Vol 5 - Special issue IEES

Entropy: Thermodynamics – Energy – Environment – Economy

List of Articles

L’Association Tunisienne des Sciences et de la Recherche (ATSR) est une organisation à but non lucratif sise à l’Institut Préparatoire aux Etudes d’Ingénieurs (IPEI), Université de Gabès en Tunisie. Elle a pour mission le développement et le rayonnement des sciences et de la recherche par l’appui aux instances gouvernementales. Elle agit aussi bien dans l’environnement académique qu’à travers la société civile.

In this work, we have studied the effect of structural disorder on the structural, magnetic and magnetocaloric properties of La_0,45Eu_0,05Ca_0,483Ba_0,017MnO₃ compound. The magnetization measurements as a function of temperature show a second ordered transition from the paramagnetic to the ferromagnetic state when the temperature decreases at T_C = 85 K. The magnetization isotherms indicate the presence of antiferromagnetic domains through the presence of a metamagnetic transition. The magnetocaloric study reveals the presence of a shoulder peak just above T_C. The origin of this peak can be linked to the field induced conversion of antiferromagnetic domains to the ferromagnetic state. The studied sample is characterized by magnetic phase separation phenomenon at low temperature due to the coexistence of both ferromagnetic and antiferromagnetic domains below T_C.

The present work aims to study the effects of using Zinc oxide in organic solar cell, as an alternative for organic polymer in active layer, in layer by layer type, which is responsible for many factors related to performance of the cell and the efficiency, such as the recombination time, fill factor, and open circuit voltage, the maximum current produced by the cell, the efficiency of the cell, and comparison between results for both models, ZnO & PCBM, with keeping the thickness of the active layer equaled, the results showed a clear differences in some factors, not big variations in others, all data was collected by using simulation software, which is help in reducing time and efforts in real experiments in the Lab.

In this paper, energy and exergy analysis of CO2–booster two-stage chiller combining transcritical cycle in cascade with a subcritical are carried out. The examined system produce refrigeration at two temperatures levels and hot water at 73°C.The necessary thermodynamic parameters for analysis are calculated using the software Engineering Equation Solver. A parametric study is conducted to investigate the effect of MT-evaporating and heat rejection temperatures on the coefficient of performance, the total lost work and the exergy lost in different components in the CO2 cycle. The largest lost was recorded in the MT compressor; followed by the high-pressure expansion valve, the Gas cooler, the intermediate pressure valve, LTV and MTV expansion valves, the compressor LT and IP Receiver.

In this article, a detailed Exergy analysis of practical steam compression refrigeration cycle is presented. The computer model has been developed to calculate the performance coefficient, exergy destruction, exergetic efficiency and efficiency defects for R134a and analyze the efficiency of Exergy. Many studies have shown that the compressor occurs most of the energy loss in the gas compression system. The present investigation has been done for evaporator temperature in the range of -10°C to 5°C.

In this work, we have investigated the magnetic and the magnetocaloric properties of polycrystalline Pr0.63A0.07Sr0.3MnO3 (A = Pr, Sm and Bi) prepared by solid-state reaction at high temperature. The magnetic study revealed that all our samples exhibit a ferromagnetic-paramagnetic transition with increasing temperature, with an important magnetocaloric effect near TC. Using theoretical calculations, we have enhanced the magnetocaloric effect for our samples, based on theoretical composites. The obtained composites exhibit important magnetocaloric effect in an extended temperature range, which indicates the possibility of using these composites for magnetic refrigeration.

The analytical resolution of general equations of thin film for a viscoelastic fluid described by an Upper Convected Maxwell model is as high as possible given the complexity of the equations. This then leads us to the need to use numerical resolution for such systems. In this paper, we present a comparative numerical study of the hydrodynamic lubrication by a Newtonian fluid and an Upper Convected Maxwell fluid at low relaxation time, both to compare and validate the computer codes developed in C++ in the field of hydrodynamic lubrication of plain bearing. Then, we present a study of the influence of the kinematic (shaft rotational speed) and geometrical characteristics (eccentricity of the bearing) on the pressure fields, stresses and the hydrodynamic force. The results obtained, show that the hydrodynamic force is more important in the case of a lubricant of type UCM than that of a Newtonian fluid. It is therefore more interesting to use a UCM lubricant than a Newtonian lubricant.

To respond to present requirements in terms of efficiency and impact on the environment, a new carburant called bio-hythane, a mixture of natural gas up to 20% hydrogen and up to 50% Carbone dioxide, from the recovery of the waste from households and agriculture, via suitable digesters, have been developed with the aim of reducing polluting emissions and optimization of combustion efficiency. The present numerical study characterizes the bio-hythane-air turbulent flame in a co-flow coaxial burner in order to determine the effects of hydrogen addition and CO2 dilution in the fuel on the velocity profiles, the turbulence intensity and the turbulent kinetic energy. The results in this study are obtained by simulation on FLUENT code and validated by experimental results found by PIV technology. The confrontation between the axial and radial profiles of longitudinal velocity and those of the turbulent kinetic energy simulated and experimental results allowed us to appreciate the numerical model used. These simulations are found to be in very good agreement with available experimental results for different configurations of the flow.

In this communication, we report the magnetic and magnetocaloric study of Pr0.5Sr0.5MnO3 and La0.5Ca0.5MnO3 compounds prepared by solid-state reaction at high temperature. The temperature dependence of magnetization indicates that each sample displays two distinct magnetic transitions: when decreasing temperature, each sample undergoes a paramagnetic-ferromagnetic transition followed by a ferromagnetic-antiferromagnetic transition. The magnetocaloric study indicates that both samples are the seat of direct (near the paramagnetic-ferromagnetic transition) and inverse (near the ferromagnetic-antiferromagnetic transition) magnetocaloric effect. The inverse magnetocaloric effect is more important for Pr0.5Sr0.5MnO3 compound due to the absence of magnetic phase separation.

A large number of biological materials have outstanding environmental and technical properties. Propolis is a biological and bioactive honeybees product. We performed investigations on the microstructural, optical, and electrical properties of the propolis films. A stable, bioactive, green, and low-cost thin layers of this biocompatible material were produced. Transmittance spectrum shows that propolis film is opaque for blue and ultraviolet (UV) radiations which are responsible of the food oxidation, nutrient losses, flavor degradation, and discoloration. Propolis film reveals an energy gap of 2.88 eV at room temperature, which enables optoelectronic applications in the UV and blue ranges. The electrical study shows that the propolis film has semiconductor behavior. At low frequency range, a large variation of the conductance (10-8 - 10-5 S) was observed for a small variation of temperature (292 - 348 K). Therefore, the propolis film exhibits potential applications as a safe negative temperature coefficient sensor in bioelectronics.

This document presents a thermodynamic analysis of a solar driven single effect lithium Chloride-water (H2O-LiCl) absorption cooling system. A flat plate collector (FPC) is used to absorb the solar radiation and serve as a source of heat necessary for the operation of the cycle. An energy and exergy-based analysis was carried out for every component of the system. This system is analyzed in respect with a broad range of performance indicators including the coefficient of performance (COP), the cooling capacity (Qevap), total and exergetic effeciency. Under steady state working conditions, the thermal and the mathematical calculation of the single effect chiller at each state point and the solar collector performance was simulated using EES tool. The final result shows that the solar absorption installation overall performance is dependent on various number of parameters (TGEN, TABS, TCOND, TEVAP). According to a parametric study it was found that the generator and evaporator temperature improves the cooling capacity and the coefficient of performance of chiller which is not the case for absorber and condenser temperatures. Furthermore, the exergy destruction is maximum at both the generator and absorber while it is less at the evaporator and condenser and approximately null at expansions valves and solution pump.