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A combined experimental and numerical analysis has been carried out to study Marangoni effects during the evaporation of droplets. The experiments are performed with pendant drops of silicone oils (with different viscosities) and hydrocarbons. The temperature of the disk sustaining the drop is rapidly increased or decreased in order to study transient heating or cooling processes. The velocity field in the droplet is evaluated monitoring the motion of tracers in the meridian plane, using a laser sheet illumination system and a video camera. Surface temperature distributions of the drops are detected by infrared thermocamera. The numerical model is based on axisymmetric Navier-Stokes equations, taking into account the presence of Marangoni shear stresses and evaporative cooling at the liquid-air interface. Marangoni flows cause a larger, more uniform surface temperature, increasing heat transfer from disk to droplet, as well as evaporation rate. When Marangoni effects are negligible, larger surface temperature differences occur along the drop surface and heat transfer is relatively small. The role of Marangoni and buoyancy flows in silicone oils with different viscosities and hydrocarbons is discussed and correlations are presented between experimental and numerical results. Keywords: Viscosity of liquids; diffusive momentum transport, Evaporation and condensation, Surface tension and related phenomena, Flows in ducts, channels, nozzles, and conduits

An experimental and numerical analysis of the behavior of drops in a liquid matrix, in presence of temperature differences, is carried out in preparation for a MAXUS sounding rocket flight to study wetting and coalescence prevention induced by thermal Marangoni effect. On-ground experimentation has been carried out using micro zone apparatus. Different pairs of liquids (drop and matrix) have been analyzed; wetting prevention has been observed with drops of different diameter and critical temperature differences have been measured for each pair. To avoid buoyancy effects similar experiments have been carried out during the 30th ESA parabolic flight campaign. The main objective of the experiments is facility tests in a parabolic flight for the MAXUS flight. During the parabolic flight a hanging drop of Silicone oil 10 mm diameter has been injected in a matrix of Fluorinert and in air; wetting prevention has been observed in presence of a temperature difference between the drop and the lower surface. The theoretical-numerical study of the problem has been carried out with a thermofluidynamic model based on the assumption of the existence of a fluid film between the drop and the lower surface.

A combined experimental and numerical analysis has been carried out to study the behavior of a bubble under a horizontal heated surface. In this configuration, the interaction between buoyancy and surface tension driven convection produces complex fluid dynamic structures. An instability occurs in the form of an oscillatory three-dimensional fluctuation of the thermal and velocity field when a critical temperature difference is exceeded. The structure of this flow regime has been investigated with transient three-dimensional simulations carried out for normal gravity and zero gravity conditions. The velocity field around the bubble has been experimentally analyzed with a ``laser sheet'' technique for the flow visualization and a Wollaston prism interferometer has been utilized to capture the oscillatory temperature field. Good correlations are shown between experimental and numerical results. Keywords: Thermal convection, Buoyancy-driven instabilities, Surface-tension-driven instability, Interactions

The behaviour of drops in non-isothermal liquids with solidification front has been experimentally and numerically investigated using transparent model fluids and optical diagnostic techniques. The experiments have been performed using Cyclohexane (melting point equal to 6.5 °C) as external matrix and Fluorinert drops. In presence of a temperature gradient, the surface tension driven flows at the drop liquid interface affect the drop/solidification front interaction. Preliminary experiments have been carried out to measure the interfacial tension of the liquid–liquid system under investigation at different temperatures and to study the fundamental behaviour of a single drop close to the melting front, in presence of a temperature gradient. Heating the system from above and cooling from below, the melting front exhibits a shape deformation as a consequence of the surface tension-driven convection around the drop. A systematic analysis has been carried out to investigate the phenomenon with droplets of different sizes. The convective flows have been visualised using particle tracers with average size of 30 μ m . The results of the numerical simulations at the experimental conditions are in sufficient agreement with the experimental results. The second part of the paper is focused on the investigation of the interaction between free droplets and a melting front, translating a horizontal cuvette between a fixed temperature gradient, with relative speed in the range 0.5– 5 μ m / s . The experiments show that when the relative distance between the droplets and the melting front is of the order of the drop radius, the droplets engulfment in the solid is prevented by a layer of liquid between the drops and the solidification front. This experimental evidence supports the assumption that a “pushing force” is induced by Marangoni effect when the droplets approach the solidification front. Numerical simulations provide further explanation and correlations with the experimental results.

an elimination diet; different substitution products have been proposed: soya milk, extensive casein/whey protein hydrolysate, hydrolysed soya and pork collagen and amino-acid-based formula. Aim: The aim of our study was to evaluate the efficacy of a new amino-acidbased formula (Nutramigen AA) for the treatment of infantile proctocolitis. Patients and methods: Twelve consecutive infants, 38 to 166 days of age, presenting with persistence of bloody stools for an average of 2 weeks with or without vomiting, failure to gain weight and colic were enrolled. In all infants the infective/inflammatory causes of rectal bleeding were excluded. Eight were on extensive hydrolysed formula, three on cow’s milk formula and one was breast fed. At entry all received an aminoacid based formula (Nutramigen AA) for three months and all were evaluated clinically every 2 weeks. After one and three months faecal calprotectin, faecal occult test and after three months hemoglobin, serum iron and ferritin were evaluated. Results: After 2 weeks of treatment, 9 of the infants (75%) demonstrated resolution of their symptoms while blood was still present, although reduced, in three; it disappeared after further 2 weeks in one and 4 weeks in two. Baseline histology, where available, varied from eosinophilic infiltration to normal findings. Only six infants had failure to thrive at presentation and this was resolved after a median of six weeks (range: 3-12 weeks). At entry fecal calprotectin/faecal occult test was abnormal/positive in all while at one and three months these tests were still abnormal/positive in 5/7 an 1/0 respectively (p

Conclusion. Our data show that infants with ALTE have a higher nonacid reflux as compared to non-ALTE infants and that in our experience GER may be implicated in the pathogenesis of ALTE in two (13%) cases (95% CI 7–26%).

A combined experimental and numerical analysis has been carried out to study the behavior of a bubble under a horizontal heated surface. In this configuration, the interaction between buoyancy and surface tension driven convection produces complex fluid dynamic structures. An instability occurs in the form of an oscillatory three-dimensional fluctuation of the thermal and velocity field when a critical temperature difference is exceeded. The structure of this flow regime has been investigated with transient three-dimensional simulations carried out for normal gravity and zero gravity conditions. The velocity field around the bubble has been experimentally analyzed with a “laser sheet” technique for the flow visualization and a Wollaston prism interferometer has been utilized to capture the oscillatory temperature field. Good correlations are shown between experimental and numerical results.