Porosity Development Research Articles

Unique CO2 adsorption of pine needle biochar-based activated carbons by induction of functionality transition

CO2 capture has become the world’s most urgent agenda nowadays. In this work, we induced functionality transition of heteroatom-rich pine needle biochar based activated carbon for CO2 adsorption by modulating activation conditions. The surface functionalities and porosity of the activated carbon derived from pine needles were investigated intensively according to the activation conditions. The transition of surface functional groups and development of porosity were observed as activation progressed. CO2 adsorption performances were determined under various conditions, and the adsorption capacities, adsorption selectivities, and cyclabilities were evaluated. From these results, different CO2 adsorption mechanisms based on the surface functionality and porosity were clearly defined. The pyridinic, pyrrolic(N- based), and Ca(OH)2(Ca-based) CO2 sorbing functional groups derived from mild activation enabled chemical sorption with great adsorption selectivity. The high porosity derived from the severe activation conditions resulted in physical adsorption with excellent cyclability at 298 K but the chemical sorption property was weakened by the shift of surface groups to graphitic-N and CaCO3 rich groups. The modulation of functional groups and porosity enabled utilizing pine needles for effective CO2 removal under various conditions.

Comparative analysis of swelling and porosity evolution in UO2 fuel via two approaches

Abstract A correlation for the volume porosity of irradiated UO2 fuel as a sum of the individual contributions of the pore and swelling porosity in terms of the local density and fractional matrix swelling is developed. By using the existing low temperature low burnup model of swelling, evolution of the matrix swelling and porosity terms are calculated for UO2 fuel in the low burnup but in the high burnup two various models are applied, the one with considering grain recrystallization and another without it but with the method of Xe depletion measurement. The purpose of the paper is comparison of fuel swelling behavior between two models at high burnups. The bulk swelling and porosity evolution in both methods are also validated by experimental data. Finally, one conclusion from this comparison is obtained, as the method which considering grain recrystallization has more rational behavior in the fuel swelling and porosity.

Coupling stress fields and vacancy diffusion in phase-field models of voids as pure vacancy phase

High vacancy concentrations in crystals may lead to formation and growth of voids, which is connected to swelling under irradiation and degradation of material properties. Recent experimental work suggests that vacancy condensation may also be involved in nucleation and evolution of porosity in early stages of ductile fracture. Mostly in the realm of irradiation effects, void formation and growth has been simulated with phase-field methods, where voids are treated as pure vacancy phases. Since vacancies induce an eigenstrain field, it is well-known that the evolution of vacancy concentrations is coupled to the elastic stress field. However, the few existing elastically coupled diffuse interface models of void growth seem to face a conceptual problem in the diffuse interface; in the center of which they predict the highest eigenstrains, which results in unrealistically high, fluctuating stresses. In the current work, we present a new model for coupling elastically driven vacancy diffusion with a diffuse interface model of void surfaces, which overcomes the named short-comings and closely reproduces the sharp interface solution. This is achieved by making the eigenstrain a function of the non-conserved order parameter used to distinguish the crystal and void phase. The model is verified for two-dimensional example problems by comparison to the analytical solution of the according sharp interface model. Eventually, the model is used to show the impact of elasto-diffusional coupling on void growth in mechanically loaded systems. We analyze the model with regard to the bi-stable energy landscape and discuss limitations and future prospects of the approach.

Phosphate-based geopolymer: Influence of municipal solid waste fly ash introduction on structure and compressive strength

Materials resulting from incorporation of solid waste incineration fly ash into phosphate-based geopolymers, to partially replace metakaolin (up to 50% wt), were studied. X-ray diffraction, scanning electron microscopy, solid-state nuclear magnetic resonance spectroscopy and infrared spectroscopy were adopted to describe the mineralogical changes and the structural modifications of the geopolymer networks which impacted on the mechanical performance (compressive strength) of the materials. The results indicated that fly ash displays a different reactivity compared with metakaolin, behaving preferentially as a source of alkali that compete with the aluminosilicate metakaolin fraction by precipitating crystalline and amorphous phosphates. At 10 wt% of metakaolin substitution with fly ash, the extent and reticulation of the amorphous geopolymer matrix is preserved, and the mechanical properties are retained. At higher waste content (30–50% wt), the fast kinetics of the acid-base reactions involving the fly ash reactive phases prevail over the metakaolin dealumination, and the nature of the material shifts to an alkali-phosphate cement/phosphate-geopolymer composite. This behaviour, together with the development of porosity and presence of low-strength phases in the ash, led to a decline in the mechanical performance with increasing amount of substitution. All in all, this work provides fundamental information in the direction of a sustainable employment of phosphate-based geopolymers, which is limited by the relatively high cost of both metakaolin and phosphoric acid. Moreover, it indicates a recycling opportunity for this type of fly ash.

Determination of Hazardous Zone of Coal Spontaneous Combustion in Ultra-Long Working Face Based on the Gob Porosity Evolution and Flow Field Distribution

Coal fire remains one of the main hazards of underground work. Spontaneous coal fires cause serious casualties and property losses. At present, most of the studies on coal spontaneous combustion have been conducted on working faces shorter than 200 m. However, the ultra-long working face gob of shallow buried coal seam is much larger, the distribution of its flow field is more complex, and, thus, risk of spontaneous combustion in the gob is higher. Exploring the evolution law of the gob flow field of ultra-long working face to quickly determine the range of the coal spontaneous combustion hazardous zone is of great significance to the safe production of similar mines. In this study, the gas flow field distribution in the gob of an ultra-long working face was measured by buried pipeline method and oxygen concentration was used as the index. It is found that the oxygen concentration decreases with the advance of the working face. Based on the flow field distribution, the oxidation zone of the gob was determined. Meanwhile, a three-dimensional (3D) numerical model of the working face was established, and the overlying stratum collapse and porosity evolution in the gob were simulated using the particle flow software, PFC3D discrete element software, for the porosity distribution law of the gob. The obtained porosity data were then imported into FLUENT using the custom function UDF to construct a 3D grid model. The flow field distribution in the gob was then numerically simulated for the seepage and migration law of the wind flow in the gob. The results reveal an arch-shaped wind flow field distribution with a swirl shape on the intake airway side. In the strike direction, the wind flow gradually becomes weaker with the advance of the working face. In the dip direction, the wind flow seepage range on the return airway side is obviously higher than that on the intake airway side. In the vertical direction, the wind flow range in the upper gob is larger than that in the middle and lower gob. The spontaneous combustion and oxidation zone of the gob is determined to be at 140.4–313.3 m on the intake airway side, 201.2–351.6 m in the middle of the gob, and 153.2–328.1 m on the return airway side. Finally, the residual coal distribution was superimposed onto the oxygen concentration distribution to obtain the spontaneous residual coal combustion hazardous zone in the gob.

A CFD-based porous medium model for simulating municipal solid waste incineration grates: A sensitivity analysis

This study starts from a generalized CFD-based porous medium model developed in previous work simulating the combustion of municipal solid waste (MSW) on incineration grates. In this paper, three specific bed models are compared: a newly developed whole moving bed model, a newly developed multi-zone model, and a fixed bed model. Although the whole moving bed model covers the entire gas flow field, this advantage is offset by a high computational cost. In the multi-zone model, different zones of the waste bed are computed consecutively. This helps to reduce the computational time by about 75% but causes a loss of accuracy in predicting the gas flow field at the transition between the zones. For the fixed bed model, the walking column approach is needed. Additional accuracy loss is introduced but the computational time is significantly reduced even further compared to the multi-zone model. Because of the trade-off between computational cost and accuracy and the great uncertainty of the model parameters in industrial practice, the fixed bed model is suggested for simulating industrial grate-firing systems. In addition to these moving bed modeling strategies, this study also investigates how sensitive model results are to the assumed minimum and maximum solid fractions, which determine the evolution of porosity along the grate. The results show that the conversion rates are relatively insensitive to these criteria within the investigated range. Conversely, the effective surface area greatly influences the combustion characteristics as it affects the drying and char conversion rate and governs the temperature difference between the solid and gas phases. This finding calls for a better understanding of the evolution of the effective surface area and equivalent particle diameter during the combustion of MSW.

Numerical simulation and investigation of methane gas distribution and extraction in goaf with U-type ventilation of working face

The accumulated methane in goaf during coal mining may leak into the working face under the airflow influence, which is possibly causing disasters such as methane gas excessive at the working face and seriously threatening the mine safety. This paper first established a three-dimensional numerical model of the mining area under U-shaped ventilation, introducing the gas state equation, continuity equation, momentum equation, porosity evolution equation, and permeability evolution equation to simulate the airflow field and gas concentration field in the mining area under the natural state. The reliability of the numerical simulations is then verified by the measured air volumes at the working face. The areas in the mining area where gas is likely to accumulate are also delineated. Subsequently, the gas concentration field in goaf under the gas extraction state was theoretically simulated for different locations of large-diameter borehole. The maximum gas concentration in goaf and the gas concentration trend in the upper corner were analyzed in detail, and the critical borehole location (17.8m from the working face) was determined as the optimum location for gas extraction from the upper corner. Finally, a gas extraction test was carried out on-site to evaluate the application effect. The results show that the measured airflow rate has a small error with the simulated results. The gas concentration in the area without gas extraction is high, with the gas concentration in the upper corner being over 1.2%, which is greater than the critical value of 0.5%. The maximum reduction in gas concentration was 43.9%, effectively reducing the gas concentration in the extraction area after employing a large borehole to extract methane gas. The gas concentration in the upper corner and the distance of the borehole from the working face are expressed as a positive exponential function. The field engineering results show that the implementation of the large borehole at a distance of less than 17.8m from the working face can control the gas in the upper corner to less than 0.5%, effectively reducing the risk of gas in the upper corner. The numerical simulation work in this paper can provide some basic support for the design of an on-site borehole to extract gas from the mining void and reduce the gas hazard in coal mines.

Influence of Creep Compaction and Dilatancy on Earthquake Sequences and Slow Slip

AbstractFluids influence fault zone strength and the occurrence of earthquakes, slow slip events, and aseismic slip. We introduce an earthquake sequence model with fault zone fluid transport, accounting for elastic, viscous, and plastic porosity evolution, with permeability having a power‐law dependence on porosity. Fluids, sourced at a constant rate below the seismogenic zone, ascend along the fault. While the modeling is done for a vertical strike‐slip fault with 2D antiplane shear deformation, the general behavior and processes are anticipated to apply also to subduction zones. The model produces large earthquakes in the seismogenic zone, whose recurrence interval is controlled in part by compaction‐driven pressurization and weakening. The model also produces a complex sequence of slow slip events (SSEs) beneath the seismogenic zone. The SSEs are initiated by compaction‐driven pressurization and weakening and stalled by dilatant suctions. Modeled SSE sequences include long‐term events lasting from a few months to years and very rapid short‐term events lasting for only a few days; slip is ∼1–10 cm. Despite ∼1–10 MPa pore pressure changes, porosity and permeability changes are small and hence fluid flux is relatively constant except in the immediate vicinity of slip fronts. This contrasts with alternative fault valving models that feature much larger changes in permeability from the evolution of pore connectivity. Our model demonstrates the important role that compaction and dilatancy have on fluid pressure and fault slip, with possible relevance to slow slip events in subduction zones and elsewhere.

Prospects of low‐temperature solid sorbents in industrial CO₂ capture: A focus on biomass residues as precursor material

AbstractAdsorption using bio‐based adsorbents has been pointed out as an economical and environmentally benign technology for CO₂ gas separation and storage. A bio‐based adsorbent can be fabricated from low‐cost worldwide available biomass feedstock and bio‐wastes from different industries (e.g., dairy manure, forestry, agriculture). As a result, it is a carbon rich material of hydrophobic nature, activated to gain high porosity development, and requires mild regeneration conditions. However, large‐scale deployment of bio‐based adsorption processes remains challenging. Our group has been intensively developing biomass‐based adsorbents in conjunction with the design of tailored CO₂ adsorption‐based cyclic processes for the envisioned application. Herein, key concepts on adsorption technology, biomass waste management, and different activation techniques for biomass‐based adsorbent precursors are discussed. This review addresses the most relevant studies in the literature, from lab experimentation on a milligram scale (volumetric and gravimetric tests) to dynamic tests in bench or large‐scale cyclic adsorption processes (i.e., pressure swing adsorption, temperature swing adsorption, vacuum swing adsorption). Therefore, the main target is to give a holistic view of the industrial applications where CO₂ separations with these materials are more suitable. Finally, concluding remarks and future perspectives of bio‐based adsorbents in carbon capture are presented. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Seismic prediction of shale reservoir quality parameters: A case study of the Longmaxi–Wufeng formation in the WY area

Shale is a crucial natural gas resource, attracting global exploration and development interest. China has abundant shale gas resources that will drive future oil and gas exploration advances by increasing reserves and production. The WY shale gas field is the most productive and has the greatest potential for exploration and development. This study analyzed high-quality shale logging response characteristics and drilling logging, seismic, and analytical test data in the WY area to establish a rock physical model of seismic attribute parameters and shale reservoir quality parameters. Seismic elastic parameters were converted into indicators that directly reflect shale reservoir quality, such as total organic carbon (TOC), high-quality reservoir thickness, porosity, brittleness index, and crack development strength. Corresponding regression equations were established to predict quality parameters.The results showed that shale reservoir quality parameters have a good correlation with seismic parameters. The TOC distribution ranged from 2% to 5% in the study area and was generally high in the north but low in the south. The high-quality shale reserve had a thickness of over 40 meters, and except for the northwest region, the porosity was nearly over 4%. The overall brittleness of the study area was favorable, and the brittleness index was over 35%, which is suitable for network fractures formation in subsequent fracturing operations. The anisotropy of shale in S1l1I was small, and the overall fractures were underdeveloped in the study area. Drilling verifications showed that the prediction results of the quality parameters of high-quality shale reservoirs were consistent with actual drilling test results with high reliability. This study provides guidance for comprehensive prediction of sweet spots and subsequent fracturing and well location deployment.In summary, this study provides valuable insights into shale gas exploration and development in the WY area by establishing a rock physical model, predicting quality parameters, and offering guidance for fracturing and well location deployment.

Quantitative characterization of the early hydration of magnesium potassium phosphate cement: In-situ experiment with low field NMR

The in-situ characterization of the rapid early reaction of magnesium potassium phosphate cement (MKPC) via common methods is quite difficult. In this study, the low field nuclear magnetic resonance (LF-NMR) method was used for in-situ monitoring the reaction degree of MgO in MKPC. The comparisons of the results with the reaction degree determined by XRD-Rietveld, BSE image analysis and TG analysis methods showed that LF-NMR is a correct and effective method for the rapid and accurate characterization of the reaction kinetics of MKPC. The in-situ kinetic data contributed to the simulation of the porosity development of MKPC, and a strong relationship between the calculated porosity and compressive strength was then established, which is expected to be used for further performance prediction.

Surface Modifications of CuO Doped Carbonaceous Nanosorbents and their CO2 Sorption Properties

In this study, carbonized apricot stones and rice husk were utilized as feedstock for the synthesis of CuO-loaded carbonized sorbents for the removal of carbon dioxide (CO2) from gas mixtures. The specific surface area of carbonized sorbents increased with increasing carbonization temperature, resulting in a porous structure with enhanced sorption capacity. The presence of pores and the development of porosity in the sorbents were confirmed by SEM images. CuO nanoparticles were well-dispersed on the surface of carbonized sorbents, and the particle sizes were between 60‒100 nm. Chemical interactions between acidic carbon dioxide and basic copper oxide led to improved adsorption properties. The sorption characteristics of the carbonized sorbents were studied under dynamic conditions, and the results showed that CuO-loaded carbonized apricot stones and rice husk had the maximum sorption capacity for CO2, with efficiencies of 98% and 91%, respectively. These findings indicate that carbonized apricot stones and rice husk can be utilized as low-cost and eco-friendly feedstock for the production of efficient CO2 sorbents.

Study on structural damage evolution of excavated slope subjected to earthquake and rainfall using electrical resistivity measurement

Earthquake and rainfall are two major factors contributing to the slope failures. To examine the evolution of slope structural damage and the failure mechanism during the shaking and rainfall process, a model test of excavated slope subjected to earthquake and rainfall has been performed. The evolution of structural damage within the slope is considered as the changing process of porosity and crack development. The unique relation between of porosity and resistivity of unsaturated soil is utilized to reveal the spatial-temporal variation of slope structural damage by electrical resistivity measurement method. The testing results show that the shaking induced cracks appear on the surface of upper soil layer at the mid-height of slope model, and the structural damage could be both accumulated on the surface and inside the slope under seismic motion. The damaged area provides preference infiltration path for rainwater flow in the following raining process, resulting in the rapid increase of water content of slope interior. The sliding body extends and develops upwards to the slope crest under rainfall condition. The failure patten suggested by the structural damage parameter is verified by the dynamic response of slope model. The structural damage parameter using resistivity is able to show the spatial-temporal evolution of structural damage inside the slope quantitatively, and reflect the porosity change of soil under continuous earthquake and rainfall conditions. The evolution of structural damage reveals that the dynamic failure mode of excavated slope under earthquake and rainfall is the upwards-developed retrogressive sliding of upper soil layer. The evaluating method using resistivity measurement is particularly promising for field test of slope where it can be used to monitor the structural damage change of soil mass subjected to complex environment conditions.

Physical-mechanical properties and thermogravimetric analysis of fired clay brick incorporating palm kernel shell for alternative raw materials

This article explores the potential of incorporating palm kernel shells (PKS) from palm oil mill waste as a clay replacement for fired clay bricks. PKS, an abundant byproduct of palm oil extraction, have high cellulose content and high calorific value, making them an ideal option for clay replacement in brick making. For this purpose, clay soil was replaced with different percentages of PKS (0, 1, 5 and 10%) and subjected to a firing temperature of 1050 °C (heating rate of 1 °C/min). The physical–mechanical properties such as shape, size, colour, dry density, water absorption, thermal conductivity, porosity and compressive strength, as well as microstructural and morphological properties (XRD, SEM-EDX and digital image) and thermal analysis data (TGA-DTA) were evaluated to determine the effects of replacing PKS in fired clay bricks. The results showed that the incorporation of PKS increased firing shrinkage and porosity and decreased dry density, compressive strength, and thermal conductivity. However, incorporating more than 5% PKS resulted in lower mechanical properties (24.6 to 11.0 MPa) and higher water absorption (3 to 12%) due to increased firing shrinkage and porosity (0.3 to 0.9% and 13 to 20%, respectively). The bricks also exhibited lower density (1799 to 1645 kg/m3) and improved thermal properties (0.54 to 0.36 W/m.K) due to the development of porosity during the firing process. While the degradation of organic components was a concern, it was determined that all organic components were completely degraded below 650 °C and the bricks matured at 950 °C. The study concluded that the use of PKS as a partial replacement for clay in brick manufacture is a viable solution for waste management.

Evolution of Mineral-Accessible Surface Area Induced by Geochemical Reactions

Mineral dissolution and precipitation reactions occur in a wide range of porous media systems, driven by deviations from an equilibrium between solid and fluid phases. Reactions occur at mineral surfaces in contact with reactive fluids or accessible mineral surface areas. These mineral surface areas can be determined using a multiscale imaging approach and have been shown to improve the simulation of mineral reaction rates in porous media compared to other estimates of reactive surface area. As reactions progress, mineral surface area evolves, and reactive transport simulations often use a simplified model assuming spherical grains to estimate mineral surface area evolution. This, however, does not depict the evolution of reactive surfaces in porous media systems with varying mineral accessibility. This work aims to quantitatively assess the evolution of accessible mineral surface area in porous media for a multimineralic system undergoing mineral dissolution reactions induced by acid exposure. Before and after the reaction, accessible mineral surface areas are determined from 2D scanning electron microscopy, and 3D X-ray computed tomography imaging of a sandstone sample. The quantified evolution of accessible surface area is compared to the calculated mineral surface area evolution using current approaches. Results show an overall increase in total surface area due to the reaction; however, individual mineral surface areas may increase or decrease. Variation is observed in mineral surface area values measured from imaging and equations used in models. The evolution of mineral surface area is largely impacted by the total surface area as well as the pore connectivity rather than porosity and volume fraction evolution.

Three-Dimensional Printed Highly Porous and Flexible Conductive Polymer Nanocomposites with Dual-Scale Porosity and Piezoresistive Sensing Functions.

Highly flexible, deformable, and ultralightweight structures are required for advanced sensing applications, such as wearable electronics and soft robotics. This study demonstrates the three-dimensional (3D) printing of highly flexible, ultralightweight, and conductive polymer nanocomposites (CPNCs) with dual-scale porosity and piezoresistive sensing functions. Macroscale pores are established by designing structural printing patterns with adjustable infill densities, while the microscale pores are developed by phase separation of the deposited polymer ink solution. A conductive polydimethylsiloxane solution is prepared by mixing polymer/carbon nanotubes with non-solvent and solvent phases. Silica nanoparticles are utilized to modify the rheological properties of the ink, making direct ink writing (DIW) feasible. 3D geometries with various structural infill densities and polymer concentrations are deposited using DIW. The solvent is evaporated during a stepping heat treatment, leading to non-solvent droplet nucleation and growth. The microscale cellular network is developed by removing the droplets and curing the polymer. Up to 83% tunable porosity is achieved by independently controlling the macro- and microscale porosity. The effect of macroscale/microscale porosity and printing nozzle sizes on the mechanical and piezoresistive behavior of the CPNC structures is explored. The electrical and mechanical tests demonstrate a durable, extremely deformable, and sensitive piezoresistive response without sacrificing mechanical performance. The flexibility and sensitivity of the CPNC structure are enhanced up to 900 and 67% with the development of dual-scale porosity. The application of the developed porous CPNCs as piezoresistive sensors for detecting human motion is also evaluated.

Numerical investigations on performance of sc-CO2 sequestration associated with the evolution of porosity and permeability in low permeable saline aquifers

Storing of supercritical carbon dioxide (sc-CO2) in the saline aquifer is studied extensively in the present work using numerical investigations. A mathematical model is developed and applied successfully to determine the movement of sc-CO2 from the injection well along the low permeable saline aquifer. The injected fluid and petrophysical properties are considered as a function of pore pressure in the formation. The impact of permeability modulus in both low and high permeable saline aquifers are studied. The impact of porosity, permeability, injection velocity, permeability anisotropy, residual water saturation, and residual gas saturation is studied. All these parameters influence the migration of sc-CO2 in the reservoir and storage capacity. It is observed that the pore pressure is highly impacted by the change in permeability and injection velocity. Porosity is inversely proportional to pore pressure buildup and directly proportional to the storing of sc-CO2 in the porous media. Due to the increase in pore pressure, the change in porosity is 14.5%, while the change in permeability is 7mD (millidarcy) for 1000 days. At a lower permeability ratio (kV/kH), due to an increase in pore pressure also, the migration of injected sc-CO2 in a vertical direction is decreased when compared with a higher permeability ratio. Thus, this work provides a better understanding of the influencing parameters for storing and migration of sc-CO2 in the low permeable saline aquifer.

The Strike-Slip Fault Effects on Tight Ordovician Reef-Shoal Reservoirs in the Central Tarim Basin (NW China)

The largest carbonate condensate field in China has been found in the central Tarim Basin. Ordovician carbonate reservoirs are generally attributed to reef-shoal microfacies along a platform margin. However, recent production success has been achieved along the NE-trending strike-slip fault zones that intersect at the platform margin. For this contribution, we analyzed the strike-slip fault effects on the reef-shoal reservoirs by using new geological, geophysical, and production data. Seismic data shows that some NE-trending strike-slip faults intersected the NW-trending platform margin in multiple segments. The research indicated that the development of strike-slip faults has affected prepositional landforms and the subsequent segmentation of varied microfacies along the platform margin. In addition, the strike-slip fault compartmentalized the reef-shoal reservoirs into multiple segments along the extent of the platform margin. We show that fractured reef-shoal complexes are favorable for the development of dissolution porosity along strike-slip fault damage zones. In the tight matrix reservoirs (porosity < 6%, permeability < 0.5 mD), the porosity and permeability could be increased by more than 2–5 times and to 1–2 orders of magnitude in the fault damage zone, respectively. This suggests that high production wells are correlated with “sweet spots” of fractured reservoirs along the strike-slip fault damage zones, and that the fractured reservoirs in the proximity of strike-slip fault activity might be a major target for commercial exploitation of the deep Ordovician tight carbonates.

Investigation of optimization methods for metal foam with two-dimensional porosity gradient in shell-and-tube latent heat storage

The latent heat thermal energy storage (LTES) strengthened by metal foam can promote the development of renewable energy and waste heat recovery. In this study, superposition method and 2D iterative method are established to optimize the 2D porosity gradient of metal foam, which is infiltrated in phase change material (PCM) for heat transfer enhancement in LTES with shell-and-tube configuration. The optimization process in these new methods takes the interaction between horizontal and vertical porosity gradient into account and the evolution of two-dimensional metal foam porosity is numerically investigated. Melting behaviors of optimal cases with different methods are compared and analyzed. The numerical results demonstrated that the optimal case obtained by 2D iterative method has best heat transfer performance. Compared with the uniform distribution, a 11.32 % reduction in full melting time can be achieved by the 2D iterative optimal case due to its better temperature uniformity and stronger natural convection.

Model-based optimization of drug release rate from a size distributed population of biodegradable polymer carriers

In the present study, a comprehensive polymer degradation-drug diffusion model is developed to describe the polymer degradation kinetics and quantify the release rate of an active pharmaceutical ingredient (API) from a size-distributed population of drug-loaded poly(lactic-co-glycolic) acid (PLGA) carriers in terms of material and morphological properties of the drug carriers. To take into account the spatial–temporal variation of the drug and water diffusion coefficients, three new correlations are developed in terms of spatial–temporal variation of the molecular weight of the degrading polymer chains. The first one relates the diffusion coefficients with the time-spatial variation of the molecular weight of PLGA and initial drug loading and, the second one with the initial particle size, and the third one with evolution of the particle porosity due to polymer degradation. The derived model, comprising a system of partial differential and algebraic equations, is numerically solved using the method of lines and validated against published experimental data on the drug release rate from a size distributed population of piroxicam-PLGA microspheres. Finally, a multi-parametric optimization problem is formulated to calculate the optimal particle size and drug loading distributions of drug-loaded PLGA carriers to realize a desired zero-order drug release rate of a therapeutic drug over a specified administration period of several weeks. It is envisaged that the proposed model-based optimization approach will aid the optimal design of new controlled drug delivery systems and, consequently, the therapeutic outcome of an administered drug.