Mostafa Khaleghi

Bio: Mostafa Khaleghi is an academic researcher from Universiti Teknologi Malaysia. The author has contributed to research in topics: Combustion & Combustor. The author has an hindex of 5, co-authored 14 publications receiving 100 citations. Previous affiliations of Mostafa Khaleghi include Sirjan University of Technology.

Simulation of a control rod ejection accident in a VVER-1000/V446 using RELAP5/Mod3.2

Abstract: In this study, the RELAP5 Mod3.2 code has been used to analyze the REA in a VVER-1000 reactor. For a conservative simulation, a 58 mm break is considered in the upper head of the reactor pressure vessel due to the impact of an ejected rod. Four cases, 104% of nominal power and 0.45$ of inserted reactivity, 71% of nominal power and 0.47$ of inserted reactivity, 54% of nominal power and 0.6$ of inserted reactivity, and 1% of nominal power and 0.9$ of inserted reactivity are the initial conditions. The relative power, pressure in the pressurizer, mass flow rate via break point, BRU-A performance, and fuel surface temperature are the investigated parameters. The results of the RELAP5 code are consistent with VVER-1000 FSAR data.

Investigations of asymmetric non-premixed meso-scale vortex combustion

Abstract: A new design of asymmetric non-premixed meso-scale vortex combustor is introduced in this paper. The flame stability, heat loss from the combustor wall as well as thermal efficiency and pollutant formation are compared in various circumstances such as air/fuel inlet velocity and equivalence ratios. Furthermore, direct photography method is used to capture visible flame structures at a wide range of equivalence ratios in order to emphasize the exceptional stability of such flames. An essential model for the stability of non-premixed flames in meso-scale combustion spaces is provided in this research. The temperature of the combustor wall is one of the most important factors that influence the temperature of the reactants (preheating phenomena) by heat conduction through the body. The results show that in the stoichiometric circumstance, when air mass flow rate is at the lowest rate (40 mg/s), the ratio of heat loss to heat generation reaches the largest value (around 55%). The average temperature of the combustor wall increases with the flow velocity for the stable flame mode and remains mostly uniform and well distributed for the vortex flame in toroidal shape. At a constant airflow rates, the exhaust temperature increases monotonously with the decrease in equivalence ratio until the flame blows off. This implies that the maximum thermal efficiency of a meso-scale combustor occurs in its lean conditions.

Thermal-hydraulic analysis of VVER-1000 residual heat removal system using RELAP5 code, an evaluation at the boundary of reactor repair mode

Abstract: Removing the residual heat from a nuclear reactor is an important safety aspect of thermal hydraulic analysis. In this study, a typical VVER-1000 reactor residual heat removal system has been evaluated using RELAP5 thermal hydraulic loop code during cool-down. Reactor cooling down starts from hot state temperature and then continues to the cool-down stages with 130 °C and 70 °C, respectively. The second stage of cooling down is the boundary of the reactor repair condition. Main cooling pump head, steam generator (SG) water level, system pressure, the level of coolant in the pressurizer (PRZ), and the temperature of fuel element are examined in a steady state condition. PRZ level, primary circuit and secondary circuit pressure/temperature, and SG water level are evaluated during 32,000 s after cool-down scenario. By comparison, it concluded that the results of RELAP5 code are in agreement with plant experimental data and final safety analysis report (FSAR). Thus, it is proved that the studied reactor is capable to remove the residual heat generated during shutdown. Moreover, RELAP5 is properly recommended for analysis of the VVER-1000 pressurized water reactor during cool-down.

Entropy generation in concentric annuli of 400 kV gas-insulated transmission line

Abstract: The object of this study is entropy generation analysis in the concentric annuli of a gas insulation transmission line enclosure (GIL) loaded with air and SF6-N2 mixture gas The inner and outer cylinders of the cavity are hot and cold, respectively Because of symmetric conditions the ½ cylinder is considered for modeling The standard k–ɛ turbulence model, the equation of entropy generation, and the conservation equations are transformed from dimensional form to non-dimensional form utilizing the definition of dimensionless parameters, stream function, and vorticity Then dimensionless governing equations are solved by a finite volume method (FVM) using an innovative ANSYS Fluent non-dimensionalization scheme Inflated layers applied to the fine grids to improve the simulation capability for turbulent modeling The effects of the Rayleigh number at Ra = 25 × 106, 17 × 109, 21 × 109, 42 × 109 and 57 × 109 are investigated The results demonstrate that the Nusselt number grows as the Rayleigh number grows and entropy generation number and the Bejan number decreases as the Rayleigh number increases The GILs have a proper morphology in geometry that reducing the high irreversibility in higher Rayleigh numbers conditions

Effects of impact loads on heated-and-cooled reinforced concrete slabs

Abstract: The potential collapse of heavy components in fires can cause dynamic loads on slabs triggering a progressive collapse of weakened slabs on lower floors. In this study, three reinforced concrete (RC) slabs heated under ISO-834 standard fire for 30, 45, and 60 min, while one slab used as a control specimen. The effects of impact loads due to the falling weight were studied using the low-velocity impact test on RC slabs. The acceleration of midspans is recorded, and the dominant frequency and crack pattern of the specimens are measured. The experimental results used to verify the finite element (FE) models. A set of parametric studies are conducted to evaluate the peak acceleration, maximum and residual displacement, load, stiffness, and absorbed energy of heated RC slabs. The outcomes of the parametric study are fed into a machine learning model called Multilayer perceptron (MLP). Results showed that the fire duration affects and reduces the peak acceleration and frequency of the slabs. The average reduction for peak acceleration was 23% for all tested slabs. Numerical results revealed that the impact load with a low energy (i.e., low mass and the height of drop) has a weak dependency on the time of exposure and reinforcement ratio. The results of this paper impact the fire safety design of the RC slabs and the evaluations of fire-exposed RC slabs.

Kinetic and Fluid Dynamics Modelling of a Methane/Hydrogen Jet Flames in Diluted Coflow

Abstract: Abstract MILD combustion is a recent development in the combustion of hydrocarbon fuels which promises high efficiencies and low NO x emissions. In this paper we analyze the mathematical and numerical modeling of a Jet in Hot Coflow (JHC) burner, which is designed to emulate a moderate and intense low oxygen dilution (MILD) combustion regime [1] . This paper initially discusses the effects of several modeling strategies on the prediction of the JHC flame structure using the CFD code FLUENT 6.3.26. Effects of various turbulence models and their boundary conditions have been studied. Moreover, the detailed kinetic mechanism adopted in the CFD simulations is successfully validated in the conditions of interest using recent literature data [2] on the effect of nitrogen dilution on the flame speeds of several CH 4 /H 2 /air lean mixtures. One of the aims of this paper is also to describe a methodology for computing pollutant formation in steady turbulent flows to verify its applicability to the MILD combustion regime. CFD results are post-processed for calculating the NO x using a numerical tool called Kinetic Post Processor (KPP). The modeling results agree with the experimental results [1] and support the proposed approach as a useful tool for optimizing the design of new burners also in the MILD combustion regime.

Impacts of inner/outer reactor heat recirculation on the characteristic of micro-scale combustion system

Abstract: Flame stability and thermal performance of two different heat recirculation micro-combustors (inner reactor heat recirculation (IHR) and outer reactor heat recirculation (OHR)) are investigated using computational fluid dynamics (CFD) and compared together. A two-dimensional steady state CFD model including temperature dependent properties, laminar flow and transport, one step chemical reaction, surface-to-surface radiation, and heat conduction within solid walls has been carried out to assess flame propagation velocity, flame thickness, excess enthalpy, heat loss, and emitter efficiency. It is observed that both cases significantly extend flammability and blow-off limits due to preheating of the reactive mixture. The maximum flame propagation velocities of IHR and OHR in stoichiometric mixture are predicted 160.2 cm/s and 126.1 cm/s, respectively. It is found that super-adiabatic flame temperature takes place when dimensionless excess enthalpy is positive and it is maximum in the stoichiometric equivalence ratio. Heat loss can be varied from 245.8 to 248.6 W for IHR and from 249.6 to 254 W for OHR configuration. Therefore, there is a relative improvement in the Thermal quenching limit of IHR. It is concluded that IHR micro-combustor profoundly affects flame characteristic and stability, but OHR presents a higher range of emitter efficiency.

The Utilisation of Palm Oil and Oil Palm Residues and the Related Challenges as a Sustainable Alternative in Biofuel, Bioenergy, and Transportation Sector: A Review

Abstract: The importance of energy demands that have increased exponentially over the past century has led to the sourcing of other ideal power solutions as the potential replacement alternative to the conventional fossil fuel. However, the utilisation of fossil fuel has created severe environmental issues. The identification of other renewable sources is beneficial to replace the energy utilisation globally. Biomass is a highly favourable sustainable alternative to renewable resources that can produce cleaner, cheaper, and readily available energy sources in the future. The palm oil industry is essentially ideal for the availability of abundant biomass resources, where the multifaceted residues are vital for energy production through the conversion of biomass waste into value-added products simultaneously. This article discusses the utilisation of palm oil and its residues in the energy and transportation sector. Assessment and evaluation on the feasibility of palm oil and its residues were made on the current valorisation methods such as thermochemical and biochemical techniques. Their potential as transportation fuels were concurrently reviewed. This is followed by a discussion on future challenges of palm oil industries that will take place globally, including the prospects from government and nongovernment organisations for the development of palm oil as a sustainable alternative replacement to fossil fuel. Hence, this review aims to provide further insight into the possibilities of palm oil and its residues towards sustainable development with reduced environmental-related issues.

Magneto-fluid dynamic and second law analysis in a hot porous cavity filled by nanofluid and nano-encapsulated phase change material suspension with different layout of cooling channels

Abstract: Heat transfer, free convective flow and entropy generation of water, Al2O3-water, and nano encapsulated phase change material (NEPCM) diluted in water as NEPCM-water suspension in a hot enclosure is studied. The enclosure is a square porous cavity which heated from below, and the remained walls are thermally insulated. The cavity is cooled by four cooling channels with three different configurations (CONF 1–3). By considering internally heat generation, the impacts of the magnetic field (Ha = 0 and 100), Darcy number (Da=0.001 and 100) and laminar Rayleigh number (Ra=104, 105, and 106) at an equal concentration of nanoparticle and NEPCM ( ϕ = 2 % ) are evaluated by finite volume method (FVM) using ANSYS Fluent. The dimensionless form of the governing equations and entropy generation are used to tune the primitive parameters of the CFD code. The validation test and grid verification check are performed to guarantee the accuracy of the results. The results show that the average Nusselt number decreases from CONF1 to CONF3. The buoyancy effect amplified in higher Rayleigh number and porous medium while the magnetic field controls the buoyancy-driven flow. In addition, at low Rayleigh number, the cavity that contains the NEPCM-water suspension is desirable due to its heat transfer capability and low irreversibility.

Experimental study on electro-spraying and combustion characteristics in meso-scale combustors

Abstract: Electro-spraying and combustion of ethanol in meso-scale combustors were experimentally investigated by using two different structures of combustors. Type A combustor consisted of two section quartz glass tubes. The glass tube served as the combustor wall and had an inner diameter of 12 mm. The inner tube was used as a stainless capillary tube with an inner diameter of 0.9 mm served as the fuel nozzle and the positive DC electrode. Type B combustor consisted of three sections of quartz glass tubes. A fuel nozzle as a positive electrode, a second ring electrode, and a grounded steel mesh forming a combined electric field. Electro-spraying behaviors under the effect of electric field were visually investigated, and the stable and uniform spraying mode which could enhance the combustion was identified and analyzed. The results demonstrated that the combined electrode design with an additional ring electrode improved the electric field distribution at the spraying region, resulting in a decrease of droplet size and an increase of droplet uniformity. Comparing with Type A combustor, CO emissions decreased and combustion efficiency increased in Type B combustor. The combustion efficiency reached its maximum value when the equivalent ratio was equal to 1.0 for both of the two combustors. For Type B combustor, the combustion efficiency was up to a maximum value of 90.5%. The results also showed that droplet size and size distribution had a dramatic impact on the performance of meso-scale combustors.