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In this work, the comparison between the Newtonian and the Power Law models was pointed out to determine the flow field within a system that includes the bypass of a narrowing zone (Stenosis) of an ideal artery. The simulations were conducted in a transient regime considering the pulsed effect inside the veins. The results show that the Power Law model does not sufficiently coincide with the Newtonian model, especially for describing the wall stresses. More specifically, the Power Law model predicts a velocity profile that remains parabolic for the entire time range analyzed, while the Newtonian model captures vorticities.

Mordenite zeolite is considered a molecular sieve because of its adsorbent material characteristics used in the industry as a gas separator. High Si/Al ratios of this zeolitic material in its crystal lattice provide high thermal stability in the structure. To minimize the production costs, this work synthesized the mordenite zeolite in absence organic template (high costs of production). For this purpose, rice husk ash (silicon source) was used from a thermoelectric plant that uses biomass for power generation under the “Moving Grade Reactor” method and metakaolin (aluminium source) derived from the construction. To obtain the zeolitic material, an alkaline treatment with sodium hydroxide and deionized water was required. Different Si/Al ratios (5, 10, 15, and 20) were used to evaluate the highest efficiency in adsorption capacity. The textural properties of mordenite as a function of specific surface area ranged from 314 to 347 m2/g, with micropore volume 0.198–0.279 cm3/g with average pore diameter ranging from 5.9 to 6.2 A. N2 adsorption/desorption isotherms obtained for mordenite presented type IV hysteresis, characteristic of microporous materials. X-ray diffraction showed crystalline phases of mordenite zeolite, mostly. The FTIR reinforces the success of mordenite synthesis by the vibration bands corresponding to the zeolitic material. TGA revealed water desorption and absence of an organic director. The mean cation-exchange capacity values ranged from 1.10 to 1.78 meq/g indicating a 62% increase of 20-mordenite zeolite compared to 5-mordenite in the zeolitization process. This result is satisfactory and promising for the use of mordenite as adsorbent material.

As it is known, the Womersley function models velocity as a function of radius and time. It has been widely used to simulate the pulsatile blood flow through circular ducts. In this context, the present study is focused on the introduction of a simple function as an approximation of the Womersley function in order to evaluate its accuracy. This approximation consists of a simple quadratic function, suitable to be implemented in most commercial and non-commercial computational fluid dynamics codes, without the aid of external mathematical libraries. The Womersley function and the new function have been implemented here as boundary conditions in OpenFOAM ESI software (v.1906). The discrepancy between the obtained results proved to be within 0.7%, which fully validates the calculation approach implemented here. This approach is valid when a simplified analysis of the system is pointed out, in which flow reversals are not contemplated.

This paper aims to investigate, through the 3D numerical analysis of an idealized arterial bypass graft, the dependence of the resistance to flow on the bypass insertion point. The computational model assumes a laminar steady-state Newtonian fluid flow and three different Reynolds numbers: 150, 250, and 400. In this study, the constructal theory has been employed, a self-standing law in physics which covers the statement of minimum flow resistance to optimize morphing architectures, i.e. the coronary artery bypass grafting. According to the Constructal Design method, the constraints are stenosis degree, junction angle, and diameter ratio, while the attachment point is defined as a design parameter. The results demonstrate that the distance between the bypass attachment point and the stenosis influences the pressure drop; more specifically, the pressure drop decreases with the augmentation of the distance. In this regard, a different distribution of the mass flows between the bypass, and the artery is observed and seemed to be the main reason for that behavior. The application of the Constructal Design method in hemodynamics is a tool to describe the biological system to search for better flow performance since it is based on the natural evolution of living systems.

Bypass grafts promote blood flow impaired by a partial obstruction (stenosis) of arteries by fat accumulation. This type of system's computational modeling is used to understand the flow characteristics and look for reasons and solutions for postoperative failures. The present work deals with the effects of changes in geometry in the performance of a system consisting of an idealized partially obstructed artery and a bypass graft. The constructal design method has been employed in previous works in the analysis of such system assuming steady-state flow. In the present work, blood flow is modeled as transient and pulsatile. The constructal design method is used to determine the performance indicator (dimensionless pressure drop), constraints (system volume and stenosis degrees–50% and 75%) and degrees of freedom: junction angle (30o ≤ α ≤ 70o) and diameter ratio (0.5 ≤ D1/D ≤ 1). The response surface methodology was used to evaluate the conditions of minimum pressure drop in transient conditions. As the junction angle decreased to 30o, and the diameter ratio increased to 1, the pressure drop decreased, and there was a considerable dependence of pressure drop on the stenosis degree. The effects of the diameter ratio were more pronounced than those of the junction angle. A resistance model based on an analogy with an electronic circuit was introduced, resulting in a correlation for the pressure drop due to the bypass. This correlation confirmed that the point $$({\alpha },{\mathrm{D}}_{1}/\mathrm{D})=({30^\circ ,1})$$ is a point of minimization of flow resistance. The application of the constructal design method in hemodynamics might be an excellent alternative to configuring enhanced performance and providing valuable results to the understanding of biological flows.

An infinitely wide horizontal porous layer saturated by a power-law fluid is heated from below by an imposed heat flux. The basic stationary state is characterised by a horizontal throughflow and a constant temperature gradient along the vertical direction. A linear stability analysis is performed by employing the method of normal modes. The eigenvalue problem obtained is solved by employing two different approaches: a hybrid analytical/numerical technique and a fully numerical technique. The critical values defining the threshold configurations for the onset of thermal convection are presented. These threshold values display a non monotonic dependence on the basic flow rate while they are monotonically increasing functions of the power-law index.

The present study investigates the planar Couette flow problem for low Reynolds numbers inside a rectangular duct with a morphing cavity serving as a vortex formation promoter. A finite element code implemented in COMSOL Multiphysics is employed to analyze the effects of the cavity aspect ratio and variations of the Reynolds number on formation and topology of the vortices within the embedded cavity. The obtained results indicate that the cavity height is influential in the number of vortices. It is shown by increasing the Reynolds number, a single vortex tends to move towards the outlet. In addition, streamlines demonstrate that small vortices in vicinity of the cavity corner tend to be enlarged with increase of the Reynolds number. The developed numerical model can be extended to the flow structure of natural systems such as an embayment subjected to parallel-to-shore currents.

A horizontal porous layer saturated by a non–Newtonian fluid is taken into account. The fluid is a Ostwald–De Waele type of fluid. The layer is heated from below while the upper boundary is isothermal. The lower boundary is impermeable and the upper one is free. A fully developed basic throughflow is considered. The basic state is perturbed by employing small amplitude perturbations such that a linear stability analysis is performed. The disturbances are assumed to be normal modes and a system of ordinary differential equations governing the perturbation dynamics is obtained. These ODEs form an eigenvalue problem that is solved numerically: both the neutral stability curves and the threshold values for the onset of convection are presented.

Requalification criteria with reference to existing buildings have to contemplate every aspect related to the performance of the external envelope. As for this, great attention has been posed to the modalities to increase the thermal performance of envelopes but practically no evidence has been dedicated to the study of condensation inside building elements. Several kinds of pathology may be caused by condensation, from the appearance of molds to the deterioration of the material itself. Ideally, the risk of condensation inside building elements should be identified before construction, during the design phase. Moreover, it is worth mentioning that both the above-mentioned factors are correlated: greater thermal insulation can lead to an increase in the risk of condensation and therefore it is necessary to work with reasoned choices on materials, thicknesses and position of the insulation. In this context, the present study is aimed at the analysis of the behaviour of moisture condensation with reference to a case study of a building exterior wall. Therefore, a numerical investigation has been carried out by means of a commercial code, based on finite element method, in accordance to the European Standard UNI EN ISO 13788. The Glaser method has been here employed, based on the steady-state diffusion theory and all the calculations were performed on a monthly basis, taking into account internal moisture production rates and outdoor climatic conditions. The results, with reference to the case study, present the occurrence of condensation during the winter months and the possibility that the moisture is completely removed during the warmer periods.