Microchannel Layers Research Articles

Thermal-hydraulic performance of an imperfectly bonded ultrathin manifold micro pin-fin channel heat sink

This study numerically investigated the thermal-hydraulic performance of an ultrathin manifold microchannel heat sink (MMHS) and an ultrathin manifold micro pin-fin channel heat sink (MMPF-HS) with gaps between the manifold and microchannel layers. Unlike previous researches, the effect of the presence of gaps on flow distribution and overall heat transfer of MMHS and MMPF-HS was analyzed. The simulation results show that the presence of the gap significantly affect the heat transfer of both heat sinks but have minimal impact on pressure drop. For the MMHS with a gap of 0.05 mm in height, the bypass effect introduced by the gaps makes the uneven flow distribution worse and causes the formation of low-speed vortexes, leading to a 25.5% increase in the average temperature and 2.1-fold increase in the temperature non-uniformity of the heating surface. MMPF-HS is more effective in mitigating the effect of gap on temperature non-uniformity compared to the original MMHS due to the structural optimization. For the MMPF-HS with a 0.05 mm height gap, the average surface temperature rises from 34.3 to 40.9 °C, and the temperature non-uniformity increases from 1.1 to 5.5 °C, which remain significantly lower than those of the original MMHS without a gap.

Thermal performance of a hybrid cooling plate integrated with microchannels and PCM

The battery thermal management system (BTMS) is critical to electric vehicle (EV) safety and performance. In this paper, a novel cooling plate integrated with liquid microchannels and phase change material (PCM) is developed for use in BTMS, and its thermal performance at a high discharge rate of 5C is investigated. To improve temperature inhomogeneity, the non-metallic inlet shell is used to transport the coolant to the axial microchannels, which significantly reduces the temperature difference by 3.8 °C. Additionally, compared with I-shaped microchannels, the design of S-shaped microchannels increases the flow area for coolant and promotes the cooling effect, controlling the maximum temperature at 34.53 °C. Then, the parameters, including the number of microchannel layers, radial extension angle, inner diameter, and PCM thickness, are optimized by the multi-objective optimization, and its energy consumption is decreased to 9.61 × 10-6Wh and its energy density raised to 108.94 Wh∙kg−1. Moreover, the cooling performance improves with the increase of the inlet velocity, and a balance between cooling performance and energy consumption is achieved when the inlet velocity is 0.06 m∙s−1. Cross-convectional flow helps to enhance the temperature uniformity of the battery module further. The hybrid liquid cooling plate takes advantage of coupling active cooling and passive cooling; the energy consumption of BTMS is reduced by 46.3% without sacrificing the cooling capacity when delaying the beginning of active cooling after PCM passive cooling for 300 s. Furthermore, the PCM-embedded hybrid cooling plate slows the heat loss of batteries in cold environments, which can maintain their temperature above 20 °C after resting for 2 h at 0 °C. This work provides a reference for the hybrid cooling plate development of cylindrical batteries.

Assessment of Vapor Formation Rate and Phase Shift between Pressure Gradient and Liquid Velocity in Flat Mini Heat Pipes as a Function of Internal Structure.

Flat mini heat pipes (FMHPs) are often used in cooling systems for various power electronic components, as they rapidly dissipate high heat flux densities. The main objective of the present work is to experimentally investigate whether differences in the rate of vapor formation occur on an internal structure containing trapezoidal microchannels and porous sintered copper powder material. Several parameters, such as hydraulic diameter and fluid velocity through the material, as a function of the internal structure porosity, were determined by calculation for a steady state regime. Reynolds number was determined as a function of porosity, according to Darcy's law, and the Nusselt number was calculated. Since the flow is Darcy-type through the porous medium inside the FMHP, the Darcy friction factor was calculated using five methods: Colebrook, Darcy-Weisbach, Swamee-Jain, Blasius, and Haaland. After experimental tests, it was found that when the porous and trapezoidal microchannel layers are wetted at the same time, the vaporization progresses at a faster rate in the porous material, and the duration of the process is shorter. This recommends the use of such an internal structure in FMHPs since the manufacturing technology is simpler, the materials are cheaper, and the heat flux transport capacity is higher.

Laser-Cutted Epidermal Microfluidic Patch with Capillary Bursting Valves for Chronological Capture, Storage, and Colorimetric Sensing of Sweat.

Flexible wearable microfluidic devices show great feasibility and potential development in the collection and analysis of sweat due to their convenience and non-invasive characteristics in health-level feedback and disease prediction. However, the traditional production process of microfluidic patches relies on resource-intensive laboratory and high-cost facilities. In this paper, a low-cost laser-cutting technology is proposed to fabricate epidermal microfluidic patches for the collection, storage and colorimetric analysis of sweat. Two different types of capillary bursting valves are designed and integrated into microchannel layers to produce two-stage bursting pressure for the reliable routing of sweat into microreservoirs in sequential fashion, avoiding the mixing of old and new sweat. Additionally, an enzyme-based reagent is embedded into the microreservoirs to quantify the glucose level in sweat by using colorimetric methods, demonstrating a high detection sensitivity at the glucose concentration from 0.1 mM to 1 mM in sweat and an excellent anti-interference performance that prevents interference from substances probably existent in sweat. In vitro and on-body experiments demonstrate the validity of the low-cost, laser-cut epidermal microfluidic patch for the chronological analysis of sweat glucose concentration and its potential application in the monitoring of human physiological information.

A narrow shape double-layer microchannel heat sink (DL-MCHS) designed for high-power laser crystal

• A narrow shape DL-MCHS is designed for the small-size high power laser crystal. • The multi-layers are inner-soldered to enhance the vertical heat transfer rate. • Extension of DL-MCHS in the length enhances the overall heat transfer capability. • Heat diffusion reduces the influence of fluid flow rate ratio in the two layers. • The DL-MCHS exhibits a low pumping power. The thermal effect-induced problem has become a bottleneck in high power laser systems. The laser crystal, which dissipates a heat flux over 150 W/cm 2 , is the most challenging component when considering the solution of the thermal problem. In this work, we designed a double-layer microchannel heat sink (DL-MCHS) for the heat release of a small-size laser crystal. The main constraints, including the high power density of the laser crystal, space restriction, and the fabrication method are taking into account. A narrow shape DL-MCHS is proposed. The microchannels are fabricated micro-mechanically, and the layers of the DL-MCHS are welded together using a vacuum brazing method. A systematic experimental study is performed to evaluate the performance of the DL-MCHS. The results show that the narrow shape DL-MCHS, which extends the volume only in its length, shows good heat transfer capability. The overall heat transfer coefficient reaches 42 × 10 3 W/(m 2 ·K). The surface temperature of the heating source is well controlled below 55 °C at a typical heat power of 234 W. When the same fluid flow rates are adopted in the two microchannel layers, the first microchannel layer (bottom) absorbs two thirds of the total heat, while the rest is absorbed in the second layer (top). In the solid base of the DL-MCHS, thermal resistance in the vertical direction is over three times that in the longitudinal direction. When the fluid flow ratio in the first microchannel layer increases, the overall heat transfer coefficient is enhanced slightly, while the temperature distribution on the heating head is little affected. Comparing the single-layer cooling pattern, the double-layer flow pattern improves the uniformity of temperature distribution on the heat sink when the counter-current flow is used, and saves the pumping power by up to 60%.

Header Shape Effect on the Inlet Velocity Distribution in Cross-Flow Double-Layered Microchannel Heat Sinks

Counter-flow double-layered microchannel heat sinks are very effective for thermal control of electronic components; however, they require rather complicated headers and flow maldistribution can also play a negative role. The cross-flow configuration allows a much simpler header design and the thermal performance becomes similar to that provided by the counter-flow arrangement if the velocity distribution in the microchannels is not uniform. The aim of this work is to show the possibility of achieving a favorable flow distribution in the microchannels of a cross-flow double-layered heat sink with an adequate header design and the aid of additional elements such as full or partial height baffles made of solid or porous materials. Turbulent RANS numerical simulations of the flow field in headers are carried out with the commercial code ANSYS Fluent. The flow in the microchannel layers is modeled as that in a porous material, whose properties are derived from pressure drop data obtained using an in-house FEM code. It is demonstrated that, with an appropriate baffle selection, inlet headers of cross-flow microchannel heat sinks yield velocity distributions very close to those that would allow optimal hotspot management in electronic devices.

A novel two-layer-integrated microfluidic device for high-throughput yeast proteomic dynamics analysis at the single-cell level.

Current microfluidic methods for studying multicell strains (e.g., m-types) with multienvironments (e.g., n-types) require large numbers of inlets/outlets (m*n), a complicated procedure or expensive machinery. Here, we developed a novel two-layer-integrated method to combine different PDMS microchannel layers with different functions into one chip by a PDMS through-hole array, which improved the design of a PDMS-based microfluidic system. Using this method, we succeeded in converting 2×m×n inlets/outlets into m+n inlets/outlets and reduced the time cost of loading processing (from m×n to m) of the device for studying multicell strains (e.g., m-types) in varied multitemporal environments (i.e., n-types). Using this device, the dynamic behavior of the cell-stress-response proteins was studied when the glucose concentration decreased from 2% to a series of lower concentrations. Our device could also be widely used in high-throughput studies of various stress responses, and the new concept of a multilayer-integrated fabrication method could greatly improve the design of PDMS-based microfluidic systems.

Rapid Capture and Extraction of Sweat for Regional Rate and Cytokine Composition Analysis Using a Wearable Soft Microfluidic System

Rapid Capture and Extraction of Sweat for Regional Rate and Cytokine Composition Analysis Using a Wearable Soft Microfluidic System

Microfluidic two-phase interactions under variable liquid to cross-flow gas momentum flux ratios

Volume of fluid (VOF) and large eddy simulations (LES) are coupled to investigate the microfluidic two-phase interactions during the liquid emergence into the cross-flow gas in a super-hydrophobic micro-channel. Spatio-temporal evolution of the gas/liquid interface is presented for nine different cases of the liquid to gas momentum flux ratios, gas/liquid Reynolds numbers and gas/liquid Weber numbers. With increased momentum of the gas flow, the liquid topology is found deflected towards the downstream. Under variable gas resistance effects, the liquid flow emerging through the square pore may or may not develop a circular cross-section governed by the axis-switching phenomenon. At strong gas inertia, vortex shedding in the downstream of the liquid generates vorticular ligaments in the wake region. Shearing effects on the liquid surface are increased at higher liquid injection velocities and/or gas densities. Depending on the competing effects of the viscous diffusion versus gas/liquid inertia, different combinations of the interactions among the three building blocks of the fluid flow problems (boundary layer, shear layer and wake) are described in microfluidics scales. The complexity of the liquid topology is found correlated with the occurrence of the phenomena such as the Kelvin–Helmholtz (KH) instability, the horseshoe vortex system, stationary/shedding vortices in the wake of the liquid topology as well as their interaction with the micro-channel wall boundary layers.

A large-area hemispherical perforated bead microarray for monitoring bead based aptamer and target protein interaction.

Herein, we present a large-area 3D hemispherical perforated microwell structure for a bead based bioassay. Such a unique microstructure enables us to perform the rapid and stable localization of the beads at the single bead level and the facile manipulation of the bead capture and retrieval with high speed and efficiency. The fabrication process mainly consisted of three steps: the convex micropatterned nickel (Ni) mold production from the concave micropatterned silicon (Si) wafer, hot embossing on the polymer matrix to generate the concave micropattened acrylate sheet, and reactive ion etching to make the bottom holes. The large-area hemispherical perforated micropatterned acrylate sheet was sandwiched between two polydimethylsiloxane (PDMS) microchannel layers. The bead solution was injected and recovered in the top PDMS microchannel, while the bottom PDMS microchannel was connected with control lines to exert the hydrodynamic force in order to alter the flow direction of the bead solution for the bead capture and release operation. The streptavidin-coated microbead capture was achieved with almost 100% yield within 1 min, and all the beads were retrieved in 10 s. Lysozyme or thrombin binding aptamer labelled microbeads were trapped on the proposed bead microarray, and the in situ fluorescence signal of the bead array was monitored after aptamer-target protein interaction. The protein-aptamer conjugated microbeads were recovered, and the aptamer was isolated for matrix assisted laser desorption/ionization time-of-flight mass spectrometry analysis to confirm the identity of the aptamer.

Three-dimensional fit-to-flow microfluidic assembly

Three-dimensional microfluidics holds great promise for large-scale integration of versatile, digitalized, and multitasking fluidic manipulations for biological and clinical applications. Successful translation of microfluidic toolsets to these purposes faces persistent technical challenges, such as reliable system-level packaging, device assembly and alignment, and world-to-chip interface. In this paper, we extended our previously established fit-to-flow (F2F) world-to-chip interconnection scheme to a complete system-level assembly strategy that addresses the three-dimensional microfluidic integration on demand. The modular F2F assembly consists of an interfacial chip, pluggable alignment modules, and multiple monolithic layers of microfluidic channels, through which convoluted three-dimensional microfluidic networks can be easily assembled and readily sealed with the capability of reconfigurable fluid flow. The monolithic laser-micromachining process simplifies and standardizes the fabrication of single-layer pluggable polymeric modules, which can be mass-produced as the renowned Lego(®) building blocks. In addition, interlocking features are implemented between the plug-and-play microfluidic chips and the complementary alignment modules through the F2F assembly, resulting in facile and secure alignment with average misalignment of 45 μm. Importantly, the 3D multilayer microfluidic assembly has a comparable sealing performance as the conventional single-layer devices, providing an average leakage pressure of 38.47 kPa. The modular reconfigurability of the system-level reversible packaging concept has been demonstrated by re-routing microfluidic flows through interchangeable modular microchannel layers.

Nanoporous Elements in Microfluidics for Multiscale Manipulation of Bioparticles

Solid materials, such as silicon, glass, and polymers, dominate as structural elements in microsystems including microfluidics. Porous elements have been limited to membranes sandwiched between microchannel layers or polymer monoliths. This paper reports the use of micropatterned carbon-nanotube forests confined inside microfluidic channels for mechanically and/or chemically capturing particles ranging over three orders of magnitude in size. Nanoparticles below the internanotube spacing (80 nm) of the forest can penetrate inside the forest and interact with the large surface area created by individual nanotubes. For larger particles (>80 nm), the ultrahigh porosity of the nanotube elements reduces the fluid boundary layer and enhances particle-structure interactions on the outer surface of the patterned nanoporous elements. Specific biomolecular recognition is demonstrated using cells (≈10 μm), bacteria (≈1 μm), and viral-sized particles (≈40 nm) using both effects. This technology can provide unprecedented control of bioseparation processes to access bioparticles of interest, opening new pathways for both research and point-of-care diagnostics.

Electrochemical oxygen separation and compression using planar, cosintered ceramics

Cosintered, planar electrochemical devices were used to separate and compress oxygen at pressures as high as 2 MPa. Thin samaria-doped ceria electrolytes (CSO) were mechanically supported by porous electrodes and dense microchannel layers. Composite electrodes, comprised of CSO and La 1 − x Sr x Co 0.2Fe 0.8O 3 − δ (LSCF) particles, were used for cathodic and anodic reactions. The incoming air and the separated oxygen were manifolded through microchannel layers composed of La 1 − y Ca y MnO 3 (LCM), a dense electrically conductive ceramic. Multiple green ceramic tape layers were featured by laser cutting before lamination. The laminated structure was cosintered to produce a functional microchanneled electrochemical device or couple suitable for electrically driven oxygen separation at temperatures > 600 °C. Multiple couples were assembled into stacks and connected electrically in series to generate the oxygen flow desired. The high chemical expansion of the electrodes resulted in microcracking, which facilitated the operation of this planar device without damage to the electrolyte. The thermal expansion of the LCM can be tailored to eliminate residual tensile stress in the electrolyte. Fabrication challenges include the different initial sintering temperatures and varying sintering rates of the materials. Good bonding between layers during cosintering enables the device to withstand internal oxygen pressures high enough to be used for many applications requiring pressurized high-purity oxygen; without the aid of an auxiliary mechanical endload.

Processing of three-dimensional metallic microchannels by spacer method

Metallic microchannels with a three-dimensional (3D) configuration were fabricated by the spacer method. When spacing aluminum wires were shaped into a 3D-spiral configuration in an initial powder compact, they were easily replicated after the sintering and dissolution, resulting in 3D-spiral microchannels in a bulky copper body. This suggests that the spacer method is an effective way of fabricating complex 3D configuration microchannels, compared to conventional fabrication methods, for example, aligning and stacking two-dimensional microchannel layers. The compaction conditions for initial powder compacts, such as compaction pressure, spacing materials and compaction mode (uniaxial or isostatic), severely influence the shape and surface roughness of the resulting microchannels.

Experimental and Numerical Study of a Stacked Microchannel Heat Sink for Liquid Cooling of Microelectronic Devices

One of the promising liquid cooling techniques for microelectronics is attaching a microchannel heat sink to, or directly fabricating microchannels on, the inactive side of the chip. A stacked microchannel heat sink integrates many layers of microchannels and manifold layers into one stack. Compared with single-layered microchannels, stacked microchannels provide larger flow passages, so that for a fixed heat load the required pressure drop is significantly reduced. Better temperature uniformity can be achieved by arranging counterflow in adjacent microchannel layers. The dedicated manifolds help to distribute coolant uniformly to microchannels. In the present work, a stacked microchannel heat sink is fabricated using silicon micromachining techniques. Thermal performance of the stacked microchannel heat sink is characterized through experimental measurements and numerical simulations. Effects of coolant flow direction, flow rate allocation among layers, and nonuniform heating are studied. Wall temperature profiles are measured using an array of nine platinum thin-film resistive temperature detectors deposited simultaneously with thin-film platinum heaters on the backside of the stacked structure. Excellent overall cooling performance (0.09°C∕Wcm2) for the stacked microchannel heat sink has been shown in the experiments. It has also been identified that over the tested flow rate range, counterflow arrangement provides better temperature uniformity, while parallel flow has the best performance in reducing the peak temperature. Conjugate heat transfer effects for stacked microchannels for different flow conditions are investigated through numerical simulations. Based on the results, some general design guidelines for stacked microchannel heat sinks are provided.

D225 微細管内流動における凝縮挙動に関する研究(管内沸騰・凝縮)

It is requested to develop a small and high performance heat exchanger for small size energy equipments such as fuel cells and CO_2 heat pumps, and so on. In author's previous studies, a high pressure resistant microchannel layers stacked heat exchanger has been developed. The device is manufactured by diffusion bond technique. It can be used under high pressure condition larger than 15MPa. Due to the high pressure resistance, the heat exchanger can be applied for high flow rate condition with boiling and condensation. The objectives of the present study are to estimate the heat transfer performance of the heat exchanger and to investigate the thermal hydraulic behavior in the microchannel. The flow pattern is observed by fabricating visualization system for one channel to observe the flow condensation behavior in microchannel. In the experiment, the microchannel of Pyrex glass is surrounded by the subcooling water. The flow patterns can visualized from the side of the microchannel. Flow patterns observations are conducted for various diameters of the maicrochannel, flow rates and temperatures of the subclooled water. It is observed that the continuous flow transition from annular and injection flow to slug-bubble flow in the microchannel.

Transport Controlled Pattern Photopolymerization in a Single-Component System

The purpose of the present paper is to extend the concept of pattern photopolymerization-induced phase separation of a binary blend to a single-component system containing pure photoreactive monomers with a minute level of photoinitiators. The patterning formation process was simulated in the framework of Cahn−Hilliard equation coupled with the photoreaction kinetic equation. Unlike binary systems undergoing photopolymerization-induced phase separation driven by thermodynamic force, the mechanism of pattern formation in the single-component system is essentially a photoreaction-induced transport phenomenon. Of particular interest is the observation of polymer concentration profiles evolving from a sinusoidal wave to various truncated ones. On the basis of two-wave interference optics, the microchannel layers have been fabricated. Resultant morphology was characterized using optical and atomic force microscopes. A two-dimensional light scattering device was utilized to study the diffraction patterns from t...