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The use of rapid prototyping techniques (RPT) to manufacture micro channels suitable for high operation pressures and μPIV
Abstract
Purpose
– This paper aims to present a new methodology to manufacture micro-channels suitable for high operating pressures and micro particle image velocimetry (μPIV) measurements using a rapid-prototyping high-resolution 3D printer. This methodology can fabricate channels down to 250 μm and withstand pressures of up to 5 ± 0.2 MPa. The manufacturing times are much shorter than in soft lithography processes.
Design/methodology/approach
– The novel manufacturing method developed takes advantage of the recently improved resolution in 3D printers to manufacture an rapid prototyping technique part that contains the hose connections and a micro-channel useful for microfluidics. A method to assemble one wall of the micro-channel using UV curable glue with a glass slide is presented – an operation required to prepare the channel for μPIV measurements. Once built, the micro-channel has been evaluated when working under pressure and the grease flow behavior in it has been measured using μPIV. Furthermore, the minimum achievable channels have been defined using a confocal microscopy study.
Findings
– This technique is much faster than previous micro-manufacturing techniques where different steps were needed to obtain the micro-machined parts. However, due to current 3D printers ' resolutions (around 50 μm) and according to the experimental results, channels smaller than 250-μm2 cross-section should not be used to characterize fluid flow behaviors, as inaccuracies in the channel boundaries can deeply affect the fluid flow behavior.
Practical implications
– The present methodology is developed due to the need to validate micro-channels using μPIV to lubricate critical components (bearings and gears) in wind turbines.
Originality/value
– This novel micro-manufacturing technique overcomes current techniques, as it requires less manufacturing steps and therefore it is faster and with less associated costs to manufacture micro-channels down to 250-μm2 cross-section that can withstand pressures higher than 5 MPa that can be used to characterize microfluidic flow behavior using μPIV.
... For their developed work, Yang et al. [25] performed the comparative study and found good agreement between predicted and existing model. The use of AM in micro-manufacturing technique has been presented by Farré-Lladós et al. [26] as shown in Fig. 18. Their developed process shows that AM can manufacture micro-channels much faster than previous micro-manufacturing techniques. ...
... Luo et al. [28] have been demonstrated mechanical properties, microstructure and deposition behaviour of cold sprayed built parts. By using their developed in-situ [26] micro-forging-assisted CS approach they are able to improve porosity as compared to conventional CS by virtue of which they were able to improve mechanical properties as shown in Fig. 20. Klein et al. [29] have demonstrated the application of AM in the layer-by-layer fabrication of optically transparent glass as shown in Fig. 21. ...
... (a) Solar-powered 3D printer [33] (b) Pressure housing [34] (c) GEnxt engine [36] (d) 3D printed small jet engine [35] (e) Printed Pneuflex actuator [37] (f) Bitblox printed Infrared remote controller [38] (g) 3D Printed Li-Ion battery [39] (h) Soft robot built by 3D printing [40] Fig. 26 List of distinguished AM/3D printing applications ...
Additive manufacturing (AM) becomes the successful commercial technology because of the interdisciplinary applications of this technology in different sectors. This review paper categorises the interdisciplinary applications of AM into three different sectors as prototyping, rapid tooling and direct part production. Each application sectors provide reviews on how normally AM processes have been adopted, albeit how and why they are utilised has also been presented. In this paper, sufficiently novel and important observations have been presented which include AM fabricated metamaterial, microelectrode arrays, micro-channel, mesoscale burner, marine parts, monolith structures, biofuel microstructured and assembly with photovoltaic. In this way, the present approach provides significant insights into different additive manufacturing application sectors. In addition, to provide an overall view, interdisciplinary applications listed in the current study are sufficiently adequate for a review in terms of number of research works considered from the literature and various resources available in the public domain. The current research also shows that the AM can provide future scope in different fields such as cold spray, direct fabrication of electromechanical devices on the macroscale, radio-frequency structures and similar applications.
... Microfluidic technology has developed rapidly over the past few decades. Opticaldriven microfluidic motion has always been a hot issue in the field of microfluidics (Kotz et al., 2004;Psaltis et al., 2006;Lamhot et al., 2009;Delville et al., 2009;Park et al., 2010;Baigl, 2012;Kumari et al., 2012;Wu et al., 2012;Xu et al., 2013;Farré-Llad os et al., 2016). Because of the characteristics of "small size and slow speed" of microfluidics, the Reynolds number is low, and the viscous force and surface tension play a dominant role instead of inertial force. ...
Purpose
The purpose of this study is to use a weak light source with spatial distribution to realize light-driven fluid by adding high-absorbing nanoparticles to the droplets, thereby replacing a highly focused strong linear light source acting on pure droplets.
Design/methodology/approach
First, Fe 3 O 4 nanoparticles with high light response characteristics were added to the droplets to prepare nanofluid droplets, and through the Gaussian light-driven flow experiment, the Marangoni effect inside a nanofluid droplet was studied, which can produce the surface tension gradient on the air/liquid interface and induce the vortex motion inside a droplet. Then, the numerical simulation method of multiphysics field coupling was used to study the effects of droplet height and Gaussian light distribution on the flow characteristics inside a droplet.
Findings
Nanoparticles can significantly enhance the light absorption, so that the Gaussian light is enough to drive the flow, and the formation of vortex can be regulated by light distribution. The multiphysics field coupling model can accurately describe this problem.
Originality/value
This study is helpful to understand the flow behavior and heat transfer phenomenon in optical microfluidic systems, and provides a feasible way to construct the rapid flow inside a tiny droplet by light.
... The channel was made using VeroWhitePlus RGD835 (polymeric material from Stratsys, Eden Prairie, MN, USA) manufactured using a 3D printer from Stratasys, model Object 30. The process to seal the channel was as per Farre-Llados et al. [16]. ...
In this paper, the flow dynamics of polymer greases was investigated using micro-particle image velocimetry. Polymer greases have a different thickener structure, compared to widely used lithium-based greases, and they have the well-known ability to release oil. How these properties affect grease deformation and its ability to flow is investigated and compared to the corresponding behavior of a lithium complex grease with the same consistency. Two main tests were carried out, where velocity profiles in a straight channel were measured and analyzed, and velocity evolution during the transition period from a no-flow to a fully-established flow was measured, respectively. It was found that the polymer grease flow dynamics is different from that of the lithium grease. This indicates that the internal structure of the grease and the grease ability to bleed oil have a strong influence on the deformation on a global scale, which in turn entails other lubricating abilities for the two grease types.
... Multi-material printing aspects are considered for design innovations Electrochemical applications (Ambrosi and Pumera, 2016;Bakker 2006;Vaezi, 2013;Ivanova et al., 2013;Hirt et al., 2017) Three-dimensional printing of metal electrodes such as platinum, conductive copper, and gold electrodes is challenging Mostly layering metal using cost-effective means needs more research and prototypes Sample handling with oxidation and reduction potentials is of significance Integrated reaction wares with software for chemical processing and printing is yet to evolve Printing conditions for process specific variables, conditions require a framework Complex design methodologies are in place. Prototypes are not yet commercialized like seen for other few sensing products Microfluidic applications (Macdonald et al., 2014;Yazdi et al., 2017;Farré-Llad os et al., 2016) PDMS molding for post-treatment is tough. Variations in AM processes are required often. ...
Purpose-The purpose of this paper is to describe, review, classify and analyze the current challenges in three-dimensional printing processes for combined electrochemical and microfluidic fabrication areas, which include printing devices and sensors in specified areas. Design/methodology/approach-A systematic review of the literature focusing on existing challenges is carried out. Focused toward sensors and devices in electrochemical and microfluidic areas, the challenges are oriented for a discussion exploring the suitability of printing varied geometries in an accurate manner. Classifications on challenges are based on four key categories such as process, material, size and application as the printer designs are mostly based on these parameters. Findings-A key three-dimensional printing process methodologies have their unique advantages compared to conventional printing methods, still having the challenges to be addressed, in terms of parameters such as cost, performance, speed, quality, accuracy and resolution. Three-dimensional printing is yet to be applied for consumer usable products, which will boost the manufacturing sector. To be specific, the resolution of printing in desktop printers needs improvement. Printing scientific products are halted with prototyping stages. Challenges in three-dimensional printing sensors and devices have to be addressed by forming integrated processes. Research limitations/implications-The research is underway to define an integrated process-based on three-dimensional Printing. The detailed technical details are not shared for scientific output. The literature is focused to define the challenges. Practical implications-The research can provide ideas to business on innovative designs. Research studies have scope for improvement ideas. Social implications-Review is focused on to have an integrated three-dimensional printer combining processes. This is a cost-oriented approach saving much of space reducing complexity. Originality/value-To date, no other publication reviews the varied three-dimensional printing challenges by classifying according to process, material, size and application aspects. Study on resolution based data is performed and analyzed for improvements. Addressing the challenges will be the solution to identify an integrated process methodology with a cost-effective approach for printing macro/micro/nano objects and devices.
... In the meantime, additive manufacturing (AM) has spread widely due to its flexibility, suitability, and being user friendly [1]. Examples include the complex geometric parts (difficult to make by traditional subtractive methods), biomedical parts requiring customization [2], micro-channels suitable for high operating pressures and micro-particle image velocimetry [3], orthoses [4], medical rapid prototyping-assisted customized surgical guides to improve the accuracy of complex surgeries [5], multi-body structures and non-assembly mechanisms [6][7][8], etc. Hence, developing a mechanism manufactured by AM technology to convert a rotary motion to a linear motion is attractive for application such as capsule robots [9] which need a customized and miniaturized actuation mechanism. ...
This paper focuses on the development of a 3D-printed threadless ball screw (TLBS) for the applications that require miniaturization, customization, and accuracy controllability. To enhance the efficiency of the TLBS, a novel model of the TLBS for analyzing the mechanical efficiency is presented to obtain the key affecting factors. From these factors, the design parameters for fabrication are determined. For miniaturization, a novel 3D-printed one-piece preloaded structure of light weight of 0.9 g is implemented as the TLBS nut part. Experimental results show that the measured mechanical efficiency of TLBS is close to that predicted by the theoretical model with a normalized root mean square error of 3.16%. In addition, the mechanical efficiency of the present TLBS (maximum efficiency close to 90%) is better than that of the lead screw and close to the ball screw. The unique characteristic of the present TLBS is that its total torque loss is a weak function of the load, a phenomenon not observed in either the ball screw or the lead screw. This characteristic is advantageous in enhancing the controllability of accuracy at different loads.
... Multi-material printing aspects are considered for design innovations Electrochemical applications (Ambrosi and Pumera, 2016;Bakker 2006;Vaezi, 2013;Ivanova et al., 2013;Hirt et al., 2017) Three-dimensional printing of metal electrodes such as platinum, conductive copper, and gold electrodes is challenging Mostly layering metal using cost-effective means needs more research and prototypes Sample handling with oxidation and reduction potentials is of significance Integrated reaction wares with software for chemical processing and printing is yet to evolve Printing conditions for process specific variables, conditions require a framework Complex design methodologies are in place. Prototypes are not yet commercialized like seen for other few sensing products Microfluidic applications (Macdonald et al., 2014;Yazdi et al., 2017;Farré-Llad os et al., 2016) PDMS molding for post-treatment is tough. Variations in AM processes are required often. ...
Purpose
The purpose of this paper is to describe, review, classify and analyze the current challenges in three-dimensional printing processes for combined electrochemical and microfluidic fabrication areas, which include printing devices and sensors in specified areas.
Design/methodology/approach
A systematic review of the literature focusing on existing challenges is carried out. Focused toward sensors and devices in electrochemical and microfluidic areas, the challenges are oriented for a discussion exploring the suitability of printing varied geometries in an accurate manner. Classifications on challenges are based on four key categories such as process, material, size and application as the printer designs are mostly based on these parameters.
Findings
A key three-dimensional printing process methodologies have their unique advantages compared to conventional printing methods, still having the challenges to be addressed, in terms of parameters such as cost, performance, speed, quality, accuracy and resolution. Three-dimensional printing is yet to be applied for consumer usable products, which will boost the manufacturing sector. To be specific, the resolution of printing in desktop printers needs improvement. Printing scientific products are halted with prototyping stages. Challenges in three-dimensional printing sensors and devices have to be addressed by forming integrated processes.
Research limitations/implications
The research is underway to define an integrated process-based on three-dimensional Printing. The detailed technical details are not shared for scientific output. The literature is focused to define the challenges.
Practical implications
The research can provide ideas to business on innovative designs. Research studies have scope for improvement ideas.
Social implications
Review is focused on to have an integrated three-dimensional printer combining processes. This is a cost-oriented approach saving much of space reducing complexity.
Originality/value
To date, no other publication reviews the varied three-dimensional printing challenges by classifying according to process, material, size and application aspects. Study on resolution based data is performed and analyzed for improvements. Addressing the challenges will be the solution to identify an integrated process methodology with a cost-effective approach for printing macro/micro/nano objects and devices.
... Hydraulics, and components that benefit from internal flow optimization in general, are a common application of redesign for AM in the literature. [61]. In addition, AM is much used in the improvement of cooling channels in moulds and other components that heat up. ...
The progression of additive manufacturing—from being limited to producing prototypes to being a valuable technology in producing end-use components—has been noted by many researchers and companies. Nevertheless, the industrial opportunities of this progress are not clear to new users of the technology because the number of end-use applications for additive manufacturing is vast and growing rapidly. The major advantages of using additive manufacturing lie in the increased freedom of design and the possibility to produce components that have previously been impractical. On the other hand, additive manufacturing can also be used in situations where the component does not benefit from the additional design freedom. In such cases, the advantage of using additive manufacturing must come from operational benefits, such as improved delivery speed or cheaper manufacturing cost.
To clarify the opportunities, the thesis proposes categorizing the end-use applications from the point of view of design into "components designed for additive manufacturing", "components redesigned for additive manufacturing", and "components not designed for additive manufacturing". Each of these categories has their use in industrial applications and can help achieve specific technical and operational benefits. In the thesis, the categories are provided with design workflows that draw from the design process of Pahl & Beitz and are augmented with relevant previous research from the field of design for additive manufacturing.
To investigate the industrial opportunities in the form of technical and operational advantages of the categories, the thesis demonstrates the use of the categories and their workflows by providing a case study for each. In the case studies, the design process of the components is demonstrated with the help of the developed design workflows, and the technical and operational benefits of each component are evaluated. The case studies of the categories involve the design of a novel highperformance heat exchanger, the redesign of a digital hydraulic valve manifold, and the production of a memory cover for use in the repair of a portable computer. In addition, the thesis contains a focus group study in the category "components not designed for additive manufacturing" to discover in which scenarios it could be employed.
In the final section of the thesis, the technical and operational advantages of using additive manufacturing in each of the categories are collected and presented. The main technical advantages discovered in the investigations were the creation of new functionalities and improvement of performance, and the main operational benefits were the simplification of supply chains and shorter repairs. The thesis gives researchers in the field of design for additive manufacturing a framework to communicate their findings in a way that can be understood easily by practitioners not previously intimately familiar with designing for additive manufacturing.
... Recently, 3D printing technology has experienced a rapid development owing to their capability of producing 3D objects directly from computer models (Kulkarni et al., 2000;MacDonald and Wicker, 2016), and is widely used in microfluidics (Farré-Llad os et al., 2016;Wang et al., 2017;Yazdi et al., 2016), flexible electronic devices (Zarek et al., 2016), tissue engineering (Bourzac, 2017;Tarik-Arafat et al., 2014), clinical medicine (Naftulin et al., 2015;Gibson et al., 2006) and automotive and aerospace industries (Cheng and Lai, 2008;Ehud and Dror, 2011;Joshi and Sheikh, 2015). In traditional stereolithography apparatus (SLA) process, 3D objects are produced by selectively solidifying photo-curable resin in a layer-by-layer manner Kataria and Rosen, 2001;Zhang et al., 1999). ...
Purpose
The purpose of this paper is to explore the possibility of an enhanced continuous liquid interface production (CLIP) with a porous track-etched membrane as the oxygen-permeable window, which is prepared by irradiating polyethylene terephthalate membranes with accelerated heavy ions.
Design/methodology/approach
Experimental approaches are carried out to characterize printing parameters of resins with different photo-initiator concentrations by a photo-polymerization matrix, to experimentally observe and theoretically fit the oxygen inhibition layer thickness during printing under conditions of pure oxygen and air, respectively, and to demonstrate the enhanced CLIP processes by using pure oxygen and air, respectively.
Findings
Owing to the high permeability of track-etched membrane, CLIP process is demonstrated with printing speed up to 800 mm/h in the condition of pure oxygen, which matches well with the theoretically predicted maximum printing speed at difference light expose. Making a trade-off between printing speed and surface quality, maximum printing speed of 470 mm/h is also obtained even using air. As the oxygen inhibition layer created by air is thinner than that by pure oxygen, maximum speed cannot be simply increased by intensifying the light exposure as the case with pure oxygen.
Originality/value
CLIP process is capable of building objects continuously instead of the traditional layer-by-layer manner, which enables tens of times improvement in printing speed. This work presents an enhanced CLIP process by first using a porous track-etched membrane to serve as the oxygen permeable window, in which a record printing speed up to 800 mm/h using pure oxygen is demonstrated. Owing to the high permeability of track-etched membrane, continuous process at a speed of 470 mm/h is also achieved even using air instead of pure oxygen, which is of significance for a compact robust high-speed 3D printer.
... In the present study, a curved 250×1000 µm 2 micro-channel manufactured based on the process presented in Farré-Lladós et al. [16] was used (see Fig. 4(a)). The channels had a mini- [15]. ...
... In the present study, a curved 250×1000 µm 2 micro-channel manufactured based on the process presented in Farré-Lladós et al. [16] was used (see Fig. 4(a)). The channels had a mini- [15]. ...
The increase of power generated by wind turbines has increased the stresses applied in all of its parts, which causes the appearance of premature failures. In particular, pitch and yaw gears suffer of excessive wear, mainly due to inappropriate lubrication. This paper presents a novel method to automatically lubricate the wind turbine pitch gear during operation. A micro-nozzle to continuously inject fresh grease between the teeth in contact was designed, manufactured and installed in a test bench of a 2 MW wind turbine pitch system. The test bench was used to characterize the fatigue behavior of the gear surface using conventional wind turbine greases under real cyclic loads. The measurements of wear evolution in a pitch gear with and without micro-nozzle show a decrease of 70% of the wear coefficient after 2x104 cycles.
... In the present study, a curved 250×1000 µm 2 micro-channel manufactured based on the process presented in Farré-Lladós et al. [16] was used (see Fig. 4(a)). The channels had a mini- [15]. ...
... Fig. 3b shows the 3D model of the RPT part and Fig. 4 the steps followed to manufacture the micro-channel. More details about the 3D printing operation to build the present channels can be found in the paper by Farré et al. [11]. Fig. 1 shows a schematic drawing of the micro-channel and the locations where the µPIV measurements have been performed in the straight section and the elbow. ...
The flow of lubricating greases in an elbow channel have been modeled
and validated with velocity profiles from flow visualizations using micro
Particle Image Velocimetry. The elbow geometry induce a non-symmetric distribution
of shear stress throughout its cross section, as well as varying shear
rates through the transition from the elbow inlet to the outlet. The flow has
been modeled both for higher flow rates and for creep flow. The influence of
the grease rheology and flow conditions to wall slip, shear banding and an
observed stick-slip type of motion observed for low flow rates are presented.
The effect on the flow of the applied pressure is also modeled showing that
the flow is sensitive to the pressure in the angular (ϕ) direction of the elbow.
For high pressures it is shown that the flow is reversed adjacent to the elbow
walls.
... Fig. 3b shows the 3D model of the RPT part and Fig. 4 the steps followed to manufacture the micro-channel. More details about the 3D printing operation to build the present channels can be found in the paper by Farré et al. [11]. Fig. 1 shows a schematic drawing of the micro-channel and the locations where the µPIV measurements have been performed in the straight section and the elbow. ...
The flow of lubricating greases in an elbow channel has been modeled and validated with velocity profiles from flow visualizations using micro-particle image velocimetry. The elbow geometry induces a nonsymmetric distribution of shear stress throughout its cross section, as well as varying shear rates through the transition from the elbow inlet to the outlet. The flow has been modeled both for higher flow rates and for creep flow. The influence of the grease rheology and flow conditions to wall slip, shear banding and an observed stick–slip type of motion observed for low flow rates are presented.
The effect on the flow of the applied pressure is also modeled showing that the flow is sensitive to the pressure in the angular () direction of the elbow. For high pressures, it is shown that the flow is reversed adjacent to the elbow walls.
Both stereolithographic printing of microfluidics and inkjet printing of electronics are promising tools for the fabrication of lab‐on‐a‐chip devices. However, the combination of these two technologies has been a challenge so far, as the 3D‐printed components usually have to be bonded manually to the substrates functionalized with printed electronics. Here, a surface modification method is demonstrated for enabling the direct stereolithographic printing of microfluidic structures onto a variety of different substrates that are usually employed for printed electronics. The approach makes use of an acrylate‐terminated silane that covalently binds substrate and polymer network of the 3D print. The bonding strength is quantified and the compatibility of the concept with printed electrodes in a microfluidic channel is evaluated.
A critical feature of state-of-the-art microfluidic technologies is the ability to fabricate multilayer structures without relying on the expensive equipment and facilities required by soft lithography-defined processes. Here, three-dimensional (3D) printed polymer molds are used to construct multilayer poly(dimethylsiloxane) (PDMS) devices by employing unique molding, bonding, alignment, and rapid assembly processes. Specifically, a novel single-layer, two-sided molding method is developed to realize two channel levels, non-planar membranes/valves, vertical interconnects (vias) between channel levels, and integrated inlet/outlet ports for fast linkages to external fluidic systems. As a demonstration, a single-layer membrane microvalve is constructed and tested by applying various gate pressures under parametric variation of source pressure, illustrating a high degree of flow rate control. In addition, multilayer structures are fabricated through an intralayer bonding procedure that uses custom 3D-printed stamps to selectively apply uncured liquid PDMS adhesive only to bonding interfaces without clogging fluidic channels. Using integrated alignment marks to accurately position both stamps and individual layers, this technique is demonstrated by rapidly assembling a six-layer microfluidic device. By combining the versatility of 3D printing while retaining the favorable mechanical and biological properties of PDMS, this work can potentially open up a new class of manufacturing techniques for multilayer microfluidic systems.
There have been numerous reviews that focus on the use of microfluidic devices prepared with such materials as polydimethyl siloxane (PDMS), thermoplastics, and glass using soft lithography, hot embossing, micromilling, and injection molding fabrication techniques.1-4 The additive manufacturing or 3-dimensional (3D) printing process provides many advantages compared to the aforementioned techniques, including one-step production of complex multimaterial designs, decreased fabrication time, the ability to integrate a variety of components, and an ever increasing material pool. 3D printing encompasses stereolithography (SLA), selective laser sintering (SLS), inkjet and polyjet printing, fused deposition modeling (FDM), laminated object manufacturing (LOM), and direct printing (metal and bioprinting) technologies. In academic labs, 3D printing is now commonly viewed as a means to obtain a final product, as opposed to an exclusively prototyping tool. For these reasons, 3D printing has emerged as a popular fabrication tool for a variety of disciplines.5 This popularity is evidenced in the diversity of recent articles where 3D printing has found application; including electrochemical,6 tissue engineering,7 biological,8 microfluidics and lab-on-a-chip,9,10 medicine,11 custom labware,12 and environmental studies.13 With decreased printer and material costs, 3D printers are becoming commonplace in analytical laboratories. This review highlights 3D printing techniques and applications in analytical and biochemical science, with an emphasis on research emerging in the last two years.
Grease is extensively used to lubricate various machine elements such as rolling bearings, seals, and gears. Understanding the flow dynamics of grease is relevant for the prediction of grease distribution for optimum lubrication and for the migration of wear and contaminant particles. In this study, grease flow is visualized using microparticle image velocimetry (μPIV). The experimental setup includes a concentric cylinder configuration with a rotating shaft to simulate the grease flow in a double restriction seal geometry with two different grease pocket sizes. It is shown that the grease is partially yielded in the large grease pocket geometry and fully yielded in the small grease pocket. For the small grease pocket, it is shown that three distinct grease flow layers are present: a high shear rate region close to the stationary wall, a bulk flow layer, and a high shear rate boundary region near the rotating shaft. The grease shear thinning behavior and its wall slip effects have been identified. The μPIV experimental results have been compared with a numerical model for both the large and small gap size. It is shown that the flow is close to one-dimensional in the center of the small pocket. A one-dimensional analytical model based on the Herschel-Bulkley rheology model has been developed, showing good agreement with the measured velocity profiles in the small grease pocket. Furthermore, wall slip effects and shear banding are observed, where the latter imply that using the assumption of uniform shear in conventional concentric cylinder rheometers may result in erroneous rheological results.
In this work we characterize a novel possibility for PDMS (PolyDiMethylSiloxane) casting/ micromolding methods with the utilization of molding forms fabricated by a commercially available novel acrylic photopolymer based 3D printing method. The quality and absolute spatial accuracy of 1) different 3D printing modes (‘matt’ vs. ‘glossy’); 2) the molded PDMS structures and 3) the subsequently produced complementary structures made of epoxy resin were investigated. The outcome of these two form transfer technologies were evaluated by the cross sectional analysis of open microfluidic channels (trenches) with various design. Our results reveal the spatial accuracy in terms of real vs. CAD (Computer Aided Design) values for the 3D printed acrylic structures and the limits of their form transfer to PDMS, then to epoxy structures. Additionally the significant differences between the various spatial directions (X, Y, Z) have been characterized, and the conclusion was drawn that the ‘glossy’ printing mode is not appropriate for 3D printing of microfluidic molds.
This work aims to test the ability of liquid carbon dioxide to remove grease from bearings in wind turbines. Currently, the removal of grease from wind turbines offshore in the North Sea is done by dismantling the bearing covers and scraping off the grease. This procedure is long, labour intensive and raises maintenance cost. Another issue is the environmental policy, the approval for newly introduced chemicals for flushing purposes are procedurally long. If the problems with grease removal could be solved in a different way other than manual removal or using chemicals, it will open many new market opportunities and would carved out a niche for the wind turbine maintenance industry. The solution of flushing grease could lower cost, time and reduce environmental impact by applying Supercritical Carbon Dioxide. The oil based grease SKF LGWM 1 was designed to handle extreme pressure and low temperature conditions. The grease covered the main bearing for 4 - 5 y in a wind turbine at Horns Rev 1 Offshore Wind Farm in the North Sea, 14 km from the west coast of Denmark. The series of experiments focused on higher pressures and temperatures as well as the use of some co-solvents. The highest recovery by pure carbon dioxide is 26 % and was achieved at 60 MPa and 80 degrees C while the addition of Kirasol-318SC improved the recovery by 8 % at the same conditions. Outgassing losses increase with the addition of kirasol. The low recoveries and high pressures obtained by the experiment do not provide an applicable method for grease removal; however it can be implemented for the removal of the contaminants from grease wastes.
A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.
The grease flow in a rectangular channel is investigated using microparticle image velocimetry. Of certain interest is to study the behavior close to the boundary where wall slip effects are shown to be present. Three greases with different consistencies (NLGI00, NLGI1, and NLGI2) have been used, together with three wall materials (steel, brass, and polyamide) with different surface roughness. The pressure drop is also varied. It is shown that the velocity profile is strongly dependent on the consistency, having a dominating plug flow structure for a stiff grease. Furthermore, it is shown that wall slip effects occur in a thin shear layer close to the boundary where a very large velocity gradient is present. An analytical solution for the velocity across the channel is described using a Herschel-Bulkley rheology model. The model fits well with the measured velocity profile for all three above-mentioned greases.
A novel method, a 3D printing technique, in particular, acrylic photopolymer material-based Rapid Prototyping (RPT) have been used to 1) fabricate molds for PDMS (PolyDiMethylSiloxane) casting; 2) fabricate RPT-based microfluidics and 3) fabricate RPT-based research instrument platforms. 3D RPT-based molds have been fabricated in order to cast a PDMS flow cell for a Surface Plasmon Resonance (SPR) instrument, and to cast a PDMS chamber for cell lysis in a nanobiological sensor. 3D printing has been utilized to create and test several acrylic photopolymer resin-based prototypes for different microfluidic structures (chaotic mixers, reagent and buffer reservoirs, fluid homogenizers) to be deployed for gynecological cervical sample preparation. Besides, RPT technique has been used also to fabricate platform elements for various microfluidic applications.
Poly(dimethylsiloxane) or PDMS is an excellent material for replica molding, widely used in microfluidics research. Its low elastic modulus, or high deformability, assists its release from challenging molds, such as those with high feature density, high aspect ratios, and even negative sidewalls. However, owing to the same properties, PDMS-based microfluidic devices stretch and change shape when fluid is pushed or pulled through them. This paper shows how severe this change can be and gives a simple method for limiting this change that sacrifices few of the desirable characteristics of PDMS. A thin layer of PDMS between two rigid glass substrates is shown to drastically reduce pressure-induced shape changes while preserving deformability during mold separation and gas permeability.
The conventional microfluidic H filter is modified with multi-insulating blocks to achieve a flow-through manipulation and separation of microparticles. The device transports particles by exploiting electro-osmosis and electrophoresis, and manipulates particles by utilizing dielectrophoresis (DEP). Polydimethylsiloxane (PDMS) blocks fabricated in the main channel of the PDMS H filter induce a nonuniform electric field, which exerts a negative DEP force on the particles. The use of multi-insulating blocks not only enhances the DEP force generated, but it also increases the controllability of the motion of the particles, facilitating their manipulation and separation. Experiments were conducted to demonstrate the controlled flow direction of particles by adjusting the applied voltages and the separation of particles by size under two different input conditions, namely (i) a dc electric field mode and (ii) a combined ac and dc field mode. Numerical simulations elucidate the electrokinetic and hydrodynamic forces acting on a particle, with theoretically predicted particle trajectories in good agreement with those observed experimentally. In addition, the flow field was obtained experimentally with fluorescent tracer particles using the microparticle image velocimetry (mu-PIV) technique.
We study the elastic deformation of poly(dimethylsiloxane) (PDMS) microchannels under imposed flow rates and the effect of this deformation on the laminar flow profile and pressure distribution within the channels. Deformation is demonstrated to be an important consideration in low aspect ratio (height to width) channels and the effect becomes increasingly pronounced for very shallow channels. Bulging channels are imaged under varying flow conditions by confocal microscopy. The deformation is related to the pressure and is thus non-uniform throughout the channel, with tapering occurring along the stream-wise axis. The measured pressure drop is monitored as a function of the imposed flow rate. For a given pressure drop, the corresponding flow rate in a deforming channel is found to be several times higher than expected in a non-deforming channel. The experimental results are supported by scaling analysis and computational fluid dynamics simulations coupled to materials deformation models.
Miniaturization is a central theme in technology. As the computer industry knows, smaller microelectronic devices have made computers faster, cheaper and more portable. These advances in microelectronics have also spawned a huge variety of other tiny devices. For example, micro-electro-mechanical systems are now being used in medicine as disposable blood-pressure sensors, and in the automotive industry as tiny accelerometers in airbags that protect drivers in crashes.
Polydimethylsiloxane (PDMS) is one of the most common materials used for the flow delivery in the microfluidics chips, since it is clear, inert, non-toxic and non-flammable. Its inexpensiveness, straightforward fabrication and biological compatibility have made it a favorite material in the exploratory stages of the bio-microfluidic devices. If small footprint assays want to be performed while keeping the throughput, high pressure-rated channels should be used but PDMS flexibility causes an important issue since it can generate a large variation of microchannel geometry. In this work, a novel fabrication technique based on the prevention of PDMS deformation is developed. A photo-sensible thiolene resin (Norland Optical Adhesive 63 -NOA 63) is used to create a rigid coating layer over the stiff PDMS micropillar array, which significantly reduces the pressure-induced shape changes. This method uses the exact same softlithography manufacturing equipment. The verification of the presented technique was investigated experimentally and numerically and the manufactured samples showed a deformation 70% lower than PDMS conventional samples. This article is protected by copyright. All rights reserved.
Grease is commonly used to lubricate various machine components such as rolling bearings and seals. In this paper the flow of lubricating grease passing restrictions is described. Such flow occurs in rolling bearings during relubrication events where the grease is flowing in the transverse (axial) direction through the bearing and is hindered by guide rings, flanges etc, as well as in seals where transverse flow occurs, for example during so-called breathing caused by temperature fluctuations in the bearing. This study uses a 2D flow model geometry consisting of a wide channel with rectangular cross-section and two different types of restrictions to measure the grease velocity vector field, using the method of Micro Particle Image Velocimetry. In the case of a single restriction, the horizontal distance required for the velocity profile to fully develop is approximately the same as the height of the channel. In the corner before and after the restriction, the velocities are very low and part of the grease is stationary. For the channel with two flow restrictions, this effect is even more pronounced in the “pocket” between the restrictions. Clearly, a large part of the grease is not moving. This condition particularly applies to the cases with a low-pressure drop and where high consistency grease is used. In practice this means that grease is not replaced in such “corners” and that some aged/contaminated grease will remain in seal pockets.
Microparticle image velocimetry (μPIV) is used to measure the grease velocity profile in small seal-like geometries and the radial migration of contaminant particles is predicted. In the first part, the influence of shaft speed, grease type, and temperatures on the flow of lubricating greases in a narrow double restriction sealing pocket is evaluated. Such geometries can be found in, for example, labyrinth-type seals. In a wide pocket the velocity profile is one-dimensional and the Herschel-Bulkley model is used. In a narrow pocket, it is shown by the experimental results that the side walls have a significant influence on the grease flow, implying that the grease velocity profile is two-dimensional. In this area, a single empirical grease parameter for the rheology is sufficient to describe the velocity profile.In the second part, the radial migration of contaminant particles through the grease is evaluated. Centrifugal forces acting on a solid spherical particle are calculated from the grease velocity profile. Consequently, particles migrate to a larger radius and finally settle when the grease viscosity becomes large due to the low shear rate. This behavior is important for the sealing function of the grease in the pocket and relubrication.
The aim of this paper is to present the main results of the First International PIV
Challenge which took place in Göttingen (Germany) on 14 and 15 September 2001.
This workshop was linked to the PIV01 International Symposium which was
held in the same place the week after. The present contribution gives the
objectives of the challenge, describes the test cases and the algorithms used
and presents the main results obtained together with some discussion
and conclusions on the accuracy and robustness of both PIV and PTV
algorithms. As it is not possible to detail all the results obtained, this
contribution should serve as a guide for the use of the full database of
images and results which is available at http://www.pivchallenge.org.
High pressure-rated channels allow microfluidic assays to be performed on a smaller footprint while keeping the throughput, thanks to the higher enabled flow rates, opening up perspectives for cost-effective integration of CMOS chips to microfluidic circuits. Accordingly, this study introduces an easy, low-cost and efficient method for realizing high pressure microfluidics-to-CMOS integration. First, we report a new low temperature (280 °C) Parylene-C wafer bonding technique, where O(2) plasma-treated Parylene-C bonds directly to Si(3)N(4) with an average bonding strength of 23 MPa. The technique works for silicon wafers with a nitride surface and uses a single layer of Parylene-C deposited only on one wafer, and allows microfluidic structures to be easily formed by directly bonding to the nitride passivation layer of the CMOS devices. Exploiting this technology, we demonstrated a microfluidic chip burst pressure as high as 16 MPa, while metal electrode structures on the silicon wafer remained functional after bonding.
3D biomimetic microvascular networks of nearly arbitrary design are patterned by omnidirectional printing of a fugitive organic ink into a photopolymerizable hydrogel matrix. This novel approach hinges critically on tailoring the chemical and rheological properties of the fugitive ink as well as the photopolymerizable hydrogel reservoir and fluid filler. These hydrogel-based, microvascular constructs may find potential application in 3D cell culture, tissue engineering, organ modeling, and autonomic healing.
Poly(dimethylsiloxane) (PDMS) microchannels are commonly used microfluidic structures that have a wide variety of biological testing applications, including the simulation of blood vessels to study the mechanics of vascular disease. In these studies in particular, the deformation of the channel due to the pressure inside is a critical parameter. We describe a method for using fluorescence microscopy to quantify the deformation of such channels under pressure driven flow. Additionally, the relationship between wall thickness and channel deformation is investigated. PDMS microchannels of varying top wall thickness were created using a soft lithography process. A solution of fluorescent dye is pumped through the channels at constant volume flow rates and illuminated. Pressure and fluorescence intensity are measured at five positions along the length of the channel. Fluorescence measurements are then used to determine deformation, using the linear relationship of dye layer thickness and intensity. A linear relationship between pressure and microchannel deformation is measured. Pressure drops and deformations closely correspond to values predicted by the model in most cases. Additionally, measured pressure drops are found to be up to 35% less than the pressure drop in a rigid-walled channel, and channel wall thickness is found to have an increasing effect as the channel wall thickness decreases.
This Review summarizes methods for constructing systems and structures at micron or submicron scales that have applications in microbiology. These tools make it possible to manipulate individual cells and their immediate extracellular environments and have the capability to transform the study of microbial physiology and behaviour. Because of their simplicity, low cost and use in microfabrication, we focus on the application of soft lithographic techniques to the study of microorganisms, and describe several key areas in microbiology in which the development of new microfabricated materials and tools can have a crucial role.
We report on a microfabrication technique for realizing
re-configurable micro fluidics devices using polymethylsiloxane material
(PDMS). The mechanical characteristics of the material, including the
Young's modulus and the adhesion energy have been determined
experimentally. The magnitude of Young's modulus ranges from
8.7×105 Pa to 3.6×105 Pa. The adhesion
energy is a function of the PDMS composition as well as chemical
treatment. A method for efficiently developing flow interconnects has
been demonstrated
High pressure lubricant pump for steelworks
- W Egham
- Ep
Egham W EP (2006), "High pressure lubricant pump for steelworks". European Patent EP1914425B1.
Re-configurable Fluid Circuits by PDMS Elastomer Micromachining
- D Armani
- C Liu
- N Aluru
Armani D, Liu C and Aluru N (1999), "Re-configurable Fluid Circuits by PDMS Elastomer
Micromachining" Proc. Annual International Workshop on Micro Electro Mechanical Systems,
Orlando, Florida 17-21 January 222-227.
Lubricating grease shear flow and boundary layers in a concentric cylinder configuration
- J Li
- L G Westerberg
- E Höglund
- T S Lundström
- P Baart
- P Lugt
Li J, Westerberg L G, Höglund E, Lundström T S, Baart P, Lugt P (2013), "Lubricating grease shear
flow and boundary layers in a concentric cylinder configuration" Proc. 3rd International Tribology
Symposium of IFoMM (International Federation for the Promotion of Mechanism and Machine
Science), Luleå, 19-21March 2013.
High pressure lubricant pump for steelworks
- W E P Egham