Department of Energy Conversion (1980 - Present)
Numerical Simulation of Thermo-Fluids
Mechanical Engineering, Massachusetts Institute of Technology, Boston, USA
Mechanical Engineering
Mechanical Engineering, Tehran Polytechnics, Tehran, Iran
Mechanical Engineering
Mechanical Engineering, Tehran Polytechnics, Tehran, Iran
Air curtains are used as an industrial tool to control heating and cooling, over time they have been found to be useful for controlling fire and dust. In this paper, the effect of air curtain on fire was investigated in two different positions (above the door in a horizontal mode and next to the door in a vertical mode). Examination of fire requires careful simulation of toxic species and heat transfer; therefore, the combustion model of flamelet generated manifold (FGM) is used to investigate all toxic species. However, in this study, toxic samples of CO and CO2 are studied. After verifying the combustion model, the vertical air curtain was studied in different heat release rate (HRR) of 62.9, 500, and 5000 kW and in different positions of
In this paper, the effect of the combustion and turbulence sub-grid scale (SGS) model on the simulation of pool fire turbulence field has been studied in open source CFD software, OpenFOAM. Two combustion models of Eddy Dissipation Model (EDM) and infinite fast chemistry, with the one-equation and Smagorinsky SGS model, is evaluated for a large-scale pool fire. In general, fast kinetic-based combustion models predict excessive heat release rate. The mean squared of the velocity fluctuations is over-predicted. In this simulation, the turbulence models have no significant effect on the results. In fact, the effect of the combustion model is dominant. The EDM combustion model is more compatible when used with the one-equation SGS model and imp
One of the critical issues in fire dynamic simulation is the selection of suitable combustion model. Typically, combustion models based on infinite fast chemistry are used in fires. In this paper, the flamelet generated manifold (FGM) has been used as a combustion model and the fireFoam solver of OpenFOAM has been used. Two distinct FGMs, with and without radiation coupling, have been investigated to illustrate the role of radiation in simulations. The energy equation with discrete ordinates radiation model is used for coupling of FGM with radiation. These models will be examined in two scenarios of the pool and compartment fire. The FGM with the heat equation is in a good agreement with the experiments. In addition, the basic FGM has a dev
Compartment fire is a hazardous phenomenon because of the generated poisonous and high-temperature gases. Air curtain systems can be used in order to control the fire spread. This paper examines the numerical simulation method with a focus on the combustion model which can model the poisonous gases and investigates the effect of air curtain on fire. The results of the flamelet generated manifold (FGM) combustion model, which considers all of the poisonous species with detail, in compartment fire with single and multi-floor building have been verified. A three-floor compartment fire scenario with methane as a fuel of 62.9, 500, and 5000?kW heat release rate, which represents over to under-ventilation, was selected as a test case. The impact
Nonequilibrium molecular dynamics simulations is applied to investigate the simultaneous effect of rarefaction and wall force field on the heat conduction characteristics of nano-confined rarefied argon gas. The interactive thermal wall model is used to specify the desired temperature on the walls while the Irving–Kirkwood expression is implemented for calculating the heat flux. It is observed that as the temperature differences between the walls increases by lowering the temperature of the cold wall, the number of adsorbed gas atoms on the cold wall increases notably due to the increment in the residence time of the gas atoms. Consequently, the interfacial thermal resistance between the gas and the cold wall reduces which results in a re
The interactive thermal wall model is applied in three-dimensional molecular dynamics simulations to investigate the combined effect of the wall force field, the wall stiffness, the wall atom mass and the wall/gas interaction potential strength on the heat transfer characteristics of static rarefied argon gas within a nanochannel. By increasing the wall stiffness, a reduction in the heat flux through the gas medium occurs which leads to a higher temperature jump. As the wall atom mass is increased up to twice the argon atom mass, the heat flux is enhanced notably and a minimum temperature jump can be found at this point. Further increase in the wall atom mass results in reducing the heat flux and consequently increasing the temperature jump
Underfloor air distribution (UFAD) systems are on the way of development owing to their substantial energy saving potential as well as their capability for establishing thermally comfortable environments. Comprehensive evaluating these systems necessitates considering multiple effective factors ranging in several levels, which significantly augments the number of test cases and can even make the conducting of research impossible. Proposing a methodology for combining CFD results and the Taguchi optimization algorithm using the multi-response signal to noise (MRSN) analysis, the present study addresses this issue. In order to investigate the performance of UFAD systems applied in a densely occupied classroom from three fundamental viewpoints
The use of materials with high reflectivity on the surfaces of inner walls plays a significant role in enhancing the performance of ultraviolet (UV) reactors. In this study, the reactor efficiency is evaluated by changing the materials of the inner wall surfaces of the multi-lamp reactor from stainless steel to aluminum. The effect of water UV transmittance, flow rate, lamp power, and different modes of active lamps is studied on the effectiveness of inner wall reflection. Four turbulence models including standard k-ε, realizable k-ε, standard k-ω and SST k-ω, are used for the simulation of the flow field in a cross-flow UV reactor. The discrete ordinates model is applied to calculate the UV radiation field. The prediction of the veloci
The effect of the wall force field and the wall physical characteristics on the interfacial phenomena of a 5.4?nm nanoconfined gas medium are investigated by applying three-dimensional molecular dynamics simulations. Assuming that a range of 1?nm from each wall is affected by the wall force field, the gas distribution changes notably in this region which covers 40% of the channel height. Therefore, a combined effect of the wall force field and the wall stiffness, its mass as well as the interaction strength determines the interfacial phenomena such as interfacial thermal resistance (ITR) at the gas/solid interface. The increment in interaction strength of the gas/solid atoms leads to an increase in the amount of adsorbed gas on the wall whi
This study presents a dynamic simulation-optimization of a solar-assisted desiccant cooling system integrated with a ground source heat exchanger (SDCS-GSHE). Solar and ground source energies are used for regenerating the desiccant wheel (DW) and a pre-cooling process, respectively. The system is considered as an alternative for extremely hot and humid regions. Determinant design parameters of the SDCS-GSHE that are associated with the DW, GSHE, and solar loop components directly affect the system behavior and, consequently, the provided thermal comfort, as well as the solar fraction (SF). Therefore, a multi-objective genetic algorithm optimization is invoked to determine all viable optimum design parameters to set up the system. Also, an e
Molecular dynamics simulations of static argon gas at three different levels of rarefaction are conducted for a channel of 5.4?nm height to investigate the simultaneous effect of the wall force field and the gas temperature on the stress distribution along the channel height. Using the interactive thermal wall model, different temperatures are applied on the channel walls to be able to investigate the effect of the wall temperature and the induced heat flux through the gas medium on the stress distribution. Considering the monoatomic neutral argon gas, the kinetic, particle-particle virial, and surface-particle virial are considered for computing the stress distribution along the channel height. The normal stress components in the bulk gas
The present study investigates underfloor air distribution (UFAD) systems by using the combination of computational fluid dynamics (CFD) and the Taguchi optimization algorithm. A multi-objective optimization approach is used to analyze the efficiency of UFAD systems from the viewpoints of thermal comfort, indoor air quality (IAQ), and energy consumption. The supply air temperature, the air change rate per hour (ACH), and the height of the return air vent factors are considered in order to achieve the optimum operating condition. First, numerical validation has been done for an office room model, and then optimization has been performed for this space. The optimization results state that setting the supply air temperature and AC
This work investigates the hourly operation of the U?kan configuration of the desiccant system that uses ground and solar energies in combination. In this system, the ground source heat exchanger (GSHE) is used as a cooling component after the desiccant wheel (DW)(post-cooler) together with using simultaneously before (pre-cooler) and after the DW. The validity of this configuration is evaluated in several hot-humid regions, and an economic assessment is performed to confirm the system cost-feasibility. This study examines the impact of the return air ratio on the level of thermal comfort established, system COP, energy consumed for regeneration, and solar fraction (SF). Here, a guideline for sizing various components in the system is demon
The identification of the type of regime has an essential effect on the selection of sub-grid scale and discretization methods, regarding the accuracy and computational time. In order to investigate the role of sub-grid scale and time discretization method in a pool fire modeling by the Large Eddy Simulation (LES), three sub-grid scales Smagorinsky, one-equation and Wall-Adapting Local Eddy-Viscosity (WALE) and three time discretization methods of first-order Euler method, second-order Crank Nicolson and backward second-order were investigated. The results indicate that WALE and one-equation sub-grid scale have an acceptable prediction, while Smagorinsky has a significant error with the experimental results. Different time discretization me
In this paper, a fire whirl in a high-rise room with a gap in one corner is investigated. Methanol fuel is intended. Large Eddy Simulation method was used and the OpenFoam software, one-equation sub-grid model and eddy dissipation combustion model were performed. Results in two different conditions (fuel bed of 5.8 and 7 cm) were obtained and compared with the experimental results. By comparing the numerical results with the experimental results, it is observed that the numerical results of the mean temperature in the middle and corner of the room are consistent with the experimental results. The results of the various sub-grid models in the center line show that the WALE model fits better with the experimental results and also the performa
Using discretization technique is one of the challenges associated with numerical modeling. In the Large Eddy Simulation (LES) method, this issue becomes more critical because it affects the sub-grid scale (SGS) model and creates errors. Using an LES method, we investigated the numerical errors and compatibility of different discretization methods with SGS in pool fire modeling. First-order, central, and second-order upwind and linear upwind stabilized transport (LUST) schemes were examined in Smagorinsky (S_SGS) and k-equation (K_SGS) sub-grid scales. First-order upwind and second-order upwind methods estimated the velocity field, temperature, and perturbation with a significant error, so that in the plume area, there was 90% error with th
simulation of blood flow in bypass grafts can help medical evaluation. Numerical simulation of blood flow in Configurations recommended by the surgeon Such as the configurations of Y is the aim of this study in order to predict hemodynamic parameters of this configuration in a patient with double stenosis 65 and 50 percent is examined at rest and during exercise. The computational domain was created from CT images from the human cardiac. In this study, blood is assumed homogeneous, non-Newtonian and pulsatile. For real modeling of flow and blood pressure, lumped model is used in outlet at rest and exercise states.The results indicate using this configuration is compensated the pressure drop and flow and time average wall shear stress has re
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