Sharif Digital Repository

In this research, direct conversion of wet algal biomass into biodiesel using supercritical methanol was studied. In this process, microalgal lipids simultaneously was extracted and converted to biodiesel under high pressure and temperature conditions without using any catalyst. Several experiments have been performed to optimize the methanol amount and it has been revealed that the best performance was achieved by using methanol/wet biomass ratio of 8:1. The effect of using various co-solvents in increasing the efficiency of the supercritical process was investigated. It has been shown that hexane was the most effective co-solvent and its optimal ratio respect to wet biomass was 6:1. The... 

In this work, attempt is made to development of active non-precious metal catalysts (NPMCs) for the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs) based on the heat treatment of poly-aniline/transition metal/carbon precursors. All the materials have been characterized by X-ray diffraction (XRD) small and wide angle, N2 adsorption-desorption isotherms, high-resolution transmission electron microscopy (TEM), Scanning electron microscope (SEM) and X-ray photo-electron spectroscopy (XPS). Moreover for electrochemical evaluation of samples, Rotating Disk electrode (RDE) technique and Fuel Cell test were employed. The results showed that onset potential for the optimized... 

In this work, the effect of the number of stages on the productivity of a multi-effect active solar still was experimentally investigated for the first time. Moreover, system performances in continuous and non-continuous modes were compared. For this purpose, indoor experiments were conducted on 4 similar solar still devices with different stages (1-4 stages) in order to accurately control the environmental conditions. In addition, water production was hourly measured during the whole 24-h experiment. The results show that with increased number of stages, distillate production can be predicted with a quadratic function. Moreover, adding a maximum of 6 and 10 additional stages can... 

Design of centrifugal compressors can be accomplished using methods provided in text books and open literature. In this general approach, after determination of dimensions in meridional plane, blade profiles are designed using aerodynamic methods. Then, some blades are trimmed at the beginning to avoid inlet blockage. But there is no clear guidance on how this trimming must be performed. With this widely implemented method, splitter blades have the same profile as main ones. In this research, blade profiles and dimensions of the compressor impeller are not changed while the effect of changes in the position and angle of splitters leading edge are investigated. An optimization scheme is... 

The use of solar energy concentration systems for achieving performance enhancements in the Photovoltaic/thermal hybrid solar systems and reduction of initial costs is an idea that has been studied for years. In this article a new structure for parabolic trough photovoltaic/thermal collector is proposed and its thermal and electrical performances are experimentally investigated. The receiver of this concentrator contains a triangular channel with an outer surface covered with photovoltaic cells and thermoelectric modules with a specific arrangement so that in addition to absorbing heat, a larger portion of the solar radiation is directly converted to electricity. Hence, the performance of... 

Engines that extract energy from low-grade heat sources, e.g., from other processes, have received considerable attention recently. The use of Fluidyne, which is a liquid piston Stirling engine, is quite popular. Herein, we explore the use of liquid-to-vapor phase change in a Fluidyne. This provides two considerable differentiators; (1) exploitation of very low temperature difference ΔT≈30 K, and (2) relatively low temperature ΔT≈330 K heat sources, for producing mechanical work, and thus electrical energy. The influence of three operating parameters, i.e., input heat flux, working fluid, and filling ratio, on the performance of the engine was characterized. Their optimum values, which yield... 

The fabrication of high performance, solution-processed CIGS family solar cells is based on high-temperature crystallization processes in chalcogen-containing atmosphere and/or using dangerous solvents like hydrazine. The non-hydrazine sulfurization- and selenization-free reports typically suffer from poor grain structures. We report a facile strategy to overcome grain growth limitations at very low temperature processing (250 °C). Selenium free Superstrate configuration CuInS2 (CIS) solar cells are fabricated using a nanocrystals ink which avoiding from high temperature selenization or/and sulfurization is targeted. We investigated the effect of intentional M doping (M = Sb, Zn, Cd and Sn)... 

In this paper a scheduling optimization framework is developed to enhance power plants operational decision making process. The proposed framework optimizes plant schedule including operating conditions and maintenance intervals simultaneously and on an hourly basis. In a long term operation plant performance deteriorates due to components aging. This study employs equivalent operating hour (EOH) approach to describe components aging impact on the plant performance deterioration and consequently plant long term profit. Modeling of components aging increases system simulation accuracy in long term operation and the optimum decision variables would be more reliable and realistic. Validity and... 

The present study conducts a comprehensive comparative techno-economic analysis of some near-term sensible thermal energy storage (TES) alternatives to the ‘standard’ two-tank molten salt system for concentrated solar power (CSP) plants. As such, we conducted detailed, relative annual transient simulations for single-medium thermocline (SMT), dual-media thermocline (DMT), and shell-and-tube (ST) systems. To be consistent with recent literature, the DMT and ST systems use concrete with a porosity of 0.2 (e.g. where concrete occupies 80% of the system) as their low cost filler material. The systems were integrated into a validated 19.9 MWe Gemasolar CSP model, which has a solar multiple of... 

In this investigation, seismic behavior and design coefficients of the ribbed bracing system (RBS) are evaluated by considering various archetypes that reflect configuration variability. RBS is a lateral bracing system with a unique mechanics that prevents buckling-induced damage by allowing free deformation of brace under compression. After successful experimental validation and numerical evaluation of RBS specimens in previous studies, FEMA P695 methodology is adopted in this study to subject 48 archetype structures to incremental dynamic analysis (IDA) procedure. Evaluation of the probabilistic collapse capacity of the archetypes against the code requirements reveals that RBS system can... 

In this study, we implement a numerical model to predict secondary organic aerosol (SOA) formation from semi- and intermediate-volatility organic compounds emitted from in-use gasoline and diesel vehicles. The model is formulated based on the volatility basis set (VBS) approach, and it accounts for OH oxidation of unspeciated low-volatility organics, which are classified by their volatility. This model incorporates SOA formation data from smog chamber and emission measurements of vehicle exhaust in a Hybrid framework to calculate the contribution of both traditional and non-traditional SOA precursors to total SOA formation observed in photo-oxidation experiments. Emission and SOA formation... 

This study develops a photosynthetic microalgae microbial fuel cell (PMMFC) engaged Chlorella vulgaris microalgae to investigate effect of light intensities and illumination regimes on simultaneous production of bioelectricity, biomass and wastewater treatment. The performance of the system under different light intensity (3500, 5000, 7000 and 10,000 lx) and light/dark regimes (24/00, 12/12, 16/8 h) was investigated. The optimum light intensity and light/dark regimes for achieving maximum yield of PMMFC were obtained. The maximum power density of 126 mW m−3, the coulombic efficiency of 78% and COD removal of 5.47% were achieved. The maximum biomass concentration of 4 g l−1 (or biomass yield... 

Pulsating heat pipes (PHPs) are compact cooling equipment used for various applications. This type of heat pipes can be used in renewable energy systems, cooling electronic devices, heat recovery systems and many other applications. Since PHPs have superior thermal performance, by applying them in energy systems enhance their efficiency. In addition, PHPs are a reliable medium for cooling various devices which have high heat flux. In this study, various works conducted on the applications of PHPs are reviewed and analyzed. It is concluded that PHPs are efficient and reliable devices for utilization in various energy systems. Moreover, at very low temperatures, such as cryogenic applications,... 

In this paper, a mathematical model for performance prediction of a high-speed planing hull in forward acceleration motion has been developed. Three degrees of freedom have been considered for solving the problem. Utilizing previous empirical equations of displacement ships, motion of the vessel in displacement regime has been simulated. In order to model pre-planing and planing regimes, 2D + T theory has been used. Equations for prediction of performance of a surface piercing propeller (SPP) and an engine have been presented. Validity of the proposed method has been assessed by comparing its results against previous experimental data, and good agreement between experimental and mathematical... 

In this article, to improve the precision, performance and robustness of an industrial boiler-turbine, two robust controllers are designed. First, a robust adaptive variable structure control scheme (RAVSC) is proposed to control a nonlinear multi-inputs multi-outputs (MIMO) model of an industrial boiler-turbine unit, in the presence of significant uncertainties and external disturbances. To guarantee the reliable performance of the RAVSC, appropriate adaption and control laws are introduced to compensate the uncertainties and modeling imprecisions and guarantee the convergence to the sliding surface. Then, the robustness and stability of the proposed RAVSC is proved via Lyapunov stability... 

Heave and pitch motion of an oscillating airfoil in uniform flow will cause generation of forwarding thrust. Applying a combination of these two motions on flexible foil, one can increase thrust and therefore the efficiency. This is the way that most fishes and other flying animals uses to consume less energy. In this paper, hydrodynamic forces and efficiency of an oscillating airfoil is investigated. A code is developed based on potential flow formulation in combination with Time Stepping Method (TSM) with nonlinear free shear layer dynamic approach to predict the wake behind the lifting bodies. A linear Morino type Kutta condition has been implemented on panels adjacent to trailing edge.... 

The application of artificial neural network to compressor performance map prediction is investigated. Different types of artificial neural networks such as general regression neural network, rotated general regression neural network proposed by the authors, radial basis function network, and multilayer perceptron network are considered. Two different models are utilized in simulating the performance map. The results indicate that while the rotated general regression neural network has the least mean error and best agreement to the experimental data; it is however, limited to interpolation application. On the other hand, if one considers a tool for interpolation as well as extrapolation... 

The performance of a vertical ground source heat pump system (GSHPS) largely depends on the fluid temperature leaving the borehole heat exchanger (BHE) that may be affected by the short-term behavior of the BHE. Although considerable research has been carried out to analyze the short-term transient response of the BHEs, few studies have investigated its impact on dynamic simulation of GSHPS. Therefore, this paper presents a numerical approach based on a transient BHE model to evaluate the performance of a residential GSHPS over short and long timescales. The numerical results are compared with the results of EnergyPlus software. It is shown that the proposed model can appropriately predict... 

N-annulated perylene based materials show outstanding and tunable optical and physical properties, making them suitable to be charge transport materials for optoelectronic applications. However, this type of materials has so far not been well studied in solar cells. Here, we develop a new hole transport material (HTM), namely S5, based on perylene building block terms, for organic-inorganic hybrid perovskite solar cells (PSCs). We have systematically studied the influences of the film thickness of S5 on their photovoltaic performance, and a low concentration of S5 with a thinner HTM film is favorable for obtaining higher solar cell efficiency. S5 shows excellent energy alignment with... 

Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar's material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs,...