Drying Of Porous Materials Research Articles

Shrinkage properties of porous materials during drying: a review

The shrinkage characteristic of porous materials is an important consideration in the drying process, as it can significantly impact the texture of the dried product and energy utilization. This phenomenon is influenced by numerous factors, including the structure of the cells, drying conditions, and the glass transition temperature. To gain a deeper understanding of the drying process, it is necessary to develop theoretical models that account for the simultaneous heat and mass transfer processes at the cellular level, as well as simulation tools to analyze the associated changes in drying morphology. In this paper, we highlight several key factors affecting shrinkage during the drying of porous materials, and also outline drying modeling, morphological simulation, and drying technology design considerations to provide guidance for improving the drying quality of porous materials as well as energy conversion efficiency.

Manufacture Dry Porous Carbonate Materials with Crack Free

Manufacture Dry Porous Carbonate Materials with Crack Free

Manufacture Dry Porous Carbonate Materials with Crack Free

pickering foam is a water foam stabilized using solid particles, and this foam can be used as a material in the production of lightweight porous insulating materials. This is done by pouring it into molds, then drying and finally foaming it. One of the most important problems accompanying the drying of bicarbonate foam is the phenomenon of shrinkage in the models resulting from the liquid leaving it by evaporation, resulting in capillary pressures generated inside it. Due to the shrinkage phenomenon, defects and cracks sometimes occur during the drying process that appear on the surface. The process of defects and cracks formation during the drying process depends on the drying conditions such as temperature, relative humidity, and the type of used support angle θ (in addition to the mechanical specifications of the models). Understanding the drying procedures helps researchers and workers in the production of such porous materials, and in choosing the appropriate drying conditions and avoiding any defects in the product. In this study, the effect of the mechanical specifications of the model was investigated by adding surface tension-reducing agents at different concentrations to the models during the drying process, as well as studying the effect of the contact angle (θ) of the support on the probability of crack formation and the mechanical specifications of the dried model. It was found that the value of the contact angle (θ) has a direct effect on cracks and defects. Increasing the value of the contact angle from θ = 30° to θ = 150° leads to a reduction or treatment of the cracks that appear in the models. It was also found that adding surface tension-reducing agents such as SLES and SDS leads to crack formation in the models, and increasing the concentration of surface tension-reducing agents such as SLES and SDS leads to foam collapse. However, adding surface tension-reducing agents such as C8AC and C10AC did not show any cracks for all concentrations. As for the mechanical properties of the dry models, they are directly affected by the type of surfactant (C10AC and C8AC), which led to the formation of models with porosities higher than 90%. As for the concentration of the surfactant, it has an effect on the wet model, while it does not affect 90%. From the mechanical specifications (porosity and density) of the model after drying

Preparation of Vancomycin-Loaded Aerogels Implementing Inkjet Printing and Superhydrophobic Surfaces.

Chronic wounds are physical traumas that significantly impair the quality of life of over 40 million patients worldwide. Aerogels are nanostructured dry porous materials that can act as carriers for the local delivery of bioactive compounds at the wound site. However, aerogels are usually obtained with low drug loading yields and poor particle size reproducibility and urges the implementation of novel and high-performance processing strategies. In this work, alginate aerogel particles loaded with vancomycin, an antibiotic used for the treatment of Staphylococcus aureus infections, were obtained through aerogel technology combined with gel inkjet printing and water-repellent surfaces. Alginate aerogel particles showed high porosity, large surface area, a well-defined spherical shape and a reproducible size (609 ± 37 μm). Aerogel formulation with vancomycin loadings of up to 33.01 ± 0.47 μg drug/mg of particle were obtained with sustained-release profiles from alginate aerogels for more than 7 days (PBS pH 7.4 medium). Overall, this novel green aerogel processing strategy allowed us to obtain nanostructured drug delivery systems with improved drug loading yields that can enhance the current antibacterial treatments for chronic wounds.

Drying of porous materials at pore scale using lattice Boltzmann and pore network models

Drying at macroscale shows a first drying period with constant drying rate followed by second drying period showing a receding moisture front, phenomena that can be tailored upon need. In order to study the drying of materials, we present a new hybrid computational method, where the dynamics of the liquid-vapor interfaces is modelled by lattice Boltzmann modelling (LBM) in the two-phase pores, while the single-phase flow in the pores filled solely by vapor or liquid is solved by pore network model (PNM). This hybrid method is validated by comparison with reference full LBM simulations. The hybrid method combines the advantages of both methods, i.e., accuracy and computational efficiency. LBM and the hybrid LBM-PNM method are used to study the drying of porous media at pore scale. We analyse two different pore structures and consider how capillary pumping effect can maximize the drying rate. Finally, we indicate how optimized drying rates are relevant when designing facade or pavement solutions that can mitigate higher surface temperatures in urban environments by evaporative cooling.

Quasi-averaged formulation of Stefan's linear problem in drying of cylindrical beam

In the process of drying of porous materials there is a moving surface separating the dried and wet areas in the body. This surface is a phase transition, which significantly depends on the properties of the material and the temperature, which is due to the external influence of the drying agent and is a function of coordinates and time, and the movement of boundaries is a consequence of phase transitions. The paper presents the properties of the material, namely: heat capacity, density, thermal conductivity coefficients to be the functions of the porosity of the material, densities and heat capacities of body components.

Mathematical modeling and research of heat and moisture transfer processes in porous media

A mathematical model, numerical algorithm, solution, and results of the computational experiment on a computer are developed to predict the process of heat and moisture transfer in porous media, taking into account such factors as the internal heat and moisture release of a porous natural product on the example of raw cotton and its products of hulling, seeds of various crops. It also considers the effect of temperature and moisture content changes in the environment on the storage and drying of porous materials. In this study, the developed mathematical support of the object under research makes it possible to predict the change in temperature and moisture content at arbitrary points of the porous body and serves to prevent the loss of quality and spontaneous combustion of materials under solar radiation and to analyze and make managerial decisions. Based on the method of coordinate-wise splitting, a numerical algorithm for calculating three-dimensional heat and moisture transfer problems in areas of the parallelepiped type is presented. An implicit second-order difference scheme for calculating the required functions is presented. Based on the numerical calculations performed, it was established that moisture and heat transfer and their exchange with the environment occurs in the upper layers of the cotton pile; in the inner layers, there is an increase in temperature and moisture due to the respiration of raw cotton and its seeds, which depends on the degree of moisture of the raw cotton and their products of hulling.

Porosity-dependent velocities of longitudinal and transverse waves in dry porous materials

New relations are presented to better evaluate the longitudinal and transverse velocities in porous materials under the dry state, respectively. The models are based on semi analytically derived bulk and shear moduli-porosity correlations for dry porous materials. The accuracy and robustness are validated by fitting the published elastic waves-porosity data of different porous materials and a further sensitivity analysis, respectively. The accuracy of the proposed models is averagely higher than that of the empirical Phani’s equation and theoretical Ramakrishnan’s equation. There is an advantage over the Ramakrishnan’s equation to predict the zero-porosity velocity from the data lack of dense porous specimens. The proposed models have a good predictive performance for porous materials with critical porosity and can provide the value of critical porosity, but attention also should be paid to increased sensitivity in this case.

Supercritical drying of thermoresponsive gels based on N-isopropylacrylamide

Thermoresponsive materials are of great interest for medicine, pharmacy and food industry. During the production of these materials they are often taken into their dry state, requiring gentle processes with minimum effect over their properties. In this study, supercritical drying process was used to obtain dry products from thermoresponsive N-Isopropylacrylamide based gels and compared to other typical drying processes like hot air- and freeze- drying. Depending on the method, different degrees of modification of the structure were observed, which have a significant influence on the final properties of the materials and on their rehydration. Results show that supercritical technology can be used to produce dry porous materials with less collapsed structure or modified properties than conventional or freeze drying techniques while keeping the thermoresponsive nature, which is translated into materials with higher porosity and surface area, and slightly improved swelling degree. Swelling kinetics results showed that materials dried by conventional drying displayed sigmoidal anomalous behavior, those dried by freeze-drying exhibited a two-stage anomalous behavior, and materials obtained by supercritical drying presented behaviors close to Fickian which is of great interest for further drug release applications.

MATHEMATICAL MODEL FALL MATERIAL PARTICLES IN A VORTEX APPARATUS

The results of test calculations obtained on the basis of mathematical models of the motion of material particles and gas dynamics of the coolant flow in a vortex apparatus during heat treatment are given in the article. The task of this paper is to determine the dependencies between the flow velocity, the place where the particle is introduced into the apparatus, and the specific trajectory of the particle.The efficiency of heat and mass transfer during the drying of porous materials in vortex devices is largely determined by the ratio of the geometric dimensions of the device, since the hydrodynamic performance of the apparatus depends on them. The drying of materials in the vortex apparatus occurs during the period of the dispersion of particulate material in the apparatus during their interaction with air currents. Obviously, the longer this process, the more effective it is.Analyzing the obtained results of the work, the author concludes that the duration of heat treatment of the particles of the material up to the moment of its completion may be different and depends, in the main, on the intensity of washing of the particle with the flow of the coolant. In general, the calculated information obtained can be the basis for designing and optimizing the design of the device in terms of reducing energy costs. The shape of the trajectory, its extent determine the overall dimensions of the device and the flow characteristics of the coolant. Depending on the required intensity of heat treatment, the location of the particles entering and the velocity of the coolant can vary.Analysis of the results of the calculations given in the paper allows us to make a qualitative conclusion that, in general, the particles that get into the vortex apparatus closer to the side wall last longer in its volume, and, consequently, are longer dried, which is more prefe-rable from a technological point of view.The data obtained can be used in the calculation of heat-mass-exchange vortex devices.

Microstructure and thermal conductivity of cement-based foam:A review

This paper presents a review of existing studies on the microstructure and thermal conductivity of cement-based foam. Previous studies on constituent materials, measurement techniques for thermal properties, characterization of microstructure, the thermal conductivity of cement-based foam and conductivity models for the dry porous material are included in the discussion. Based on the review, the following research areas have been identified: (i) Influence of pozzolanic admixtures and different cast densities on the thermal conductivity of cement-based foam (ii) Effect of microstructure on the thermal conductivity (iii) Governing hydrated products and their impact on the conductivity (iv) The applicability of existing model for predicting the thermal conductivity of cement-based foam.

From Pickering foams to porous carbonate materials: crack-free structuring in drying ceramics

Particle-stabilized foams have attracted considerable research interest, due to their long term stability (months to years) and the possibility to use them as precursors for production of porous materials with hierarchical porosity. In our previous study [Lesov et al., J. Colloid Interface Sci. 504 (2017) 48–57] we clarified the role of the rheological properties of the foamed suspensions and the type of foam film stabilization in the production of porous silica materials with low mass density and excellent insulating properties. In the current study we extend our approach to prepare lightweight carbonate ceramics with controlled density, shrinkage and good mechanical properties. To prepare the wet foam precursors, we tested a series of eight anionic surfactants which were previously reported to provide sufficient hydrophobization of CaCO3 particles and long-term stability of the liquid foams. From those surfactants, the medium-chain fatty acids led to crack-free porous materials with superior mechanical strength, compared to the conventional surfactants. We study the reasons for the formation of cracks in drying Pickering foams and, on this basis, propose optimal conditions for obtaining dry porous carbonate materials with required porosity. Mechanistic explanations are proposed for the main observed effects.

Development of the experimental stand for investigation of heating and drying phenomena in the porous building materials with one surface of the sample exposed to the flowing air

The paper presents development of the experimental stand for investigation of heating and drying phenomena in the porous building materials with one surface of the sample exposed to the flowing air. Moreover, results of preliminary measurements which verify the range of operating conditions achieved by the stand are shown. These conditions were assumed in the following range: 15℃-60℃, 10-90% and 0.1-10 m/s for temperature, relative humidity and velocity of the flowing air, respectively. In order to control the parameters of air used for heating and drying of porous materials, a closed-loop concept of the stand was proposed and equipped with several elements, i.e., the cooler (vapour condenser), fan with variable rotational speed, humidifier and heater. Furthermore, two parallel measurement ducts which allow to obtain two air streams with identical parameters were proposed. This enables two measurements at one time as well as faster verification of the repeatability of the performed measurements. The temperature measurements at the top surface and inside the sample are carried out applying the IR thermography and several K-type thermocouples, respectively, while overall moisture amount and the moisture content distribution in the specimen are found using tensometric force and electrical resistance meters, respectively.

Intermittent Drying of Porous Materials: A Review

Hygroscopic materials can suffer variations in water content and temperature according to ambient air conditions. In the case of agricultural products, control the moisture and temperature is of paramount importance for the conservation of their quality and to avoid losses. In this context, the drying is one of the most widely used methods for this purpose. Various drying techniques are reported in the literature,in order to increasingly improve the final product quality and saving energy used. The purpose of this paper is to discuss and analyze the latest advances in intermittent drying research from the standpoint of quality after-drying product and energy efficiency. The most applied modeling techniques are highlighted and considerations for its use are shown.

Study on formaldehyde emissions from porous building material under non-isothermal conditions

Based on an improved model of formaldehyde emissions from building material under non-isothermal conditions, the mechanisms of formaldehyde emissions in dry porous building material are discussed. The formaldehyde emissions in an ordinary particle board are simulated under the different non-isothermal conditions, using floor heating and air circulation heating systems. The concentration of formaldehyde that remained in the board is strongly affected by the thermal boundary condition. Experiments demonstrating the emission of formaldehyde during floor heating and air circulation systems are carried out in a controlled environmental chamber. The experimental results validate the proposed model qualitatively. The present work showed that the equilibrium concentration in an airtight chamber having floor heating system is higher than that in an air circulation heating system.

Migration of sodium chloride in dry porous materials

Groundwater can saturate soil above the water table within the capillary fringe associated with the pore size of the parent soil. External evaporation has been viewed as a mechanism for enhancing upward flow, potentially creating problems of salt heave beneath roads and foundations if the groundwater is saline, analogous to concerns with efflorescence in masonry. The role of internal evaporation in promoting crystallization, and especially in altering the transport process of the pore fluid, has been recognized but is only partially understood. The purpose of this paper is to examine evidence for the upward percolation of brine accompanying salt crystallization inside a porous granular material. A series of experiments are described using vertical flow columns packed with dry sand above a reservoir of saline fluid, to explore whether salt transport could take place by autogenous wicking above the initial capillary fringe. The conditions inside the columns were monitored at specific elevations with sensors measuring bulk electrical conductivity, dielectric constant and relative humidity. Dendritic salt crystallization was observed inside the sand, accompanying surface heave. Ultimately, efflorescence on the surface led to the formation of a salt crust. Some implications for the potential damage to roads and foundations in arid regions, and to masonry subject to rising damp, are discussed.

Preparation of the monolith of hierarchical macro-/mesoporous calcium silicate ultrathin nanosheets with low thermal conductivity by means of ambient-pressure drying.

Calcium silicate monolith was prepared by the hydrothermal reaction of a slurry of SiO2 , calcium hydroxide, and surfactant (OP-10) obtained by high-energy ball milling, followed by drying at ambient pressure. By using this strategy, the shrinkage due to the collapse of pores during the drying of porous materials, which is a commonly observed phenomena, was successfully avoided. It has a unique microstructure of hierarchical macro-/mesoporous ultrathin calcium silicate nanosheets with a layered gyrolite crystalline structure. Very interestingly, the calcium silicate nanosheets can be peeled off to give a single-layer nanosheet (1.23 nm) of gyrolite by ultrasonication. The monolith has a low apparent density (0.073 g cm(-3) ) and low thermal conductivity (0.0399 W K(-1) m(-1) ). The reasons behind why the formation of the unique hierarchical macro-/mesoporous ultrathin nanosheets avoids shrinkage during the hydrothermal reaction and drying, and considerably decreases the thermal conductivity, is discussed.

Experimental Study on the Formaldehyde Emission under Non-isothermal Conditions

The adverse effects of formaldehyde on the indoor air quality is of serious concern. An experimental apparatus is fabricated to investigate the features of formaldehyde migration from dry porous building materials under non-isothermal conditions. The coupled heat and formaldehyde migration process in an ordinary particle board is investigated in both floor heating system and air circulation system. The instantaneous concentration of formaldehyde in the chamber, the instantaneous temperature of the air, and the instantaneous temperature of the top surface of the board is studied. The temperature of the bottom surface of the board is maintained at 15°C throughout the process. As shown in the experimental process, the equilibrium concentration of formaldehyde increases with an increase in the temperature of air. The equilibrium concentration in an airtight chamber having floor heating system is higher than that in an air circulation heating system. The experimental results validated proposed model. Therefore, it is necessary to improve the ventilation of the rooms using such systems.

Drying of particle-loaded foams for production of porous materials: mechanism and theoretical modeling

Particle-loaded wet foams are appropriate precursors for production of novel porous materials with hierarchical porous structure, ranging from tens of micrometers down to a few nanometers. Such porous materials could be further modified (sintered, impregnated, hydrophobized, etc.) to serve as catalyst supports, porous filters, insulating materials, templates for composite materials, etc. A particular obstacle for the design of such materials is the observed extensive shrinkage during drying of the wet foam precursor. This shrinkage has three important consequences – significant reduction of the size of the final porous material (as compared to the precursor template), significant evolution in the pore size distribution during sample drying, and possible cracking of the material upon drying. The major aims of the current study are (1) to clarify the main mechanism of shrinkage of foams prepared from silica suspensions with high particle concentration, and (2) to describe quantitatively the relation between the properties of the foamed suspension and the final dry porous material obtained from this suspension. The performed experiments and the data interpretation convincingly show that the foamed suspensions shrink until the particle concentration in the foam walls reaches close packing, at which the percolated particle structure is able to resist the high capillary pressures, developed in the process of drying. The volumetric shrinkage of the individual bubbles was found to be equal to that of the macroscopic foam sample. Equations are derived and verified to relate the particle concentration and the bubble fraction in the foam precursor with the final mass density of the obtained porous material and with the degree of shrinkage in the drying process. Three stages of foam drying and shrinking were observed: (1) an induction period with no sample shrinkage, despite the water loss, (2) rapid shrinkage, and (3) final water evaporation at constant volume of the sample. These stages were explained by considering the three basic physical regimes of convective drying of porous materials, as defined by Coussot (European Phys. J. B 15 (2000) 557–566). The equations derived in the current study allow one to design in advance the foam precursors needed to obtain a dry porous material with desired properties.

Drying Clay Bricks with Variable Young's Modulus

Abstract Drying of porous materials is a critical step in the production of many materials such as ceramics. Accurate simulation of shrinkage and the stresses induced may be used to predict cracking and distortion. One of the characteristic features of materials like clay and ceramics is the change of their mechanical properties during drying as the moisture content is changed. The aim of the present work is to analyse the stresses occurred during drying of a known ceramic material. The effect of considering young's modulus variations in intensity of stress during drying process was investigated and the results are reported.