Simulation of Low Speed Gas Flow Over Backward Facing Step in Microchannels

2006 ◽  
Author(s):  
Umit Kursun ◽  
Jayanta S. Kapat
Keyword(s):  
Thermal Management ◽  
Gas Flow ◽  
Early Stage ◽  
Direct Simulation Monte Carlo ◽  
Backward Facing Step ◽  
Flow Process ◽  
Low Speed ◽  
Macro Scale ◽  
Early Stage Design ◽  
Real Flow

Proper design of thermal management solutions for future nano-scale electronics or photonics will require knowledge of flow and transport through micron-scale ducts. As in the macro-scale conventional counterparts, such micron-scale flow systems would require robust simulation tools for early-stage design iterations. This paper concentrates on such a flow process, namely pressure-driven gas flow over a backward facing step in a microchannel. A well-known particle-based method, Direct Simulation Monte Carlo (DSMC) is used as the simulation tool. Separating the macroscopic velocity from the molecular velocity through the use of the Information Preservation (IP) method eliminates the high-level of statistical noise as typical in DSMC calculations of low-speed flows. The non-isothermal IP method is further modified to incorporate the pressure boundary conditions, which are expected to be more prevalent in design of thermal management systems. The applicability of the method in solving a real flow situation is verified using the backward facing step flow in a micro geometry. The flow and heat transfer mechanisms at different pressures in Knudsen transient regime are investigated. The range of parameters for this investigation are: Re from 0.03 to 0.64, Ma from 0.013 to 0.083, and Kn from 0.24 to 4.81, all based on maximum values.

scholarly journals Impact of Heterogeneity on the Transient Gas Flow Process in Tight Rock

Energies ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 3559 ◽  
Author(s):  
Jia ◽  
Tsau ◽  
Barati ◽  
Zhang
Keyword(s):  
History Matching ◽  
Gas Flow ◽  
Preferential Flow ◽  
Early Stage ◽  
Ideal Gas ◽  
Flow Path ◽  
Flow Process ◽  
The Core ◽  
Porosity And Permeability ◽  
Preferential Flow Path

There exits a great challenge to evaluate the flow properties of tight porous media even at the core scale. A pulse-decay experiment is routinely used to measure the petrophysical properties of tight cores including permeability and porosity. In this study, 5 sets of pulse-decay experiments are performed on a tight heterogeneous core by flowing nitrogen in the forward and backward directions under different pressures under pore pressures approximately from 100 psi to 300 psi. Permeability values from history matching are from about 300 nD to 600 nD which shows a good linear relationship with the inverse of pore pressure. A preferential flow path is found even when the microcrack is absent. The preferential path causes different porosity values using differential initial upstream and downstream pressure. In addition, the porosity values calculated based on the forward and backward flow directions are also different, and the values are about 1.0% and 2.3%, respectively, which is the primary novelty of this study. The core heterogeneity effect significantly affects the very early stage of pressure responses in both the upstream and downstream but the permeability values are very close in the late-stage experiment. We proposed that that there are two reasons for the preferential flow path: the Joule–Thomson effect for non-ideal gas and the core heterogeneity effect. Based on the finding of this study, we suggest that very early pressure response in a pulse-decay experiment should be closely examined to identify the preferential flow path, and failure to identify the preferential flow path leads to significant porosity and permeability underestimation.

scholarly journals Development of an Efficient Particle Approach for Micro-Scale Gas Flow Simulations

2009 ◽  
Author(s):  
Quanhua Sun ◽  
Feng Li ◽  
Jing Fan ◽  
Chunpei Cai
Keyword(s):  
Cell Size ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Gas Flows ◽  
Dsmc Method ◽  
Low Speed ◽  
Micro Scale ◽  
Information Preservation ◽  
Cfd Method

The micro-scale gas flows are usually low-speed flows and exhibit rarefied gas effects. It is challenging to simulate these flows because traditional CFD method is unable to capture the rarefied gas effects and the direct simulation Monte Carlo (DSMC) method is very inefficient for low-speed flows. In this study we combine two techniques to improve the efficiency of the DSMC method. The information preservation technique is used to reduce the statistical noise and the cell-size relaxed technique is employed to increase the effective cell size. The new cell-size relaxed IP method is found capable of simulating micro-scale gas flows as shown by the 2D lid-driven cavity flows.

scholarly journals DSMC Simulation of Rarefied Gas Flow over a Backward- Facing Step: Effect of Expansion ratio

2019 ◽  
Author(s):  
Deepak Nabapure ◽  
Pratijay Guha ◽  
K Ram Chandra Murthy
Keyword(s):  
Flow Field ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Expansion Ratio ◽  
Backward Facing Step ◽  
Rarefied Flow ◽  
Step Effect ◽  
Dsmc Simulation ◽  
Limiting Case

Numerical simulations have been performed to study the effect of expansion ratio on the hypersonic rarefied flow past a backward-facing step. The Direct Simulation Monte Carlo (DSMC) method is used for the present study. An opensource solver named dsmcFoam has been used for this purpose. The solver has been validated with well-established results from the literature and good agreement is found among them. Simulations have been carried out for expansion ratios (ER) of 2,4,6,8,10 in the transition regime. The different flow field properties such as velocity, pressure and temperature have been studied. The profiles have found to be influenced by the compressibility and rarefaction effects. Limiting case of ER=8 and above has no influence on the flow field properties.

scholarly journals Investigation of Subsonic and Hypersonic Rarefied Gas Flow Over a Backward Facing Step

2019 ◽  
Author(s):  
Deepak Nabapure ◽  
Jayesh Sanwal ◽  
Sreeram Rajesh ◽  
K Ram Chandra Murthy
Keyword(s):  
Mach Number ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Flow Characteristics ◽  
Direct Simulation Monte Carlo ◽  
Primary Objective ◽  
Gas Flows ◽  
Backward Facing Step ◽  
Rarefied Gas Flows ◽  
Velocity Pressure

In the present study the Direct Simulation Monte Carlo (DSMC) method, which is one of most the widely used numerical methods to study the rarefied gas flows, is applied to investigate the flow characteristics of a hypersonic and subsonic flow over a backward-facing step. The work is driven by the interest in exploring the effects of the Mach number on the flow behaviour. The primary objective of this paper is to study the variation of velocity, pressure, and temperature with Mach number. The numerical tool is validated with well-established results from the literature and a good agreement is found among them. The flow is analyzed and some comments on the characteristics of the flow are also added.

scholarly journals A COMPARISON OF STRUCTURED LIGHT SCANNING AND PHOTOGRAMMETRY FOR THE DIGITISATION OF PHYSICAL PROTOTYPES

2021 ◽  
Vol 1 ◽  
pp. 11-20
Author(s):  
Owen Freeman Gebler ◽  
Mark Goudswaard ◽  
Ben Hicks ◽  
David Jones ◽  
Aydin Nassehi ◽  
...  
Keyword(s):  
Early Stage ◽  
Structured Light ◽  
Superior Performance ◽  
Specific Design ◽  
Model Quality ◽  
Stage Design ◽  
Design Changes ◽  
Structured Light Scanning ◽  
Early Stage Design

AbstractPhysical prototyping during early stage design typically represents an iterative process. Commonly, a single prototype will be used throughout the process, with its form being modified as the design evolves. If the form of the prototype is not captured as each iteration occurs understanding how specific design changes impact upon the satisfaction of requirements is challenging, particularly retrospectively.In this paper two different systems for digitising physical artefacts, structured light scanning (SLS) and photogrammetry (PG), are investigated as means for capturing iterations of physical prototypes. First, a series of test artefacts are presented and procedures for operating each system are developed. Next, artefacts are digitised using both SLS and PG and resulting models are compared against a master model of each artefact. Results indicate that both systems are able to reconstruct the majority of each artefact's geometry within 0.1mm of the master, however, overall SLS demonstrated superior performance, both in terms of completion time and model quality. Additionally, the quality of PG models was far more influenced by the effort and expertise of the user compared to SLS.

Study on the Deposition Profile Characteristics in the Micron-Scale Trench Using Direct Simulation Monte Carlo Method

1998 ◽  
Vol 120 (2) ◽  
pp. 296-302 ◽  
Author(s):  
Masato Ikegawa ◽  
Jun’ichi Kobayashi ◽  
Morihisa Maruko
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Boundary Conditions ◽  
Gas Flow ◽  
Direct Simulation Monte Carlo ◽  
Low Pressure ◽  
Sputter Deposition ◽  
Direct Simulation ◽  
Simulation Monte Carlo ◽  
Profile Characteristics

As integrated circuits are advancing toward smaller device features, step-coverage in submicron trenches and holes in thin film deposition are becoming of concern. Deposition consists of gas flow in the vapor phase and film growth in the solid phase. A deposition profile simulator using the direct simulation Monte Carlo method has been developed to investigate deposition profile characteristics on small trenches which have nearly the same dimension as the mean free path of molecules. This simulator can be applied to several deposition processes such as sputter deposition, and atmospheric- or low-pressure chemical vapor deposition. In the case of low-pressure processes such as sputter deposition, upstream boundary conditions of the trenches can be calculated by means of rarefied gas flow analysis in the reactor. The effects of upstream boundary conditions, molecular collisions, sticking coefficients, and surface migration on deposition profiles in the trenches were clarified.

Diabatic Nozzle Flow with Constant Small Stage Efficiency

1960 ◽  
Vol 64 (598) ◽  
pp. 632-635 ◽  
Author(s):  
R. A. A. Bryant
Keyword(s):  
Gas Flow ◽  
Nozzle Flow ◽  
Flow Conditions ◽  
One Dimensional ◽  
Real Flow ◽  
Stage Efficiency ◽  
Frictional Effects

The concept of small stage efficiency is introduced when studying one-dimensional gas flow in nozzles in order to permit a closer approximation of real flow conditions than is possible from an isentropic analysis. It is more or less conventional to assume the flow conditions are adiabatic whenever the small stage efficiency is used. That is to say, small stage efficiency is generally considered in relation to flows contained within adiabatic boundaries, in which case it becomes a measure of the heat generated by internal frictional effects alone.

Mixing Enhancement of Two Gases in a Microchannel Using DSMC

2013 ◽  
Vol 307 ◽  
pp. 166-169 ◽  
Author(s):  
Masoud Darbandi ◽  
Elyas Lakzian
Keyword(s):  
Gas Flow ◽  
Flow Analysis ◽  
Direct Simulation Monte Carlo ◽  
Equilibrium Composition ◽  
Mass Composition ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Result Section ◽  
Flow Through ◽  
Simulation Monte Carlo

Microgas flow analysis may not be performed accurately using the classical CFD methods because of encountering high Knudsen number regimes. Alternatively, the gas flow through micro-geometries can be investigated reliably using the direct simulation Monte Carlo (DSMC) method. Our concern in this paper is to use DSMC to study the mixing of two gases in a microchannel. The mixing process is assumed to be complete when the mass composition of each species deviates by no more than ±1% from its equilibrium composition. To enhance the mixing process, we focus on the effects of inlet-outlet pressure difference and the pressure ratios of the incoming CO and N2 streams on the mixing enhancement. The outcome of this study is suitably discussed in the result section.

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