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The authors report on measurements of the growth rate of hexamethylenetetramine ( HMT ) crystalline layers, when grown by physical vapor transport ( PVT ) in closed ampoules. The measurements are done in-situ by making use of a telemetric system, by which, at regular time intervals, photographs of the source material volume are taken as is being reduced because of mass transfer. After storing the photographs, in real time, in a pc, a suitable software allows to calculate the mass transport rate during growth. A regular and consistent decrease of the growth rate, as time increases, is always observed in the various growth runs, each of which being carried out for about 80 hours at a source temperature of 94 °C under 1 °C undercooling. Similar decreases have been previously reported for other materials and variously explained. In our case, the growth rate decrease is explained on the basis of a uni-dimensional PVT model as mainly due to the desorption of volatile impurities which introduce diffusional barriers to the vapour mass transport in a very-low pressure ( less than 1 mbar ) PVT system. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

SELENE (SELf rewetting fluids for thermal ENErgy management) is a microgravity experiment proposed to the European Space Agency (ESA) in response to the Announcement of Opportunities for Physical Sciences. Main objectives of the microgravity research onboard ISS include the quantitative investigation of heat transfer performances of "self-rewetting fluids" and "nano self-rewetting fluids" in model heat pipes and validation of adequate theoretical and numerical modelling able to predict their behaviour in microgravity conditions. This article summarizes the results of ground-based research activities in preparation of the microgravity experiments. They include: 1) thermophysical properties measurements; 2) study of thermo-soluto-capillary effects in micro-channels; 3) numerical modelling; 4) thermal and concentration distribution measurements with optical (e.g. interferometric) and intrusive techniques; 5) surface tension-driven effects and thermal performances test on different capillary structures and heat pipes; 6) breadboards development and support to definition of scientific requirements.

The present paper reports on the research activities in both experimental and numerical field carried out at MARS center for the realization of an experiment on the thermo-solutal-capillary migration of a dissolving drop, composed by a liquid binary mixture having a miscibility gap. The experiment will be carried out onboard of the sounding rocket MAXUS 5, by using the INEXMAM facility. The main goals of the analysis are ensuring that the diagnostic equipment performances cope with the stringent resolution requirements dictated by the physics and assessing of the experiment time profile.

A computer code for the unsteady 3-dimensional analysis of convection and diffusion has been applied to the three-component system Sucrose(1)-Sodium chloride(2)-Water. Numerical results show the evolution of convective motions due to gravitational instabilities that arise as a consequence of diffusion (double diffusive convection), in agreement with theory and experiment. The evolution of convection was also observed directly and some pictures of these motions have been reported.

A finite difference method has been developed to simulate water flow in a 2D porous medium with boundary conditions specified in terms of pressure and temperature. The method computes steady-state solutions for temperature, pressure and fluid velocities. With an appropriate choice for boundary conditions it is possible to simulate the behaviour of a geothermal system with an incremental pressure and/or temperature applied to a finite part of the base. Pressure and temperature changes produce a change in the fluid flow regime leading to different final temperatures, pressures and fluid velocities (steady state). The method is particularly suitable for simulating the coupled mechanical and thermalfluid-dynamical effects at calderas, when increases in pressure and heat flow from a magma chamber perturb the conditions of the uppermost aquifer system. Several tests performed with realistic values for the parameters of the porous medium show that increases of pressure at the base are efficiently propagated in the upper medium by water flow, so that the effective centre of overpressure is shifted to considerably shallower levels. This effect can strongly modify the shape of ground deformations at calderas, and strongly amplify the peak values. The proposed method has been applied to the explanation of the very peculiar ground deformation observed at Campi Flegrei during 1982–1984, which showed very high uplifts (1.8 m) and a strong concentration in a small area (3×3 km 2 ). An integrated mechanical–thermalfluid-dynamical model for this caldera is proposed, which could be generalised to other areas.

Mechanical and thermal-fluid-dynamical contributions to unrest phenomena at active calderas are quantitatively evaluated, and a mixed mechanical-thermal-fluid-dynamical model is developed, to explain the unrest phenomena at Campi Flegrei caldera. Mechanical modelling involves the use of analytical and finite element formulations. Thermal-fluid-dynamical effects are considered in the framework of a one-dimensional approximation, solved by an analytical method. The results shed new light about the coupled effect of mechanically and thermally induced perturbations and variations in the geothermal fluid circulation regime. Unrest episodes at Campi Flegrei are interpreted in terms of the joint effect of a first, essentially mechanical, phase due to overpressure in a magma chamber and to a progressive amplification and final decay due to the circulating water. The elastic response of the rocks to the migrating front of overpressure is shown to be strongly conditioned by the caldera structure, which produces a concentration of strain in the inner part, and a stress concentration, causing the local seismicity, around the caldera borders. Thermal-fluid-dynamical effects are also shown to have important implications on the evolution of the volcanic system towards critical phenomena, which must be considered for a meaningful evaluation of volcanic hazard.

When a catalytic membrane is employed in a non-isothermal bioreactor its activity increases as a direct function of the applied temperature gradient and decreases when both average temperature or substrate concentration increase. To know the physical cause responsible for this behaviour substrate fluxes have been studied under isothermal conditions (diffusion) and non-isothermal conditions (thermodialysis). Strong analogies between the behaviour of the catalytic membrane and the substrate fluxes produced by the process of thermodialysis have been observed. By introducing diffusive and thermodiffusive substrate fluxes in appropriate mass balance equations the substrate concentration profiles into the catalytic membrane have been deduced by computer simulation. In absence of catalysis and under non-isothermal conditions the profiles are higher than the ones corresponding under comparable isothermal conditions, while the contrary occurs in the presence of catalysis. The percentage increases of enzyme activity, calculated by the curves of the substrate concentration profiles, show the same temperature and concentration dependence than those actually observed with the catalytic membrane. The role of thermodialysis in affecting the enzyme activity in non-isothermal bioreactor has been discussed and demonstrated.

This paper reports on the results of the experiment PULSAR (Pulsating and Rotating Instabilities in Oscillatory Marangoni Flows), performed on the MAXUS 3 Sounding Rocket launched last November from the Swedish base in Kiruna. Aim of the experiment was the study of the oscillatory Marangoni convection in a cylindrical liquid bridge of silicone oil with kinematic viscosity of 5cSt. The experiment was motivated by preliminary on-ground numerical simulations and microscale experimental studies, that have pointed out that the oscillatory Marangoni instability appears at the beginning in the form of a pulsating regime, caused by a hydro-thermal standing wave, and then it turns to a rotating regime, caused by a traveling wave. The height of the bridge was equal to the disk diameter (20mm), and the imposed temperature difference was 15K during the first 460 s and 20K in the second part of the experiment, until the end of the microgravity period. The analysis of the temperature profiles, measured by thermocouples located near the disks at the same radial and axial coordinate but at different azimuthal coordinates (shifted at 90°), and the surface temperature distribution, measured by an infrared thermocamera, show that a pulsating and a mixed pulsating-rotating regimes have been established during the experiment. Unfortunately during the flight the accelerations level caused by two centrifuges with some biological samples in an adjacent module were above the expected values, so that disturbing g-jitter were encountered at different times during the microgravity mission. The effects are clearly visible and the numerical simulations had to make different assumptions to correlate the experimental results

The Altcriss project was submitted in response to ESA AO-2004. It was approved in March 2005 and begun in December 2005 with Progress 21-P launch from Baikonur. It is currently operating on board the International Space Station, performing a survey of the radiation environment and the effectiveness of shielding materials from cosmic rays. It uses the active silicon detector Sileye-3 and a series of passive dosimeters (CR-39, TLD). The detectors have currently been operational in different location of the Pirs (docking) and Service module of the Russian section of the Station. The project is expected to continue up to 2008.

We develop a model for describing water flow in a porous medium under the effect of thermal and pressure gradients. The model simulates geothermal systems in calderas. Given the boundary conditions and the fluid-dynamical properties of the medium, the model allows computation, in fluid-dynamical stationary states, of parameters characterizing the flow, such as flow velocity and temperature and pressure distributions at depth. The model is applied to investigate the effects of the local geothermal system on the unrest episodes at Campi Flegrei caldera. Using experimentally determined fluid-dynamical parameters for the caldera rocks, we show that changes of water flow in shallow aquifers under the effect of pressure and/or temperature variations within the geothermal system can be very important in the genesis and evolution of unrest crises. In particular, they can strongly amplify the effect of pressure increase in the magma chamber on ground uplift. They can also explain the timescales of evolution of ground movements in terms of transit times of the water front and of the connected temperature fronts due to advective transport. On such grounds an integrated mechanic-thermal fluid-dynamical model was built, allowing us to give a semiquantitative, global explanation to the genesis and evolution of unrest phenomena. Results obtained here can be generalized to other similar calderas.

The activity of β-galactosidase, immobilized by grafting technique on Teflon membranes preactivated with four different monomers, has been characterized from the biochemical and biophysical points of view. The monomers used were acrylic acid or acrylamide, or methacrylic acid and 2-hydroxyethyl methacrylate. When 2-hydroxyethyl methacrylate was used in the second grafting, the first three monomers have been used in the first modification step. The behavior of the free and immobilized enzyme has been analyzed as a function of temperature and pH. For each catalytic membrane, we have found general equations relating the absolute enzyme activity to pH and temperature. From these expressions, the experimental conditions giving the best yield of each catalytic membrane have been calculated. The kinetic parameters for the four membranes have also been determined. The advantages of using these membranes in nonisothermal bioreactors are also indicated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 613–623, 1998

It is well known that thermocapillary convection arises in liquid bridges when the support discs are heated differentially and uniformly. Upon increasing the temperature difference, the convective flow shows a transition from an axisymmetric to an oscillatory regime. This phenomenon has been investigated both experimentally and theoretically, but prior experimental results exhibit some discrepancies with respect to the predictions of stability analyses. The present paper discusses experimental results obtained under microgravity conditions, comparing them with previous experimental observations made on ground and in space and with recent theoretical models of the instability. The results agree with the description of oscillations in terms of superposition of hydrothermal waves. Finally, a possible mechanism for a “pulsating” instability is proposed, together with a new scaling law for the oscillation frequencies at onset; this law, which correlates the critical frequency to the fluid properties, the geometrical parameters and the critical temperature difference, agrees with all the available experimental data.

It is known that thermocapillary convection in differentially and uniformly heated liquid bridges shows a transition (Marangoni instability) from an axisymmetric to an oscillatory regime. The “Onset” experiment, performed during the D2 Spacelab mission on the Advanced Fluid Physics Module (AFPM), was aimed to investigate this transition at various bridge geometries; in particular the goal was to determine the critical temperature difference applied to the end disks supporting the liquid bridges, and to study the structure of the flow at the onset of the Marangoni instability. The paper reports the main results, obtained analyzing the experimental data (temperatures and velocities). The evaluation of the transition (onset) condition obtained from temperature data was achieved with the aid of signal processing techniques. The onset determinations have been also validated by analysis of flow field velocities. The results concerning frequency and amplitude of temperature oscillations in the neighbourhood of the onset of Marangoni instability are reported. We provide an evaluation of the heat fluxes through the plates. A comparison between numerical and experimental results related to the two-dimensional flow field is made, a satisfactory agreement is reached.

The Second German Spacelab mission (D2) includes five Fluid Science experiments performed on the Advanced Fluid Physics Module (AFPM). MARS research group has been directly involved in the preparation and execution of the Onset experiment, whose principal investigator (PI) was Prof. R. Monti. On this occasion a support infrastructure has been developed to assist the PI in the experiment execution; these support tools have been also used by other PI's of the AFPM experiments. The objective of this paper is to give a detailed description of the MARS control room, of the equipment and s/w codes specifically developed to support the D2 mission, and of the operations performed during the mission.

When a catalytic membrane is employed in a non-isothermal bioreactor its activity increases as a direct function of the applied temperature gradient and decreases when both average temperature or substrate concentration increase. To know the physical cause responsible for this behaviour, substrate fluxes have been studied under isothermal conditions diffusion and non-isothermal conditions thermodialysis . Strong analogies between the behaviour of the catalytic membrane and the substrate fluxes produced by the process of thermodialysis have been observed. By introducing diffusive and thermodiffusive substrate fluxes in appropriate mass balance equations the substrate concentration profiles into the catalytic membrane have been deduced by computer simulation. In absence of catalysis and under non-isothermal conditions the profiles are higher than the ones corresponding under comparable isothermal conditions, while the contrary occurs in the presence of catalysis. The percentage increases of enzyme activity, calculated by the curves of the substrate concentration profiles, show the same temperature and concentration dependence than those actually observed with the catalytic membrane. The role of thermodialysis in affecting the enzyme activity in non-isothermal bioreactor has been discussed and demonstrated.

It is well known that thermocapillary convection arises in liquid bridges when the isothermal support discs are at different temperatures. As the temperature difference increases the convective flow shows a transition from a steady axisymmetric to an oscillatory regime. Although a number of experiments have been performed and a considerable number of publications have appeared during the past ten years on oscillatory thermocapillary convection in liquid bridges, a definitive understanding of the physical mechanisms of the onset of instability and a coherent picture of the thermo-fluid-dynamic field has not yet emerged. On this subject the “Onset” experiment has been successfully performed during the D2 Spacelab mission using the Advanced Fluid Physics Module (AFPM). The experiment has investigated this transition for various bridge geometries and has provided quantitative measurements, which allow one to characterise the flow at the onset of the instability. The paper discusses the experimental observations, compars them with the available theoretical models of the instability. This comparison provides a validation of the oscillation description in terms of hydrothermal waves and also a new interpretation of the experimental results obtained previously. Finally a new scaling law for the oscillation frequencies at the onset is presented which agrees with all available experimental data.

The space experiment TRAMP (Thermal Radiation Aspects of Migrating Particles) flown in 1999 onboard the mission Foton 12 sponsored by the European Space Agency (ESA), was conceived to reveal and measure a new kind of forces, named Thermal Radiation Forces (TRF). The experiment was dramatically disturbed by the occurrence of undesired convective motions due to the rotation of the spacecraft. Apart from that, corrosion occurred in some parts of the flight apparatus, resulting in the presence of gas bubbles inside the experimental liquid, completely compromising the results. Consequently, the experiment did not allow to reveal and/or to measure TRF, but it turned out to be useful in another way, as a very sensitive accelerometer, since the accelerations deduced from velocity measurements concurred with those measured by the Quasi-Steady Acceleration Measurement (QSAM) system.

[1] The Campi Flegrei caldera is characterized by well known episodes of fast uplift, called “bradyseism,” the last of which produced ∼1.8 m of maximum vertical displacement in the period 1982–1984. Less known is a particular aspect of Campi Flegrei unrests, detected only in the last 20 years, namely, the occurrence of “miniuplift” episodes, characterized by relatively small positive vertical displacements (in the range 0.03–0.11 m). Miniuplift episodes occurred in 1989, 1994, and 2000 and, probably, one or two times in the period 1972–1982. These small ground uplifts were also accompanied by moderate seismicity. Each of them was followed by a short phase of relatively quick subsidence, after which the previous rate of subsidence of the period was resumed. An order-of-magnitude analysis of the forces, energy, and power that can cause the onset and determine the evolution of these events is derived on the basis of a thermal-fluid-dynamical approach. It allows the quantitative correlation of the power input from the energy source with the rate of energy dissipation in the geologic system during the miniuplifts. In order to assess the likelihood of our fluid-dynamical model for these episodes, theoretical ground displacements have been computed. These displacements result from the changes in pressure as a function of depth predicted by the fluid-dynamical model for reasonable perturbations of the geothermal system, described as changes of the Peclet number. Theoretical results agree extremely well with the observed amounts of the miniuplifts.

The behaviour of the enzyme invertase, located on the cell wall of baker's-yeast cells and entrapped in a gelatin membrane, was studied under isothermal and non-isothermal conditions. The reaction rate linearly increased with the applied transmembrane temperature gradient, with reference either to the average temperature or to the temperature on the warm side of the catalytic membrane. These results were obtained both when the bioreactor was operated under conditions of closed volumes and when the substrate-containing solutions are recirculated. The mathematical relationships have been elaborated between the temperatures read in the working solutions and those on the two faces of the catalytic membrane. Since the temperature difference across the membrane is smaller than that indicated by the thermocouples, the observed effects are greater than expected. The potential advantages of the use of a non-isothermal bioreactor in processes of industrial interest are discussed.

The paper deals with surface tension driven flows, induced by imposed temperature differences, in axisymmetric liquid bridges. This configuration is connected to processes of crystal growth from melt by the floating zone method. The field equations are solved via a two-dimensional, unsteady, finite difference numerical code in terms of vorticity, stream function and temperature. The Poisson equation for the pressure field is solved, by using Briley's correction, and the free surface shape is computed under the assumption of small capillary number. The flow field structure and behaviour are discussed in terms of non-dimensional characteristic numbers and the aspect ratio A = R L , with R and L, respectively, the radius and the length of the bridge. Stream lines, isotherms, velocity profiles, surface shapes are given and discussed. In particular, we report the maximum of the surface velocity, the maximum of the surface deformation and the bulk heat transfer coefficient (Nusselt number) as functions of the aspect ratio.

This article summarizes the activities in preparation of a microgravity experiment to be carried out by using a small technological payload onboard a microsatellite developed by the Italian Space Agency. A dedicated hardware will be developed to investigate innovative heat pipes filled with self-rewetting fluids, i.e. dilute aqueous alcoholic solutions with unique surface tension properties. After a general introduction of the scientific background, the paper is focused on the main activities in preparation of the flight experiment, on the design of the flight hardware and on the experimental planned procedure. The laboratory results achieved on ground in preparation of a flight experiment are also presented, including measurements of fluids physical properties and preliminary heat pipes performances characterization test. From the engineering point of view, the activities dealing with heat pipes filling and sealing are included. The activities for heat pipe characterization conclude the paper.

We present an order-of-magnitude analysis of the Navier-Stokes equations in a time-dependent, incompressible and Boussinesq formulation. The hypothesis employed of two different length scales allows one to determine the different flow regimes on the basis of the geometrical and thermodynamical parameters alone, without solving the Navier-Stokes equations. The order-of-magnitude analysis is then applied to the field of protein crystallization, and to the flow field around a crystal, where the driving forces are solutal buoyancy-driven convection, from density dependence on species concentration, and sedimentation caused by the different densities of the crystal and the protein solution. The main result of this paper is to provide predictions of the conditions in which a crystal is growing in a convective regime, rather than in the ideal diffusive state, even under the typical microgravity conditions of space platforms.

The crystn. of the collagen-like polypeptide, (Pro-Pro-Gly)10 [(PPG)10], onboard the International Space Station (ISS) in microgravity using the Advanced Protein Crystn. Facility showed parallel and coherent crystal motions. The residual acceleration profiles and the history of the ISS Increment 3 mission allowed a quant. interpretation of these motions. Two events detd. the obsd. crystal motions: the undocking of the Space Shuttle and a change in the ISS attitude required for power generation. No correlation between these motions and crystal quality was apparent.

Single chains of the collagen-model polypeptide with sequence (Pro-Pro-Gly)(10), hereafter referred to as (PPG)(10), aggregate to form rod-shaped triple helices. Precipitation diagrams of (PPG)(10) as a function of pH and various molecular mass poly(ethylene glycol) concentrations have been measured. These results were used to design experiments to test the quality of (PPG)(10) crystal grown on ground (in gelled and free solutions) and in space in two different facilities, the Advanced Protein Crystallization Facility based on the free-interface diffusion technique and the Granada Crystallization Facility based on counter-diffusion technique. Experiments were monitored by optical microscopy on earth. X-ray diffraction analysis of the grown crystals reveals the benefit of the counter-diffusion technique. (C) 2008 Elsevier B.V. All rights reserved.

The behaviour of a diffusion boundary between distilled water and a 1% sodium chloride solution during a parabolic flight has been observed. The presence of a few percent of Earth gravity pulses during the micro gravity conditions is sufficient to largely perturb the diffusion boundary that stabilises again during the subsequent normal gravity conditions present inside the aircraft at the end of each parabola. A numerical simulation of the boundary behaviour agrees with the experimental observation.

Diffusion has a central role in protein crystal growth both in microgravity conditions and on ground. Recently several reports have been focused on the importance to use the generalized Fick's equations in n-component systems where crystals grow. In these equations the total flux of each component is produced by the own concentration gradient (main flow) and by the concentration gradient of the other components (cross-flow) present in the system. However in literature the latter effect is often neglected, and the so-called pseudo-binary approximation is used. Lin et al. (1995) proposed a mathematical model to evaluate the concentration profile of the species present around a growing protein crystal. Although the model is reliable, it suffers of the pseudo-binary approximation (neglecting cross term diffusion coefficients and using binary diffusion coefficients), probably because of the lack of multicomponent diffusion data. The present model is based on the experimental set-up proposed by Lin et al. (1995). Nevertheless we have included the coupled diffusion effects, according to the correct description of the matter transport through the generalized Fick's equations. The crystal growth rate is calculated for different gravity levels. The model has been applied to the ternary lysozyme-NaCl-water and quaternary lysozyme-poly(ethylene glycol) (PEG)-NaCl-water systems using recent diffusion data.

Recently, some of us have proposed predictive equations for the four diffusion coefficients, Dij, in a ternary system of hard spheres. These equations have been tested successfully for some ternary systems of interest in protein crystallization: mixture of PEGs in aqueous solution, and the system lysozyme–NaCl–H2O. These equations supply the tools for a correct coupled analysis of the diffusion phenomena occurring in crystallization processes. Using the previous approach for the dependence of the four diffusion coefficients on the solute concentrations, a numerical analysis of transport phenomena in a model system that can simulate protein crystal growth has been carried out. The set of equations is based on the incompressible form of the two-dimensional and time dependent Navier–Stokes equations. The hypothesis of variable thermodynamic properties (diffusion and dynamical viscosity) and the Bousinnesq approximation for the momentum equation have been considered. The study has been performed by means of a numerical code based on a finite difference method. The influence of the coupled diffusion has been evaluated at different gravity levels.