Macroscopic Balance Research Articles

A Gas hold‐up model for slurry bubble columns

AbstractA phenomenological model of the gas bubble hold‐up in slurry bubble columns is presented. The slurry moves upward in the core of the column and downward in the annulus, resembling the riser and downer of an air‐lift loop reactor, respectively. The model virtually divides the column in a riser and a downer. The cross‐sectional areas of the riser and the downer are experimentally found to be approximately equal. A macroscopic momentum balance over the riser and downer gives the liquid circulation velocity. The gas bubble hold‐up is modeled for two size classes: small and large. In the homogeneous regime only small gas bubbles are present. Above the regime transition velocity the churn‐turbulent regime exists, characterized by the presence of small and large gas bubbles. High speed video imaging shows that the gas flow up to the regime transition velocity generates small gas bubbles and that the gas flow in excess of the regime transition velocity generates large gas bubbles. Small gas bubbles are present in the riser and in the downer and have a constant slip velocity. The Wallis drift‐flux model describes the small gas bubble hold‐up in the riser and in the downer. Large gas bubbles are only present in the riser. The rise velocity of the large gas bubbles is the sum of the liquid velocity and the slip velocity according to the Davies‐Taylor equation. The large gas bubble hold‐up is obtained from the volume of gas flowing in large gas bubbles and the rise velocity of the large gas bubbles. For a given column diameter, column height, regime transition velocity, and physical properties of a gas–liquid system, the model predicts the total gas hold‐up, the hold‐up of the small and the large gas bubbles, and the average superficial liquid velocity in the riser and in the downer. Two parameters in the model are determined from experiments in a 29‐cm ID bubble column: the ratio of the small gas bubble hold‐up in the downer to that in the riser, and the energy dissipation at the top and bottom of the column. The model describes the gas hold‐up and liquid velocity data from literature with these parameter values within an error of 6%. The model shows that there is no effect of scale on the gas hold‐up for columns larger than 15 cm in diameter. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Solidification of Precirol ® by the expansion of a supercritical fluid saturated melt: From the thermodynamic balance towards the crystallization aspect

The following article presents the thermodynamic and crystallization aspects of the solidification through expansion of a melted fat, Precirol ®, previously saturated with supercritical CO 2. A simplified macroscopic energy balance is used to understand the mixture behaviour during expansion. It allows the quantification of the CO 2 to be added to the mixture in order to control the state and the temperature of the compound at the outlet of the expansion device. The required physico-chemical parameters were determined experimentally. The variation of the operating parameters appearing in the energy balance revealed three regions/areas of possible states for the expanded lipid: solid, molten or solid–liquid equilibrium. This, together with the outlet temperature could be tuned by varying not just the inlet or saturation conditions, but also the ratio of supercritical CO 2 to be expanded with the saturated fat. As for the crystallization aspect, the variation of chemical potential, which is the driving force, was calculated; the critical radius of nuclei and the nucleation rates were estimated according to the classic melt media theory. The main assumptions were that solidification occurred mainly at atmospheric pressure and that only homogeneous nucleation took place. The orders of magnitude obtained put in light the necessity to determine precisely the viscosity of the melt saturated fat and the solid/melt interfacial tension.

Oscillations of the spin polarization in a two-dimensional Rashba system in a quantizing magnetic field

The kinetics of two-dimensional conduction electrons in a quantizing magnetic field and electric field are investigated with spin-orbit coupling taken into account. Macroscopic energy balance equations for the spin subsystem and the transverse components of the spin are constructed and solved; the polarization of the carrier spins by the electric field in the quantizing magnetic field is determined. General expressions are obtained for the transverse relaxation time of the conduction electron spins at high magnetic fields. It is shown that in a quantizing magnetic field the oscillations of the spin polarization become anomalously large.

Principles of polymer processing

1. History, Structural Formulation of the Field Through Elementary Steps, and Future Perspectives. 1.1 Historical Notes. 1.2 Current Polymer Processing Practice. 1.3 Analysis of Polymer Processing in Terms of Elementary Steps and Shaping Methods. 1.4 Future Perspectives: From Polymer Processing to Macromolecular Engineering. 2. The Balance Equations and Newtonian Fluid Dynamics. 2.1 Introduction. 2.2 The Balance Equations. 2.3 Reynolds Transport Theorem. 2.4 The Macroscopic Mass Balance and the Equation of Continuity. 2.5 The Macroscopic Linear Momentum Balance and the Equation of Motion. 2.6 The Stress Tensor. 2.7 The Rate of Strain Tensor. 2.8 Newtonian Fluids. 2.9 The Macroscopic Energy Balance and the Bernoulli and Thermal Energy Equations. 2.10 Mass Transport in Binary Mixtures and the Diffusion Equation. 2.11 Mathematical Modeling, Common Boundary Conditions, Common Simplifying Assumptions, and the Lubrication Approximation. 3. Polymer Rheology and Non-Newtonian Fluid Mechanics. 3.1 Rheological Behavior, Rheometry, and Rheological Material Functions of Polymer Melts. 3.2 Experimental Determination of the Viscosity and Normal Stress Difference Coefficients. 3.3 Polymer Melt Constitutive Equations Based on Continuum Mechanics. 3.4 Polymer Melt Constitutive Equations Based on Molecular Theories. 4. The Handling and Transporting of Polymer Particulate Solids. 4.1 Some Unique Properties of Particulate Solids. 4.2 Agglomeration. 4.3 Pressure Distribution in Bins and Hoppers. 4.4 Flow and Flow Instabilities in Hoppers. 4.5 Compaction. 4.6 Flow in Closed Conduits. 4.7 Mechanical Displacement Flow. 4.8 Steady Mechanical Displacement Flow Aided by Drag. 4.9 Steady Drag-induced Flow in Straight Channels. 4.10 The Discrete Element Method. 5. Melting. 5.1 Classification and Discussion of Melting Mechanisms. 5.2 Geometry, Boundary Conditions, and Physical Properties in Melting. 5.3 Conduction Melting without Melt Removal. 5.4 Moving Heat Sources. 5.5 Sintering. 5.6 Conduction Melting with Forced Melt Removal. 5.7 Drag-induced Melt Removal. 5.8 Pressure-induced Melt Removal. 5.9 Deformation Melting. 6. Pressurization and Pumping. 6.1 Classification of Pressurization Methods. 6.2 Synthesis of Pumping Machines from Basic Principles. 6.3 The Single Screw Extruder Pump. 6.4 Knife and Roll Coating, Calenders, and Roll Mills. 6.5 The Normal Stress Pump. 6.6 The Co-rotating Disk Pump. 6.7 Positive Displacement Pumps. 6.8 Twin Screw Extruder Pumps. 7. Mixing. 7.1 Basic Concepts and Mixing Mechanisms. 7.2 Mixing Equipment and Operations of Multicomponent and Multiphase Systems. 7.3 Distribution Functions. 7.4 Characterization of Mixtures. 7.5 Computational Analysis. 8. Devolatilization. 8.1 Introduction. 8.2 Devolatilization Equipment. 8.3 Devolatilization Mechanisms. 8.4 Thermodynamic Considerations of Devolatilization. 8.5 Diffusivity of Low Molecular Weight Components in Molten Polymers. 8.6 Boiling Phenomena: Nucleation. 8.7 Boiling-Foaming Mechanisms of Polymeric Melts. 8.8 Ultrasound-enhanced Devolatilization. 8.9 Bubble Growth. 8.10 Bubble Dynamics and Mass Transfer in Shear Flow. 8.11 Scanning Electron Microscopy Studies of Polymer Melt Devolatilization. 9. Single Rotor Machines. 9.1 Modeling of Processing Machines Using Elementary Steps. 9.2 The Single Screw Melt Extrusion Process. 9.3 The Single Screw Plasticating Extrusion Process. 9.4 The Co-rotating Disk Plasticating Processor. 10. Twin Screw and Twin Rotor Processing Equipment. 10.1 Types of Twin Screw and Twin Rotor-based Machines. 10.2 Counterrotating Twin Screw and Twin Rotor Machines. 10.3 Co-rotating, Fully Intermeshing Twin Screw Extruders. 11. Reactive Polymer Processing and Compounding. 11.1 Classes of Polymer Chain Modification Reactions, Carried out in Reactive Polymer Processing Equipment. 11.2 Reactor Classification. 11.3 Mixing Considerations in Multicomponent Miscible Reactive Polymer Processing Systems. 11.4 Reactive Processing of Multicomponent Immiscible and Compatibilized Immiscible Polymer Systems. 11.5 Polymer Compounding. 12. Die Forming. 12.1 Capillary Flow. 12.2 Elastic Effects in Capillary Flows. 12.3 Sheet Forming and Film Casting. 12.4 Tube, Blown Film, and Parison Forming. 12.5 Wire Coating. 12.6 Profile Extrusion. 13. Molding. 13.1 Injection Molding. 13.2 Reactive Injection Molding. 13.3 Compression Molding. 14. Stretch Shaping. 14.1 Fiber Spinning. 14.2 Film Blowing. 14.3 Blow Molding. 15. Calendering. 15.1 The Calendering Process. 15.2 Mathematical Modeling of Calendering. 15.3 Analysis of Calendering Using FEM. Appendix A: Rheological and Thermophysical Properties of Polymers. Appendix B: Conversion Tables to the International System of Units (SI). Appendix C: Notation. Author Index. Subject Index.

ASSESSING THE MAIN REACTIONS IN A BIOPROCESS: APPLICATION TO CHEESE RIPENING

The aim of this paper is to select the main reactions of a bioprocess from a set of plausible metabolic pathways provided by expert knowledge. We use a methodology aiming at determining the pseudo-stoichiometric coefficient matrix of a macroscopic mass balance based model. First, the size of the system is identified and a subspace where the bioprocess dynamics lives is established. In a second step, the set of a priori plausible reactions is compared with the identified subspace and the most adequate reactions are selected. This approach is applied to cheese ripening experimental data. As the main result the method leads to the identification of a metabolic network that can be the base for dynamical model development.

Strain Tailoring in 3C‐SiC Heteroepitaxial Layers Grown on Si(100)

AbstractDue to the large differences in lattice parameters and thermal expansion coefficients, the heteroepitaxial growth of 3C–SiC on Si mainly results in highly defective layers on strongly bent wafers. The defects may not be detrimental for very basic applications, but the bow is. In this article, we review several attempts to reduce the final curvature after epitaxial growth of 3C‐SiC. One is the use of the “checkerboard” carbonization process which creates a macroscopic balance of the stress by the formation of a regular network of compressed and tensed areas. Another approach proposes to create, in situ, a random patchwork of tensed and compressed areas during the carbonization step. The other attempts use substrates other than standard Si, namely silicon on insulator and Si–Ge substrates for compliance effect and closer thermal expansion mismatch with SiC, respectively. All techniques provoke a significant reduction of the strain in the deposited 3C‐SiC layers.

Short-Term Metabolome Dynamics and Carbon, Electron, and ATP Balances in Chemostat-Grown Saccharomyces cerevisiae CEN.PK 113-7D following a Glucose Pulse

The in vivo kinetics in Saccharomyces cerevisiae CEN.PK 113-7D was evaluated during a 300-second transient period after applying a glucose pulse to an aerobic, carbon-limited chemostat culture. We quantified the responses of extracellular metabolites, intracellular intermediates in primary metabolism, intracellular free amino acids, and in vivo rates of O(2) uptake and CO(2) evolution. With these measurements, dynamic carbon, electron, and ATP balances were set up to identify major carbon, electron, and energy sinks during the postpulse period. There were three distinct metabolic phases during this time. In phase I (0 to 50 seconds after the pulse), the carbon/electron balances closed up to 85%. The accumulation of glycolytic and storage compounds accounted for 60% of the consumed glucose, caused an energy depletion, and may have led to a temporary decrease in the anabolic flux. In phase II (50 to 150 seconds), the fermentative metabolism gradually became the most important carbon/electron sink. In phase III (150 to 300 seconds), 29% of the carbon uptake was not identified in the measurements, and the ATP balance had a large surplus. These results indicate an increase in the anabolic flux, which is consistent with macroscopic balances of extracellular fluxes and the observed increase in CO(2) evolution associated with nonfermentative metabolism. The identified metabolic processes involving major carbon, electron, and energy sinks must be taken into account in in vivo kinetic models based on short-term dynamic metabolome responses.

Moisture, acidity and temperature evolution during cacao drying

Theoretical moisture and temperature evolution during cacao fixed bed drying were estimated with non-steady heat and mass transfer equation both in particle and bed. The model takes into account the cacao internal profiles and the air macroscopic balance of moisture, acidity and temperature. The results showed that the theoretical model predicts the experimental evolution of these state variables during cacao drying at three different conditions with average % of error lower than 18%.

Relativistic kinetics of phonon gas in superfluids

The relativistic kinetic theory of the phonon gas in superfluids is developed. The technique of the derivation of macroscopic balance equations from microscopic equations of motion for individual particles is applied to an ensemble of quasi-particles. The necessary expressions are constructed in terms of a Hamilton function of a (quasi-)particle. A phonon contribution into superfluid dynamic parameters is obtained from energy-momentum balance equations for the phonon gas together with the conservation law for superfluids as a whole. Relations between dynamic flows being in agreement with results of relativistic hydrodynamic consideration are found. Based on the kinetic approach a problem of relativistic variation of the speed of sound under phonon influence at low temperature is solved.

A simple feedback control of Escherichia coli growth for recombinant aldolase production in fed-batch mode

Fed-batch production of recombinant fuculose-1-phosphate aldolase (FucA) by Escherichia coli XL1 Blue MRF′ (pTrcfuc) has been automated by using a simple feedback specific growth rate control strategy. Non-induced continuous cultures were conducted in order to characterize substrate consumption and carbon dioxide production yields and rates. In fed-batch cultures, substrate feeding rate was adjusted using on-line biomass estimation based on exhaust gas analysis and macroscopic mass balances. Overexpression of recombinant protein induced by isopropyl-β- d-thiogalactopyranoside (IPTG) under trc promoter did not affect significantly the control of specific growth rate during 7 h after induction. Growth and protein production curves were parallel until high level of protein expression started to inhibit cell growth. The proposed specific growth rate control strategy has been successfully applied to both non-induced and induced fed-batch cultures that do not exhibit severe growth rate depression.

New developments in differential ebulliometry: Experimental and theoretical

A new ebulliometer has been developed in which superheat is discharged from the vapour–liquid mixture issuing from the Cottrell pump before it impinges on an otherwise vacuum-insulated temperature sensor. The convoluted chamber through which the mixture passes should also assist the attainment of phase equilibrium in binary mixtures. Measurements for several solvents showed unusually broad plateau regions with slopes much smaller than those reported by other researchers. Vapour pressures for several solvents were in close agreement with literature values. For the measurement of limiting activity coefficients, a new experimentally very simple procedure was developed for finding the difficult-to-determine evaporation ratio, ϕ, based on the steady-state macroscopic energy balance. Results are presented for two pure solvents, viz. ethylacetate and cyclohexane. Exact equations, based on material balances and equilibrium relationships involving ϕ then permit calculation of limiting activity coefficients. Measured temperature-composition data are presented for the ethylacetate (1)–toluene (2) and hexane (1)–ethylacetate (2) systems and the ebulliometer characterization procedure is illustrated for three binary systems. Exact differential equations for the temperature and pressure derivatives with respect to composition, and incorporating the full Gibbs-Duhem equation, are derived. These can be used to find the very useful temperature–pressure derivative (∂ T/∂ p) x 1 at any composition and also form the basis for a new thermodynamic consistency test.

Molecular dynamics simulations of microwave effects on water using different long-range electrostatics methodologies

Non-equilibrium molecular dynamics (NEMD) simulations of water have been carried out in the presence of an external electromagnetic field of frequency 100 GHz and RMS intensity 0.1 V/Å in the isothermal–isobaric ensemble from 260 to 400 K and in the pure Newtonian case from ambient temperatures to the supercritical state. The rigid, non-polarizable SPC, SPC/E, TIP4P, TIP4P-Ew and the polarizable TIP4P-FQ potentials were used for a system of 256 molecules, along with both the Lekner and Ewald techniques to handle long-range electrostatics, in an effort to assess the impact of different long-range electrostatics methodologies on the results. Significant alterations in molecular mobility and hydrogen bonding patterns were found relative to zero-field conditions. The heating profiles were compared to that predicted from a macroscopic energy balance, and the TIP4P-FQ model was found to be superior in this aspect. Although the Lekner and Ewald techniques yielded similar results in the case of the non-polarizable potentials, some significant differences were noted between them for the TIP4P-FQ model at lower temperatures.

On the macroscopic–mesoscopic mixture of a magnetorheological fluid

This paper is concerned with the modelling of a magnetorheological (MR) fluid in the presence of an applied magnetic field as a twofolded mixture—a macroscopic fluid continuum and mesoscopic multi-solid continua. By assigning to each solid particle a vectorial mesoscopic variable, which is defined as the nearest relative position vector with respect to other particles, the solid medium of the MR fluid is further treated as a mixture consisting of different components, specified by these mesoscopic variables. The treatment of multi-solid continua is similar to that in the mesoscopic theory of liquid crystals. However, the key difference lies in the fact that the time-discontinuity of the defined vectorial mesoscopic variable will give rise to a ‘pseudo’ chemical reaction in the solid continuum. The equation of the phenomenological mesoscopic distribution function of the solid continuum then has an additional production term from the pseudo chemical reaction, analogous to the collision term appearing in the Boltzmann equation. The mesoscopic and macroscopic balance equations are then derived and by assuming the special constitutive relations the macroscopic equation for the second moment of the distribution function can be obtained.

Macroscopic Mass and Energy Balance of a Pilot Plant Anaerobic Bioreactor Operated Under Thermophilic Conditions

Intensive poultry production generates over 100,000 t of litter annually in West Virginia and 9 x 10(6) t nationwide. Current available technological alternatives based on thermophilic anaerobic digestion for residuals treatment are diverse. A modification of the typical continuous stirred tank reactor is a promising process being relatively stable and owing to its capability to manage considerable amounts of residuals at low operational cost. A 40-m3 pilot plant digester was used for performance evaluation considering energy input and methane production. Results suggest some changes to the pilot plant configuration are necessary to reduce power consumption although maximizing biodigester performance.

Hygro-thermo-chemo-mechanical modelling of concrete at early ages and beyond. Part I: hydration and hygro-thermal phenomena

Part 1 of the paper presents a new numerical model of hygro-thermal and hydration phenomena in concrete at early ages and beyond. This is a solidification-type model where all changes of material properties are expressed as functions of hydration degree, and neither as maturity nor as equivalent hydration period as in maturity-type models. A mechanistic approach has been used to obtain the governing equations, by means of an averaging theory of Hassanizadeh and Gray, also called hybrid mixture theory. The developments start at the micro-scale and balance equations for phases and interfaces are introduced at this level and then averaged for obtaining macroscopic balance equations. Constitutive laws are directly introduced at macroscopic level. The final equations, mass (water species and dry air), energy and momentum balance equations, have been written in terms of the chosen primary variables: gas pressure, capillary pressure, temperature and displacements. An evolution equation for the internal variable, hydration degree, describes hydration rate as a function of chemical affinity, considering in addition to the existing models, an effect of the relative humidity on the process. The model takes into account full coupling between hygral, thermal and chemical phenomena, as well as changes of concrete properties caused by hydration process, i.e. porosity, density, permeability, and strength properties. Phase changes and chemical phenomena, as well as the related heat and mass sources are considered. Two examples showing possibilities of the model for analysis of autogenous self-heating and self-desiccation phenomena, as well as influence of the ambient relative humidity and the concrete element dimensions upon hygro-thermal performance and shrinkage of the elements, are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd.

A combined multicell‐WENO solver for the Boltzmann‐Poisson system of 1D semiconductor devices

PurposeTo present a new direct solution method for the Boltzmann‐Poisson system for simulating one‐dimensional semiconductor devices.Design/methodology/approachA combination of finite difference and finite element methods is applied to deal with the differential operators in the Boltzmann transport equation. By taking advantage of a piecewise polynomial approximation of the electron distribution function, the collision operator can be treated without further simplifications. The finite difference method is formulated as a third order WENO approach for non‐uniform grids.FindingsComparisons with other methods for a well‐investigated test case reveal that the new method allows faster simulations of devices without losing physical information. It is shown that the presented model provides a better convergence behaviour with respect to the applied grid size than the Minmod scheme of the same order.Research limitations/implicationsThe presented direct solution methods provide an easily extensible base for other simulations in 1D or 2D. By modifying the boundary conditions, the simulation of metal‐semiconductor junctions becomes possible. By applying a dimension by dimension approximation models for two‐dimensional devices can be obtained.Practical implicationsThe new model is an efficient tool to acquire transport coefficients or current‐voltage characteristics of 1D semiconductor devices due to short computation times.Originality/valueNew grounds have been broken by directly solving the Boltzmann equation based on a combination of finite difference and finite elements methods. This approach allows us to equip the model with the advantages of both methods. The finite element method assures macroscopic balance equations, while the WENO approximation is well‐suited to deal with steep gradients due to the doping profiles. Consequently, the presented model is a good choice for the fast and accurate simulation of one‐dimensional semiconductor devices.

Extensions to the Macroscopic Navier–Stokes Equation

A development is provided showing that for any phase, by not neglecting the macroscopic terms of the deviation from the intensive momentum and of the dispersive momentum, we obtain a macroscopic secondary momentum balance equation coupled with a macroscopic dominant momentum balance equation that is valid at a larger spatial scale. The macroscopic secondary momentum balance equation is in the form of a wave equation that propagates the deviation from the intensive momentum while concurrently, in the case of a Newtonian fluid and under certain assumptions, the macroscopic domi- nant momentum balance equation may be approximated by Darcy's equation to address drag dominant flow. We then develop extensions to the dominant macroscopic Navier- Stokes (NS) equation for saturated porous matrices, to account for the pressure gradient at the microscopic solid-fluid interfaces. At the microscopic interfaces we introduce the exchange of inertia between the phases, accounting for the relative fluid square velocities and the rate of these velocities, interpreted as Forchheimer terms. Conditions are provided to approximate the extended dominant NS equation by Forchheimer quadratic momentum law or by Darcy's linear momentum law. We also show that the dominant NS equation can conform into a nonlinear wave equation. The one-dimensional numerical solution of this nonlinear wave equation demonstrates good qualitative agreement with experiments for the case of a highly deformable elasto-plastic matrix.

Prediction of temperature and thermal inertia effect in the maturation stage and stockpiling of a large composting mass

A macroscopic non-steady state energy balance was developed and solved for a composting pile of source-selected organic fraction of municipal solid waste during the maturation stage (13,500 kg of compost). Simulated temperature profiles correlated well with temperature experimental data (ranging from 50 to 70 °C) obtained during the maturation process for more than 50 days at full scale. Thermal inertia effect usually found in composting plants and associated to the stockpiling of large composting masses could be predicted by means of this simplified energy balance, which takes into account terms of convective, conductive and radiation heat dissipation. Heat losses in a large composting mass are not significant due to the similar temperatures found at the surroundings and at the surface of the pile (ranging from 15 to 40 °C). In contrast, thermophilic temperature in the core of the pile was maintained during the whole maturation process. Heat generation was estimated with the static respiration index, a parameter that is typically used to monitor the biological activity and stability of composting processes. In this study, the static respiration index is presented as a parameter to estimate the metabolic heat that can be generated according to the biodegradable organic matter content of a compost sample, which can be useful in predicting the temperature of the composting process.

Hydrodynamics Characterization of Rotor-Stator Mixer with Viscous Fluids

The hydrodynamics generated by a rotor-stator mixer has been characterized experimentally in terms of power draw and flow patterns with viscous Newtonian and shear-thinning fluids. The power consumption was correlated to the impeller speed and represented by means of the dimensionless power number versus Reynolds number curve. The impeller shear rate constant, determined from a macroscopic balance as well as with the Metzner–Otto method, was found to be dependent on the fluid rheological properties. An attempt was also made to determine the pseudo-cavern (well-mixed region surrounded by a stagnant fluid) dimension as a function of the hydrodynamic parameters. Results show that the shape and magnitude of the pseudo-caverns in the vicinity of the rotor-stator mixer are central to the understanding of the relationship between the power draw and the ability of the impeller to mix the fluid into the vessel.

Modelling the coupled evolution of hydration and porosity of cement-based materials

A modelling of the relationship between the evolution of endogenous hydration and that of porosity of cement-based materials was carried out. The mass balance equations of anhydrous and hydrates were written in molecular scale, then, transposed in macroscopic scale by using the volume averaging technique. The combined system of obtained equations (porosity equation and macroscopic mass balances) was solved numerically. The model validation was done in two steps in the case of two mortars cured during 2, 7 and 21 days. Simulation results of hydration rates were compared to the experimental results obtained by SEM images analysis and the theoretical evolution in time of the porosity was checked against MIP results. Globally, a good correlation between simulation results and experimental ones was noticed. However, to less disturbing the hydration process of the material, it seems desirable to improve the drying mode of the samples before SEM analyses or MIP tests.