Light-Weight, Fast-Cycling, Shape-Memory Actuation Structures

2011 ◽  
Author(s):  
Aaron Stebner ◽  
Joseph Krueger ◽  
Anselm J. Neurohr ◽  
David C. Dunand ◽  
L. Catherine Brinson ◽  
...  
Keyword(s):  
Shape Memory ◽  
Surface Area ◽  
Numerical Study ◽  
Hot Isostatic Pressing ◽  
Milling Process ◽  
Constitutive Law ◽  
Micro Channel ◽  
Micro Channels ◽  
Increase Surface Area ◽  
Time Required

While bulk shape memory alloys (SMAs) have proven a successful means for creating adaptive aerospace structures in many demonstrations, including live flight tests, the time required to cool such actuators has been identified as a property that could inhibit their commercial implementation in some circumstances. To determine best practices for improving cooling times, several approaches to increase the surface area and reduce the mass of existing bulk actuator technologies have been examined. Specifically, geometries created using traditional milling and EDM techniques were compared with micro-channel geometries made possible by a new electrochemical milling process developed at Northwestern. The latter technique involves imbedding steel space-holders in a matrix of NiTi powders, hot isostatic pressing the preform into a dense composite, and then electro-chemically dissolving the steel. Thus, in a two-step process, it is possible to create an actuation structure with numerous micro-channels with excellent control of geometry, shape, size and placement, to reduce weight and increase surface area (and thus decrease response time) without compromising actuator performance. In this paper, the new, lighter-weight, faster cycling shape-memory alloy actuation structures resulting from each technique are reviewed. Their performances are compared and contrasted through the results of a numerical study conducted with a 3D SMA constitutive law developed specifically to handle the complex, non-proportional loadings that arise in porous structures. It is shown that using micro-channel technology, cooling times are significantly reduced relative to traditional machining techniques for the same amount of mass reduction.

Design Study of Shape Memory Alloy Honeycombs for Energy Absorption

2011 ◽  
Author(s):  
Ryan T. Watkins ◽  
John A. Shaw ◽  
Nicolas Triantafyllidis ◽  
David Grummon
Keyword(s):  
Shape Memory ◽  
Energy Absorption ◽  
Mechanical Response ◽  
Numerical Study ◽  
Honeycomb Structure ◽  
Constitutive Law ◽  
Large Strains ◽  
Design Study ◽  
Energy Absorbers ◽  
Absorption Characteristics

Shape memory alloys (SMA), which exhibit the shape memory effect and superelasticity, utilize a reversible solid-solid state phase transformation to recover large strains. Likewise, honeycomb structures under in-plane loading take advantage of deformation kinematics to amplify the structure’s macroscopic strain. The combination of a sparse honeycomb structure made of an SMA material can recover larger deformations than would be possible with either conventional metal honeycombs or monolithic SMAs. NiTi honeycombs and corrugations of about 5% relative density with robust properties were demonstrated recently [1]. Potential future applications include high performance energy absorbers, light-weight deployable devices, and high stroke actuators. This numerical study focuses on the design of superelastic SMA hexagonal honeycombs under in-plane compression for application to reusable energy absorbers. A design study with respect to honeycomb geometric parameters was performed to gain a better understanding of the geometric effects on energy absorption characteristics. A nonlinear finite element method was used to simulate their mechanical response using a hysteretic, trilinear, constitutive law to model the superelastic behavior of SMAs. Bloch wave analysis was used to evaluate the stability characteristics of the honeycomb structure. The corresponding energy absorption characteristics, under constraints of local strain limits, structural stability and allowable force levels, were evaluated to determine the optimum honeycomb geometries. It was found that diamond-like honeycombs, with greater height than width, had the best energy absorption properties.

scholarly journals A Numerical Study of Sub-Millisecond Integrated Mix-and-Inject Microfluidic Devices for Sample Delivery at Synchrotron and XFELs

2021 ◽  
Vol 11 (8) ◽  
pp. 3404
Author(s):  
Majid Hejazian ◽  
Eugeniu Balaur ◽  
Brian Abbey
Keyword(s):  
Molecular Dynamics ◽  
Flow Rate ◽  
Numerical Study ◽  
Three Dimensional ◽  
Microfluidic Devices ◽  
Liquid Jets ◽  
Mixing Efficiency ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Time Required

Microfluidic devices which integrate both rapid mixing and liquid jetting for sample delivery are an emerging solution for studying molecular dynamics via X-ray diffraction. Here we use finite element modelling to investigate the efficiency and time-resolution achievable using microfluidic mixers within the parameter range required for producing stable liquid jets. Three-dimensional simulations, validated by experimental data, are used to determine the velocity and concentration distribution within these devices. The results show that by adopting a serpentine geometry, it is possible to induce chaotic mixing, which effectively reduces the time required to achieve a homogeneous mixture for sample delivery. Further, we investigate the effect of flow rate and the mixer microchannel size on the mixing efficiency and minimum time required for complete mixing of the two solutions whilst maintaining a stable jet. In general, we find that the smaller the cross-sectional area of the mixer microchannel, the shorter the time needed to achieve homogeneous mixing for a given flow rate. The results of these simulations will form the basis for optimised designs enabling the study of molecular dynamics occurring on millisecond timescales using integrated mix-and-inject microfluidic devices.

Numerical study of capillary-driven flow in square micro-channel by lattice Boltzmann method

2019 ◽  
Vol 19 (1) ◽  
pp. 12
Author(s):  
Mohamed El Amine Ben Amara ◽  
Patrick Perré ◽  
Abdolreza Kharaghani ◽  
Sassi Ben Nasrallah
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Numerical Study ◽  
Micro Channel ◽  
Boltzmann Method

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

Experimental and Numerical Study of Methanol-Water Mixture Single-Phase Heat Transfer in a Micro-Channel Heat Sink

2012 ◽  
Author(s):  
Chun K. Kwok ◽  
Matthew M. Asada ◽  
Jonathan R. Mita ◽  
Weilin Qu
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Sink ◽  
Single Phase ◽  
Numerical Study ◽  
Pure Water ◽  
Molar Fraction ◽  
Water Mixture ◽  
Micro Channel ◽  
Numerical Predictions

This paper presents an experimental study of single-phase heat transfer characteristics of binary methanol-water mixtures in a micro-channel heat sink containing an array of 22 microchannels with 240μm × 630μm cross-section. Pure water, pure methanol, and five methanol-water mixtures with methanol molar fraction of 16%, 36%, 50%, 63% and 82% were tested. Key parametric trends were identified and discussed. The experimental study was complemented by a three-dimensional numerical simulation. Numerical predictions and experimental data are in good agreement with a mean absolute error (MAE) of 0.87%.

Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels

2006 ◽  
Author(s):  
Renqiang Xiong ◽  
J. N. Chung
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Micro Channel ◽  
Pressure Drops ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Shape And Size

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re<100. Those vortices appear and continue to develop with the Re number when Re> 100-300, and the shape and size of the vortices almost remain constant when Re>1000. The bend loss coefficient Kb was observed to be related with the Re number when Re<100, with the Re number and channel size when Re>100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.

Experimental Study on Roughness Effect for Laminar Micro-Channel Gas Flow

2001 ◽  
Author(s):  
Jih-Hsing Tu ◽  
Fangang Tseng ◽  
Ching-Chang Chieng
Keyword(s):  
Experimental Study ◽  
Surface Roughness ◽  
Friction Factor ◽  
Gas Flow ◽  
Micro Channel ◽  
Micro Machining ◽  
Roughness Effect ◽  
Relative Roughness ◽  
Smooth Channel ◽  
Micro Channels

Abstract Present study investigates the roughness effect on laminar gas flow for microchannels ranging from 40 to 600 μm with various roughness heights (40–82 nm) by systematical experiments. The micro-channels are manufactured by micro-machining technology and KOH anisotropic etching is employed to achieve various roughness patterns. Experimental results shows that higher product levels of Reynolds number (Reh) and friction factor (f) are obtained for microchannels of larger size and smaller relative roughness and friction factor f approaches to laminar flow theory value f0 for very smooth channel but the ratio of (f/f0) decreases as the surface roughness increases.

An Investigation on Micro Slip Flows in Micro Channels

2010 ◽  
Author(s):  
Gh. Reza Salehi ◽  
Masoud JalaliBidgoli ◽  
Saeed ZeinaliDanaloo ◽  
Kazem HasanZadeh
Keyword(s):  
Flow Rate ◽  
Pressure Ratio ◽  
Slip Flow ◽  
Accommodation Coefficient ◽  
Flow Rate Ratio ◽  
Numerical Representation ◽  
Micro Channel ◽  
Parallel Plates ◽  
Dimensionless Numbers ◽  
Micro Channels

In this paper, distributions of velocity and flow rate of micro channels are studied. Moreover, the parameters which influence them were also discussed, as well as their effects and relevant curves. In the Analytical study, the governing equation in specific micro flows is obtained. This equation is specifically investigated for slip flow in two micro parallel plates (micro channel).At the next step numerical representation shows the influence of the related parameters in micro channel flow such as Knudsen number, thermal -accommodation coefficient, mass flow rate ratio and pressure ratio (outlet to inlet), Tangential Momentum Accommodation Coefficient with relative curves, and flow rate distribution in slippery state to no slip state has been compared as the another part of this solution. Finally, the results of investigating parameters and dimensionless numbers in micro channels are reviewed.

A Study on the Strength under Pressure of Micro Heat Exchanger

2006 ◽  
Vol 326-328 ◽  
pp. 265-268
Author(s):  
Taek Joon Son ◽  
Young Shin Lee
Keyword(s):  
Stainless Steel ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Structural Analysis ◽  
Thin Plate ◽  
Thin Plates ◽  
Micro Channel ◽  
Design Guideline ◽  
Micro Heat Exchanger ◽  
Micro Channels

The strength of micro heat exchanger under pressure is studied in this paper. Micro heat exchanger is made with brazing technology. It is constructed of stainless steel thin plates with micro channels and in/out port for fluid flow. Micro channels in thin plates are formed by etching and all parts including thin plates are joined by brazing. The study on the strength under pressure is performed by structural analysis. For structural analysis, one layer of micro heat exchanger body is considered. It is composed of thin plate with micro channel and brazing filler which is used to join thin plates. This paper shows the tendency of stress behavior and gives design guideline of micro heat exchanger.

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