•Performance of two-plate contact capacitive level sensor has margin for improvement.•Level sensor gap reduction causes sensitivity and responsiveness improvements.•Level sensor responsiveness vs ...vibration robustness tradeoff effectively attainable.•Level sensor static and dynamic features improved with modest production cost rise.•An easy-to-follow design strategy for level sensors on helicopters is envisaged.
Cylindrical capacitors are largely employed in avionic industry as contact submerged probes of level sensors for in-flight oil-level monitoring for many reasons: their high robustness, their long MTBF (Mean Time Between Failures), maintenance-free character, virtually infinite resolution readings and last, relatively low cost. However, the cylindrical capacitors suffer from low sensitivity mainly due to small oil permittivity. This is clearly a disadvantage which collides with the ever-increasing demand for higher static and dynamic performances. To improve that, the approach adopted here consists in tweaking the conventional design of this kind of sensors guided by the study of their limitations in terms of static errors and poor responsiveness caused by phenomena of capillarity, high viscosity, and vibrations. Indeed, sensitivity doubling is proved to be achieved without compromising the indispensable former qualities. This is shown by the results of electrostatic, fluid mechanics, and structural dynamics analyses presented with enough details. Numerical simulations have been carried out and are here presented to confirm results. To summarize, with respect to the conventional capacitive level sensors currently available on the market, the achievements of the proposed design are i) an improved sensitivity that, for engine oils, is greater than 700pF/m, ii) a lower cost even though extra-costs for surface perforation must be accounted for, iii) cancellation of systematic error due to capillary phenomena and iv) improved dynamic response. Also, accurate experimental verifications are being carried out and will be shared in a future paper.
MXenes, with their remarkable attributes, stand at the forefront of diverse applications. However, the challenge remains in sustaining their performance, especially concerning Ti3C2Tx MXene ...electrodes. Current self‐healing techniques, although promising, often rely heavily on adjacent organic materials. This study illuminates a pioneering water‐initiated self‐healing mechanism tailored specifically for standalone MXene electrodes. Here, both water and select organic solvents seamlessly mend impaired regions. Comprehensive evaluations around solvent types, thermal conditions, and substrate nuances underline water's unmatched healing efficacy, attributed to its innate ability to forge enduring hydrogen bonds with MXenes. Optimal healing environments range from ambient conditions to a modest 50 °C. Notably, on substrates rich in hydroxyl groups, the healing efficiency remains consistently high. The proposed healing mechanism encompasses hydrogen bonding formation, capillary action‐induced expansion of interlayer spacing, solvent lubrication, Gibbs free energy minimizing MXene nanosheet rearrangement, and solvent evaporation‐triggered MXene layer recombination. MXenes' resilience is further showcased by their electrical revival from profound damages, culminating in the crafting of Joule‐heated circuits and heaters.
A water‐triggered self‐healing process for standalone MXene electrodes is developed, emphasizing water's role as the optimal healing solvent due to its facilitation of hydrogen bonding. This work also reveals high healing efficiencies across hydroxylated substrates, illuminating MXene's recovery potential from severe damage, as well as applicability in the development of conducting circuits and heaters.
Capillary bridges between soft substrates Wexler, Jason S; Heard, Tiara M; Stone, Howard A
Physical review letters,
02/2014, Letnik:
112, Številka:
6
Journal Article
Recenzirano
A wetting droplet trapped in the thin gap between two elastic bodies will deflect the bodies towards one another. The deformation increases the total capillary adhesion force by increasing the ...contact radius and narrowing the gap height. For flat droplets, with a large ratio of radius to gap height, the Laplace pressure causes surface deformations that are orders of magnitude larger than those induced by a sessile droplet of the same radius. We present experiments, scalings, and closed-form solutions that describe the deformation. Using variational techniques, we also show that the problem exhibits a bifurcation, where the gap spontaneously closes due to an incremental increase in drop volume.
We present a crossed dipole with frequency and polarization agility using electrochemically actuated liquid metal. For the first time, this antenna uses multidirectional displacement of liquid metal ...to enable frequency and polarization reconfiguration without the need for mechanical pumps or semiconductor devices. The dipole arms are composed of liquid metal that can be shortened and lengthened within the capillaries by applying DC voltages to each arm. Varying the lengths of the dipole arms generates two independently tuned, linearly polarized resonances from 0.8 to 3 GHz and polarization that can be switched from linear to circular over a portion of this band (0.89-1.63 GHz). Moreover, a circuit model predicts the circular polarization frequency from the input impedance. Simulation and experimental results validate the antenna concept and analysis techniques.
Robust and controllable wet attachment like tree frog toe pads attracts worldwide attention owing to potential applications in wet climbing robots, medical devices, and wearable sensors. Instead of ...conventional uniform pillars, nonuniform pillar arrays with features of inclination and gradients are discovered as typical structures on tree frog toe pads, whereas their effects on wet friction have been ignored. Micro‐nano in situ observation demonstrates that such a nonuniform pillar surface brings about unique multi‐dimensional self‐splitting behaviors in interfacial liquid films and contact stress distribution to enhance the wet attachment. The self‐splitting of the interfacial liquid film breaks the thick large area liquid film into an immense number of more uniform and robust tiny thin liquid bridges. Furthermore, the contact stress is redistributed by the inclined and gradient pillar array with contact stress self‐splitting, where the peak normal separating stress decreases ≈91% and lateral stress transmission increases ≈63%. Such contact stress self‐splitting further improves the liquid film self‐splitting by forming sturdy thin liquid films even under a larger load, which generates more robust capillarity with enhanced strong friction. Finally, theoretical models are built for the multi‐dimensional self‐splitting enhanced wet attachment, and applications in robotic and medical fields are performed to validate its feasibility.
A nonuniform pillar array with inclined and gradients pillars is developed, inspired by the tree frog's toe pad. Multi‐dimensional self‐splitting effects are observed to redistribute the liquid film and contact stress to create a more uniform and robust liquid films with enhanced wet attachment. This work provides wet friction regulating strategy with the potential to be applied to robots or precision medicines.
A breadboard approach for electrophoretic separations with contactless conductivity detection is presented. This is based on miniature off-the-shelf components such as syringe pumps, valves, and ...pressure controllers which could be set up in a very compact overall arrangement. It has a high flexibility for different tasks at hand, and the common operations of hydrodynamic injection and capillary flushing are automated. For demonstration of the versatility of the proposition, several very diverse configurations and modes of electrophoresis were successfully implemented, namely, standard capillary zone electrophoresis, pressure assisted zone electrophoresis, the simultaneous separation of cations and anions by dual-capillary zone electrophoresis, the separation of cationic amino acids by isotachophoresis, as well as the separation of small carboxylic acids by gradient elution moving boundary electrophoresis. The system also allows fast separations, as demonstrated by the analysis of six inorganic cations within 35 s. The approach addresses respective limitations of either conventional capillary electrophoresis instruments as well as electrophoretic lab-on-chip devices, while maintaining a performance in terms of detection limits and reproducibility comparable to standard instrumentation.
Spontaneous imbibition is an important mechanism for oil recovery in naturally fractured reservoirs. Understanding the effects of fluid viscosity on spontaneous imbibition is important for the design ...of injection projects and the prediction of reservoir production performances. We previously focused on the effects of the nonwetting-phase viscosity on spontaneous imbibition ( Meng Energy Fuels 2015, 29, 686−694 ), and we now investigate the effects of the wetting-phase viscosity on spontaneous imbibition. Different wetting-phase viscosities were obtained by mixing glycerol with synthetic seawater, and the wetting-phase viscosities varied from 1 to 61.5 mPa s. Experiments on cocurrent imbibition were conducted with both glass-bead and quartz-sand packings with different wetting-phase viscosities. The geometry of the glass bead was spherical and regular with a narrow size distribution, and the geometry of the quartz sand was angular and irregular with a wide size distribution. The residual oil saturation in glass-bead packing was much lower than that in quartz-sand packing because of the different pore geometries and different pore size distributions of the packings. Unlike in conventional water flooding experiments, the residual oil saturation was found to be independent of the wetting-phase viscosity for both glass-bead and quartz-sand packings. Capillary number calculations showed the remarkable result that the capillary number also seemed to be independent of the wetting-phase viscosity, which might result in similar residual oil saturations for different wetting-phase viscosities. In addition, a modified scaling group aimed at cocurrent imbibition was developed, and the correlation of the imbibition data was improved by use of the modified scaling group.
In this paper, we investigate the large-time behavior for the non-isentropic compressible Navier–Stokes equations with capillarity in the whole space
R
d
(
d
≥
3
). Under an additional smallness ...assumption of the low frequencies of initial data, the time-decay estimates of
L
q
–
L
r
type for global strong solutions near constant equilibrium (away from vacuum) can be deduced by establishing the time-weighted energy inequality. On the other hand, a pure energy approach (without the spectral analysis) different from the time-weighted energy method is performed, which allows us not only to get the time-decay rates but also to remove the smallness condition of low frequencies of initial data. The treatment of new nonlinear terms arising from capillary mainly depends on non classical Besov product estimates and the refined use of Sobolev embeddings and interpolations.
In his seminal paper on the solution of the infiltration equation, Philip (1969), https://doi.org/10.1016/b978-1-4831-9936-8.50010-6 proposed a gravity time, tgrav, to estimate practical convergence ...time and the time domain validity of his infinite time series expansion, TSE, for describing the transient state. The parameter tgrav refers to a point in time where infiltration is dominated equally by capillarity and gravity as derived from the first two (dominant) terms of the TSE. Evidence suggests that applicability of the truncated two‐term equation of Philip has a time limit requiring higher‐order TSE terms to better describe the infiltration process for times exceeding that limit. Since the conceptual definition of tgrav is valid regardless of the infiltration model used, we opted to reformulate tgrav using the analytic implicit model proposed by Parlange et al. (1982), https://doi.org/10.1097/00010694-198206000-00001 valid for all times and related TSE. Our derived gravity times ensure a given accuracy of the approximations describing transient states, while also providing insight about the times needed to reach steady state. In addition to the roles of soil sorptivity (S) and the saturated (Ks) and initial (Ki) hydraulic conductivities, we explored the effects of a soil specific shape parameter β, involved in Parlange's model and related to the type of soil, on the behavior of tgrav. We show that the reformulated tgrav (notably tgrav=F(β)S2/Ks−Ki2, ${t}_{\text{grav}}=\,F(\beta ){S}^{2}/{\left({K}_{s}-{K}_{i}\right)}^{2},$ where F(β) is a β‐dependent function) is about three times larger than the classical tgrav given by tgrav,Philip=S2/Ks−Ki2 $\,{t}_{\text{grav},\text{Philip}}={S}^{2}/{\left({K}_{s}-{K}_{i}\right)}^{2}$. The differences between the classical tgrav,Philip and the reformulated tgrav increase for fine‐textured soils, attributed to the time needed to attain steady‐state infiltration and thus i + nfiltration for inferring soil hydraulic properties. Results show that the proposed tgrav is a better indicator of time domain validity than tgrav,Philip. For the attainment of steady‐state infiltration, the reformulated tgrav is suitable for coarse‐textured soils. Still neither the reformulated tgrav nor the classical tgrav,Philip are suitable for fine‐textured soils for which tgrav is too conservative and tgrav,Philip too short. Using tgrav will improve predictions of the soil hydraulic parameters (particularly Ks) from infiltration data compared to tgrav,Philip.
Key Points
A new formulation for infiltration characteristic time, tgrav, is provided
The reformulated tgrav seems to be a better criterion for convergence time of Philip's truncated infiltration equations
The usage of reformulated tgrav improves predictions of soil hydraulic parameters
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In the industrial smelting process for titanium metal, liquid TiCl4 is supplied on molten magnesium and reduced to porous titanium in a closed steel or stainless steel container at ...800–900 °C. In the present study, in-situ observation on the magnesiothermic reduction of TiCl4 was performed by microfocus X-ray fluoroscopy. We successfully observed that the molten magnesium creeps up on container walls rapidly and that porous titanium is mainly deposited and grows on the walls by reduction of gaseous TiCl4 by the magnesium. This unique behavior of magnesium is attributed to the capillary action of molten magnesium through pores of titanium deposited on the walls.
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