Journal PapersJournal of the Brazilian Society of Mechanical Sciences and Engineering , Volume 42 , Issue 4, 2020 March 28, {Pages }
Abstract
In this paper, a parametric study of anode channel clogging of a proton exchange membrane fuel cell (PEMFC) is presented using the numerical volume of fluid method. The droplet size distribution in the present research is considered close to reality. Therefore, three droplets with different sizes are initially placed on the anode channel wall. The droplet sizes are obtained based on the distribution of the saturated liquid water along the whole channel under a specific working condition and the amount of condensed water in the channel, using the PEMFC code. Finally, the dynamic behavior of the droplets is investigated and compared to that of a single droplet with the same total volume. Numerical results show that, in the case of three dropl
Journal PapersProceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering , 2020 January , {Pages 0954407020958581 }
Abstract
In this paper, the importance of turbulence effects on the procedure of droplet’s secondary breakup is studied. In the process of modeling the secondary breakup of a droplet, it is a common practice to presume that the droplet is moving in a laminar flow. However, it is evident that the critical Weber number is profoundly affected by the intensity of turbulence presented in the flow. As a result, the abovementioned supposition may lead to significant computational inaccuracy. This paper tends to perform a modification that considers the effects of turbulent flow on the secondary breakup of droplets. It is shown that the results obtained by the modified model are more precise and in a better agreement with experimental data. In this paper,
Journal PapersArchive of Applied Mechanics , 2020 November 11, {Pages 16-Jan }
Abstract
In this paper, water droplet behavior and its removal process in the anode gas flow channel (GFC) of a proton exchange membrane fuel cell (PEMFC) with partial blockage are numerically investigated using a three-dimensional volume of fluid model. The governing equations are solved using the finite volume method. The effects of the droplet emergence location (, blockage ratio (, longitudinal ratio (, contact angle ( and current density on the water management characteristics, such as droplet shape, removal time, instantaneous and time-averaged pressure drop and water coverage ratio (WCR), are studied. Researchers have already considered the blocking effect on the PEMFC performance without considering the water droplet movement, but the resul
Numerical Investigation of Ethanol and Acetone spray injection into gaseous enviroment
Hassan Khaleghi, Ala Sadooghi
Journal PapersAmirkabir Journal of Mechanical Engineering , 2020 November 10, {Pages }
Abstract
In this paper, the effect of evaporating sprays of Ethanol and Acetone injected into a cylindrical gaseous environment is numerically investigated. To make this investigation the Eulerian gas phase equations together with the Lagrangian liquid phase equations are solved assuming a two-way coupling between the two phases. According to the results, after a certain time from the start of injection, the overall percentage of total evaporation of acetone becomes significantly higher than ethanol, but at the early spraying time, both alcohols had similar overall evaporation rates. Also, in terms of spray tip penetration, they have almost the same amount of progress and more or less the same behaviour. Also due to the almost identical injection fl
Auto-ignition of single n-heptane droplets in low-temperature and high-pressure air using Lagrangian–Eulerian approach
Ahmad Kazemi Fard, Hassan Khaleghi, Reza Ebrahimi
Journal PapersProceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering , 2019 January 22, {Pages 0954407018820783 }
Abstract
The objective of this research is to investigate the evaporating, mixing, and auto-ignition processes of isolated fuel droplets using Lagrangian–Eulerian numerical approach. By using Peng–Robinson equation for the phase-equilibrium, the gas solubility at the droplet surface is considered at high-pressure ambient gases. Using perfectly stirred reactor combustion model and a low-temperature detailed mechanism for the n-heptane, the auto-ignition of the premixed fuel vapor–air mixture is verified at a constant pressure. Then, the auto-ignition of a fuel droplet with 60 ?m diameter is studied at various low air temperatures. The analysis indicated that the results are strongly mesh dependent in this approach. Therefore, in order to pred
Journal PapersJournal of Energy Storage , Volume 26 , 2019 December 1, {Pages 101021 }
Abstract
The effects of working conditions of the proton exchange membrane fuel cell (PEMFC) on the amount of produced water on the walls of the anode gas flow channel (GFC) were numerically investigated. For this purpose, a single-region, steady, two-dimensional, along-the-channel and non-isothermal model was used. Results showed quantitatively that by increasing the working temperature (Tcell), decreasing the relative humidity at the anode GFC inlet (RHa), increasing the current density (i) and increasing the hydrogen stoichiometry ratio (SH2), the amount of produced water is reduced and consequently, water flooding is prevented. The numerical results also demonstrated that how the size of water droplet increases along the channel. In fact the inc
Effects of Two-Way Turbulence Interaction on the Evaporating Fuel Sprays
H Khaleghi, M Ahmadi, H Farani Sani
Journal PapersJOURNAL OF APPLIED FLUID MECHANICS , Volume 12 , Issue 5, 2019 September 1, {Pages 1407-1415 }
Abstract
This article discusses the importance of using different turbulence modulation models in simulation of evaporating sprays. An in-house CFD code has been modified to take into account the effect of considering turbulence modulation by standard or consistent models. These models may predict an augmentation (consistent model) or a reduction (standard model) in the turbulence kinetic energy of continuous phase. Calculations are done in a Eulerian-Lagrangian framework and the effect of injected droplets on turbulent kinetic energy and its rate of dissipation is included in the equations of the continuous phase. Results are shown to be valid by comparing them to Sandia spray A configuration experimental data. Results show that considering the ef
In the present paper, the turbulent reacting flow within a porous media is modeled by developing a computer code. Separate energy equations for fluid and solid phases and the k-ε turbulence equations have been applied by non-thermal equilibrium and double decomposition methods, respectively and the fuel consumption rate is obtained from one-step Arrhenius equation. Turbulence modeling helped to obtain closer results compared with experimental data. Turbulence caused an increase to the effect of diffusion and heat transfer in the preheat zone which resulted in a lower maximum temperature in the combustion zone. In the case of excess air combustion, no temperature difference is observed in the upstream zone. The results showed that with decr
Effects of Gas Cross-over through the Membrane on Water Management in the Cathode and Anode Sides of PEM Fuel Cell.
K Mohammadzadeh, H Khaleghi, HR Abolfazli, M Seddiq
Journal PapersJournal of Applied Fluid Mechanics , Volume 11 , Issue 4, 2018 August 1, {Pages }
Abstract
Water management in a proton exchange membrane fuel cell (PEMFC) is numerically modeled by considering the 2D, non-isothermal steady flow assumptions. Governing equations are solved in all cell layers including cathode and anode electrodes by finite volume method using a single-region approach. The effect of gas cross-over through the membrane is studied on cell performance. This consideration, not only improves the general accuracy of modeling but also makes it possible to model energy losses due to direct reaction of reactant gases. The effect of some key variables such as liquid water diffusivity, current density, membrane thickness, etc. on PEMFC conditions such as the amount of saturated liquid water, power density, cell temperature, c
Journal PapersAtomization and Sprays , Volume 28 , Issue 10, 2018 January , {Pages }
Abstract
In this paper, a new spray/wall impingement model is developed and tested. This model is based on the momentum conservation law and experimental observations. A new formula is derived for the motion of a droplet in the spread regime of the wall impaction model based on analysis of droplet evolution dynamic with consideration of surface tension, and viscous and drag forces. Following the experimental findings, the new model consists of four representative regimes which are stick, rebound, spread, and splash. To validate the new model, numerical calculations are made using several experimental cases as well as a nonevaporating impinging spray on a flat wall. The results of the model are compared with the experimental data of spray tip penetra
CORRELATIONS FOR EVAPORATION HISTORY OF FUEL DROPLETS RELEASED INTO A HIGH-PRESSURE NITROGEN CROSS-FLOW PREMIXER
Ahmad Kazemi Fard, Hassan Khaleghi
Journal PapersAtomization and Sprays , Volume 28 , Issue 5, 2018 January , {Pages }
Abstract
We report on the fundamentals of a new method for injection of fuel droplets into a cross-flow within a premixer, to improve its performance. We investigate evaporation history of various-sized n-heptane droplets in high-pressure and-temperature nitrogen gas, using a Lagrangian–Eulerian numerical approach. Deploying the Peng–Robinson equation and Van der Waals mixing rule for phase equilibrium of the n-heptane–nitrogen system, we consider gas solubility at the droplet surface and real gas behavior in high pressures. A number of different-sized droplets are injected both individually and collectively into cross-flow. The results indicate that in this situation, the interaction among droplets is negligible. To demonstrate coherence amon
The algorithm for Detection of number of transmitting antennas plays an important role in design of intelligent receiver for interception of MIMO communications systems, because foremost it is necessary to know the number of transmitters. Since MDL is a standard solution for this problem, its performance analysis an important task. Previous works provide analysis in which the eigenvalues of covariance matrix of received signal are assumed to be known. Thus the impact of channel impairments on these eigenvalues and consequently the MDL performance is not studied. In this paper, the eigenvalues of covariance matrix of received signal are assumed to be unknown and the error probability of MDL is given based on the spatially correlated MIMO cha
Investigation of the effect of spray fuel injection pattern on evaporation of droplets in the gas turbine pre-mixer
Ahmad Kazemi Fard, Hassan Khaleghi, Reza Ebrahimi
Journal PapersAmirkabir Journal of Mechanical Engineering , Volume 52 , Issue 4, 2018 July 23, {Pages 833-846 }
Abstract
In a liquefied gas turbine combustor, due to the limited length of the premix tube, the evaporation process of fuel droplets is not completely carried out inside the tube and the droplets enter the combustion chamber. The presence of droplets in the combustor causes the reactions occur in the non-premix mode and the emission of NOx increases as a result. To avoid the emission of this pollutants, it’s necessary the droplets are evaporated completely in a limited space. In here, a mechanism is proposed for spraying the droplets. In which, fuel droplets with hollow-cone spray pattern are injected in the opposite direction of the air. In this type of injection, due to the relative velocity of droplets and subsequent enhancement of the droplet
In this research, Large Eddy Simulation of in-cylinder flow during suction and compression stroke in an axisymmetric engine is performed. A computer code using Smogorinsky subgrid model is developed to solve the governing equations of the flow. A proper understanding of flow during suction and compression strokes, gives better information for fuel/air mixture and combustion. The results show that the advantage of LES model is the ability of computing turbulence characteristics in various crank angles of engine cycle. This advantage of model is highlighted by calculating RMS values of axial velocity in comparison with experimental ones. The results show that axial velocity fluctuations during intake reaches to a higher level than in compress
One of the most important parts of a telecommunications system is the synchronization establishment between the transmitter and receiver. So in situations where the synchronization patterns are unknown to the receiver, it is necessary to find the frame structure and bit patterns, Otherwise is impossible transform the bit stream into clear text, or into reliable, cryptographic text, for further processing. Frame structures of different protocols at the physical layer have a fixed or variable lengths and each of these frames have one or more repetitive bit-patterns, depending on the application.. In this paper, a new algorithm for blind detection of bit-patterns in the different frame structures and the BSC channel noise is presented. In this
This paper studies the problem of the convolutional code parameters estimation in noisy scenario. Among the methods that have been proposed for this problem, the rank-based method has attracted most of the research. In this method, the receiver cuts the received sequence up into vectors of lengthl to form the rows of matrix C (l), for max l= 1, ?, l max. The code parameters are estimated based on the rank of these matrices. To this end, the relation between the code parameters and the rank of C (l) should be known. To do this, the previous works proposed an experimental relation; however, it is not established in the general case. This paper analytically computes the rank relation and proposes a method to extract the rate k/n convolutional
Numerical Study of Turbulence in Diesel Spray Combustion Using Large Eddy Simulation
M Keshtkar, H Khaleghi, S Yazdanparast, M Khoramdel
Journal PapersTarbiat Modares University , 2016 January , {Pages }
Abstract
Under modern direct injection diesel engine conditions, the spray and combustion processes are known to be controlled by mixing. In large eddy simulation method, large eddies are solved directly and small scales are modeled, so it can potentially improve the predictive capability by better capturing the large-scale mixing of ambient air with the fuel vapor. In this paper, turbulent spray combustion is studied using the LES method together with partially stirred reactor model using EPISOSPRAY code. To develop this code, LES method is applied in an Eulerian–Lagranian approach in which conservation equations of both phases are solved and then results of LES are compared with those of Reynolds averaged of Navier-Stocks.Simulation of spray com