Moisture and water transport in clay bricks are essential contributing factors towards brick decay in buildings. Experimental work is reported comparing water absorption and porosity of handmade and ...solid fired clay bricks from Paraguay. Their respective porosities were estimated by gravimetric test and, their pore distribution, degree of anisotropy and morphology were examined by SEM. Although it was found that both samples have a common composition (XRD), a higher degree of porosity was found in handmade bricks, which also absorb water at a higher rate accelerating the decay process. Experimental data is reported on the exponential kinetics behavior of water absorption similar to the one observed in capillary tubes, but with an additional diffusive process. A phenomenological model is proposed for water absorption in both types of bricks which compared with the standard model of water absorption available in the literature, produces a better representation of the experimental data.
•Pressure drop in a homogeneous channel is larger than in heterogeneous channel.•The pressure drop decreases with an increase of channel heterogeneity.•Droplet behavior in fractionally-wet channel is ...different to homogeneous channel.•The fluid-fluid menisci often form saddle-shaped interfaces.
This study presents droplet dynamics due to capillarity-wettability interaction through a constricted capillary channel. Previous research has investigated the droplet motion in a constricted capillary channel with a two-dimensional geometry and uniform wettability to determine the critical pressure necessary for the droplet to pass through the constriction, but did not consider the change of pressure as the droplet crosses through a constricted geometry. To explore the dynamic behavior of droplet motion across a constriction, a direct numerical simulation of a droplet in a three-dimensional fractionally-wet constricted channel is performed where we have two different contact angles on opposing faces of the constriction. The results show that the fractional wettability condition significantly affects the evolution of fluid-fluid and fluid-solid interfaces, pressure drop, and displacement patterns. We show that droplet dynamics in a fractionally-wet channel do not necessarily follow the same behavior as in a uniform capillary channel and cannot be predicted using uniform wettability surfaces depicted by an average contact angle. In particular, the pressure difference needed to push the droplet through the restriction with fractional wettability is lower than that for a uniform channel with a constant contact angle representing the less favorable wettability state. The fluid-fluid meniscus often forms saddle-shaped interfaces with curvature of opposite sign in orthogonal directions. Moreover, the effects of droplet size, capillary number, viscosity ratio, and constriction shape are elucidated. The pressure difference increases with droplet size and capillary number. Triangular cross-sections can be accessed at a lower pressure because of wetting layer flow.
The development of flexible lithium–sulfur (Li–S) batteries with high energy density and long cycling life are very appealing for the emerging flexible, portable, and wearable electronics. However, ...the progress on flexible Li–S batteries was limited by the poor flexibility and serious performance decay of existing sulfur composite cathodes. Herein, we report a freestanding and highly flexible sulfur host that can simultaneously meet the flexibility, stability, and capacity requirements of flexible Li–S batteries. The host consists of a crisscrossed network of carbon nanotubes reinforced CoS nanostraws (CNTs/CoS-NSs). The CNTs/CoS-NSs with large inner space and high conductivity enable high loading and efficient utilization of sulfur. The strong capillarity effect and chemisorption of CNTs/CoS-NSs to sulfur species were verified, which can efficiently suppress the shuttle effect and promote the redox kinetics of polysulfides. The sulfur-encapsulated CNTs/CoS-NSs (S@CNTs/CoS-NSs) cathode in Li–S batteries exhibits superior performance, including high discharge capacity, rate capability (1045 mAh g–1 at 0.5 C and 573 mAh g–1 at 5.0 C), and cycling stability. Intriguingly, the soft-packed Li–S batteries based on S@CNTs/CoS-NSs cathode show good flexibility and stability upon bending.
Although interstitial fluid (ISF) contains biomarkers of physiological significance and medical interest, sampling of ISF for clinical applications has made limited impact due to a lack of simple, ...clinically useful techniques that collect more than nanoliter volumes of ISF. This study describes experimental and theoretical analysis of ISF transport from skin using microneedle (MN) patches and demonstrates collection of >1 μL of ISF within 20 min in pig cadaver skin and living human subjects using an optimized system. MN patches containing arrays of submillimeter solid, porous, or hollow needles were used to penetrate superficial skin layers and access ISF through micropores (μpores) formed upon insertion. Experimental studies in pig skin found that ISF collection depended on transport mechanism according to the rank order diffusion < capillary action < osmosis < pressure-driven convection, under the conditions studied. These findings were in agreement with independent theoretical modeling that considered transport within skin, across the interface between skin and μpores, and within μpores to the skin surface. This analysis indicated that the rate-limiting step for ISF sampling is transport through the dermis. Based on these studies and other considerations like safety and convenience for future clinical use, we designed an MN patch prototype to sample ISF using suction as the driving force. Using this approach, we collected ISF from human volunteers and identified the presence of biomarkers in the collected ISF. In this way, sampling ISF from skin using an MN patch could enable collection of ISF for use in research and medicine.
•The effects of the micro-post array (MPA) and its arrangements on the maximum allowable input power for a micro pulsating heat pipe (MPHP) are experimentally investigated.•The experimental results ...show that the maximum allowable input power for the MPHPs with the MPAs placed in alternating channels and in alternating pairs of channels are enhanced by 44 % and 36%, respectively, compared to the maximum allowable input power for the bare MPHP.•The MPHP with the MPA placed in all channels does not operate at all at any input power.
This study is performed to experimentally investigate the effects of the micro-post array (MPA) and its arrangements on the maximum allowable input power for a micro pulsating heat pipe (MPHP). The maximum allowable input powers for MPHPs with the MPAs in three different arrangements are measured and compared to that for the conventional MPHP (without the MPA). To do this, ten-turn MPHPs with and without the MPA are fabricated using MEMS techniques. The overall dimensions of the MPHPs are 53 × 38 × 1.5 mm3, and the width and the height of the meandering rectangular channels are 1500 µm and 660 µm, respectively. The MPA in each case is placed on the bottom surfaces of the channels. The dimensions of the MPA are analytically determined in such a way to maximize the rate of the capillarity-induced flow by solving the Brinkman-extended Darcy's equation: the diameter, the pitch and the height are determined to be 33 µm, 97 µm, and 80 µm, respectively. The MPA is placed in three different arrangements: in alternating pairs of channels, in alternating channels, or in all channels. Ethanol is selected as the working fluid. The experiments are conducted in a horizontal orientation, and the flow is visualized with high-speed photography. The experimental results show that the MPA can have either a favorable or an adverse effect depending on its arrangement. If the MPA is placed in alternating channels, the maximum allowable input power is enhanced by 44%, compared to that for the conventional MPHP, and if it is placed in alternating pairs of channels, the maximum allowable input power is enhanced by 36%. On the other hand, the MPHP does not operate at all at any input power if the MPA is placed in all channels. Therefore, in case of the MPHP where a vapor plug oscillates in its own channel, the MPA should be placed in alternating pairs of channels or in alternating channels to enhance the maximum allowable input power for an MPHP.
Double phase problems with variable growth Cencelj, Matija; Rădulescu, Vicenţiu D.; Repovš, Dušan D.
Nonlinear analysis,
December 2018, 2018-12-00, 20181201, Letnik:
177
Journal Article
Recenzirano
Odprti dostop
We consider a class of double phase variational integrals driven by nonhomogeneous potentials. We study the associated Euler equation and we highlight the existence of two different Rayleigh ...quotients. One of them is in relationship with the existence of an infinite interval of eigenvalues while the second one is associated with the nonexistence of eigenvalues. The notion of eigenvalue is understood in the sense of pairs of nonlinear operators, as introduced by Fučík, Nečas, Souček, and Souček. The analysis developed in this paper extends the abstract framework corresponding to some standard cases associated to the p(x)-Laplace operator, the generalized mean curvature operator, or the capillarity differential operator with variable exponent. The results contained in this paper complement the pioneering contributions of Marcellini, Mingione et al. in the field of variational integrals with unbalanced growth.
The development of passively driven microfluidic labs on chips has been increasing over the years. In the passive approach, the microfluids are usually driven and operated without any external ...actuators, fields, or power sources. Passive microfluidic techniques adopt osmosis, capillary action, surface tension, pressure, gravity-driven flow, hydrostatic flow, and vacuums to achieve fluid flow. There is a great need to explore labs on chips that are rapid, compact, portable, and easy to use. The evolution of these techniques is essential to meet current needs. Researchers have highlighted the vast potential in the field that needs to be explored to develop rapid passive labs on chips to suit market/researcher demands. A comprehensive review, along with patent analysis, is presented here, listing the latest advances in passive microfluidic techniques, along with the related mechanisms and applications.
Different approaches employed in the passively driven microfluidics and LOC devices.
We present a stable numerical scheme for modelling multiphase flow in porous media, where the characteristic size of the flow domain is of the order of microns to millimetres. The numerical method is ...developed for efficient modelling of multiphase flow in porous media with complex interface motion and irregular solid boundaries. The Navier–Stokes equations are discretised using a finite volume approach, while the volume-of-fluid method is used to capture the location of interfaces. Capillary forces are computed using a semi-sharp surface force model, in which the transition area for capillary pressure is effectively limited to one grid block. This new formulation along with two new filtering methods, developed for correcting capillary forces, permits simulations at very low capillary numbers and avoids non-physical velocities. Capillary forces are implemented using a semi-implicit formulation, which allows larger time step sizes at low capillary numbers. We verify the accuracy and stability of the numerical method on several test cases, which indicate the potential of the method to predict multiphase flow processes.
Solar desalination is a cost-effective and eco-friendly technique that uses solar energy to turn impure water into clean drinking water. In a study conducted in southeastern Algeria, four similar ...solar stills were used to examine how palm stems affect the distillation process. The first still served as a control (SSR), the second had 9 stems (MSS1), the third had 6 stems (MSS2), and the fourth had 3 stems (MSS3). Results showed significant improvements in pure water production, with MSS1 yielding 5080 ml, MSS2 producing 4060 ml, and MSS3 generating 3680 ml, compared to the CSS still's output of 3320 ml. This means notable improvement rates of 53.01%, 22.90%, and 10.84% for MSS1, MSS2, and MSS3, respectively. In terms of thermal efficiency, MSS1, MSS2, MSS3, and CSS achieved efficiency levels of 57.90%, 51.57%, 48.39%, and 45.30%, respectively. The time required to recover the manufacturing costs of the devices varied between 32 and 48 days, respectively. These results highlight the positive impact of integrating palm stems on solar distillation performance, thanks to what? Is it thanks to the low thermal conductivity of the stem? Of course not, it is thanks to the stem-water zone which promotes the evaporation of water under the action of capillarity.
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