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Drying processes in porous materials and their optimization are of interest in research and in many industrial applications. X-ray micro-computed tomography presents a versatile instrument for the ...

A simultaneous impact of three water drops (aligned with equidistant spacing) onto a solid wall covered by a thin liquid film is predicted by direct numerical simulation using the multiphase code Free Surface 3D (FS3D) which is based on the volume-of-fluid (VOF) method and uses the piecewise linear interface calculation (PLIC) method to reconstruct the interface. The numerically reproduced splashing morphology is qualitatively and quantitatively compared with available experimental data and theoretical models. The results show the reliability of the numerical tool (FS3D) to predict quantitatively the complex phenomena involved in detail, like the evolution of crown geometry and the liquid structures resulting from the interaction between the different crowns. The comparison evidenced also the most important critical aspects of the numerical simulation of such complex phenomena, not often reported or even considered in the available open literature (e.g. the early lamella rupture observed in the simulation, caused by a limited numerical resolution, antagonist to the inadequacy of related rupture models). This phenomenon is still a challenging research topic (from both the experimental and the numerical side) and its study is still a necessary step for gaining detailed knowledge for improving the stochastic simulations of multiple drops impact onto liquid films.

Bioartificial Liver (BAL) devices are extracorporeal systems designed to support or recover hepatic function in patients with liver failure. The design of an effective BAL remains an open challenge since it requires a complex co-optimisation of cell colonisation, biomaterial scaffold and BAL fluid dynamics. Building on previous evidence of suitability as a blood perfusion device for detoxification, the current study investigated the use of RGD-containing p(HEMA)-alginate cryogels as BAL scaffolds. Cryogels were modified with alginate to reduce protein fouling and functionalised with an RGD-containing peptide to increase hepatocyte adhesion. A novel approach for characterisation of the internal flow through the porous matrix was developed by employing Particle Image Velocimetry (PIV) to visualise flow inside cryogels. Based on PIV results, which showed the laminar nature of flow inside cryogel pores, a multi-layered bioreactor composed of spaced cryogel discs was designed to improve blood/hepatocyte mass exchange. The stacked bioreactor showed a significantly higher production of albumin and urea compared to the column version, with improved cell colonisation and proliferation over time. The cell-free cryogel-based device was tested for safety in a bile-duct ligation model of liver cirrhosis. Thus, a stacked bioreactor prototype was developed based on a surface-engineered cryogel design with optimised fluid dynamics for BAL use.

Micro computed tomography is a powerful tool for the inspection of porous media since it essentially provides the possibility to reconstruct a three dimensional volume of an object at micrometric spatial resolution. The technique is non-intrusive, while still being capable of dealing with matter that is opaque at the wavelengths of visible light. The processing of the obtained data such as segmentation and morphology characterization in multi-phase porous systems is a challenging research topic for the comprehension of countless physical problems in a variety of technical applications. This research project is dedicated to the investigation and optimization of all aspects along the process chain, starting from the preparation of adequate porous samples towards the acquisition of the computed tomographies and data processing until pore-scale fluid displacement processes in multi-phase systems can eventually be visualized and characterized. Presented here are the production process of a regular glass bead pack, the data acquisition and processing methods and the obtained results for tomographic experiments during which the pack is containing distilled water, doped with potassium iodide and air and is subjected to drying in ambient atmosphere. The sample design allows validation of values derived from tomographic data with analytically predictable values.

The present manuscript presents the application of X-ray computed microtomography (microCT) as a non-intrusive technique to calculate the local and global mass transfer rates around arbitrary shaped particles. The technique is validated on the case of mass transfer around a spherical particle in free convection. A review of available experimental and numerical investigations for spherical particle is reported in comparison to the obtained results. The 3-dimensionality of the microCT approach allows the calculation of the local curvature. The correlation between local curvature and mass transfer rate is, therefore, made experimentally feasible for arbitrary shaped particles.

We identify the physical mechanism through which newly developed quaternary ammonium salt (QAS) deposit control additives (DCAs) affect the rheological properties of cavitating turbulent flows, resulting in an increase in the volumetric efficiency of clean injectors fuelled with diesel or biodiesel fuels. Quaternary ammonium surfactants with appropriate counterions can be very effective in reducing the turbulent drag in aqueous solutions, however, less is known about the effect of such surfactants in oil-based solvents or in cavitating flow conditions. Small-angle neutron scattering (SANS) investigations show that in traditional DCA fuel compositions only reverse spherical micelles form, whereas reverse cylindrical micelles are detected by blending the fuel with the QAS additive. Moreover, experiments utilising X-ray micro computed tomography (micro-CT) in nozzle replicas, quantify that in cavitation regions the liquid fraction is increased in the presence of the QAS additive. Furthermore, high-flux X-ray phase contrast imaging (XPCI) measurements identify a flow stabilization effect in the region of vortex cavitation by the QAS additive. The effect of the formation of cylindrical micelles is reproduced with computational fluid dynamics (CFD) simulations by including viscoelastic characteristics for the flow. It is demonstrated that viscoelasticity can reduce turbulence and suppress cavitation, and subsequently increase the injector’s volumetric efficiency.

Experiments and numerical simulations of cavitating flow inside a single-orifice nozzle are presented. The orifice is part of a closed flow circuit, with diesel fuel as the working fluid, designed to replicate the main flow pattern observed in high-pressure diesel injector nozzles. The focus of the present investigation is on cavitation structures appearing inside the orifice, their interaction with turbulence and the induced material erosion. Experimental investigations include high-speed shadowgraphy visualization, X-ray micro-computed tomography (micro-CT) of time-averaged volumetric cavitation distribution inside the orifice as well as pressure and flow rate measurements. The highly transient flow features that are taking place, such as cavity shedding, collapse and vortex cavitation (also known as ‘string cavitation’), have become evident from high-speed images. Additionally, micro-CT enabled the reconstruction of the orifice surface, which provided locations of cavitation erosion sites developed after sufficient operation time. The measurements are used to validate the presented numerical model, which is based on the numerical solution of the Navier–Stokes equation, taking into account compressibility of both the liquid and liquid–vapour mixture. Phase change is accounted for with a newly developed mass transfer rate model, capable of accurately predicting the collapse of vaporous structures. Turbulence is modelled using detached eddy simulation and unsteady features such as cavitating vortices and cavity shedding are observed and discussed. The numerical results show agreement within validation uncertainty with the obtained measurements.

The development and the following inactivation of a carbon-based biocathode in single chamber and membraneless MFCs was investigated in this work. The electrochemical behavior of the biocathode has been analyzed over time during the MFC life. X-Ray Micro-Computed Tomographies (microCTs) have been carried out at progressive stages, documenting the building over time of a layer of scale deposition becoming thicker and thicker up to the cathode inactivation. The technique provides cross-sectional (tomographic) grayscale images and 3D reconstruction of volumes. Lighter color indicates lower X-ray attenuation (i.e., lower atomic density) thus allowing distinguishing biofilm from inorganic fouling on the basis of the average atomic number Z of each voxel (3D pixel). MicroCT was combined with Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) in order to qualitatively recognize chemical species in each different layer of the cathode's section. Results correlated the presence of biofilm and calcium carbonate deposits, prevalently in the inner part of the cathode, with the produced electric current over time. A specific microCT-related software quantified the time-dependent carbonate scale deposition, identifying a correlation between the decreasing performances of the device and the increasing quantity of scale deposition that penetrates the cathode cross section in time.

In the present work, experimental investigations of single and double drop impacts into a deep pool of the same liquid are presented. For the first time, vortex interactions of two synchronised spherical drops of equal size are presented and compared to the evolution of undisturbed vortex rings generated by single drop impacts. High-speed images show novel and not yet documented vortex structures. The results show that vortex rings can be generated for drop Weber numbers well above the boundaries given in the literature, but with a different structure. Reynolds numbers of the relaminarised vortex rings depend on the presence of an outer vortex ring and are found to be significantly lower, if this structure was suppressed.

The interaction between an atomized fluid and a solid surface has a great importance in many fields, both in adiabatic conditions and when heat transfer is involved. To investigate the behavior of many drops in contact with a surface, the first step is to study a single one of them and in that, surface wettability is key parameter. Wettability analyses are usually performed by contact angle measurement, in most cases using the sessile drop or captive bubble techniques. Such techniques require optical acquisition of a side view of the drop or bubble, with a series of drawbacks when conventional optics are used, in particular for not uniform, not planar or rough base surfaces. X-ray micro-computed tomography is therefore used to acquire a 3D scan of a drop gently deposited on a surface, with the aim to reconstruct the drop surface and to perform contact angle measurements on true cross-sections of the drop-surface couple. Comparison with contact angle measurements performed on conventional images is performed. The results evidence that the proposed technique is very promising for surface characterization and to get more accurate and detailed information about wettability characteristics.

The cathode performances are one of the main limitations related with microbial fuel cell (MFC) that strongly limit the overall output. The low power produced is an important problem that has to be addressed for the scale up of the MFCs. Cathodic overpotential is particularly high at circumneutral pH when carbonaceous or metallic catalysts are used [1]. Overpotentials are much lower for enzymes but enzymatic biocathodes are expensive and not durable [2]. Single chamber membrane-less MFCs are preferred due to the lower cost and higher power output. In membrane-less MFCs, both electrodes (anode and cathode) are exposed directly to the electrolyte or carbon-rich solution. The presence of growing bacteria inside the chamber generates electron acceptor-rich and electron donor-rich zones, which serve as cathode and anode, respectively. In fact, bacteria consume rapidly the oxygen inside the chamber creating anaerobic conditions that are useful for electrogenic bacteria for colonizing the anode electrode and oxidize organics. The cathode used is an air-breathing cathode and it is porous and allows oxygen to penetrate through the anodic solution. A biofilm is formed also on the cathode surface consuming the oxygen and forming a natural and cheap membrane that separate the cathode from the solution and stop the oxygen leaking inside the chamber, thus ensuring anaerobic conditions. Strict anaerobes grow quickly within 1 week of operations as recently showed [3]. It has been showed previously that the biofilm formation on the cathode initially increased the cathodic reduction reaction [4]. In this work, we analyzed the cathode performances and the MFC overall performance along 6 months operations [5]. At the end of the experimentation, the cathode has been examined with X-Ray Micro Computed Tomography (microCT), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) for characterizing the organic/inorganic layer on the cathode surface facing the solution [5]. Single chamber MFC with volume of 125 mL was used and the cell was fed with raw wastewater and sodium acetate. The results obtained showed that cathode reduction reaction increased in the first 15 days but then decreased continuously over time [5]. The initial increase might be due to the formation of an initial biofilm layer that probably enhanced the cathodic reduction reaction. Over time, precipitation of compounds and fouling might take place. It has been speculated that thick biofouling decreased the performances. After 6 months, part of the cathode was dried and analyzed with SEM/EDX and the other part was analyzed as it is using microCT [5]. SEM has the great potential of very high resolution but images have to be taken after treating the sample and consequently change the morphology of the biofilm after drying it. Moreover, SEM is not able to pass through objects and consequently only the surface can be analyzed. The coupling with EDX allowed to identify sodium (Na) on the external part of the cathode and calcium (Ca) on the internal face [5]. Na and Ca were present in form of carbonate. The production of OH- due to the cathodic reaction, caused the alkalinization of solution at the interface with the cathode making the precipitation of carbonate species on the cathode is very probable. MicroCT images allowed making a complete 3D scan of the entire cathode analyzed. Interestingly, the different components (cathode, carbonate and biofilm) were clearly distinguishable (Figure 1). In fact, a compact and continuous thick layer of carbonate was clearly visible between the cathode and the biofilm (Figure 1, white color). Those results obtained using microCT clearly showed that the thick, not porous carbonate layer and not the biofilm itself might increase the proton mass transport resistance from the solution to the catalytic sites and lowering dramatically the cathode output during long terms operation. Reference [1] C. Santoro, F. Soavi, A. Serov, C. Arbizzani, P. Atanassov. Biosensors and Bioelectronics. 2016, 78, 229-235. [2] C. Santoro, S. Babanova, B. Erable, A. Schuler, P. Atanassov. Bioelectrochemistry. 2016, 108, 1-7. [3] M. Grattieri, S. Babanova, C. Santoro, E. Guerrini, S.P.M. Trasatti, P. Cristiani, M. Bestetti, P. Atanassov. Electroanalysis, 2015, 27(2), 327-335. [4] P. Cristiani, M.L. Carvalho, E. Guerrini, M. Daghio, C. Santoro, B. Li. Bioelectrochemistry, 2013, 92, 6-13. [5] M. Santini, M. Guilizzoni, M. Lorenzi, P. Atanassov, E. Marsili, S. Fest-Santini, P. Cristiani, C. Santoro. Biointerphases. 2015, 10, 031009. Figure 1. Cross Section of the cathode analyzed using microCT. Figure 1

The impact of liquid drops on heated surfaces is a phenomenon of relevance in many applied fields, like in direct injection internal combustion engine, where the fuel drops impact on the hot piston wall, or in spray cooling, etc. The first step to a deeper understanding of the phenomenon is to try to investigate the effects produced by the impact of single drops on a heated surface, among these the so called secondary atomisation, i.e. the formation of small droplets after the impact of the primary drop on the wall, is considered of paramount importance for many applications. The use of non-intrusive optical techniques is necessary in this field and the paper describes the application of three of such techniques to the analysis of the secondary atomisation produced by single millimetric drop impacting on a heated aluminium surface under different regimes of phase transition. Phase Doppler anemometry is used to measure the size and velocity of the secondary droplets in a size range between 2μm and 250μm. However, the impact produces droplets having also drops of larger diameter (up to 700 μm) and to extend the range of the measured size an image analysis technique based on a high resolution CCD camera was also used. The present configuration allowed to detect droplets having a size from 30μm on, and a proper analysis of the results from this technique, together with those coming from the PDA measurements, consented to obtain the "extended" secondary droplet size distribution from 2μm to few mm. A PIV (particle image velocimetry) technique was also applied to collect information about the velocity of the secondary droplets acquiring the images produced by a double shot strobolamp and using the cross-correlation method. Results are compared and the advantages and disadvantages of each technique are discussed.

Highly hydrophobic surfaces have been intensively investigated in the last years because their properties may lead to very promising technological spillovers encompassing both everyday use and high-tech fields. Focusing on textiles, hydrophobic fabrics are of major interest for applications ranging from clothes to architecture to environment protection and energy conversion. Gas diffusion media - made by a gas diffusion layer (GDL) and a microporous layer (MPL) - for fuel cells are a good benchmark to develop techniques aimed at characterizing the wetting performances of engineered textiles. An experimental investigation was carried out about carbon-based, PTFE-treated GDLs with and without MPLs. Two samples (woven and woven-non-woven) were analysed before and after coating with a MPL. Their three-dimensional structure was reconstructed and analysed by computer-aided X-ray microtomography (CT). Static and dynamic wettability analyses were then carried out using a modified axisymmetric drop shape analysis technique. All the surfaces exhibited very high hydrophobicity, three of them near to a super-hydrophobic behavior. Water drop impacts were performed, evidencing different bouncing, sticking and fragmentation outcomes for which critical values of the Weber number were identified. Finally, a CT scan of a drop on a GDL was performed, confirming the Cassie-Baxter wetting state on such surface.

The paper reports an experimental study of single millimetric water drop impacts onto a hot aluminium alloy (AlMg3) surface. The main aim of this investigation was to evidence the effect of the heat transfer mechanism on the secondary atomisation, but the effect of impact velocity and surface characteristics on the impact outcomes were also studied. Two non-intrusive measurement techniques, namely Phase Doppler Anemometer and image analysis, were used to describe the time evolution of the secondary droplet diameters and to study the effect of surface temperature, surface roughness and impact velocity on the impact outcomes. The morphology of drop impact is described for two different boiling regimes and quantitative results about the arithmetic mean and Sauter mean diameters of the secondary droplets are reported. An attempt to correlate the Sauter mean diameter of secondary drops with the nominal surface temperature is also reported.

The present paper reports an experimental study aimed at characterizing the effects of heat transfer on the secondary atomization, which occurs during droplet impact on hot surfaces at conditions reproducing those occurring at fuel injection in internal combustion engines. The experiments consider single isooctane and water droplets impacting at different angles on a stainless steel surface with known roughness and encompass a range of Weber numbers from 240 to 600 and heat transfer regimes from the film-vaporization up to the Leidenfrost regime. The mechanisms of secondary breakup are inferred from the temporal evolution of the morphology of the impact imaged with a CCD camera, together with instantaneous measurements of droplet size and velocity. The combination of a technique for image processing with a phase Doppler instrument allows evaluating extended size distributions from 5.5 μm up to a few millimetres and to cover the full range of secondary droplet sizes observed at all heat transfer regimes and impaction angles. Temporal evolution of the size and velocity distributions are then determined. The experiments are reported at impact conditions at which disintegration does not occur at ambient temperature. So, any alteration observed in droplet impact behavior is thermally induced. The analysis is relevant for port fuel injection systems, where droplets injected to impact on the back surface of the valves, behave differently depending on fuel properties, particularly when the use of alcohols is considered, even as an additive to gasoline.

Power output limitation is one of the main concerns that need to be addressed for full-scale applica- 28 tions of the microbial fuel cell technology. Fouling and biofilm growth on the cathode of single 29 chamber microbial fuel cells (SCMFC) affects their performance in long-term operation with 30 wastewater. In this study, the authors report the power output and cathode polarization curves of a 31 membraneless SCMFC, fed with raw primary wastewater and sodium acetate for over 6 months. At 32 the end of the experiment, the whole cathode surface is analyzed through x-ray microcomputed to- 33 mography (microCT), scanning electron microscopy, and energy-dispersive x-ray spectroscopy 34 (EDX) to characterize the fouling layer and the biofilm. EDX shows the distribution of Ca, Na, K, 35 P, S, and other elements on the two faces of the cathode. Na-carbonates and Ca-carbonates are pre- 36 dominant on the air (outer) side and the water (inner) side, respectively. The three-dimensional 37 reconstruction by x-ray microCT shows biofilm spots unevenly distributed above the Ca-carbonate 38 layer on the inner (water) side of the cathode. These results indicate that carbonates layer, rather 39 than biofilm, might lower the oxygen reduction reaction rate at the cathode during long-term 40 SCMFC operation

An experimental study about the anisotropic wetting behavior of a surface patterned with parallel grooves is presented as an application example of a novel technique for investigation of complete and partial anisotropic wetting on structured surface by X-ray microtomography. Shape of glycerin droplets on such surface is investigated by X-ray micro computed tomography (microCT) acting as a non-intrusive, full volume 3D microscope with micrometric spatial resolution. The reconstructed drop volumes enable to estimate the exact volumes of the drops, their base contours, and 3D static contact angles, based on true cross-sections of the drop-surface couple. Droplet base contours are compared to approximate geometrical contour shapes proposed in the literature. Contact angles along slices parallel and perpendicular to the grooves direction are compared with each other. The effect of the sessile drop volume on the wetting behavior is discussed. The proposed technique, which is applicable for any structured surface, enables the direct measure of Wenzel ratio based on the microCT scan in the wetted region usually inapproachable by any others. Comparisons with simplified models are presented and congruence of results with respect to the minimum resolution needed is evaluated and commented.

X-ray computed tomography (CT) is a well-known technique nowadays, since its first practical application by Sir. G. Hounsfield (Nobel price for medicine 1979) has continually benefited from optimising improvements, especially in medical applications. Indeed, also application of CT in various engineering research fields provides fundamental informations on a wide range of applications, considering that the technique is not destructive, allowing 3D visualization without perturbation of the analysed material. Nowadays, it is technologically possible to design and realize an equipment that achieve a micrometric resolution and even improve the sensibility in revealing differences in materials having very radiotransparency, allowing i.e. to distinguish between different fluids (with different density) or states of matter (like with two-phase flows). At the University of Bergamo, a prototype of an X-ray microCT system was developed since 2008, so being fully operative from 2012, with specific customizations for investigations in thermal-fluid dynamics and multiphase flow researches. A technical session held at the UIT International Conference in L'Aquila (Italy), at which this paper is referring, has presented some microCT fundamentals, to allow the audience to gain basics to follow the "fil-rouge" that links all the instrumentation developments, till the recent applications. Hereinafter are reported some applications currently developed at Bergamo University at the X-ray computed micro-tomography laboratory.

X-ray computed tomography (CT) is well-known and widely used in the medical sector for diagnosis of various illnesses. The technique is based on the absorption (i.e. attenuation) of the ionising electromagnetic radiation by the object. The amount of energy to be absorbed depends on the density and its thickness; the transmitted radiation through the object is then compared to the incident radiation that leads to a reconstruction of attenuation coefficients versus spatial position in the object. Thus, the resulting three-dimensional slices of the object are used (a) to identify internal geometric features of objects, and (b) to distinguish between media of different densities, i.e. liquid and air/vapour. In this study, the geometry extraction capability has been applied on time-averaged cavitation pocket shapes, as well as, the capability of density differentiation measurements on Diesel fuel flows. Results appear promising and pose a challenge in providing quantitative measurements of cavitation vapour fraction inside an injection hole.

The paper reports an experimental analysis of the secondary atomisation produced by the impact of a single drop on a solid heated surface. Different wall temperatures were used to study different boiling regimes. The size of secondary drops produced by the impact was measured by two techniques, namely the phase Doppler anemometry (PDA) and the image analysis technique (IAT); this allowed to extend the measurable size range from 5.5 μm up to few mm. Two impacting walls with different surface roughness were used to show the effect of this parameter on different atomisation regimes. The liquid viscosity was also varied in a limited range by using water–glycerol mixtures. Image analysis allowed also to define the details of the morphology of drop spreading and break-up.

Simplified impingement models are largely used in numerical simulation of spray impingement on solid walls, since the direct simulation of multiple drop impact is outside of the present computer capabilities. These models are usually semiempirical, based on single-drop impact experimental data and some reasonable constraints to allow extrapolation to different impact conditions. This article presents a comparison of the most commonly used drop impingement models in the present scientific literature and in commercial codes. A classification of the models and a unified scheme is proposed in terms of driving variables and outcomes. Every model is then analyzed and its peculiarities and possible weaknesses are pointed out, especially those related to the physical consistency. Finally, a comparison among the various models for a possible use in Gasoline Direct Injection (GDI) and diesel spray simulation is presented.

An experimental technique for the estimation of the temporal-averaged vapour volume fraction within high-speed cavitating flow orifices is presented. The scientific instrument is designed to employ X-ray micro computed tomography (microCT) as a quantitative 3D measuring technique applied to custom designed, large-scale, orifice-type flow channels made from Polyether-ether-ketone (PEEK). The attenuation of the ionising electromagnetic radiation by the fluid under examination depends on its local density; the transmitted radiation through the cavitation volume is compared to the incident radiation, and combination of radiographies from sufficient number of angles leads to the reconstruction of attenuation coefficients versus the spatial position. This results to a 3D volume fraction distribution measurement of the developing multiphase flow. The experimental results obtained are compared against the high speed shadowgraph visualisation images obtained in an optically transparent nozzle with identical injection geometry; comparison between the temporal mean image and the microCT reconstruction shows excellent agreement. At the same time, the real 3D internal channel geometry (possibly eroded) has been measured and compared to the nominal manufacturing CAD drawing of the test nozzle.

Fuel cells are electrochemical power generation system which may achieve high energy efficiencies with environmentally friendly emissions. Among the different types, Proton Exchange Membrane fuel cells (PEMFC) seem at present one of the most promising choices. A very important component of a PEMFC is the gas diffusion layer (GDL), which has the primary role of managing water in the cell, allowing reactant gases transport to the catalyst layer while keeping the membrane correctly hydrated and preventing electrode flooding. Therefore, GDLs have to be porous and very hydrophobic. Carbon clothes or carbon papers coated with a hydrophobizing agent – typically a fluoropolymer – are used. Given the complex chemistry and morphology of the GDLs, wettability analyses on them present some critical issues when using the conventional contact angle measurement techniques. In this paper, the deposition of a drop on a GDL (produced using polytetrafluoroethylene-co-perfluoroalcoxy vinyl ether as the fluorinated polymer) was investigated by means of micro computed tomography (microCT) and numerical simulation. The microCT facility operational at the University of Bergamo was used to acquire a 3D tomography of a water drop deposed on a sample GDL. The reconstructed drop dataset allows thorough understanding of the real drop shape, of its contact area and contact line. The GDL dataset was used to create a realistic mesh for the numerical simulation of the drop deposition, which was performed using the OpenFOAM® interFOAM solver.

Oil-water relative permeability and capillary pressure of a water-wet digital core are computed using the finite-volume/volume of fluid method and mimicking traditional laboratory steady-state experiments carried out on a water saturated sample. Commercial software is used for immiscible multiphase fluid flow simulations, carried out on a low-cost multicore workstation, and the porescale data are upscaled to derive relative permeability and capillary pressure curves as function of water saturation. The digital sample is obtained by high resolution X-ray computed tomography scanning. [Received: March 13, 2013; Accepted: June 25, 2013]

The investigation of multiphase interfaces and contact lines is a challenging research topic for comprehension of countless physical problems, both natural and imitated from nature, at the microscale (nearly 1 μm). In presence of a three-phase interaction (liquid–gas–solid, or two immiscible liquids and a solid), different forces influence the evolution of the system and lead it towards its mechanical equilibrium. Even for the seemingly very simple case of drops on solid surfaces, there are many attempts to investigate the involved effects, with the main aim to profitably replicate them for functional applications (biomimetics). Here we show that it is possible to visualize the real multiphase interface by X-ray micro-computed tomography (microCT), which is essentially a full volume 3D microscope, non-intrusive, with micrometric spatial resolution and suitable to operate even with matter opaque at visible wavelength. Consequently, microCT can also be applied to investigate complex wetting scenarios, to validate the theoretical models already available for such cases.

The experimental investigation of flow through porous media is inherently difficult due to the lack of optical access. The recent developments in the fields of X-ray micro-tomography (micro-CT hereafter), digital sample reconstruction by image-processing techniques and fluid-dynamics simulation, together with the increasing power of super-computers, allow to carry out pore-scale simulations through digitally-reconstructed porous samples. The scientific relevance of pore-scale simulations lies in the possibility of upscaling the pore-level data, yielding volume-averaged quantities useful for practical purposes. One of the best-known examples of upscaling is the calculation of absolute and relative permeability of reservoir rocks. This contribution presents a complete work-flow for setting up pore-scale simulations, starting from the micro-CT of a (in general small) porous sample. Relevant applications are discussed in order to reveal the potential of the proposed methodology.

The paper reports an experimental investigation by LDV and high-speed camera visualization, of the fluid motion underneath water drop impacting onto a deep pool of the same liquid for different drop impact velocities in the low Weber number regime in isothermal conditions. Vortex ring structures could be very sensitive of pool and ambient temperature, which may both affect the crater evolution (through the influence on surface tension) and directly the vortex ring evolution by changing the Reynolds number through the variation of the viscosity. The measured velocity field is compared to the visualization results to clarify some peculiar regimes of crater evolution (like bubble entrapment, vortex ring motion, etc.) during the expansion and the recoiling phase.

Using a fluorescence microscopical method it has been possible directly to demonstrate adrenergic nerve fibres in the feline Gasserian ganglion. The nerves enclose non-fluorescent ganglion cells or run within the ganglion without any relation to perikarya. Thick bundles of adrenergic nerves are found near as well as inside the ganglion. The significance of this adrenergic nerve system is discussed.

Electron microscopic examination of muscle spindles of tenuissimi and lumbrical muscles of 4 cats, one of which was treated with 5-hydroxydopamine (5-HDA), revealed that within the capsular spindle interior and at the extracapsular polar regions there are bundles of thin axons (less than 0.5 μm) not previously described.Only following 5-HDA treatment did some of these axons exhibit large dense (80 nm) vesicles which were never seen in semi-serial sections in the other axons of the bundle. Small dense core vesicles were never observed in these thin spindle axons of both control and 5-HDA treated cats. Bundles of thin axons with and without large dense vesicles following 5-HDA treatment were also observed a few microns away from intrafusal neuromuscular junctions and from intrafusal muscle fiber membranes. Also, following 5-HDA treatment thin axons with large dense vesicles were seen in bundles which included larger unmyelinated axons, presumably of the λ-type, devoid of large dense vesicles. No special unequal distribution was observed of the thin spindle axons in respect to nuclear chain or nuclear bag fibers in the equatorial, the juxta-equatorial, the intracapsular polar or the extracapsular polar regions of the muscle spindles. Despite the absence of small dense core vesicles in the reported thin spindle axons, the possibility is discussed that the axons exhibiting large dense vesicles following 5-HDA treatment are postganglionic sympathetic, and the suggestion is made that the remainder of the thin axons in the bundle,i.e., these devoid of the large dense vesicles in semi-serial sections, are cholinergic. The possibility not previously reported of a significant direct,i.e., non-humoral, contribution of the sympathetic nervous system to motor integration via ‘sympathetic bias’ on the muscle spindles in addition to the λ-bias is discussed.

The present electron microscopic study verified the existence of postganglionic sympathetic fibers within Pacinian corpuscles previously reported by use of the fluorescence histochemical technique of Falck and Hillarp for the cellular localization of the biogenic amines11,12. Thin (less than 0.5 μm) unmyelinated nerve fibers different from the main axon were found at 4 different sites within the Pacinian corpuscle:site 1, in one or two bundles among the outer lamellae of the proximal myelinated segment;site 2, as a single fiber or as two separate fibers in the inner core region of the unmyelinated terminal segment, a few lamellae away from the main axon;site 3, as a single fiber or as two separate fibers in the inner core region of the unmyelinated terminal segment closely apposed to the main axon without intervening lamellae; andsite 4, in the adventitia of arterioles within the proximal myelinated segment. Dense core vesicles (60 nm) are present within thin axons found at sites 1–4. It is suggested that the axon profiles devoid of dense core vesicles may be either preterminal postganglionic sympathetic axons or non-sympathetic fibers; and that the axon bundle(s) of site 1 may be the Timofeew19 fibers which were originally reported to be present in the outer lamellae of Pacinian corpuscles. The significance of the present findings is discussed in view of Mountcastle's5 unifying proposition, which is a modern restatement of Merkel's4 original point of view, that all sensory nerve endings are chemoreceptors.

Intracellular recording from hippocampal neurons of kittens 1 to 18-days-old was carried out to examine the postsynaptic potentials (PSPs) evoked by fornix stimulation at early developmental stages in which axodendritic pathways constitute the major input to hippocampal neurons. Fornix stimulation in neonatal kittens (

The flow inside a purpose built enlarged single-orifice nozzle replica is quantified using time-averaged X-ray micro-computed tomography (micro-CT) and high-speed shadowgraphy. Results have been obtained at Reynolds and cavitation numbers similar to those of real-size injectors. Good agreement for the cavitation extent inside the orifice is found between the micro-CT and the corresponding temporal mean 2D cavitation image, as captured by the high-speed camera. However, the internal 3D structure of the developing cavitation cloud reveals a hollow vapour cloud ring formed at the hole entrance and extending only at the lower part of the hole due to the asymmetric flow entry. Moreover, the cavitation volume fraction exhibits a significant gradient along the orifice volume. The cavitation number and the needle valve lift seem to be the most influential operating parameters, while the Reynolds number seems to have only small effect for the range of values tested. Overall, the study demonstrates that use of micro-CT can be a reliable tool for cavitation in nozzle orifices operating under nominal steady-state conditions.