places where fractures intersect. This effect causes discrepancies between direct and equivalent continuum flow modeling approaches, which ought to be taken into account when modeling flow at the network scale.</p><p>In this study, we compare direct flow simulations of small fracture networks to their continuum representation obtained with several techniques in order to find an upscaling approach that takes these intersection effects into account. Direct flow simulations are conducted by solving the Stokes equations in 3D using our open-source finite-difference software LaMEM. Continuum flow simulations are realized with a newly developed parallel finite-element code, which solves fully anisotropic 3D Darcy flow with specific permeability tensors for each voxel. The direct flow simulations serve as benchmarks to optimize the continuum flow models by comparing resulting permeabilities. We tested two different schemes to generate the equivalent continuum representation: </p><p>(1) Fully resolved isotropic permeability discretizations (fracture permeability is obtained from a refined cubic law) where voxel sizes are a fraction of the minimal hydraulic aperture of the FN or</p><p>(2) coarse anisotropic permeability discretizations (permeability tensors are rotated according to fracture orientation) with voxel sizes larger than the minimal hydraulic aperture of the FN.</p><p>We then assess different scenarios to incorporate the intersection effects by adding, averaging and/or multiplying the permeabilities of the intersecting fractures within intersection voxels. Preliminary results for scheme 1 suggest that a simple addition of both intersecting fracture permeabilities delivers the best fit to the results of the direct flow simulations, if the voxel size is about 68% of the minimal hydraulic aperture. Scheme 2 systematically underestimates the direct flow permeabilities by about 26%.</p>

scholarly journals Experimental Study on Stress-Dependent Nonlinear Flow Behavior and Normalized Transmissivity of Real Rock Fracture Networks

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Qian Yin ◽  
Hongwen Jing ◽  
Richeng Liu ◽  
Guowei Ma ◽  
Liyuan Yu ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Rock Fracture ◽  
Hydraulic Gradient ◽  
Nonlinear Flow ◽  
Fracture Networks ◽  
Critical Hydraulic Gradient ◽  
Boundary Load ◽  
Flow Through ◽  
Stress Dependent ◽  
Rock Fracture Networks

The mechanism and quantitative descriptions of nonlinear fluid flow through rock fractures are difficult issues of high concern in underground engineering fields. In order to study the effects of fracture geometry and loading conditions on nonlinear flow properties and normalized transmissivity through fracture networks, stress-dependent fluid flow tests were conducted on real rock fracture networks with different number of intersections (1, 4, 7, and 12) and subjected to various applied boundary loads (7, 14, 21, 28, and 35 kN). For all cases, the inlet hydraulic pressures ranged from 0 to 0.6 MPa. The test results show that Forchheimer’s law provides an excellent description of the nonlinear fluid flow in fracture networks. The linear coefficient a and nonlinear coefficient b in Forchheimer’s law J=aQ+bQ2 generally decrease with the number of intersections but increase with the boundary load. The relationships between a and b can be well fitted with a power function. A nonlinear effect factor E=bQ2/(aQ+bQ2) was used to quantitatively characterize the nonlinear behaviors of fluid flow through fracture networks. By defining a critical value of E = 10%, the critical hydraulic gradient was calculated. The critical hydraulic gradient decreases with the number of intersections due to richer flowing paths but increases with the boundary load due to fracture closure. The transmissivity of fracture networks decreases with the hydraulic gradient, and the variation process can be estimated using an exponential function. A mathematical expression T/T0=1-exp⁡(-αJ-0.45) for decreased normalized transmissivity T/T0 against the hydraulic gradient J was established. When the hydraulic gradient is small, T/T0 holds a constant value of 1.0. With increasing hydraulic gradient, the reduction rate of T/T0 first increases and then decreases. The equivalent permeability of fracture networks decreases with the applied boundary load, and permeability changes at low load levels are more sensitive.

A Novel AFM Chip for Fountain Pen Nanolithography - Design and Microfabrication

2003 ◽  
Vol 782 ◽  
Author(s):  
Keun-Ho Kim ◽  
Nicolaie Moldovan ◽  
Changhong Ke ◽  
Horacio D. Espinosa
Keyword(s):  
Thin Films ◽  
Atomic Force Microscopy ◽  
Fluid Flow ◽  
Numerical Simulations ◽  
Gold Substrate ◽  
Force Microscopy ◽  
Atomic Force ◽  
Air Interface ◽  
Flow Through ◽  
Afm Probe

ABSTRACTA novel atomic force microscopy (AFM) probe has been developed to expand the capability and applications of dip-pen nanolithography (DPN) technology. This new probe has integrated microchannels and reservoirs for continuous ink feed, which allow “fountain-pen” writing called “Fountain Pen Nanolithography” (FPN). Ink is transported from the reservoirs through the microchannels and eventually dispensed onto substrates via a volcano-like dispensing tip. Numerical simulations have been performed to select optimal materials and suitable tip shapes providing a stable fluid-air interface in the tip. Microchannel and dispensing tip have been fabricated by surface micromachining, in particular employing 3 layers of thin films. Fluid flow through the microchannels has been experimentally examined. The probe was used to write on a gold substrate.

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