Analysis of the surface state's influence on the thermohydraulic behavior of an incompressible fluid in convective laminar flow through a microchannel with corrugated surfaces

Le travail entrepris dans cet article présente une étude numérique thermo-énergétique de l'écoulement convectif laminaire dans un microcanal rectangulaire lisse ou la présence de discontinuités sur ses parois. Les ondulations présentent les discontinuités de la surface du mur. La paroi inférieure du microcanal portée à une température constante et uniforme. Le nombre de Reynolds utilisé, Re, a été choisi dans la gamme (50 à 350). La solution du système d'équations régissant le problème a été réalisée par un schéma de volumes finis associé à l'algorithme SIMPLE (Semi Implicit Method for Pressure Linked Equation) pour surmonter le problème de couplage pression-vitesse. L'étude s'est concentrée principalement sur les effets des deux paramètres pertinents : le nombre de Reynolds et la forme géométrique des microcanaux. Les deux champs de vitesse axiale et de température ont été analysés, et le nombre moyen de Nusselt, le coefficient de frottement et la quantité de chaleur évacuée. Les résultats montrent que la structure de l'écoulement est fortement perturbée par la présence de discontinuités sur les parois, et le nombre de Nusselt moyen augmente toujours la fonction du nombre de Reynolds pour les quatre cas étudiés, tandis que l'évolution du coefficient de frottement peut être croissante ou décroissant en fonction du nombre de Reynolds

Three-dimensional analysis of flow characteristics in a heat exchanger equipped with a perforated heat sink

Finning or perforations are frequently used in heat exchange devices to increase the heat exchange between the contact surfaces and the surrounding fluid. Thus, the work undertaken in this paper is in the same context to search for a new design to improve the thermohydrodynamic performance of a heat exchanger.  In this context, the latter considered being equipped with a solid or perforated heat sink to identify the perforations' efficiency in optimizing the heat exchanger's performance. The thermohydrodynamic phenomenon governed by the partial differential equations system derived from the laws of conservation: continuity equation for mass, Navier-Stokes equations for momentum, and the energy equation. For the numerical solution, the finite volume method used, and the problem of pressure-velocity coupling intervening at the level of the Navier-Stokes equations solved using the SIMPLE algorithm. Calculations are made for a perforated deflector with different diameters and an unperforated deflector. For both cases, the inlet velocity was chosen in a range from 0.0018 to 0.009 m/s. The results are presented either as maps for the isothermal fields and velocity contours obtained for the meridian planes shown in the figures or as curves for the axial velocity and heat flow. Finally, a qualitative comparison of the different calculated results made, and it could deduce that a perforated deflector is much more efficient than a solid or solid deflector fixed at the same position. The increase in terms of transfers can go from 1.33% to 12.97%, and an excellent material reduction (from 2.32% to 55.85%) corresponds to a low flow resistance compared to the non-perforated case

Is early defoliation a sustainable management practice for mediterranean vineyards? case studies at the portuguese Lisbon winegrowing region

Context and purpose of the study - Recently early defoliation (ED) has been tested in several highyielding grapevine varieties and sites aiming at reducing cluster compactness and hence, regulating yield and susceptibility to botrytis bunch rot infection. The reported results have been generally positive, encouraging growers to use this canopy management technique as an alternative for replacing the conventional time-consuming cluster thinning and, simultaneously, as a sustainable practice to reduce the use of fungicides. However, ED increases berry sunburn risks and/or can induce carry-over effects on vigor and node fruitfulness as shown in the two case studies reported in this work. Material and methods- Two ED experiments were set up at a commercial vineyard located in the Lisbon winegrowing region with the varieties Aragonez, syn. Tempranillo (2013-2015) and Semillon (2018). In both experiments the ED treatment was compared with the non-defoliated (ND; control) using a randomized complete block design with 4 replicates per treatment. The ED treatment consisted of the removal of 5-6 basal leaves and any laterals at pre-flowering. Vegetative (leaf area and pruning weight) and reproductive components (%fruit-set, cluster number, cluster weight, yield) and berry composition were assessedinfo:eu-repo/semantics/publishedVersio

Can Mediterranean terroirs withstand climate change ? Case studies at the Alentejo portuguese winegrowing region

XII Congreso Internacional TerroirClimate change introduced new challenges to vinegrowers in the Mediterranean areas such as the hot and dry winegrowing region of Alentejo, south Portugal. Warmer and drier conditions are harmful for grape yield and berry quality attributes and for vine’s longevity, mainly when optimal thresholds are exceeded. Therefore winegrowers are forced to move from rainfed to irrigated production systems making Alentejo’ wine production strongly based on available water resources for irrigation. This work aims to review and discuss ecophysiological and agronomical data obtained in irrigation trials set up at different terroirs of Alentejo. In the last four decades, classical bioclimatic temperature-based indices showed a significantly positive trend, while the dryness index present a negative trend over time. Furthermore, ecophysiological data collected in deficit irrigation experiments are reviewed and discussed, focusing on the effects of drought and heat stress on vigour, yield and berry composition. Emphasis is given on the indirect effects of leaf senescence on cluster exposure and consequences on berry temperature and composition. In order to promote the sustainability and quality of wine production in these hot and dry terroirs short- to longterm adaptation measures are suggested. The limitations and risks of using deficit irrigation during heat waves are also underlinedinfo:eu-repo/semantics/publishedVersio

Adenosine-mono-phosphate-activated protein kinase-independent effects of metformin in T cells

The anti-diabetic drug metformin regulates T-cell responses to immune activation and is proposed to function by regulating the energy-stress-sensing adenosine-monophosphate-activated protein kinase (AMPK). However, the molecular details of how metformin controls T cell immune responses have not been studied nor is there any direct evidence that metformin acts on T cells via AMPK. Here, we report that metformin regulates cell growth and proliferation of antigen-activated T cells by modulating the metabolic reprogramming that is required for effector T cell differentiation. Metformin thus inhibits the mammalian target of rapamycin complex I signalling pathway and prevents the expression of the transcription factors c-Myc and hypoxia-inducible factor 1 alpha. However, the inhibitory effects of metformin on T cells did not depend on the expression of AMPK in T cells. Accordingly, experiments with metformin inform about the importance of metabolic reprogramming for T cell immune responses but do not inform about the importance of AMPK

Numerical Evaluation the Impact of the Inserts Shape on Thermo-Flow Behavior in a Heat Exchanger

The improvement of transfers in a heat exchanger can be achieved either by increasing its coolant thermal conductivity or by modifying its geometrical configuration. In this paper, we will be interested in the latter technique by choosing a three-dimensional configuration represented by a channel of rectangular section, on which solid fins of square, circular, or diamond section (vortex generator) have been transversally mounted, which are moreover adiabatic and non-rotating. A convective and forced airflow traverses the channel, and the study focused in principle on the effects of the shape of the fins on the structure of the flow and the rate of heat transfer. The problem is governed by the Navier-Stokes system, coupled with the energy equation de-scribing the thermal process. The resolution of the equation system governing the hydrodynamic phenomenon is performed numerically in three dimensions. To do this, the governing equations of the thermo-hydrodynamic phenomenon are discretized by a finite volume scheme. As for turbulence, it is modeled using the standard model k-ɛ, and the problem of pressure-velocity coupling is solved by the SIMPLE algorithm (Semi Implicit Method for Pressure Linked Equation). The computed results are presented as curves for the Nusselt number, friction factor, thermal enhancement factor, or amount of heat dissipated, and as a map for the contour of the axial velocity norm and the temperature field distribution