Mesoscopic modeling of flow and dispersion phenomena in fractured solids

AbstractThe problem of hydrodynamic dispersion in porous media is considered and numerical predictions of the mixing degree in a single intersection are provided. The flow field in the intersection and adjacent pores or fractures is calculated using a lattice Boltzmann model for single phase flow. A particle-tracking scheme is used, subsequently, that monitors the migration of solute particles in the area of the intersection taking into account the local flow field and a Brownian field. Mixing is quantified in terms of the probability of solute transfer across the junction into the opposite fracture. To circumvent the problem of large computational times for cases of fast flow compared to diffusion, a lattice Boltzmann advection–diffusion model is used, that offers significant savings on computational time without sacrificing accuracy. It is shown that the solute dispersion in a fracture network is a strong function of the Reynolds number, even if the Peclet number remains constant, due to the extensive recirculation areas that may develop in regions close to the junction

Role of Radiology in the Preoperative Detection of Arterial Calcification and Celiac Trunk Stenosis and Its Association with Anastomotic Leakage Post Esophagectomy, an Up-to-Date Review of the Literature

Surgical resection of the esophagus remains a critical component of the multimodal treatment of esophageal cancer. Anastomotic leakage (AL) is the most significant complication following esophagectomy, in terms of clinical implications. Identifying risk factors for AL is important for modifying patient management and improving surgical outcomes. This review aims to examine the role of radiological risk factors for AL after esophagectomy, and in particular, arterial calcification and celiac trunk stenosis. Eligible publications prior to 25 August 2021 were retrieved from Medline and Google Scholar using a predefined search algorithm. A total of 68 publications were identified, of which 9 original studies remained for in-depth analysis. The majority of these studies found correlations between calcifications in the aorta, celiac trunk, and right post-celiac arteries and AL following esophagectomy. Some studies suggest celiac trunk stenosis as a more appropriate surrogate. Our up-to-date review highlights the need for automated quantification of aortic calcifications, as well as the degree of celiac trunk stenosis in preoperative computed tomography in patients undergoing esophagectomy, to obtain robust and reproducible measurements that can be used for a definite correlation.publishedVersionPeer reviewe

Transient thermal conduction with variable conductivity using the Meshless Local Petrov–Galerkin method

A numerical solution of the transient heat conduction problem with spatiotemporally vari- able conductivity in 2D space is obtained using the Meshless Local Petrov–Galerkin (MLPG) method. The approximation of the field variables is performed using Moving Least Squares (MLS) interpolation. The accuracy and the efficiency of the MLPG schemes are investigated through variation of (i) the domain resolution, (ii) the order of the basis functions, (iii) the shape of the integration site around each node, (iv) the conductivity range, and (v) the volumetric heat capacity range. Steady-state boundary conditions of the essential type are assumed. The results are compared with those calculated by a typical Finite Element method. Specific rectangular-type integration sites are introduced during both steady-state and transient MLPG integration, in order to provide complete surface coverage of the domain without overlapping, and the accuracy of the method is demonstrated in all cases studied. Computational efficiency is also investigated with this MLPG method and found to be slower than FE methods during construction stage, but it clearly surpasses that of FEM approaches during the solution stage on a wide parameter range

Photoelectrocatalytic H2 and H2O2 Production Using Visible-Light-Absorbing Photoanodes

Hydrogen and hydrogen peroxide have been photoelectrocatalytically produced by electrocatalytic reduction using simple carbon electrodes made by depositing a mesoporous carbon film on carbon cloth. Visible-light-absorbing photoanodes have been constructed by depositing mesoporous CdS/TiO2 or WO3 films on transparent fluorine-doped tin oxide (FTO) electrodes. Both produced substantial photocurrents of up to 50 mA in the case of CdS/TiO2 and 25 mA in the case of WO3 photoanodes, and resulting in the production of substantial quantities of H2 gas or aqueous H2O2. Maximum hydrogen production rate was 7.8 µmol/min, and maximum hydrogen peroxide production rate was equivalent, i.e., 7.5 µmol/min. The same reactor was employed for the production of both solar fuels, with the difference being that hydrogen was produced under anaerobic and hydrogen peroxide under aerated conditions. The present data promote the photoelectrochemical production of solar fuels by using simple inexpensive materials for the synthesis of catalysts and the construction of electrodes

Computational Study of Hemodynamic Field of an Occluded Artery Model with Anastomosis

In this research work, the hemodynamic field of an occluded artery with anastomosis by means of computational simulation has been studied. The main objective of the current study is the investigation of 3D flow field phenomena in the by-pass region and the effect of the bypass graft to stenosis volume flow ratio on their formation. The anastomosis type was end-to-side with a 45° angle, while stenosis imposed a 75% area blockage of the aorta vessel and the total volume flow was 220 lt/h. The computational study of the flow field was utilized via a laminar flow model and three turbulence models (k—ε RNG, standard k—ω, and k—ω SST). Numerical results were compared qualitatively with experimental visualizations carried out under four different flow conditions, varying according to the flow ratio between the stenosis and the anastomotic graft. Comparison between computational results and experimental visualization findings exhibited a good agreement. Results showed that SST k—ω turbulence models reproduce better visually obtained flow patterns. Furthermore, cross-sectional velocity distributions demonstrated two distinct flow patterns down the bypass graft, depending on the flow ratio. Low values of flow ratio are characterized by fluid rolling up, whereas for high values fluid volume twisting was observed. Finally, areas with low wall shear stresses were mapped, as these are more prone to postoperative degradation of the bypass graft due to the development of subendothelial hyperplasia

Computational Study of Hemodynamic Field of an Occluded Artery Model with Anastomosis

In this research work, the hemodynamic field of an occluded artery with anastomosis by means of computational simulation has been studied. The main objective of the current study is the investigation of 3D flow field phenomena in the by-pass region and the effect of the bypass graft to stenosis volume flow ratio on their formation. The anastomosis type was end-to-side with a 45° angle, while stenosis imposed a 75% area blockage of the aorta vessel and the total volume flow was 220 lt/h. The computational study of the flow field was utilized via a laminar flow model and three turbulence models (k—ε RNG, standard k—ω, and k—ω SST). Numerical results were compared qualitatively with experimental visualizations carried out under four different flow conditions, varying according to the flow ratio between the stenosis and the anastomotic graft. Comparison between computational results and experimental visualization findings exhibited a good agreement. Results showed that SST k—ω turbulence models reproduce better visually obtained flow patterns. Furthermore, cross-sectional velocity distributions demonstrated two distinct flow patterns down the bypass graft, depending on the flow ratio. Low values of flow ratio are characterized by fluid rolling up, whereas for high values fluid volume twisting was observed. Finally, areas with low wall shear stresses were mapped, as these are more prone to postoperative degradation of the bypass graft due to the development of subendothelial hyperplasia