•A new microchannel configuration is developed by incorporating capillary micro-pinfin fences and multiple micro-nozzles.•Significant enhancement of flow boiling performance is achieved on both ...DI-water and HFE-7100.•A CHF up to 944 W/cm2 is demonstrated with an enhancement of ~300% on DI-water at a mass velocity of 600 kg/m2 s.•A CHF of 287 W/cm2 is shown with an enhancement of 56% at a mass velocity of 2772 kg/m2 s on HFE-7100.•120% higher HTC at a moderate mass velocity of 693 kg/m2 s has been realized on HFE-7100.
Phase-change heat transfer is a promising approach for high-power electronics cooling. However, the chaotic two-phase transport and dominant laminar flow in microchannels inhibits flow boiling performance. Thus, the ability to coordinate the two-phase transport in a highly favorable fashion would be highly desired. In this study, a new microchannel configuration by incorporating capillary micro-pinfin fences and multiple micro-nozzles has been proposed to sustain thin liquid film evaporation, promote mixing and global liquid supply simultaneously. A new boundary layer covered with thin liquid film is activated by the capillary micro-pinfin fences along the sidewalls of the channel. Additionally, the sustainable thin liquid film is maintained using capillary effect, which can promote the capillary-driven flow inside the gap between micro-pinfin fences and the sidewalls. As a result, significantly enhanced flow boiling has been achieved on both DI-water and HFE-7100. A critical heat flux (CHF) up to 944 W/cm2 has been demonstrated using DI-water at a mass velocity of 600 kg/m2 s, accounting for a 43% enhancement compared to the configuration of multiple micro-nozzles without capillary micro-pinfin fences. Compared to the base configuration of plain wall microchannels, the enhancement of CHF is over threefold at a mass velocity of 389 kg/m2s. Equally important, this new microchannel configuration works well on dielectric fluids, which is challenging to promote CHF due to their unfavorable thermophysical properties. A CHF of 287 W/cm2 with a noticeable enhancement of 56% has been achieved at a mass velocity of 2772 kg/m2 s on HFE-7100 at room temperature. Moreover, the enhancements of heat transfer coefficient (HTC) on HFE-7100 are more noticeable compared to that of DI-water. For example, 120% higher HTC at a moderate mass velocity of 693 kg/m2 s has been realized. All the enhancements are achieved without the escalating pressure drop.
The construction market has at its disposal more and more technical solutions in sealing materials that allow cost reduction and short term execution for construction companies. Among these solutions ...are the so called gypsum blocks. In spite of their countless advantages when it comes to their use as masonry sealing material, there are limits to the use of gypsum blocks: due to their low resistance to deterioration by rain, their use as external sealing is not recommended. Therefore, the aim of the present work was the development of experimental apparatus for the analyses of capillary phenomena in representative samples of gypsum blocks for sealing. The development of these apparatus for capillarity tests was based on models for tests of liquid water flow in porous media – standardized by procedure 11.2 according to RILEM TC 25-PEM (1980). By means of the obtained results it was possible to verify the high accuracy of the apparatus, seeing that considerable differences were observed in values of capillary absorption coefficient for specimens with water/gypsum ratios of 0.5; 0.6; 0.7 and 0.8 (results varied from 14.75 g cm-2h-0,5 for ratio 0.5 and 58.99 g cm-2h-0,5 for ratio 0.8). Additionally, tests with water repellent additives were carried out, verifying that the developed apparatus is able to identify the influence of these additives in representative specimens of gypsum blocks.
Parallel lithographic deposition of polymers onto counterpart substrates is a widely applied surface manufacturing operation. However, polymers may only be soluble in organic solvents or are ...insoluble at all. Solvent evaporation during stamping may trigger hardly controllable capillarity‐driven flow processes or phase separation, and polymer solutions may spread on the counterpart substrates. Solvent‐free stamping of melts prevents these drawbacks. Here, a stamp design for the deposition of melts is devised, which intrinsically circumvents ink depletion. The stamps’ topographically patterned contact surfaces with protruding contact elements contacting the counterpart substrates consist of a nanoporous gold layer with a thickness of a few micrometers. The nanoporous gold layer is attached to a molten polymer layer, which is support for the nanoporous gold layer and ink reservoir at the same time. The nanoporous gold layer in turn stabilizes the topography of the stamps’ contact surfaces. As examples, arrays of submicron microdots of polystyrene and poly(vinylidenefluoride‐trifluoroethylene) (PVDF‐TrFE) are manufactured. The P(VDF‐TrFE) microdots are partially crystalline, ferroelectric, and can be locally poled. It is envisioned that the methodology reported here can be automatized and may be extended to functional low‐molecular‐mass compounds, such as active pharmaceutical ingredients.
Composite stamps for the solvent‐free high‐temperature capillary stamping of polymer melts consisting of thin nanoporous gold layers attached bulk molten polymer reservoirs are reported. The nanoporous gold layer stabilizes the topographically patterned contact surface and the polymer melt supports the nanoporous gold layer; polymer microstructures may be produced without ink depletion and problems related to the presence of solvents.
In this work, theoretical modelling, quasi-three-dimensional (quasi-3D) simulations and micromodel experiments are conducted to study spontaneous imbibition with gravity in porous media micromodels. ...By establishing the force balance governing the spontaneous imbibition process, we develop a theoretical model for predicting the imbibition length against time in a rectangular capillary. The theoretical model is then extended to the prediction of a compact displacement process in a micromodel by using an equivalent width, which is derived by analogising the micromodel to a rectangular capillary. By simulating spontaneous imbibition in a rectangular capillary with various aspect ratios ($\varepsilon$), we show that the application condition of the quasi-3D method is $\varepsilon \leqslant 1/3$. Next, we simulate spontaneous imbibition in micromodels with various geometries and flow conditions. Fingering and compact displacement are identified for varying viscosity ratios and gravitational accelerations. At low (high) viscosity ratio of wetting to non-wetting fluids, an upward (downward) gravity can promote the stability of the wetting front, favouring the transition from fingering to compact displacement. In addition, we find that the depth-oriented interface curvature dominates the capillary effect during the imbibition, and such a mechanism is considered by introducing an equivalent contact angle into the theoretical model. With the help of equivalent width and contact angle, the theoretical model is shown to provide satisfactory prediction of the compact displacement process. Finally, a micromodel experiment is presented to further verify the developed theoretical model and the quasi-3D simulation.
•Nickel oxide polycrystalline nanowires are grown via hydrothermal way & calcination.•The nanosensor undergoes a thermal gradient, becoming a virtual array.•7 hazardous gases are tested, giving each ...a different thermal fingerprint.•The nanosensor shows categorization (100%) and quantitative prediction (error <15%).
Monitoring of hazardous gases is nowadays very important, since the urbanized environment is more subject to this kind of pollutants. Therefore, a capillary network of small gas sensors capable to check the quality of the environment is necessary. Metal oxide gas nanosensors are small economic devices that can be easily integrated in any context, however they unfortunately lack of selectivity. We present an approach using hydrothermally grown nickel oxide nanowires working at different temperatures and creating a virtual sensors array, thus exploiting the thermal fingerprints (sensor response as a function of temperature) of the gases. Using only one nanostructured material (nickel oxide) and different machine learning techniques, the system can easily discriminate any of 7 harmful gases (C2H5OH, H2, CO, LPG, CO2, NH3 and H2S, all of them reducing gases) with an accuracy of 100%. Furthermore, the nanosensor also evaluates the gas concentration with an average error lower than 15%. Our results show that, exploiting thermal fingerprints from a temperature gradient, single metal oxide resistive nanosensors can efficiently discriminate specific hazardous gases.
Most natural building materials are hygroscopic and permeable to water vapour. These two characteristics have the potential to improve the longevity and indoor air quality of buildings. However, the ...potential of winter condensation due to vapour diffusion and the risk of mold growth should be assessed for safeguarding the longevity of building assemblies.
This study investigates the relative importance of driving rain, plaster capillarity and the presence of a vapour barrier on the moisture content of building materials and the risk of mold growth for a hygroscopic and permeable building envelope (HPBE). Hygrothermal simulations of a single-family house in Denmark mainly made of wood and clay are performed with WUFI. Results indicate that the presence of an overhang is essential to ensure the durability of a HPBE rendered with a capillary active lime-based plaster while the presence of an overhang has a negligible impact for a mineral cement-based plaster. Including a vapour barrier did not introduce significant changes on the moisture content of this wall assembly. Simulation results indicate that the type of plaster and the wind-driven rain exposure are the most critical variables affecting the hygrothermal performance of this wall assembly.
•A permeable building envelope made of clay and wood was modelled with WUFI.•Impacts from driving rain, plaster capillarity and vapour barrier are investigated.•Results show that overhangs are essential for a capillary active plaster.•Including a vapour barrier did not introduce significant moisture content changes.•Cladding capillarity uptake and rain loads are more important that vapour diffusion.
The combination of enzymes, as recognition elements for specific analytes, and of electrogenerated chemiluminescence (ECL) as a readout method has proven to be a valuable strategy for sensitive and ...specific analytical detection. However, ECL is intrinsically a 2D process which could potentially limit the analysis of inhomogeneous samples. Here, we show how a bulk ECL signal, generated by thousands of carbon microbeads remotely addressed via bipolar electrochemistry, are implemented as a powerful tool for the concomitant ECL sensing and imaging of two enzymatic substrates. We selected two enzymes (glucose dehydrogenase and choline oxidase) that react with their respective model substrates and produce in situ chemical species (β-nicotinamide adenine dinucleotide (NADH) and H2O2) acting as coreactants for the ECL emission of different luminophores (Ru(bpy)32+ at λ = 620 nm and luminol at λ = 425 nm, respectively). Both enzymes are spatially separated in the same capillary. We demonstrate thus the simultaneous quantitative determination of both glucose and choline over a wide concentration range. The originality of this remote approach is to provide a global chemical view through one single ECL image of inhomogeneous samples such as a biochemical concentration gradient in a capillary configuration. Finally, we report the first proof-of-concept of dual biosensing based on this bulk ECL method for the simultaneous imaging of both enzymatic analytes at distinct wavelengths.
A miniaturepolymer Bragg grating (PBG) sensor is fabricated and employed for ultrasonic imaging of seismic physical models (SPMs). The sensing Bragg grating is inscribed into an ultraviolet (UV) glue ...polymer waveguide with a femtosecond laser. The uniform polymer waveguide is fabricated by sealing the UV glue into a capillary fibre through capillary effect. By using line-by-line inscription technique, the laser beam is scanned transversely to periodically modulate the refractive index of the polymer waveguide, leading to the formation of the PBGs with various grating lengths. The sensor response to ultrasonic waves are investigated experimentally. When compared to single-mode fiber Bragg grating and phase-shifted fiber Bragg grating, the PBG with the same reflectivity presents a higher response amplitude due to its lower Young's modulus. Besides, the sensor has a good spectral stability when transferred from air to water due to the waterproof coating on the sensor end. Finally, the sensor is used to scan a large-scale 3D SPM and the structural features, such as fault, fluctuation, and depositional termination, can be distinctly reconstructed. The proposed PBG sensor provides a new technique with easy fabrication, high sensitivity, and good stability for high-fidelity ultrasonic imaging of seismicphysical models.
•Visualization of displacement patterns of immiscible flow.•Phase diagram for three-dimensional porous media.•Characterization of invading fluid morphology.•Invasion dynamics for typical capillary ...and viscous fingering.
The immiscible fluid displacement pattern, controlled by the balance of viscous and capillary forces has a significant effect on the recovery or storage efficiency in subsurface processes. The phase diagram of displacement patterns has been extensively studied for the two-dimensional (2D) micromodel; however, that of the three-dimensional (3D) porous media has received little attention. This work experimentally studied the immiscible drainage displacement in an unconsolidated packed bed at the pore scale with a wide range of capillary number Ca and viscosity ratio M using X-ray micro-tomography. Three typical displacement patterns, namely viscous fingering, capillary fingering, and stable displacement, were observed in 3D porous media. The rough location of three displacement patterns on the Ca–M diagram was consistent with previous studies in 2D micromodel. The boundaries for three regimes were determined based on the quantitative analyses of the saturation distribution as functions of Ca and M. Compared with the result in 2D micromodel, a broader transition zone between different regimes was found in 3D porous media. The characterizations of finger structures (e.g. fractal dimension and finger width) were applied to reveal the mechanism of how the injected fluid invades the pores and throats inside porous media for different displacement patterns. The average fractal dimension of capillary fingerings was 2.58 ± 0.05, which agrees with the 2.55 defined by the invasion percolation theory. For the viscous fingering, where the viscous force dominates the invasion process, the invading fluid follows a several preferential flow paths in the same direction as the injection and the finger width was only 1 to 2 pore bodies. Besides, the invasion dynamics under continuous injection conditions were compared for typical viscous and capillary fingerings. This study may improve our understanding of the dynamics of displacement processes jointly governed by the viscous/capillary forces in 3D porous media. Furthermore, the phase diagram under various conditions (i.e. a wide range of Ca and M) can help to find a suitable reservoir conditions for subsurface processes.
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