Effect of a magnetic field on the couette forced convection of a buongiorno’s nanofluid over an embedded cavity

The paper investigates the effect of a magnetic field on the forced convection of a nanofluid in a channel with an embedded cavity. The nanofluid is described by the Buongiorno’s model, and a fixed temperature boundary condition is prescribed. The governing equations are written in a dimensionless form and solved numerically by employing COMSOL Multiphysics. The obtained velocity, temperature and concentration fields are presented as function of the governing parameters, and the Nusselt number on the upper boundary is evaluated as well. Particular attention is paid to the effect of the inclination angle of the magnetic field, showing that variations up to 40% may affect the Nusselt number

Influence of Nanoparticles and Magnetic Field on the Laminar Forced Convection in a Duct Containing an Elastic Fin

In the present paper, an investigation of the effect of a magnetic field and nanoparticles suspended in pure water on the forced flow in a duct containing an elastic rectangular fin is performed. The nanofluid, i.e., CuO nanoparticles suspended in water, flow in the duct with an inlet fully developed velocity profile and a cold temperature. The lower boundary of the duct is kept at a hot temperature, while the upper boundary is adiabatic. According to the ALE formulation, numerical simulations of the laminar flow are carried out, by employing the software package Comsol Multiphysics, to solve the governing equation system: mass, momentum, energy, and deformation. The behavior of the Nusselt number, of the temperature and velocity fields as well as of the stress profiles are presented and interpreted. As a result, the addition of CuO nanoparticles to pure water improves the local and global heat transfer rate by up to 21.33% compared to pure water. On the other hand, it causes an additional deformation of the elastic fin as well as the increase of the stress due to the presence of the nanoparticles, leading to an increase of its maximum displacement of 34.58% compared to the case of pure water flow. Moreover, the enhancement of the flexibility of the fin (and thus its deformation) leads to a relative reduction in terms of convective heat transfer rate, especially downstream of the fin

Numerical Analysis of the Unsteady Mixed Convection of a Nanofluid in a Concentric Tube Heat Exchanger

In the present work, a numerical investigation of the unsteady mixed convection and entropy generation of a nanofluid in an annular cylindrical space is presented using the Buongiorno’s two-phase flow model. It deals with a concentric tube heat exchanger where the inner cylinder rotates with a constant frequency and is maintained at hot temperature, while the outer cylinder is cold. The aim of the present investigation is to highlight the effects of some parameters on the hydrodynamic, thermal and mass behavior of the considered nanofluid as well as on the system irreversibility, namely: the inertia (1 ≤ Re ≤ 20), the buoyancy (0 ≤ Ri ≤ 5), the mass diffusion (0.1 ≤ Le ≤ 10) and the vertical positions of the inner cylinder (-0.4 ≤ H ≤ 0.4). Moreover, at specific parameters, an optimal position in terms of heat transfer has been determined. The flow of the nanofluid is two-dimensional and governed by the equations of continuity, momentum, energy as well as volume fraction conservation. After performing a finite element method mesh test and validation with the literature, the Nusselt number and the entropy generation are discussed. The results show that the heat transfer rate and entropy generation increase with increasing values of Richardson and Reynolds number, especially when positioning the inner cylinder in the lower part. On the other hand, the nanoparticles migration under the thermophoretic diffusion decrease with the increase of the Lewis number, which consequent decrease of the heat transfer rate

Is body size a good indicator of fecundity in the genus Thaumetopoea? A story told by two intrageneric Mediterranean forest defoliators

Body size correlates with several factors such as reproductive fitness, environmental changes, the quality and quantity of food during critical development stages, and the feeding season. For the Palearctic moths of the genus Thaumetopoea (Lepidoptera; Notodontidae), the larval development is crucial and differs between species according to their feeding season; larvae of the pine processionary moth Thaumetopoea pityocampa (Denis & Schifferm\ufcller 1775) feed during winter while larvae of its congeneric cedar processionary moth Thaumetopoea bonjeani (Powell 1922) develop during summer in North Africa. This discrepancy in lifecycles leads to different reproductive traits such as egg batch length, number of eggs per batch, eggs protection mechanisms and female body size. According to Darwin's fecundity advantage hypothesis (1871), female body size should have a positive influence on reproductive fitness, since larger females supposedly have higher fecundity. The universal allometric scaling phenomenon rule proposed by Rensch (1950) predicts that the degree of sexual size dimorphism tends to decrease with the increase of female body size. Here, two morphometrical parameters that is, body size and scale size, estimated from body measurements of individuals of both species, feeding on the same host Atlantic cedar Cedrus atlantica (Manetti & Carri\ue8re 1855) (Pinales; Pinaceae) in Algeria were proposed. The aim was to find out traits that might rule the competition for food and space, in particularly fecundity and body size. Results of the present study highlight a female-biased sexual size dimorphism in both species. The positive correlation between female body size and fecundity shown in this study weakly supports Darwin's hypothesis. Finally, the intrageneric test performed leads to conclude that Rensch's rule does not hold in the considered species

Climate Warming and Past and Present Distribution of the Processionary Moths (Thaumetopoea spp.) in Europe, Asia Minor and North Africa

International audiencePine processionary moth, Thaumetopea pityocampa, is a model insect indicator of global warming, the northwards and upwards range expansion of this Mediterranean species being directly associated with the recent warming up. The knowledge about the drivers of moth expansion is synthesized. A first standardized mapping of the northern expansion edge, from Western Europe to Turkey, is presented, then detailed for 20 countries of Europe, Asia Minor and North Africa, including future trends. Additional data about the responses of the other Thaumetopoea species are given. Finally, the chapter points out the importance of the man-mediated introductions in the expansion process