Porosity Of Porous Materials Research Articles

Investigation of heat transfer characteristics of the self driving temperature-sensitive magnetic fluid through a nonmagnetic porous in a heating pipe

A temperature-sensitive magnetic fluid (TSMF) is a functional fluid that can be driven by both a magnetic field and a temperature difference. In this research, non-magnetic porous materials are inserted into a circular pipe to enhance heat transfer and increase the driving force. To evaluate heat transfer performance, measurements are conducted on flow rates and thermal resistance for different lengths and porosity of porous materials. A one-dimensional numerical simulation is employed to compare and predict the heat transfer performance under various porosity conditions also used in this study. As a result, when the porosity of the porous body is 80 % and the length is 10 mm, the flow rate is maximized. This is because the effect of increasing the driving force is stronger than the flow-blocking effect of the porous materials. The numerical results show the same trend as the experiment, and the decrease in flow rate is directly dependent on the length of the porous material.

Nanofluid Based Pipe Flow Analysis in Absorber Pipe of Flat Plate Solar Collector: Effects of Inclination and Porosity

Nanofluid applications in solar collectors are an emerging area for enhanced heat transfer resulting in heat gain for domestic and industrial use. In the present work, the performance of a Flat Plate Solar Collector (FPSC) having water-CuO-based nanofluid has been studied. The effect of the tilting angle of cylindrical pipe and porosity of porous material is investigated for this nanofluid-based FPSC. A numerical approach has been adopted to stimulate the governing equations in the tube. The similarity transformation simplifies the model (PDEs) into ordinary differential equations (ODEs). The governing non-dimensional PDEs along with their appropriate boundary conditions are solved numerically using the 4th order Runge-Kutta method cum shooting technique. The impacts of significant and relevant physical parameters and physical quantities of interest are analyzed. From the present study, it is observed that amplification of tilting angle and curvature parameter ameliorates the heat transfer rate while that of porosity parameter controls it effectively. A similar approach can be employed for other solar collectors to assess the heat transfer augmentation by using nanofluids instead of existing fluids.

Effect of porous materials on explosion characteristics of low ratio hydrogen/methane mixture in barrier tube

The effect of porous materials on the explosion characteristics of low ratio hydrogen/methane mixture in barrier tube was studied. The hydrogen ratio in the mixture is 0%–20%. The porosity of porous material is 20 PPI, 40 PPI and 60 PPI. The flame front structure, flame front velocity and overpressure data of the mixture were obtained by using high-speed camera and pressure sensor. The experimental results show that porous materials with the same porosity have similar quenching effects on pure methane explosion and low ratio hydrogen/methane premixed explosion. The greater the porosity, the better the quenching and decompression effect. The porous material with porosity of 60 PPI can meet its ability to attenuate flame front velocity and pressure wave even when adding low ratio hydrogen. The incremental effects of flame velocity and overpressure caused by the explosion of mixed gas with low ratio hydrogen under porous materials in the barrier tube are kept in a safe and controllable range. The research results provide a reference for the subsequent hydrogen mixed natural gas pipeline project.

Porosity Prediction of Porous Materials Deposited by Semi-Molten Spraying Particles

To determine the relationship between the deposition characteristics of semi-molten particles and the porosity of porous materials prepared by flame spraying, metal powders of Mo and 316L were used and the melting degree of deposition particles was controlled. Based on the experimental observations, a three-dimensional, random-stacking model was established by introducing the slipping characteristics of semi-molten particles, which could help predict the porosity of the generated porous metal materials. The results show that the maximum porosity of porous materials deposited by semi-molten particles was about 82%. A one-to-one relationship was observed between the melting degree of particles and the porosity of deposited samples. The three-dimensional random model could successfully predict the porosity of porous materials by combining the melting degree and slipping characteristics of spray particles, and the predicted values were consistent with the experimental results. The results of this study are useful to control the pore structure of porous materials deposited by semi-molten spraying particles.

Comparative analysis of water condensate porosity using mercury intrusion porosimetry and nitrogen and water adsorption techniques in porous building stones

Condensate porosity in porous materials has a significant influence on comfort, energy consumption, and material’s strength and durability. The variation of the moisture content of the material for a given variation of relative humidity describes the moisture storage capacity and has to be determined experimentally through the water sorption isotherm. However, the characterisation of sorption isotherm is very time-consuming, mostly for high relative humidity conditions, which may cause experimental errors and reproducibility problems.This paper aims to estimate experimental water condensate porosity using mercury intrusion porosimetry and nitrogen adsorption technique considering pores smaller than 0.1 μm for a wide range of porous sedimentary rock types with different petrographic characteristics. Particularly for nitrogen adsorption characterisation, we interpolated the pore volume using BJH method applied to the desorption branch. In the water adsorption test, condensate porosity is obtained with the maximum adsorbed water at RH = 100%.The ratio between water condensate porosity and total porosity in the studied porous stones is important and varies from 2 to 38%. Nitrogen adsorption technique provides the best estimation of condensate porosity (R2 = 0.979) and an effective estimation of water condensate porosity. The correlation between condensate porosity using MIP is moderate (R2 = 0.892) and presents a wider dispersion for all the range of condensate porosity. A mathematical expression that fits the shape and curvature of the water isotherm was also analysed in terms of pore structure. These studies are scarce for porous stones and our results provide valuable information for these widely used construction and building material.

Experimental Study on Explosion of Premixed Methane-air with Different Porosity and Distance from Ignition Position

ABSTRACT In order to suppress the overpressure and flame damage caused by the explosion of premixed methane-air, a self-built duct with a 10 × 10 × 100 cm was used to conduct an experimental study on the explosive characteristics and propagation rules of 9.5% methane under the effect of different porous materials at a fixed position. The methods of suppressing methane-air explosion in confined space are optimized. By analyzing the effect of porosity and distance of the porous material on the explosion, the overpressure and flame propagation characteristics after the methane-air explosion and under the influence of the dual factors are studied. It provides data support to explain the mechanism of blocking and suppressing premixed methane-air explosion when porous materials with different porosity and different positions. Studies have shown that the different porosity of porous materials and the position from the explosion source have significant and different effects on the propagation of overpressure and flame. The 10 PPI porous material has a strong promoting effect on the overpressure and flame propagation after the explosion, it accelerates the overpressure rising rate and increases the overpressure peak, and enhances the turbulence intensity of the explosion flame and accelerates the flame propagation rate. The 20 PPI porous material failed to suppress the explosion during the acceleration phase, but had certain suppression on the explosion flame in other phases. The effect of 30 PPI porous material to suppress explosion overpressure and flame depends on where it is placed. Both 20 PPI and 30 PPI porous materials can quench the flame and block the propagation of high-temperature carbonaceous products. This research results have theoretical value and guiding significance for the prevention and emergency treatment of methane explosion accidents.

A novel method to measure the porosity of porous materials

ABSTRACTPorosity is the single most important feature of porous materials. On the basis of the research work, a new method to measure the porosity of porous materials is proposed in this paper. This method is a system of equations composed of six formulas, so it is called model equation method. It is not only applicable to space holder technique but also applicable to metal prepared by pure powder metallurgy. Compared with mass volume method and immersion medium method, our new method is more simple and efficient. More importantly, it can be used as a standard measure. This study provides a fundamental basis for the measurement of porosity in porous materials.

Mesoscopic exploration on mass transfer in porous thermochemical heat storage materials

Mass transfer is the key characteristic that affects the charging and discharging performance of the porous materials used in thermochemical heat storage systems. Therefore, an algorithm is required to simulate the transport process within heat storage materials and to accurately evaluate the effective diffusion coefficient. This study is about porous calcium oxide, which is widely used in CaO-Ca(OH)2 or CaO-CaCO3 heat storage systems. In this paper, the fractal porous media that resemble real heat storage materials are reconstructed by a random walk method. Furthermore, the gas diffusion process through complicated porous microstructures within fractal porous media is simulated by an efficient lattice Boltzmann method. Results indicate that thermochemical heat storage materials have great fractal characteristic and materials with larger fractal dimension have more diffusion resistance. The effective gas diffusion coefficients of CaO and Ca(OH)2 are obtained from the ratios of effective gas diffusion coefficient and bulk gas diffusion coefficient that are 0.228 and 0.188 for CaO and Ca(OH)2, respectively. Additionally, it is found that calcium oxide samples prepared at higher temperatures have the poorer exothermic performance because of the poorer gas diffusion. Moreover, the correlation between the effective diffusion coefficients and the porosity of porous materials is numerically predicted and evaluated. The fractal model-LBM method developed in this paper may serve as a great tool for easy estimation of effective diffusion coefficients and mass transfer.

Heat generating porous matrix effects on Brownian motion of nanofluid

PurposeThe purpose of this study is to indicate the effect of mounting heat generating porous matrix in a close cavity on the Brownian term of CuO-water nanofluid and its impact on improving the Nusselt number.Design/methodology/approachBecause of the presence of heat source in porous matrix, couple of energy equations is solved for porous matrix and nanofluid separately. Thermal conductivity and viscosity of nanofluid were assumed to be consisting of a static component and a Brownian component that were functions of volume fraction of the nanofluid and temperature. To explain the effect of the Brownian term on the flow and heat fields, different parameters such as heat conduction ratio, interstitial heat transfer coefficient, Rayleigh number, concentration of nanoparticles and porous material porosity were investigated and compared to those of the non-Brownian solution.FindingsThe Brownian term caused the cooling of porous matrix because of rising thermal conductivity. Mounting the porous material into cavity changes the temperature distribution and increases Brownian term effect and heat transfer functionality of the nanofluid. Besides, the effect of the Brownian term was seen to be greatest at low Rayleigh number, low-porosity and small thermal conductivity of the porous matrix. It is noteworthy that because of decrement of thermal conduction in high porosities, the impact of Brownian term drops severely making it possible to obtain reliable results even in the case of neglecting Brownian term in these porosities.Originality/valueThe effect of mounting the porous matrix with internal heat generation was investigated on the improvement of variable properties of nanofluid.

What is the Smallest Atom as a Probe for Characterizing Nanostructures?

In gas adsorption techniques for characterizing the surface structure of solids and the porosity of porous materials, a smaller adsorptive is expected to be useful as a probe to detect finer structures. According to the periodic table, the smallest noble gas atom is helium. However, in cryogenic systems, light atoms such as helium behave as atoms larger than the size estimated from their electron shell structures because of the uncertainty in the position of the atom arising from quantum effects. Here, to unveil the smallest atom as a probe, we perform path integral grand canonical Monte Carlo simulations for the adsorption of noble gases on pore and solid surface models at the respective boiling temperature of each noble gas. First, we show that helium gas behaves exactly as an atom larger than its classically estimated size at low temperatures; in pores, however, it is smaller than in the bulk phase because quantum delocalization is suppressed by the pore walls and helium anomalously acts as a spheroidal atom in confined space. Second, a systematic comparison of the simulation results reveals that neon can enter an extremely small space helium is unable to enter, suggesting that the effective size of the atom at cryogenic temperatures is determined by the size of the electron cloud and wave nature of an atomic nucleus; consequently, neon is the smallest and most suitable noble gas as a probe to access more in-depth information on atomistic scale nanostructures.

Correlation Between Elastic Modulus, Shear Modulus, Poisson's Ratio and Porosity in Porous Materials

Prediction of porous materials mechanical properties is crucial for their industrial applications. Now numerical models containing some errors or analytical semi-empirical models are used. Percolation theory model is suitable to describe porosity dependence of Young's and shear modulus and Poisson's ratio over whole porosity range as it includes critical porosity. Moreover, it is able to explain Poisson's ratio porosity independence as well its decrease with increased porosity (see Fig).

Correlation between Poisson's ratio and porosity in porous materials

Correlation between Poisson's ratio and porosity in porous materials

Porosity of porous materials containing calcium silicate hydrates

Porosity of porous materials containing calcium silicate hydrates

Inverse problem in air-saturated porous media via reflected waves

Direct and inverse scattering problem in air filled porous materials is solved. A simple ultrasonic reflectivity method is proposed for measuring the porosity of porous materials having a rigid frame. The proposed method is based on a temporal model of the direct and inverse scattering problem for the propagation of transient ultrasonic waves in a homogeneous isotropic slab of porous material having a rigid frame. This time domain model of wave propagation was initially introduced by the authors [Z. E. A. Fellah and C. Depollier, J. Acoust. Soc. Am. 107, 683 (2000)]. The viscous and thermal losses of the medium are described by the model devised by Johnson et al. [D. L. Johnson, J. Koplik, and R. Dashen, J. Fluid. Mech. 176, 379 (1987)] and J. F. Allard (Chapman and Hall, London, 1993)] modified by a fractional calculus-based method applied in the time domain. The reflected acoustic wave by air filled porous media can be approximated by the reflected wave at the first interface. The expression of the reflection coefficient is reduced to a simple expression depending on porosity, tortuosity, and incidence angle. An expression of the porosity function of the tortuosity and incidence angle is obtained by solving the inverse problem. Experimental and numerical validation results of this method are presented. This method has the advantage of being rapid and efficient.

Sound propagation attenuation in lined annular-variable area ducts using bulk-reacting liners

The sound propagation through the annular lined variable-area ducts is controlled by the design parameters of the duct liner. The bulk-reacting liners are liners that permit propagation of sound in more than one direction. This research presents the solution of the three-dimensional complex partial differential equations of the sound wave propagation in the duct, using the method of multiple scales. The effect of liner design parameters such as, duct liner length, duct outer diameter, liner thickness, resistivity, and porosity of porous material on sound attenuation has been computed by a special computer program. The results show that the attenuation of sound is directly proportional to the liner length, liner thickness and porosity to some extent, and inversely proportional to liner resistivity and duct area.

Correlation between shear modulus and porosity in porous materials

Correlation between shear modulus and porosity in porous materials

Correlation between Young's modulus and porosity in porous materials

where E is the effective Young’s modulus of porous material with porosity p, E0 is Young’s modulus of solid material, pc is the porosity at which the effective Young’s modulus becomes zero and f is the parameter dependent on the grain morphology and pore geometry of porous material [1]. As was noted by Wagh et al. [2], fittings of the experimental data to Equation 1 often give pc= 1 [1, 3] and do not explain the data accurately. In recent experimental works, either pc≡ 1 is preferably used [4–6] or a linearized model ( f ≡ 1) by Lam et al. [7] is used, where pc is considered to be an initial powder porosity. In this letter, it will be shown that the empirical relationship shown in Equation 1 is identical with the percolation theory equation for the behavior of Young’s and shear modulus with porosity. Further, the applicability of the percolation model for Young’s modulus of porous materials will be demonstrated and the results will be discussed. The porous materials are preferably prepared from powders, the particle size and shape of which can vary significantly. During the powder consolidation, various porosities can be achieved by varying the technological parameters such as temperature, external pressure or time. Compacting starts from just touching powder particles and goes to the lower porosity by the creation and growth of the necks between particles. The subsequent closure of the pore channels leads to the elimination of the pores. Three various porosity ranges can be usually identified, e.g., Danninger et al. [8] observed for sintered iron the following porosity ranges: 1. porosity≤3%: fully isolated pores of nearly spherical or elliptical shape 2. porosity ≥20%: fully interconnected pores of complex shape 3. porosity between 3% and 20%: both isolated and interconnected pores are present in various amounts. This indicates that the powder consolidation is in general a connectivity problem, which is studied by the percolation theory [9]. According to the percolation theory, there exists a critical volume fraction nc, called a percolation threshold, at which a solid phase forms a continual network spanning the whole system. At and above the percolation threshold, the geometrical, physical and mechanical properties of the system behave as