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The aim of this work is to propose an electrothermal model for predicting the electron mobility, the effective thermal conductivity, and the operating temperature of AlGaN/GaN HEMT devices. The suggested model comprises an enhanced ballistic-diffusive model (BDE) coupled with a drift-diffusion model (D-D). Furthermore, the given model considers total electron mobility, which depends on mobility degradation caused by phonon interactions, surface imperfections, and carrier mobility inside the bulk GaN material. The model is validated based on available experimental and numerical results, and good concordance is observed. It is found that the degradation of the drain current is due to electron mobility and effective thermal conductivity degradation. The output characteristic's degradation due to changing device temperature is analyzed. We demonstrate that for gate biases of −1 V, 0 V, and 1 V, operating temperatures of 390 K, 470 K, and 570 K are obtained when the drain currents are 0.1 A, 0.24 A, and 0.38 A, respectively. Furthermore, we demonstrate that the temperature is maximal in the active region. The temporal temperature evolution presents the same trends with the same amplitude compared to the experimental data, and the error does not exceed 5%. [ABSTRACT FROM AUTHOR]

This work deals with a numerical investigation of a hydrodynamic–elastic problem within the framework of a double enclosure solar collector technological configuration. The solar collector presents two enclosures separated by an elastic absorber wall. The upper enclosure is filled with air, whereas the lower one is filled with Fe3O4/water nanofluid. The mathematical model governing the thermal and flow behaviors of the considered nanofluid is elaborated. The effects of imposed hot temperatures, the Rayleigh number and air pressure on the nanofluid's temperature contours, velocity magnitude distribution, temperature evolution, velocity magnitude evolution and Nusselt number evolutions are numerically investigated. The numerical results show and assess how the increase in the Rayleigh number affects convective heat transfer at the expense of the conductive one, as well as how much the Nusselt number and the nanofluid velocity magnitude and temperature are affected in a function of the imposed hot temperature type (uniformly or right-triangular distributed on the elastic absorber wall). Moreover, the results evaluate how increases in the air pressure applied on the elastic absorber wall affects the nanofluid's temperature distribution. [ABSTRACT FROM AUTHOR]

Featured Application: The specific application of this work is particularly useful for promoting industrial applications working on solar energy storage and transfer. In fact, the investigated nanofluid enclosure presents a finned absorber plate heated by solar energy and considered as a hot top wall. The fins below the absorber plate permit to enhance the heat transfer from the hot absorber plate to the nanofluid. Cold temperatures are imposed partially on right and left walls, while the remaining walls are insulated. The effects of Rayleigh number, enclosure inclination and fins height on nanofluid flow and heat transfer are investigated. This work investigates a hydrodynamic problem involving the Fe3O4-Water nanofluid. The novelty of this investigation lies in the fact that the nanofluid free convection is evaluated within a specific rectangular enclosure having a finned absorber plate as the top wall, heated by solar energy. The fins below the absorber plate permit to enhance heat transfer towards the nanofluid. A numerical simulation is carried out in order to predict the influence of Rayleigh number, nanofluid layer position, enclosure inclination angle, and absorber plate fins height on the nanofluid flow (in terms of streamlines and velocity magnitude) and heat transfer (in terms of temperature and Nusselt number divided by a certain thermal conductivity ratio). Numerical results show a nanofluid buoyancy enhancement and a temperature distribution homogenization, when the Rayleigh number increases, all the more important and pushed to the right area of the enclosure, as the inclination angle of the enclosure is higher. For relatively low fin heights, the nanofluid buoyancy enhancement is all the more important and pushed to the right area of the enclosure as the inclination angle is high. As the fin height increases, the temperature distribution becomes more homogenous. [ABSTRACT FROM AUTHOR]

Over the past decade, the demands for fresh water and energy are growing faster than ever. The use of renewable energy, for seawater and brackish water desalination, is increasing and is currently under the spot light of international conferences. This article presents a theoretical and experimental work performed on a solar still with a pin fins absorber plate. In this work, a conventional active solar still, with a basin area of 0.5 m2and a glass cover at an inclination of 30° to the horizontal fixed on the top part of the still, has been designed, and tested with conventional absorber plate (thin-layer absorber plate), and pin fins absorber plate under the same climatic condition. Desalination of the brackish water using a solar still with conventional absorber plate and pin fins absorber plate is theoretically and experimentally compared. The heat transfer energy balance equations for the various elements of the active solar still are formulated, numerically solved, and validated. The experiments were conducted in the High Institute of Technological studies of Gafsa, Tunisia, during two successive winter days, 21 and 22 January 2014, respectively, for the conventional and modified solar still. The results show that using the pin fins absorber plate in the active solar still increases the daily productivity by 12%. [ABSTRACT FROM PUBLISHER]