We report the application of machine learning methods for predicting the effective diffusivity (D
) of two-dimensional porous media from images of their structures. Pore structures are built using ...reconstruction methods and represented as images, and their effective diffusivity is computed by lattice Boltzmann (LBM) simulations. The datasets thus generated are used to train convolutional neural network (CNN) models and evaluate their performance. The trained model predicts the effective diffusivity of porous structures with computational cost orders of magnitude lower than LBM simulations. The optimized model performs well on porous media with realistic topology, large variation of porosity (0.28-0.98), and effective diffusivity spanning more than one order of magnitude (0.1 ≲ D
< 1), e.g., >95% of predicted D
have truncated relative error of <10% when the true D
is larger than 0.2. The CNN model provides better prediction than the empirical Bruggeman equation, especially for porous structure with small diffusivity. The relative error of CNN predictions, however, is rather high for structures with D
< 0.1. To address this issue, the porosity of porous structures is encoded directly into the neural network but the performance is enhanced marginally. Further improvement, i.e., 70% of the CNN predictions for structures with true D
< 0.1 have relative error <30%, is achieved by removing trapped regions and dead-end pathways using a simple algorithm. These results suggest that deep learning augmented by field knowledge can be a powerful technique for predicting the transport properties of porous media. Directions for future research of machine learning in porous media are discussed based on detailed analysis of the performance of CNN models in the present work.
•The classification of the industrial energy efficiency index has been summarized.•The factors of energy efficiency and their implement in industries are discussed.•Four main evaluation methodologies ...of energy efficiency in industries are concluded.•Utilization of the methodologies in energy efficiency evaluations are illustrated.•Related polices and suggestions based on energy efficiency evaluations are provided.
Energy efficiency of high energy-consuming industries plays a significant role in social sustainability, economic performance and environmental protection of any nation. In order to evaluate the energy efficiency and guide the sustainability development, various methodologies have been proposed for energy demand management and to measure the energy efficiency performance accurately in the past decades. A systematical review of these methodologies are conducted in the present paper. First, the classification of the industrial energy efficiency index has been summarized to track the previous application studies. The single measurement indicator and the composite index benchmarking are highly recognized as the modeling tools for power industries and policy-making in worldwide countries. They are the pivotal figures to convey the fundamental information in energy systems for improving the performance in fields such as economy, environment and technology. Second, the six factors that influence the energy efficiency in industry are discussed. Third, four major evaluation methodologies of energy efficiency are explained in detail, including stochastic frontier analysis, data envelopment analysis, exergy analysis and benchmarking comparison. The basic models and the developments of these methodologies are introduced. The recent utilization of these methodologies in the energy efficiency evaluations are illustrated. Some drawbacks of these methodologies are also discussed. Other related methods or influential indicators for measuring energy efficiency performance have also been presented. Finally, the related polices and suggestions based on the energy efficiency evaluations are provided.
•The LB methods for single-phase and solid-liquid phase-change heat transfer in porous media are reviewed.•Applications of the LB methods in single-phase and solid-liquid phase-change heat transfer ...in porous media are reviewed.•Further developments of the LB method in the related areas are outlined.
Over the past 30 years, the lattice Boltzmann (LB) method has been developed into a versatile and powerful numerical methodology for computational fluid dynamics and heat transfer. Owing to its kinetic nature, the LB method has the capability to incorporate the essential mesoscopic physics, and it is particularly successful in modeling transport phenomena involving complex boundaries and interfacial dynamics. Up to now, the LB method has achieved great success in modeling fluid flow and heat transfer in porous media. Since the LB method is inherently transient, it is especially useful for investigating transient solid-liquid phase-change processes wherein the interfacial behaviors are very important. In this article, a comprehensive review of the LB methods for single-phase and solid-liquid phase-change heat transfer in porous media at both the pore scale and representative elementary volume (REV) scale. The review first introduces the fundamental theory of the LB method for fluid flow and heat transfer. Subsequently, the REV-scale LB method for fluid flow and single-phase heat transfer in porous media and the LB method for solid-liquid phase-change heat transfer are discussed in detail. Moreover, the applications of the LB methods in single-phase and solid-liquid phase-change heat transfer in porous media are reviewed. The LB modeling and predictions of the effective thermal conductivity of porous materials are also reviewed. Finally, further developments of the LB method in the related areas are briefly discussed.
Pancreatic cancer is one of the most lethal malignancies worldwide. Although the standard of care in pancreatic cancer has improved, prognoses for patients remain poor with a 5-year survival rate of ...< 5%. Angiogenesis, namely, the formation of new blood vessels from pre-existing vessels, is an important event in tumor growth and hematogenous metastasis. It is a dynamic and complex process involving multiple mechanisms and is regulated by various molecules. Inhibition of angiogenesis has been an established therapeutic strategy for many solid tumors. However, clinical outcomes are far from satisfying for pancreatic cancer patients receiving anti-angiogenic therapies. In this review, we summarize the current status of angiogenesis in pancreatic cancer research and explore the reasons for the poor efficacy of anti-angiogenic therapies, aiming to identify some potential therapeutic targets that may enhance the effectiveness of anti-angiogenic treatments.
•The advantages and classifications of S-CO2 cycles are presented.•Applications of cycles especially in nuclear and solar industries are summarized.•The theoretical and experimental analysis of ...system and component are investigated.•The comparison of working fluids and component designs are analyzed.•The challenges to improve the efficiency of S-CO2 cycle applications are concluded.
The development technology and applications of supercritical CO2 power cycle have recently been gaining a lot of attention for applications to different energy industries. The advantage of the S-CO2cycle is high-efficiency within an economic and convenient structure. The stable chemical properties make it be proper to a range of metal material applications. This study provides a detailed comprehensive study of the recent development trends of the S-CO2 power cycle and the different applications of S-CO2 power cycle in various energy industries, especially nuclear energy and solar energy. The theoretical analysis, experimental analysis and the classification of different approaches are summarized for energy sources. The comparison of working fluids, component designs are presented in the article as well. The challenges for improving the efficiency of S-CO2 power cycle applications are analyzed. The study will be a beneficial complement to understanding the recent progress.
This article presents a critical review of the theory and applications of a multiphase model in the community of the lattice Boltzmann method (LBM), the pseudopotential model proposed by Shan and ...Chen (1993) 4, which has been successfully applied to a wide range of multiphase flow problems during the past two decades. The first part of the review begins with a description of the LBM and the original pseudopotential model. The distinct features and the limitations of the original model are described in detail. Then various enhancements necessary to improve the pseudopotential model in terms of decreasing the spurious currents, obtaining high density/viscosity ratio, reducing thermodynamic inconsistency, unraveling the coupling between surface tension and equations of state (EOS), and unraveling the coupling between viscosity and surface tension, are reviewed. Then the fluid–solid interactions are presented and schemes to obtain different contact angles are discussed. The final section of this part focuses on the multi-component multiphase pseudopotential model. The second part of this review describes fruitful applications of this model to various multiphase flows. Coupling of this model with other models for more complicated multiple physicochemical processes are also introduced in this part.
•Multi-scale transport phenomena in shale gas transport is introduced.•Multi-scale simulation models describing shale transport are reviewed.•Information exchanging among micro/meso/macroscopic ...methods is analyzed.•Shale gas production genome model is put forward and clarified.•Shale gas production forecasts depend on multi- scale and -physics models.
Shale gas, although unconventional, is a prospective clean energy source. Shale gas production is a complex multi-scale process with its spatial size ranging from the nanoscale to kilometer-scale. During shale production, the gas transport process involves the diffusion of dissolved gas molecules into the matrix bulk, desorption of adsorbed gas from the micropore surface, Knudsen diffusion and slip flow of free gas in the pore, and Darcy flow or even high-speed non-Darcy flow of free gas in the fracture network. Accordingly, understanding the shale gas transport process in the shale reservoirs poses a long-standing problem to researchers and engineers. Computational modeling offers an opportunity to effectively reveal the gas multi-scale transport mechanisms and accurately predict the amount of shale production. In this review, the shale gas transport process during shale gas production is firstly introduced. Thereafter, the multi-scale transport phenomena involving shale gas molecule desorption from the shale matrix at the atomic and molecular level, diffusion in the nanopore, diffusion and seepage into the micropore, and convection and mass flow in the mesoscopic pores and macropore are elucidated. Moreover, the corresponding multi-scale simulation models that describe the above phenomena and shale production are explained. The shale gas production genome model, which provides insights into the entire process of the shale gas production model, is proposed and clarified according to the multi-scale simulation models used in the shale gas production prediction. The shale gas production genome model is convenient for elucidating shale transport mechanisms and guiding shale gas reservoir exploitation.
•The advances and challenges of pore-scale modeling are summarized.•Porous structure imaging and computational reconstruction methods are reviewed.•Recent progresses in pore-scale numerical methods ...and schemes are introduced.•Pore-scale studies of transport processes in porous media are discussed.•Application of pore-scale modeling in geoscience and fuel cells are presented.
Porous media play important roles in a wide range of scientific and engineering problems. Recently, with their increasing application in energy conversion and storage devices, such as fuel cells, batteries and supercapacitors, it has been realized that transport processes and reactions occurring in the pores and at the interfaces of different constituents significantly affect the performance of the porous media, yet these pore-scale transport phenomena are not well described or even neglected in the conventional numerical models based on the representative element volume (REV). Pore-scale modeling is an efficient tool for the simulation of pore-scale transport and reactions in porous media because of its ability to accurately characterize these processes and to provide the distribution details of important variables which are challenging for current experimental techniques to provide either due to lack of in-situ measurement capability or due to the limited spatial and temporal resolution. In the present review, the advances and challenges of the state-of-the-art pore-scale modeling are summarized. The practical applications of pore-scale modeling in the fields of geoscience, polymer exchange membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC) are discussed. Notable results from the pore-scale modeling are presented, and the challenges facing the pore-scale model development are discussed. This in-depth review is intended to give a well-rounded introduction of critical aspects on which the pore-scale modeling can shed light in the development of relevant scientific and engineering systems.
Schroeder's paradox discovered by Schroeder in 1905 refers to the phenomenon that polymers have different maximum water uptake in the liquid and saturated vapor phases. For more than a hundred years, ...people have often debated whether this phenomenon conforms to thermodynamics. As proton exchange membrane fuel cell (PEMFC) gradually becomes a promising renewable energy utilization device, its impact on the physical properties of the proton exchange membrane has been studied widely. This paper reviews the theory and experiments on Schroeder's paradox over more than 100 years, especially the exploration of perfluorosulfonic acid membranes and PEMFCs in recent decades. Since membrane water content determines the operational performance of the PEMFC, this paper discusses and analyzes the effect of Schroeder's paradox on the PEMFC performance, including mechanical properties, electrical conductivity, and water transport mechanism. The effect of this phenomenon on the non-equilibrium operation of PEMFC has been highlighted, such as cold start-up, because of the different properties of membranes in contact with liquid water and air. This review gives an introduction to critical aspects of Schroeder's paradox to serve governments and organizations to promote the application of PEMFC in different regions.
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•Schroeder's paradox in proton exchange membrane fuel cells is reviewed.•Mechanisms and experimental methods of Schroeder's paradox are critically analyzed.•Evaluated the effect of Schroeder's paradox on membrane performance.•The existence of Schroeder's paradox lower freezing point is discussed.•Future research directions of Schroeder's paradox are presented.
•Thermal conductivity of PU foam is measured under various environments by TPS method.•Spectral extinction coefficient of PU foam is measured by FTIR.•Thermal conductivity of PU foam increases ...non-monotonically with temperature.•Thermal conductivity of PU foam increases as high as 10–18% in moist air.•Radiative thermal conductivity of PU foam can be calculated by Rosseland model.
Polyurethane foams are widely used in energy conservation field and thermal conductivity is one of the most important properties. To reveal and optimize the thermal insulation performance of PU foams, the thermal conductivity of five PU foam samples formed by blowing agents of CP, CP+IP, CP+245fa and CP+245fa+LBA are measured using transient plane source method under various environment. Influences of temperature, humidity, water uptake, alternate high and low temperature, long time storage at high temperature and gas pressure of the atmosphere on the thermal conductivity of PU forms are investigated comprehensively. The mechanism of temperature that affects the thermal conductivity of PU foams is discussed. Fourier transform infrared spectroscopy is adopted to measure the spectral extinction coefficients of these five samples. With the spectral extinction coefficient, the radiative thermal conductivity is calculated from Rosseland model. Then the contributions of radiative heat transfer to the effective thermal conductivity are decomposed. The thermal conductivity of five foams increases non-monotonically with temperature. When stored in moist air, thermal conductivity can increase as high as 10–18%. Radiative thermal conductivity contributes 3.6–4.1% at −40°C, 7.3–9.0% at 20°C and 9.1–11.8% at 70°C to the effective thermal conductivity.
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