Numerical analysis of a hybrid air photovoltaic panel (PV)

During the photovoltaic conversion of solar panels, a significant amount of heat is generated, which causes an increase in the temperature of photovoltaic cells and decreases their efficiency and reliability. This negative effect of heat is caused by a part of the solar radiation that is not absorbed by the solar panels, which leads to heat and weakens its performance. Many efforts have been made to reduce this heating effect on the performance of the PV system, such as combining PV and thermal systems to form a hybrid PVT complex that produces both electricity and heat. Gambit and Fluent 6.3.26 software were used for geometry construction and numerical simulations. This work aims to improve the electrical performance of PV cells by enhancing the heat recovered from PVT panels. For this purpose, we performed a numerical simulation of three configurations (3) of PVT panels integrated with TFMS. We analyzed and compared a single air PVT module (without fins), an air PVT module with two fins, and an air PVT module with four fins. The obtained results represent the variations of the contours and the temperature profiles as well as the flow velocity as a function of the flow rates, and the results show that the use of air and the integration of fins has a significant effect on the cooling of the PVT panel elements and thus allowing to improve its performance

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

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

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

New technique to drive the central frequency and to improve bandwidth of EBG structures

In this paper, a parametric study was done to find out the superstrat influence on locating the central frequency of the band gap. The present work compares the standard mushroom like with the EBG structures which are located between the substrate and the superstrat. The main motivation is to present a theoretical contribution by comparing the equations describing the central frequency of the band gap. In that way, this work investigates a new proposed design to shift the central frequency of the forbidden band to a low frequency, by inserting meandered lines to connect each part of the unit cell, which give an added capacitance to the EBG structures, in order to reach a low profile and lightweight EBG structure. The band gap was recognized by computing the transmission coefficient S21 resorting to the suspended line method (SLM).info:eu-repo/semantics/publishedVersio

Shifting the half wave dipole antenna resonance using EBG structure

In this paper, the main motivation is to introduce a new behavior of the electromagnetic band gap (EBG) structures, it is a significant shifting the resonance frequency down of the dipole antennas, this very interesting and useful technique led to low profile, in addition to performance enhancement of dipole antennas, either on return loss or radiation pattern. Also among this EBG structure an investigation on specific absorption rate (SAR) is shown. The used dipole antenna is resonating around 3.5GHz (part of 4G bands), then by using this technique we could shift the working frequency of the same dipole antenna to 2.8GHz worldwide interoperability for microwave access (WiMAX), this new resonance is 80% lower compared with the normal resonance without any structure. The principle of this new technique still valid with other frequency, depending on the frequencies that we would like to shift the working frequency between.info:eu-repo/semantics/publishedVersio

Oxidation of iodide and iodine on birnessite (δ-MnO2) in the pH range 4-8

The oxidation of iodide by synthetic birnessite (δ-MnO2) was studied in perchlorate mediain the pH range 4-8. Iodine (I2) was detected as an oxidation product that was subsequently further oxidized to iodate (IO3). The third order rate constants, second order on iodide and first order on manganese oxide, determined by extraction of iodine in benzene decreased with increasing pH (6.3-7.5) from 1790 to 3.1 M2 s1. Both iodine and iodate were found to adsorb significantly on birnessite with an adsorption capacity of 12.7 mM/g for iodate at pH5.7. The rate of iodine oxidation by birnessite decreased with increasing ionic strength, which resulted in a lower rate of iodate formation. The production of iodine in iodide-containing waters in contact with manganese oxides may result in the formation of undesired iodinated organic compounds (taste and odor, toxicity) in natural and technical systems. The probability of the formation of such compounds is highest in the pH range 5-7.5. For pH 7.5, iodide is not oxidized to a significant extent

Theory of Current-Driven Domain Wall Motion: A Poorman's Approach

A self-contained theory of the domain wall dynamics in ferromagnets under finite electric current is presented. The current is shown to have two effects; one is momentum transfer, which is proportional to the charge current and wall resistivity (\rhow), and the other is spin transfer, proportional to spin current. For thick walls, as in metallic wires, the latter dominates and the threshold current for wall motion is determined by the hard-axis magnetic anisotropy, except for the case of very strong pinning. For thin walls, as in nanocontacts and magnetic semiconductors, the momentum-transfer effect dominates, and the threshold current is proportional to \Vz/\rhow, \Vz being the pinning potential

The impact of prior platinum therapy on survival in patients with metastatic urothelial cancer receiving vinflunine

Background: A phase III trial demonstrated an overall survival advantage with the addition of vinflunine to best supportive care (BSC) in platinum-refractory advanced urothelial cancer. We subsequently examined the impact of an additional 2 years of survival follow-up and evaluated the influence of first-line platinum therapy on survival. Methods: The 357 eligible patients from the phase III study were categorised into two cohorts depending on prior cisplatin treatment: cisplatin or non-cisplatin. Survival was calculated using the Kaplan–Meier method. Results: The majority had received prior cisplatin (70.3%). Survival was higher in the cisplatin group (HR: 0.76; CI 95% 0.58–0.99; P=0.04) irrespective of treatment arm. Multivariate analysis including known prognostic factors (liver involvement, haemoglobin, performance status) and prior platinum administration did not show an independent effect of cisplatin. Vinflunine reduced the risk of death by 24% in the cisplatin-group (HR: 0.76; CI 95% 0.58–0.99; P=0.04) and by 35% in non-cisplatin patients (HR: 0.65; CI 95% 0.41–1.04; P=0.07). Interpretation: Differences in prognostic factors between patients who can receive prior cisplatin and those who cannot may explain the survival differences in patients who undergo second line therapy. Prior cisplatin administration did not diminish the subsequent benefit of vinflunine over BSC