Porous Objects Research Articles

Phase and dark-field imaging with mesh-based structured illumination and polycapillary optics.

X-ray phase and dark-field (DF) imaging have been shown to improve the diagnostic capabilities of X-ray systems. However, these methods have found limited clinical use due to the need for multiple precision gratings with limited field of view or requirements on X-ray coherence that may not be easily translated to clinical practice. This work aims to develop a practicable X-ray phase and DF imaging system that could be translated and practiced in the clinic. This work employs a conventional source to create structured illumination with a simple wire mesh. A mesh-shifting algorithm is used to allow wider Fourier windowing to enhance resolution. Deconvolution of the source spot width and camera resolution improves accuracy. Polycapillary optics are employed to enhance coherence. The effects of incorporating optics with two different focal lengths are compared. Information apparent in enhanced absorption images, phase images, and DF images of fat embedded phantoms were compared and subjected to a limited receiver operator characteristic (ROC) study. The DF images of the moist and dry porous object (sponges) were compared. The mesh-based phase and DF imaging system constructs images with three different information types: scatter-free absorption images, differential phase images, and scatter magnitude/DF images, simultaneously from the same original image. The polycapillary optic enhances the coherence of the beam. The deblurring technique corrects the phase signal error due to geometrical blur and the limitation of the camera modulation transfer function (MTF) and removes image artifacts to improve the resolution in a single shot. The mesh-shifting method allows the use of a wider Fourier processing window, which gives even higher resolution, at the expense of an increased dose. The limited ROC study confirms the efficacy of the system over the conventional system. DF images of moist and dry porous object show the significance of the system in the imaging of lung infections. The mesh-based X-ray phase and DF imaging system is an inexpensive and easy setup in terms of alignment and data acquisition and can produce phase and DF images in a single shot with wide field of view. The system shows significant potential for use in diagnostic imaging in a clinical setting.

Optimization of convective drying performance of multiple porous moist objects in a 3D channel

In this study, a procedure for optimizing the convective drying performance of multi porous moist objects in a three dimensional channel is proposed. The numerical simulation is performed by using the finite element method and COBYLA optimization algorithm is used to find the optimum spacing between the objects without mass transfer in the first stage. Then, heat and mass transfer equations for the porous moist objects are coupled with the channel flow equations at the optimum spacing which delivers the best convective drying performance. It is observed that the flow recirculation and flow reversal in the inter-spacing with various distances between the objects resulted in thermal gradient variations along the multi object surfaces. The average Nusselt number rises for second block while it shows non-monotonic behavior for the first block when the distance between the first and second group objects are varied. Distance between the second and third objects also affected the average Nu variation for all of the objects. The lateral distance between first and second group objects resulted in up to 50% variation in the average Nu for the second block. The optimum spacing between the objects for the maximum Nusselt number of the objects are obtained as d1=5.93hc, d2=7hc and d3=0.584hc. The moisture reduction amounts for each of the object at the optimums spacing are found higher as compared to parametric variation of unsteady simulation results. The computational cost for the parametric unsteady coupled heat and mass transport equations in the channel and in the porous moist objects is 75 h 12 min while the optimization assisted simulation results reduced the computational cost to 2 h 33 minutes. Also, artificial neural networks are utilized to obtain the dynamic feature of convective drying at the optimum spacing considering various values of hot dry air temperature which delivers fast and accurate prediction results when compared to high fidelity computational fluid dynamics simulation results.

Thermal management of nanoliquid forced convective flow over heated blocks in channel by using double elliptic porous objects

Effects of using nanoliquid and double porous elliptic objects on the flow separation and convective heat transfer control for flow over multiple heated blocks in channel are numerically investigated by using finite element method. Spherical, brick, blade and cylindrical shaped alumina particles are used in water up to solid volume fraction of 2%. Impacts of Reynolds number (50≤Re ≤ 500), permeability of the porous ellipses (10−5≤Da1≤5 × 10−2 and 10−5≤Da2≤5 × 10−2), aspect ratio of the ellipses (0.25≤AR1≤1.5, 0.25≤AR2≤1.5), distance between the ellipses (0.2H ≤ sx ≤ 1.6H) and distance of the first ellipse from inlet (−H ≤ mx ≤ H) on the hydro-thermal performance are explored. The highest performance improvement is obtained by using the cylindrical shaped particles in the base heat transfer fluid at the highest solid volume fraction and the amount of heat transfer enhancement are 33% and 40.5% for hot blocks while negligible pressure drop is observed. Varying the aspect ratio of the ellipses in the perpendicular direction to the flow, up to 25% and 30% heat transfer increment are obtained for hot block with slight rise of pressure coefficient. However, when varying the horizontal location of the porous ellipses in the channel and permeability of them, there is considerable rise of pressure drop. Variation of the average heat transfer from the hot blocks with varying permeability of the ellipses are obtained as 32% and 25%. Successful hydro-thermal performance estimation results are achieved by using artificial neural networks with feed-forward network architecture of 1 hidden layer and 17 neurons.

Photoprintable Gelatin-graft-Poly(trimethylene carbonate) by Stereolithography for Tissue Engineering Applications.

The stereolithography process is a powerful additive manufacturing technology to fabricate scaffolds for regenerative medicine. Nevertheless, the quest for versatile inks allowing one to produce scaffolds with controlled properties is still unsatisfied. In this original article, we tackle this bottleneck by synthesizing a panel of photoprocessable hybrid copolymers composed of gelatin-graft-poly(trimethylene carbonate)s (Gel-g-PTMCn). We demonstrated that by changing the length of PTMC blocks grafted from gelatin, it is possible to tailor the final properties of the photofabricated objects. We reported here on the synthesis of Gel-g-PTMCn with various lengths of PTMC blocks grafted from gelatin using hydroxy and amino side groups of the constitutive amino acids. Then, the characterization of the resulting hybrid copolymers was fully investigated by quantitative NMR spectroscopy before rendering them photosensitive by methacrylation of the PTMC terminal groups. Homogeneous composition of the photocrosslinked hybrid polymers was demonstrated by EDX spectroscopy and electronic microscopy. To unravel the individual contribution of the PTMC moiety on the hybrid copolymer behavior, water absorption, contact angle measurements, and degradation studies were undertaken. Interestingly, the photocrosslinked materials immersed in water were examined using tensile experiments and displayed a large panel of behavior from hydrogel to elastomer-like depending on the PTMC/gel ratio. Moreover, the absence of cytotoxicity was conducted following the ISO 10993 assay. As a proof of concept, 3D porous objects were successfully fabricated using stereolithography. Those results validate the great potential of this panel of inks for tissue engineering and regenerative medicine.

A density measurement device for solid objects with uneven geometry

Abstract Hydrostatic measurement, a method traditionally used to measure the density of solid bodies, is not suitable for all solid bodies. This method is undesirable for solid materials that interact with water and lose their properties. In addition, this method is not suitable for porous objects because measurements in water are erroneous and can damage material samples due to the ability of some solid materials to absorb water. In this study, a new density measurement technique has been developed and evaluated to measure the density of rigid objects by means of nonstandard geometry. The density of objects with distorted geometry was measured pneumatically using communicating vessels logic and using the ideal gas equation. An experiment set has been developed, improved and evaluated. Through this technique, the measurement accuracy of the density of the sample tested was determined with an accuracy of 0.08 %.

On the Disappearance of the Steady Wake Region Behind Porous Objects Under Freestream Flow at Low Reynolds Numbers

Abstract A solid bluff object produces a recirculating wake region immediately behind it when subjected to flow separation under a steady flow condition. Similar phenomena can also be observed for a porous body. However, unlike the solid object, the porous body allows some part of the flow to go through it. A consequence of this flow penetration in porous objects is, the wake behind the body may get reduced in size and detach from the body. The wake even may disappear at some value of the porosity parameter (Darcy number). In this brief article, we compute the critical values of the porosity parameter for complete disappearance of the wake region behind two-dimensional porous bodies of circular and square shapes. A regime diagram is constructed to show the regions of wake formation, its detachment, and finally its disappearance around circular and square shaped porous bodies. The critical value of the porosity parameter increases with increasing Reynolds number, and it is found greater for the square body in comparison to the circular one. The study provides a quantitative estimation of how the porosity plays a significant role in demarcating the flow characteristics around porous objects.

Optimization of convective heat transfer performance for fluid flow over a facing step by using an elliptic porous object

In this study, numerical analysis and optimization for the convective heat transfer and fluid flow over a facing step in the presence of an elliptic shaped porous object located downstream of the step are considered. The COBYLA optimization algorithm is used to find the optimum location and size of the porous object in order to maximize average Nu number. Air and nano-diamond/Fe3O4 hybrid nanofluid as the coolant in the thermo-fluid system. It is observed that the presence of the obstacle, varying its permeability, aspect ratio and location in the channel profoundly affect the fluid flow features and improvement amount in the heat transfer rate. The average Nu number is first reduced by about 14.7% and then increased by about 6.8% when the permeability of the object is increased. The optimum value of the Nu number is found as 2.037 while the optimum location and sizes are found as (Sx, Sy, r1, r2)=(0.538H,0.4509H,0.2138H, 0.348H) when air is used as heat transfer fluid. The average heat transfer rate is reduced with higher aspect ratio while the value of Nu number at the optimum point is 33% higher as compared to case with aspect ratio of 0.5. The average Nu number variation shows non-monotonic behavior for horizontal location of the object. When the object is closer to the top wall, the average Nu number becomes higher while the value at the optimum point is 19.8% higher in the parametric study. At the optimum operating point, hybrid nanoparticle addition in the fluid brings further enhancement of 28.4% in the average heat transfer.

EFFECTIVE THERMOPHYSICAL PROPERTIES OF POWDER MATERIALS DURING SINTERING UNDER ELECTRONBEAM HEATING

Background. Development of the consolidation processes of powder products using highly concentrated energy sources is impossible without a detailed analysis of the processes of thermal conditions arising in these products. Objective. The aim of the study is to select a method for calculating the thermal conductivity of a porous body, which will be established under various conditions of electron-beam sintering of molybdenum compacts, and to study the effect of the parameters of the porous structure on the thermal conductivity. Methods. An analysis of the sintering process in finite element calculations, in problems of thermal conductivity for two-dimensional and three-dimensional domains, simulating the real porous structure of molybdenum compaction and a regular porous structure with dense packing of spheres is proposed. Results. Mathematical analysis of the contribution of re-radiation to the total thermal conductivity of the porous material is performed. The obtained dependences of the relative thermal conductivity on the porosity of the material and the relative radius of contacts between its particles are presented. Conclusions. According to the results of the mathematical analysis of the conditions of heat transfer in a porous compact of molybdenum for the case of electron-beam heating, it was found that the radiant component of the thermal conductivity of a porous body with pores of the order of 2.5 μm is four orders of magnitude less than the conductive component of its thermal conductivity. Based on the results of finite element modeling of two-dimensional and three-dimensional porous objects, a significant effect of the contact area between particles on their integral thermal conductivity has been established, especially at small sizes of these contacts. At the same time, almost linear effect of porosity on thermal conductivity was established at contact radii between particles > 0.1 Rparticles. A significant influence of the uniformity of the distribution of contacts in aporous material on the uniformity of the temperature field in it is shown.

Using the 3D model RAPID to invert the shoot dieback ratio of vertically heterogeneous Yunnan pine forests to detect beetle damage

As a significant forest disturbance factor, pine shoot beetles (PSB) have caused widespread tree mortality in Yunnan pine forests over southwestern China. Due to significant vertical heterogeneity of tree crowns, empirical remote sensing methods or one-dimensional (1D) radiative transfer (RT) models are not qualified enough to accurately retrieve the damage level of PSB damage. Therefore, three-dimensional (3D) RT models which have the ability to describe vertically complex heterogeneous canopies are more suitable for the damaged forests. In this study, shoot dieback ratio (SDR) was used to parameterize the Radiosity Applicable to Porous IndiviDual Objects (RAPID) model, in order to accurately estimate the PSB damage. Specifically, the vertically heterogeneous characteristics of the biophysical and optical properties within the canopy were carefully considered. First, we developed an approach to reconstruct damaged forest scenes through individual tree segmentation from UAV-lidar data and in situ measurements. Second, the simulated reflectance of forest scenes was compared with the actual hyperspectral and Sentinel-2 (S2) reflectance data to evaluate the performance of the parameterized RAPID. Then, the parameterized RAPID model was used to create a look-up table (LUT) containing the leaf chlorophyll content (Cab), effective leaf area index (LAIe), SDR, and dead needles LAIe (LAIdead, LAIe × SDR) as well as the corresponding simulated canopy reflectance. Furthermore, tree allometric equations were used to regularize the LUT with the intention to improve the estimation accuracy. Good agreement (RMSE: 0.015-0.031, index of agreement: 0.97-0.99) was found between the simulated reflectance and the remote sensing observations. The retrieval accuracy of the biochemical and biophysical parameters using S2 data yielded R2 = 0.55 (normalized RMSE (NRMSE) = 19%) for Cab, R2 = 0.70 (NRMSE = 15%) for the LAIe, R2 = 0.66 (NRMSE = 25%) for SDR, and R2 = 0.82 (NRMSE = 18%) for LAIdead. Using hyperspectral data with higher spatial and spectral resolution yielded better retrieval performance. This study demonstrated that 3D models (such as RAPID) have great potential to accurately invert SDR and LAIdead to assess PSB damage for the forests.

3D numerical study of heat and mass transfer of moving porous moist objects

Heat and moisture transfer of two moving moist objects in a channel with convection of hot dry air is investigated numerically. A moving mesh approach is used for providing movement by means of the Arbitrary Lagrangian-Eulerian (ALE) framework. Governing equations for flow field and porous objects are solved by finite element discretization method for the 3D transient problem. Effects of drying air velocity and temperature are simulated by means of temperature, moisture content and heat transfer distributions. Results showed the importance of varying parameters on drying behavior. It was observed that the air velocity also has an increasing effect on evaporation and most reduction in moisture content is obtained at 0.8 m/s air velocity with 63.12% loss. Besides, there are insignificant differences between heat transfer values for fixed and moving objects, differences in average heat transfer values calculated between 6 and 13% for static bed and moving bed.

An efficient method for optimizing the unsteady heat and mass transport features for convective drying of two porous moist objects in a channel

In the present study, an efficient methodology is proposed for optimizing the convective drying performance of multiple porous moist objects in a channel. As the first step of the method, a PDE constraint optimization routine is utilized to obtain the optimum values of distance between the objects for maximizing the transfer rates while in the second part, unsteady coupled field equations for the channel and porous moist object domains are invoked for convective drying of multiple objects for the optimum spacing values. Finite element method is used for the numerical simulations. It was observed that the recirculation zones established behind the rectangular objects are profoundly affected with the distance between the objects. There is 12.5% variation in the average Nu for the first block with varying the horizontal distance between the objects. The effects of vertical spacing on the average Nu is profound for the second object. while up to 80% enhancement in the average Nu is obtained when the value is changed from sy = 0 to sy = 1.5hp. However, the optimum values of the distance that maximize the heat transfer are obtained as sx = 1.1hp and sy = 1.931hp for the horizontal distance and vertical distance. At this optimum values of parameters, reduction in the moisture content becomes 33.4% and 98.015% for drying times at 1000 s and 5000 s. These values are also checked with the parametric unsteady coupled field equations for the porous moist objects which shows the improved time dependent drying features for the two blocks at the optimum points.

3D printing of porous polyimide for high-performance oil impregnated self-lubricating

Three-dimensional (3D) printing of porous polyimide (PI) with good oil storage capability for self-lubricating is realized by direct ink writing of poly(amide acid) (PAA) precursor ink followed by post thermal treatment and template removal. The ink is comprised of PAA and polymethyl methacrylate (PMMA) microspheres, where the PMMA microspheres serve as both the pore-forming agent and the rheology modifier to realize high-precision porous PI objects. The printed porous PI exhibited good mechanical performance and thermal stability, and good oil storage capability to various lubricant oils to achieve self-lubricating. Importantly, various parts with desirable complex structures, bearing retainers for example, can be readily accomplished. It is therefore promising for manufacturing high-performance lubricating parts, especially those with high complexity.

The Effect of Binder Loading on the Pore Size of 3D Printed PMMA.

Binder jetting is known to produce porous objects by depositing the binder selectively layer by layer on a powder bed. In this study, the pore size of printed parts and the correlating mechanical properties are investigated on a commercially available PMMA powder binder system. Pore sizes are measured via capillary flow porometry and mechanical properties via tensile tests. Porometry indicates that the pore size stays at a constant level of 22 µm at 5 to 10 wt% binder loading before decreasing to 6 µm at loadings of 30 wt% or higher. The results were compared with the mechanical testing and related to the agglomerate strength model of Rumpf. The highlights of the article are the application of a binder jetted part as a filter and the identification of a close relationship between porosity and mechanical strength, similar to phenomena in agglomeration science.

Macroscopic Elasticity of Porous Object: Systematic Analysis Based on Finite Element Analysis and Its Application

Macroscopic Elasticity of Porous Object: Systematic Analysis Based on Finite Element Analysis and Its Application

Numerical analysis of heat and mass transfer of a moving porous moist object in a two dimensional channel

The aim of this study is to investigate heat and mass transfer during convective drying of a moving porous medium in a 2D rectangular channel with laminar flow conditions. Finite element method is used with ALE to model the movement of the porous moist object. Hot dry air with different temperatures flowed in the channel with varying velocities and the porous object also has a movement with parallel direction to the flow. The code is validated by using experimental results. Results indicated that the heat transfer coefficient of the moving porous moist object is time dependent and varying locally. Significant impacts of increasing values of air temperature and velocity on the heat and mass transfer features are observed.

3D printing of inherently nanoporous polymers via polymerization-induced phase separation

3D printing offers enormous flexibility in fabrication of polymer objects with complex geometries. However, it is not suitable for fabricating large polymer structures with geometrical features at the sub-micrometer scale. Porous structure at the sub-micrometer scale can render macroscopic objects with unique properties, including similarities with biological interfaces, permeability and extremely large surface area, imperative inter alia for adsorption, separation, sensing or biomedical applications. Here, we introduce a method combining advantages of 3D printing via digital light processing and polymerization-induced phase separation, which enables formation of 3D polymer structures of digitally defined macroscopic geometry with controllable inherent porosity at the sub-micrometer scale. We demonstrate the possibility to create 3D polymer structures of highly complex geometries and spatially controlled pore sizes from 10 nm to 1000 µm. Produced hierarchical polymers combining nanoporosity with micrometer-sized pores demonstrate improved adsorption performance due to better pore accessibility and favored cell adhesion and growth for 3D cell culture due to surface porosity. This method extends the scope of applications of 3D printing to hierarchical inherently porous 3D objects combining structural features ranging from 10 nm up to cm, making them available for a wide variety of applications.

Critical review on porous material manufacturing techniques, properties & their applications

Generally, porosity is not a desirable characteristic of any material. In today’s Industrial scenario, this parameter becomes necessity of materials for different applications like structural, solar absorbers, and sound absorption as well as biomedical applications. Metal foams are cellular structures contain porosity which increases mechanical, thermal and other physical properties of conventional materials. There are manufacturing issues concern with these materials like homogeneity and location of pores, controlling of parameters. In this article, the techniques of manufacturing of porous materials are discussed with their limiting parameters and pros & cons. Powder metallurgy is found suitable for better porosity but the cost for this process constrain its usage among the researchers and Industry as well. Space holder method is one of the found appropriate among all other used for the manufacturing of open and closed cell foam in perspective of cost as well porosity. The orientation of space holder plays a crucial role for the development of better porous object. This article reviews the different methods of manufacturing and their properties for the better future perspective in terms of cost, structure and application of porous foams.

THE ROLE OF CROSS THERMAL BUOYANCY IN INITIATING VORTEX SHEDDING BEHIND A PERMEABLE SQUARE CYLINDER AT LOW REYNOLDS NUMBERS

A two-dimensional numerical simulation is performed to analyze the role of cross thermal buoyancy in initiating vortex shedding behind a permeable square cylinder at low Reynolds numbers. The porous cylinder is placed stationary in an unconfined fluid medium having Prandtl number Pr = 0.71 (air). The permeability of the object is considered in the range of Darcy number as 10-6 ≤ Da ≤ 10-2 with the corresponding porosity values in the range 0.629 ≤ ε ≤ 0.993 for the set of Reynolds numbers 10 ≤ Re ≤ 40. In the chosen range of Re, the flow behind the object is laminar and characterized by the formation of a steady separation bubble with two counter-rotating vortices. Heating the cylinder causes thermal buoyancy driven transport to develop, which interacts with the incoming free stream flow in a crosswise manner. The interaction gives rise to instability in the flow which intensifies with increasing strength of thermal buoyancy. Subsequently, at some critical value of the buoyancy parameter (Richardson number, Ri), the flow is characterized by the formation of Bénard-von Kármán vortex shedding. The critical Rifor all the range of Da and Re are obtained through visual investigation of the flow and thermal fields and also quantitatively from the drag and lift signals, phase portraits, and Strouhal numbers. The critical Ri decreases as Da increases at a constant Re; however, at constant Da, it increases with decreasing Re. Based on the critical Ri values for different Da and Re, a stability diagram is constructed to show the steady and unsteady zones of operation of the porous object subjected to the cross thermal buoyancy.

Investigation of time dependent heat and mass transportation for drying of 3D porous moist objects in convective conditions

Three-dimensional numerical study of convective drying process was investigated for two porous moist blocks in a channel under turbulent flow conditions by considering different parameters which are effective on heat and moisture transfer phenomena. The 3D unsteady flow and heat and mass transfer equations were solved with Galerkin weighted residual finite element method. Drying objects were rectangular shaped porous objects and effects of size and distance between the objects, velocity and temperature of inlet drying air were investigated with varying values. Transport of heat and moisture for the problem was evaluated. Obtained results showed that all of the changing parameters had significant effects on flow properties, heat and mass transfer phenomena in 3D. As the interspacing between the blocks increases, it has a positive impact on the drying process especially for second porous block even though it is not as effective as the velocity or the size. As the height of the porous block increases, due to the blockage effect it has adverse effects on the transportation phenomena.

An innovative approach to permeability estimation of the fractured-vuggy carbonate reservoirs based on 2D images

Permeability analysis is an essential process in reservoir characterization, especially when evaluating those highly heterogeneous reservoirs such as fractures-vuggy carbonate reservoirs. Because of the biased sampling, no laboratory measurement can obtain the exact permeability values of the carbonate samples that contain fractures or large vugs. Besides this fact, the heterogeneity of the secondary pore distribution could cause unstable test results of permeability, which can bring out significant uncertainty in reservoir modeling if the problem is ignored. There are two widely used indirect methods for permeability estimation: one is based on the Kozeny-Carman equation, and the other one is based on the Navier-Stokes equations. Both two estimations need to evaluate the geometry properties of the rock pore-fracture system, which will introduce artificial uncertainty into the estimation results. This paper proposed an innovative approach to permeability estimation established through counting the pores, fractures, and vugs on 2D images. By considering the area distribution of those porous objects identified on the 2D images in a specified statistical interval, the absolute permeability values of the fractured-vuggy carbonate will be calculated directly without any artificial influence. The new approach is a general way to estimate permeability and does not consider rock facies and pore types. The estimation results show a more stable manner than core analysis data, which could help to select permeability values in reservoir modeling. On the other hand, by comparing the estimation results from different statistical intervals, the heterogeneity of the parameter is revealed.