Experimental Evaluation and Modeling of Air Heating in a Ceramic Foam Volumetric Absorber by Effective Parameters

Reticulate porous ceramic reactors use foam-type absorbers in their operation which must fulfill two essential functions: favoring the volumetric effect and increasing the mass and heat transfer by acting as a support for the reactive materials. Heating these absorbers with highly inhomogeneous concentrate irradiation induces high thermal gradients that affect their thermal performance. Owing to the critical function of these component in the reactor, it is necessary to define a selection criterion for the foam-type absorbers. In this work, we performed an experimental and numerical thermal analysis of three partially stabilized zirconia (PSZ) foam-type absorbers with pore density of 10, 20, and 30 PPI (pores per inch) used as a volumetric absorber. A numerical model and an analytical approximation were developed to reproduce experimental results, and calculate the thermal conductivity, as well as volumetric heat transfer coefficient. The results show that an increase in pore density leads to an increase in the temperature difference between the irradiated face and the rear face of the absorber, this occurs because when pore density increases the concentrated energy no longer penetrates in the deepest space of the absorber and energy is absorbed in areas close to the surface; therefore, temperature gradients are created within the porous medium. The opposite effect occurs when the airflow rate increases; the temperature gradient between the irradiated face and the rear face is reduced. This behavior is more noticeable at low pore densities, but at high pore densities, the effect is less relevant because the internal structure of porous absorbers with high pore density is more complex, which offers obstructions or physical barriers to airflow and thermal barriers to heat transfer. When the steady state is reached, the temperature difference between the two faces of the absorber remains constant if the concentrate irradiation changes slightly, even changing the airflow rate. The results obtained in this work allow us to establish a selection criterion for porous absorbers that operate within solar reactors; this criterion is based on knowledge of the physical properties of the porous absorber, the environment, the working conditions, and the results expected.

Experimental study on the low-velocity impact failure mechanism of foam core sandwich panels with shape memory alloy hybrid face-sheets

Superelastic shape memory alloy (SMA) as an advanced smart material has been used to improve the impact performance of fiber-reinforced composites in recent decades. Due to the low impact toughness of the thin composite face-sheet and the poor strength of the foam core, sandwich panels are sensitive to the transverse loading. SMA fibers were embedded into the composite laminated to improve the impact resistance of the traditional foam core sandwich panel in this work. Five new types of SMA hybrid panels were prepared, and the testing panels with penetration failure were observed at the impact energy of 50 J. The impact mechanical responses and the damage morphology were analyzed, and the impact failure mechanism was also revealed. Results show that all sandwich panels were failed, the fiber breakage occurred at the impact region in the traditional panels, while part plies of the rear face-sheets split-off in the SMA hybrid panels. The impact performance of the SMA hybrid panels is improved when compared with the traditional panel, the reduction of the delamination area by 48.15% and the increase of the load-bearing threshold by 32.75% are acquired for the hybrid sandwich panel with two layers of SMA fibers in the rear face-sheet.

Effect of the Layer Sequence on the Ballistic Performance and Failure Mechanism of Ti6Al4V/CP-Ti Laminated Composite Armor

The effect of the layer sequence on the ballistic performance of Ti6Al4V (35 mm)/CP-Ti (5 mm) laminated composite armor, against a 12.7 mm armor piercing projectile, was systematically investigated, both experimentally and computationally. By introducing the Johnson–Cook constitutive model and fracture criterion, the penetrating process of the composite plate was well-simulated. Furthermore, the influence of the layer sequence on the ballistic performance and failure mechanism of the composite plate was evaluated from the perspective of energy absorption and the stress distribution. Numerical simulation results of the macro morphology and penetration depth agreed well with the experimental results. The results showed that the energy absorption histories of each layer and stress distribution of the composite plate were found to be significantly affected by the arrangement sequence. The ballistic performance of Ti6Al4V/CP-Ti was far superior to that of CP-Ti/Ti6Al4V because more energy was absorbed in the early stage of the penetration process, thereby reducing the damage to the rear face. Further studies showed that the first principal stress in both structures was radially distributed in space, but was mainly concentrated at the rear face when the CP-Ti was placed at the front. Therefore, this stress induced cracking and failure in that region and, consequently, lowered the overall ballistic performance.

Development of Energy-Based Impact Formula-Part II: Scabbing Depth, Scabbing Limit, and Perforation Limit

Numerous formulae are available for predicting the scabbing limit and perforation limit thicknesses subjected to impact loading, but no formula has yet been proposed for estimating the scabbing depth, which is the damaged depth at the rear face when the back of the concrete panel is peeled. In this paper, a new energy-based impact formula along with a theoretical background is proposed to estimate the scabbing depth, scabbing limit, and perforation limit. Based on the scabbing theory, energy–depth relation, and energy conservation law, the new formula is developed and verified with test results. Compared to other impact formulae, the proposed impact formula is found to be more effective.

Observed energy cascade from internal solitary waves to turbulence via near N-waves in the ocean

<p>High temporal resolution mooring observations reported here revealed that there exist energy cascades from internal solitary wave (ISW) to turbulent mixing via smaller, high-frequency internal waves near the maximum local buoyancy frequency (near N-waves), which are transient, inhomogeneous in space. These near N-waves, riding on the parent ISW, emerged at the trough and gradually extended to the rear face of ISW with their ampltiudes becoming larger and larger. Most of the enlargement occurred in the primary stratifed layer, where the displacements between the density surfaces are largest. The near N-waves riding on a typical ISW held approximately 5 percent of the energy of ISW during its passage. Simulations of the KdV-Burgers equation confirmed the emergence of the near N-waves due to the energy cascade, similar as in the observation. The above results point out a new route of energy cascade from ISWs to turbulence in the ocean, which would be helpful on deepening the understanding of the mechanism of wave-induced mixing and energy cascade in internal waves.</p>

EXCITONS IN FUNCTION TO THE BINDING COEFICIENT IN MONOCRISTALLINE SILICON BASE.

The exciton is a particle formed between one or more electrons intermediate levels with one or more holes in the valence band. These two particles are bonded by electrical interactions. These interactions are modeled by a coupling coefficient denoted b. Thus in this article, a study of the variation of the excess excitons density in the base in function to the binding coefficient was done. This study shows that, the excess excitons density is zero at the junction of the base and the space charge zone. By cons, in depth, the excitons density increases as a function to the coupling coefficient. Indeed, when one enters deep, interactions between holes and electrons become very important modeled by a high coupling coefficient. These result a reduction of the excess minority carriers mobility in the base and the formation of exciton complexes, hence the increase of the excess excitons density in the base. The reduction of the excess excitons density at the rear face is due to a very high excitons recombination in this region. This is due to a lack adhesion of the metal contact and disruption of the crystal lattice in this region. When the cell is under polychromatic light, the excess excitons density in the base is very high compared to that obtained when the cell is in dark.

Investigation of the Temperature Effect on the Electrical Parameters of a Photovoltaic Module at Ouargla City

To predict the I-V characteristics of the photovoltaic module, five parameters photovoltaic model Abstract: To predict the I-V characteristics of the photovoltaic module, five parameters photovoltaic model was utilized. The most influential parameters in the photovoltaic module are the solar irradiance level (E) and the temperature (T). The present research was conducted due to the high-temperature values in Ouargla city (can reach 60 °C in the hot season), which will affect remarkably the installed PV installations in this region. The experimental was done in several days cause the investigation need a constant irradiance values with different temperature. The temperature of a photovoltaic module varies according to other conditions, the temperature measurements made on the rear face of the PV module may not be indicative due to a temperature gradient in the material of the rear face of the module. Unfortunately, photovoltaic systems manufacturers do not take into consideration these environmental circumstances which negatively influence the module parameters and yielded deterioration in the system efficiency. The aim of this paper is to investigate the effect of the temperature term on the electrical performances such as the open circuit voltage (Voc), short circuit current (Isc), optimal power (Pm) and Fill Factor. The temperature distribution is non-uniform temperature on the surface of PV modules joined to that of the quality of temperature measurements affects the values of temperature coefficients found. To validate a model allows the researcher to get approximately the I-V characteristic similar to the experiment values. It use the conventional technique (Newton Raphson method) and it was compared by an artificial intelligent method which is the PSO technique, the five parameters estimated (Iph, Is, Rs, Rp, n). This proposed approach can be utilized to model any marketable PV module based on given datasheet parameters only. Statistical indicators were adopted to evaluate the performance of the proposed models; where the relative error of the PSO method comes more less the conventional method.

Dynamic Response of RC Panel with and Without Openings Subjected To Blast Loading

The dynamic response of reinforced concrete (RC) panels without and with different configuration of opening under blast load scenario is investigated in the present study. The numerical simulations were carried out using finite element method with ABAQUS application. The concrete behavior under blast loading was modelled using Concrete damaged plasticity model. The material parameters for concrete damaged plasticity model were determined using methodology proposed by [14]. The parametric study was carried out using variation in blast load due to different charge weight. It was observed that the peak displacement increases with increase in blast load. It was also observed that at lower blast load, failure of reinforced concrete panel was initiated by cracking at rear face of panel but as the blast load increases the RC panel was failed by combination of crushing of front face of panel along with cracking of rear face. It was observed that for the given blast load, the RC panel without opening is less affected by crushing failure as compared to RC panel with opening configuration studied. It was also observed that the RC panel with circular opening at center is stiffer than other opening configuration and observed to have stable structural performance against the blast load studied.