Search

The traditional Hassler-Brunner (HB) interpretation method of centrifuge capillary pressure is widely used in materials, soil, biotechnology, and especially in the petroleum industry. However, the assumptions of the traditional method cannot be simultaneously satisfied, the traditional method has been known to lead significant errors in some cases. In this paper, a new double integral method is proposed to evaluate the centrifuge capillary pressure of long tight sandstone samples. Both the changes of capillary length and interface of wetting phase and non-wetting phase fluids are considered by the new integral method, thus the average pressure and saturation derived from the proposed double integral method is more sufficient in theoretic foundation and clearer on physical meaning. By comparing with the measured capillary pressure of long tight sandstone core samples from porous plate, the capillary pressure calculated from traditional HB method is obviously smaller than the measured value, and the discrepancy increases with the decreasing core porosity. However, the average capillary pressure obtained by the proposed double integral method is remarkably consistent with the measured value. The findings of this study can help for better understanding of distribution of wetting phase fluid and average centrifuge capillary pressure in the core during centrifugal process.

We report elastocapillary interaction between a long rectangular membrane fixed along its central axis and a liquid drop dispensed at one of its ends. The introduction of the drop results in the elastocapillary-driven wrapping of the membrane along its width and a concomitant flow in the resulting conduit along its length. Depending upon the drop size (d) and capillary length scale (L_c), we identified general criteria for achieving complete wrapping of the membrane in the dry state from energy consideration. For small droplets satisfying d≲L_c, we find that the critical membrane length (W_c) required for complete wrapping is proportional to the elastocapillary length scale (L_ec). In case of large droplets with d>L_c, the wrapping behavior depends on the ratio of membrane width to elastocapillary length scale (W⁄L_ec ) and the ratio of capillary length scale to the elastocapillary length scale (L_c⁄L_ec ). Our study suggests that the critical membrane width for complete wrapping is smaller in the wet state compared to that in the dry state, which can be attributed to the existence of a transmembrane pressure in the wet state. The effect of membrane thickness and width and drop volume on the length and cross-section of the wrapped conduit and attached width of the wrapped membrane is studied. For small droplets, the resulting elastocapillary flow exhibits an inertial regime at small times, followed by a Washburn regime at intermediate times, and finally an inertial regime, and for large droplets, only an inertial regime is observed throughout.

Funding Information: This project has received funding from the Academy of Finland (under the project WTF-click-nano), Jenny and Antti Wihuri foundation, Puunjalostusinsinöörit Oy and FinnCERES. The authors also gratefully acknowledge Katrina Räty for proofreading the article. Additionally, the authors acknowledge the provision of facilities and technical support by Aalto University at OtaNano -Nanomicroscopy Center (Aalto-NMC) and D22 instrument at ILL, Dr. Lionel Porcar. Publisher Copyright: © 2021, The Author(s). The production of cellulose-based textile fibers with high toughness is vital for extending the longevity and thus developing a sustainable textile industry by reducing the global burden of microplastics. This study presented strategies to improve fiber toughness by tuning spinneret geometries. Experimental studies were conducted by spinning with different spinneret geometries and measuring the mechanical and structural properties of the spun fibers. In addition, numerical simulation tools were used to better understand the effects of spinneret geometry. The altering parameters of the spinneret geometries were the capillary diameters D, the angle of the entry cone into the spinning capillary, and the ratio of capillary length to diameter L/D. The highest fiber toughness could be achieved at a capillary aspect ratio of 1 to 2. The obtained maximum fiber toughness was 93 MPa with a tensile strength of 60 cN/tex and a concomitant elongation of 16.5%. For these fiber properties, a 13 wt% solution of a high-puritypulp with higher viscosity in [DBNH][OAc] was spun into a 1.3 dtex fiber using a D100 spinneret with a capillary of 1:1 length/diameter and an entrance angle of 8°. It was noticeable that the microvoid orientations decreased almost linearly with increasing toughness of the fibers. The morphologies of the fibers were similar regardless of the spinneret geometries and the raw materials used in the spinning process. In summary, by modulating the spinneret geometries, Ioncell fibers obtained high toughness that have the potential to replace synthetic fibers.

In this paper the two-phase propane flow through a copper capillary tube with an inner diameter of 1.1799 mm is thoroughly investigated according to metastable flow and hysteresis effects of the flow. The hysteresis effect causes ambiguity in experimental data of the two-phase pressure drop or mass flow. It is assumed that the hysteresis effect occurs when metastable flow is developed. As cause for the development of the metastable flow, the wetting ratio of the capillary tube is derived. The wetting ratio is considered to be the ratio of the length of the capillary that is covered by liquid flow only and the total capillary length. The findings are transferred into a mathematical description and supplemented into an existing homogeneous flow model. The extended model is able to simulate the general course of observed hysteresis courses and shows improvement in predicting the overall data base of previous work by being able to predict ambiguous data.

Polymer microspheres with uniform size, composition, and surface property have gained extensive researches in past decades. Conventional bottom-up approaches are using monomers or oligomers to build up desired polymer microspheres. However, directly shaping high-molecular-weight polymers into well-ordered polymer microspheres remains a great challenge. Herein, we reported a facile and efficient top-down approach to fabricate microspheres with high-molecular-weight polymer microfibers. By harnessing interfacial engineering-control during the polymer microspheres formation, uniformly sized microspheres could be produced with widely ranged diameters (from 10 µm to the capillary length of each polymer melt). The size limitation of this approach could be further extended by a controllable Plateau-Rayleigh instability phenomenon. Principally, the top-down approach allows fabrication of microspheres by various polymer melts with surface energy higher than 25 mN/m. Our work paves a way for green, cost-effective, and customizable production of a variety of functional polymer microspheres without any chemical reaction assistant.

Advancing and receding angles are physical quantities frequently measured to characterize the wetting properties of a rough surface. Thermodynamically, the advancing and receding angles are often interpreted as the maximum and minimum contact angles that can be formed by a droplet without losing its stability. Despite intensive research on wetting of rough surfaces, the gravitational effect on these angles has been overlooked because most studies have considered droplets smaller than the capillary length. In this study, however, by combining theoretical and numerical modeling, we show that the shape of a droplet smaller than the capillary length can be substantially modified by gravity under advancing and receding conditions. First, based on the Laplace pressure equation, we predict the shape of a two-dimensional Cassie-Baxter droplet on a textured surface with gravity at each pinning point. Then, the stability of the droplet is tested by examining the interference between the liquid surface and neighboring pillars and analyzing the free energy change upon depinning. Interestingly, it turns out that the apparent contact angles under advancing and receding conditions are not affected by gravity, while the overall shape of a droplet and the position of the pinning point are affected by gravity. In addition, the advancing and receding of the droplet with continuously increasing or decreasing volume are analyzed, and it is shown that the gravitational effect plays a key role in the movement of the droplet tip. Also, the gravitational effect on the degree of the stability of the droplet upon the external effect such as vibration is discussed. Finally, the theoretical predictions were validated against line tension-based front tracking modeling (LTM) that seamlessly captures the attachment and detachment between the liquid surface and the solid substrate. Our findings provide a deeper understanding on the advancing and receding phenomena of a droplet and essential insight into designing devices that utilize the wettability of rough surfaces.

Poly lactic acid (PLA) and High density polyethylene (HDPE) have been blended in a Brabender plastograph in the molten state. The melt die swell of the blends has been studied by using a capillary rheometer. Effects of the capillary dimensions, shear stress, shear rate, temperature and blending ratio on die swell of PLA/HDPE blend melts were investigated. The results showed that die swell ratio decreased with increasing of capillary length and temperature while it increased with increasing of shear stress, shear rate and capillary diameter. It was also found that the plots of die swell versus blending ratio go through a maximum for blending ratio PLA/HDPE (60/40).

A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity. Keywords: Air cooling system, Rayleigh-plateau instability, Direct contact heat exchanger, Waste heat removal system

A direct numerical simulation of the process of binary alloy separation in a thin nonuniformly heated circular capillary is carried out. The key point of this process is the assumption of the existence of a thin gas layer between the melt and the boundary of the reservoir due to the non-wetting conditions. This effect was described using the equations of interphase hydrodynamics, which made it possible to construct a phenomenological model of the processes at the melt-solid interface for mixtures of liquid metals. The problem was solved by the finite difference method in combination with an explicit scheme on the PGNIU-Kepler supercomputer at the Research and Education Center “Parallel and Distributed Computing” of the Perm State National Research University. The velocity and temperature fields, as well as the concentration of melt components in the bulk and on the surface, were determined through numerical simulation. The dynamics of the separation process is described. It is shown that the longitudinal temperature gradient and the non-wetting conditions on the lateral surface create a downward motion of the melt along the boundary, which, together with the adsorption and desorption effects, leads to the formation of volumetric nonuniformity of the concentration of the mixture components along the capillary. The experimentally observed time dependence of the difference in the volume concentrations of the components at the ends of the capillary is reproduced. The distribution of volume concentrations of the components and the surface phase along the capillary is analyzed at various values of the adsorption and desorption coefficients and the Marangoni number. The dependence of the concentration difference for the melt components at the ends of the capillary as function of its length is studied. It is found that the separation effect intensifies with an increase in the capillary length. A qualitative and quantitative comparison of most of the characteristics demonstrates a good correlation of the calculation results with the data previously obtained for the plane problem and the available experimental data. A numerical experiment shows that the motion in the surface layer is rather intense. The heavy component is transported by the convective flow to the lower part of the capillary so that its concentration increases by almost an order of magnitude on 1/8 of the capillary surface.

Boiling utilizes latent heat of vaporization of the fluid to dissipate large amount of heat at small temperature budgets. Surfaces with micro−/nano-scale wettability patterns have been shown to improve the heat transfer coefficient during pool boiling. In this work, we propose a simple and cost-effective technique to fabricate heterogenous surfaces with macroscale wettability patterns comparable to the capillary length of the boiling fluid. We demonstrate that such surfaces can enhance boiling heat transfer coefficient significantly. Four configurations (two samples of hydrophobic dots and lines each) of heterogeneous surfaces are investigated to understand the influence of the diameter, pitch and arrangement of hydrophobic regions on the hydrophilic background surface on the heat transfer coefficient. Results indicate that up to ≈66% enhancement in the heat transfer coefficient can be achieved in comparison to the bare surface. If the hydrophobic dots are spaced out sufficiently, number of dots on the surface controls the heat transfer coefficient at low heat fluxes. However, nucleation is initiated even on the hydrophilic background surface at high heat fluxes and smaller diameter dots start performing better than the larger diameter dots. Smaller pitch (< bubble departure diameter) leads to lateral coalescence among the departing bubbles in case of lined pattern configuration, thereby lowering the heat transfer coefficient. The study demonstrates that simple and cost-effective macroscale wettability patterns can separate liquid supply and vapor removal pathways to enable comparable heat transfer coefficients enhancements otherwise achieved through sophisticated and costly surface patterning techniques discussed in literature.

The relative hydraulic conductivity curve K r (h) = K/K s is a key variable in soil modeling. This study proposes a model to represent K r (h), the so-called Gardner dual (GD) model, which extends the classical Gardner exponential model to h values greater than h o, the suction value at the inflection point of the K r (h) curve in the log-log scale. The goodness of fit of GD using experimental data from UNSODA was compared to that of the MVG [two-parameter (K ro , L) Mualem-van Genuchten] model and a corresponding modified MVG model (MVGm). In 77 soils without evidence of macropore flow, GD reduced the RMSE errors by 64% (0.525 to 0.191) and 29% (0.269 to 0.193) in relation to MVG and MVGm, respectively. In the remaining 76 soils, GD generally was less accurate than MVG and MVGm, since most of these soils presented evidence of macropore flow (dual permeability). GD has three parameters and two degrees of freedom, like MVG. Two of them allow the calculation of the macroscopic capillary length, a parameter from the infiltration literature. The three parameters are highly dependent on the K r (h) data measurement in a short wet suction range around h o, which is an experimental advantage.

Nucleate pool boiling experiments were performed on plain and five laser-textured stainless-steel foils using saturated pure water, 100% ethanol, 0.4% and 4.2% mole fraction ethanol – water mixtures. All laser-textured samples contained untreated, smooth 0.5 mm wide regions and intermediate textured surfaces, that differ in the width of the laser patterned regions (from 0.5 mm to 2.5 mm). For smooth surfaces, we measured significant decreases in average heat transfer coefficients (HTC) and increases in bubble activation temperatures in comparison with the laser-textured surfaces for all the tested working fluids. Significant enhancement in HTC (280%) on a textured heating surface with 2.5-mm-wide laser pattern was recorded using pure water. For pure ethanol, the highest enhancement of 268% was achieved on a heating surface with 1.5-mm-wide laser pattern. The highest enhancement of HTC for the tested binary mixtures was obtained using 2.0-mm wide-laser-textured regions (HTC improved by 235% and 279% for the 0.4% and 4.2% mixtures, respectively). Our results indicate that laser texturing can significantly improve boiling performance when the intervals of the laser-textured patterns are close to the capillary lengths of the tested fluids.

The article presents the results of a study of the rheological behavior of binary composites based on serial polyethylene grade LDPE 15803-020 with different content of microcellulose grade Filtracell, in a wide range of temperatures and shear rates during deformation through a capillary diameter of 1 mm and a length of 5 and 30 mm. Stable flow regime is manifested in the temperature range from 160 to 200°C for composites containing microcellulose in an amount of 30 wt.%, and its partial replacement with spent microcellulose (waste production of vegetable oils) can reduce the effective viscosity to 25%, but the upper limit of the temperature range is limited to the exudation of impurities (190°C). The Bagley correction is carried out, the coefficients of the equations describing the dependences of the true shear stress, regardless of the capillary length, are calculated.

Simulations of a 1-MeV proton microbeam transmitted through an insulating macrocapillary were conducted to gather a detailed insight into the related guiding mechanisms. The calculations were performed in view of previous experiments showing guided transmission for a proton beam with a diameter of 2 μm. The simulations are in agreement with the previous results using a microbeam with a divergence of 0.6 ° , for which guided transmission was observed. This guiding is attributed to the generation of an extended charge patch, producing a broad deflection field along the capillary length. On the other hand, it is found that the transmission of the microbeam without divergence is impossible showing that the divergence plays a decisive role in the guiding process. Further results provide clear evidence that guiding can occur for usual MeV proton beams rather than only for a microbeam.

A fiber optic refractive index sensor based on tapered capillary is proposed. A multimode interferometer generated by annular high-order mode is fabricated by fused thin-walled capillary between single-mode fibers, which has high refractive index sensitivity. The experimental results show that the sensor has a piecewise-linear refractive index response with gradually increasing sensitivity in the range of 1.3328~1.4553. It is found that the increase of capillary length is beneficial to the increase of refractive index sensitivity. For the sample with 10 mm capillary, the RI sensitivity is up to 7474.959 nm/RIU, the temperature sensitivity is only 9.48 pm/°C and the measurement error is ±2.12×10-3. The results show that the sensor has good accuracy and repeatability in refractive index measurement. The sensor is suitable for high refractive index range in biological process monitoring, where high refractive index sensitivity and low temperature cross sensitivity are required.

We propose and demonstrate a half-circle interferometer using a hollow glass microsphere (HGM) resonator. The half-circle interference is induced by a mismatch between the fundamental mode in the HGM and the modes in the capillary wall. The theoretical model is verified by comparing the simulated and experimental results. The variation in capillary length induced by the axial pressure contributes the most to the half-circle interference, which features a device with a high hydrostatic pressure sensitivity of −1.099 nm/kPa. This device shows potential as a hydrostatic pressure sensor owing to its stability, high sensitivity, and robustness.

The interactions of heparan sulfate proteoglycans (HSPGs) present on the cell surface with target proteins lead to cell signaling and they are considered as viral receptors. The analysis of the recognition mechanism between HSPG and its potential ligands and high-throughput screening in drug discovery thus remain important challenges. Glycidyl methacrylate-based monoliths were thus prepared in situ in miniaturized capillary columns (internal diameter 75 μm) and HSPG was grafted onto them by the use of the Schiff base method. The quantity of grafted HSPG was in the nanogram range (11 nanograms per cm of capillary length). This is of significant importance when working with less available or expensive biological material. Other advantages of our miniaturized capillary column are as follows: (i) the immobilization process of HSPG onto the organic monolithic support was reliable and reproducible. (ii) The resultant affinity capillary column showed a strong resistance to changes in temperature and pH and a negligible non-specific interaction. So as to confirm the proper functioning of our miniaturized capillary column, the molecular recognition by HSPG of five selected compounds including three ligands of interest related to SARS-CoV-2 was studied.

Bubble formation in liquids is frequently observed in nature and applied in various industrial processes. These include pool and flow boiling for thermal management systems, where bubbles may form asymmetrically at narrow slits and in convective flows. While previous studies have focused on symmetric bubble formation at circular orifices, the dynamics of asymmetric bubble formation remains poorly understood. Here, we experimentally investigate bubble formation at rectangular orifices and examine the effects of the orifice size and aspect ratio and the gas flow rate on the bubble size. The asymmetric bubble shape evolution at the rectangular orifice is analyzed, and we find that the size of the bubble neck is controlled either by the orifice size or by the capillary length. Based on these findings, we develop a static force balance model to predict the bubble size in the quasi-static regime, where the roles of Bond number and aspect ratio are identified. The bubble size evolution in the dynamic regime is further understood by introducing a Weber number that evaluates the effect of the virtual mass force induced by gas flow. Our study provides physical understanding of the dynamics of asymmetric bubble formation and guidance to predict the bubble size at asymmetric orifices.

In obesity, the skeletal muscle capillary network regresses and the insulin-mediated capillary recruitment is impaired. However, it has been shown that in the early stage of advanced obesity, an increased functional vascular response can partially compensate for other mechanisms of insulin resistance. The present study aimed to investigate the changes in the capillary network around individual muscle fibres during the early stage of obesity and insulin resistance in mice using 3D analysis. Capillaries and muscle fibres of the gluteus maximus muscles of seven high-fat-diet-induced obese and insulin-resistant mice and seven age-matched lean healthy mice were immunofluorescently labelled in thick transverse muscle sections. Stacks of images were acquired using confocal microscope. Capillary network characteristics were estimated by methods of quantitative image analysis. Muscle fibre typing was performed by histochemical analysis of myosin heavy chain isoforms on thin serial sections of skeletal muscle. Capillary length per muscle fibre length and capillary length per muscle fibre surface were increased by 27% and 23%, respectively, around small muscle fibres in obese mice, while there were no significant comparative differences around large fibres of obese and lean mice. Furthermore, the capillarization was larger around small compared to large fibres and there was a shift toward fast type myosin heavy chain isoforms, with no significant changes in muscle fibre diameters, tortuosity and anisotropy in obese mice. Overall, the results show that obese insulin-resistant mice have selective increase in capillarization around small predominantly intermediate muscle fibres, which is most likely related to the impaired glucose metabolism characteristic of type 2 diabetes.

Previous studies have shown that diffusion-limited evaporation in the confined spaces such as tubes and gaps between parallel plates strongly depends on geometrical gap configurations. However, there is no study discussing the dependence of evaporation quantity on perimeter and curvature of the meniscus. In addition, there is no theoretical approach to predicting evaporation rates from menisci which have various interface shapes. In this study, evaporation rates in various geometrical gap configurations made of glass were experimentally measured and the dependence of evaporation quantity on perimeter and curvature of the meniscus was discussed. As the result, the different evaporation tendencies were found regarding the relation between capillary length and the characteristic length of gap configuration defined as an inner radius of a tube or a half of gap distance between parallel plates. Moreover, we derived the scaling law to relate evaporation rates to various interface shapes of menisci. The maximum evaporation rates predicted by this scaling law were consistent with the experimental data obtained in this study.

In this study, two types of mini-channel condenser are integrated into a household refrigerator in order to increase the performance of the system. Since the integration process requires the substitution of capillary tube which will be followed by charging a different amount of refrigerant, this work focuses on finding the right amount of the refrigerant and the right size of the capillary as well. This experimental study is carried out on a commercial household refrigerator in a climatic chamber with respect to IEC standards. During the experiments, two types of mini-channel condensers have been analyzed with five different capillary lengths and five varying coolant amounts in order to find the best combination for better performance. The outcomes of the study release the thresholds for either capillary length or refrigerant amount, which are 3.25 m and 50 g, respectively, that will enlighten the further studies on the same investigations.

An optimized and economical capillary electrophoretic method for both off-line and on-line study of the enzyme aldehyde oxidase and its substrate phthalazine was developed. The separation of the substrate phthalazine and its metabolite 1-phthalazinone was achieved using micellar electrokinetic chromatography (MEKC) with sodium dodecyl sulphate in the background electrolyte (BGE). The BGE consists of 25 mM sodium phosphate buffer containing 50 mM sodium dodecyl sulphate at pH 7.4. A bare-fused-silica capillary with a capillary length of 40 cm, 50 μm ID and effective length of 30 cm was used to develop the capillary electrophoresis method. Improved separation conditions were elaborated and the separation method was validated based on the ICH and EMA guidelines. The limit of detection for phthalazine and 1-phthalazinone was 8 μM and 3 μM, respectively. The limit of quantification was 25 μM for phthalazine and 10 μM for 1-phthalazinone. The linearity of the detector response was checked for 1-phthalazinone at nine different concentrations in the range 10–500 μM and the determination coefficient was 0.9994. Accuracy was tested by comparing the corrected peak area of 1-phthalazinone reference solution at 20 μM and 50 μM with the corrected peak area of 20 μM and 50 μM 1-phthalazinone in the presence of human liver cytosol (HLC). Accuracy values of +5.3% and -2.5% were obtained at 20 μM and 50 μM, respectively. The on-line enzymatic reaction was successful with the application of the method of transverse diffusion of laminar flow profiles (TDLFP), which enables the mixing as well as separation of the enzyme and substrate inside the nanoliter-scale capillary. TDLFP is examined to be precise when performing 5 consecutive injections, with a relative standard deviation of 7.16% which is within the limitation of EMA standards. This miniaturized and low-cost incubation and separation method could be further introduced into industry and extended to other substrates.