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Dr. Hadi Bordbar
Department of Civil Engineering, Aalto University, PO BOX 11000 Aalto, Finland

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0 Numerical Modeling
0 Numerical Simulation
0 Thermal Engineering
0 Engineering Thermodynamics

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Journal article
Published: 30 July 2021 in Atmosphere
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The outbreak of COVID-19 necessitates developing reliable tools to derive safety measures, including safe social distance and minimum exposure time under different circumstances. Transient Eulerian–Lagrangian computational fluid dynamics (CFD) models have emerged as a viably fast and economical option. Nonetheless, these CFD models resolve the instantaneous distribution of droplets inside a computational domain, making them incapable of directly being used to assess the risk of infection as it depends on the total accumulated dosage of infecting viruses received by a new host within an exposure time. This study proposes a novel risk assessment model (RAM) to predict the temporal and spatial accumulative concentration of infectious exhaled droplets based on the bio-source’s exhalation profile and droplet distribution using the CFD results of respiratory events in various environmental conditions. Unlike the traditional approach in the bulk movement assessment of droplets’ outreach in a domain, every single droplet is traced inside the domain at each time step, and the total number of droplets passing through any arbitrary position of the domain is determined using a computational code. The performance of RAM is investigated for a series of case studies against various respiratory events where the horizontal and the lateral spread of risky zones are shown to temporarily vary rather than being fixed in space. The sensitivity of risky zones to ambient temperature and relative humidity was also addressed for sample cough and sneeze cases. This implies that the RAM provides crucial information required for defining safety measures such as safety distances or minimum exposure times in different environments.

ACS Style

Hamid Motamedi Zoka; Mohammad Moshfeghi; Hadi Bordbar; Parham Mirzaei; Yahya Sheikhnejad. A CFD Approach for Risk Assessment Based on Airborne Pathogen Transmission. Atmosphere 2021, 12, 986 .

AMA Style

Hamid Motamedi Zoka, Mohammad Moshfeghi, Hadi Bordbar, Parham Mirzaei, Yahya Sheikhnejad. A CFD Approach for Risk Assessment Based on Airborne Pathogen Transmission. Atmosphere. 2021; 12 (8):986.

Chicago/Turabian Style

Hamid Motamedi Zoka; Mohammad Moshfeghi; Hadi Bordbar; Parham Mirzaei; Yahya Sheikhnejad. 2021. "A CFD Approach for Risk Assessment Based on Airborne Pathogen Transmission." Atmosphere 12, no. 8: 986.

Journal article
Published: 28 July 2021 in Fire Safety Journal
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Using the high-resolution experimental spectral absorption coefficients of six fuel gases and the line by line absorption spectra of CO and CH4 based on HITRAN and HITEMP spectral databases, in this paper, novel coefficients for weighted-sum-of-gray-gases (WSGG) model are presented for Heptane, Methane, Methanol, MMA, Propane, Propylene, Toluene, and CO. Moreover, for soot, the spectral absorption coefficients were calculated assuming Rayleigh regime implementing the complex index of refraction obtained from the correlations of Chang and Charalampopoulos. The presented WSGG models were coupled with those of literature for CO2 and H2O by means of the superposition method. The models were first validated in several one-dimensional benchmarks representing various levels of inhomogeneous conditions in temperature, gas concentration and soot loading. Then, the WSGG models were employed in solving a three-dimensional case representing a Heptane pool fire. Using the time averaged 3-D CFD profiles, the WSGG models solved the spectral radiative heat transfer exhibiting excellent agreement with the results of line by line calculations in terms of total radiative heat flux and radiative heat source. Moreover, the emissivity charts were provided comparing the emissivity calculated by LBL calculations with those of the new WSGG models.

ACS Style

Hosein Sadeghi; Simo Hostikka; Guilherme Crivelli Fraga; Hadi Bordbar. Weighted-sum-of-gray-gases models for non-gray thermal radiation of hydrocarbon fuel vapors, CH4, CO and soot. Fire Safety Journal 2021, 103420 .

AMA Style

Hosein Sadeghi, Simo Hostikka, Guilherme Crivelli Fraga, Hadi Bordbar. Weighted-sum-of-gray-gases models for non-gray thermal radiation of hydrocarbon fuel vapors, CH4, CO and soot. Fire Safety Journal. 2021; ():103420.

Chicago/Turabian Style

Hosein Sadeghi; Simo Hostikka; Guilherme Crivelli Fraga; Hadi Bordbar. 2021. "Weighted-sum-of-gray-gases models for non-gray thermal radiation of hydrocarbon fuel vapors, CH4, CO and soot." Fire Safety Journal , no. : 103420.

Journal article
Published: 05 June 2021 in International Journal of Heat and Mass Transfer
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The large temperature difference between the radiation source and the condensed materials in fire scenarios, makes the general form of full spectrum correlated-k method unable to accurately model both absorption and emission within the condensed phase. In this paper, a new solution form for the FSCK method is presented which accurately accounts for both. This so-called “separated” form of FSCK method solves the contributions of medium emission and boundary's incident intensity separately by implementing two different reference temperatures. The advantages of the separated FSCK method is exhibited through three case studies using the transmissivity and radiative heat source calculated by high resolution line by line calculations as the benchmark. The test cases represent a layer of six different liquid and solid hydrocarbon fuels for which the various levels of irradiation from a radiating source is introduced by the temperature of its upper wall and an effective emissivity. The case studies provide a sensitivity analysis for the magnitude and spectral form of the irradiation at the boundary. The separated form of FSCK exhibits its best performance when the incident intensity and medium emission are in the same order of magnitude. Moreover, when the peak region of the boundary's spectral irradiation is closer to the peaks of the absorption coefficient spectrum of the condensed phase, the accuracy of both separated and classical FSCK solutions decreases, though, the separated solution still provides better accuracy.

ACS Style

Farid Alinejad; Hadi Bordbar; Simo Hostikka. Improving the modeling of spectral radiation penetration into the condensed materials with the separated full spectrum correlated-k method. International Journal of Heat and Mass Transfer 2021, 176, 121448 .

AMA Style

Farid Alinejad, Hadi Bordbar, Simo Hostikka. Improving the modeling of spectral radiation penetration into the condensed materials with the separated full spectrum correlated-k method. International Journal of Heat and Mass Transfer. 2021; 176 ():121448.

Chicago/Turabian Style

Farid Alinejad; Hadi Bordbar; Simo Hostikka. 2021. "Improving the modeling of spectral radiation penetration into the condensed materials with the separated full spectrum correlated-k method." International Journal of Heat and Mass Transfer 176, no. : 121448.

Journal article
Published: 28 April 2021 in Journal of Quantitative Spectroscopy and Radiative Transfer
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Refraction of electromagnetic waves at Fresnel interfaces, i.e. the boundaries between media with different refractive indices, is important not only in explaining many natural phenomena but also in radiation heat transfer in energy conversion and combustion systems, such as solar energy, spray cooling and combustion, and the evaporation of liquid fuels in pool fires. This paper presents a novel model for the efficient consideration of Fresnel interfaces in the Finite Volume Method-based solvers of thermal radiation. By conserving the transmitted radiative heat flux at the Fresnel interface, the new model accurately estimates the directional distribution of radiative intensities on the second side of the interface. To do so, a matrix of weighting coefficients is obtained, representing the transferred radiation energy from the control angles on the first side of the Fresnel interface into each control angle on the second side. To assess the accuracy of the novel ordinate weighting method (OWM), its predictions are compared with the analytical solutions that we obtained for one- and two-layer slabs with various combinations of absorption and scattering properties. The validations are shown for normalized heat flux and irradiation, reflectivity, transmissivity, and intensity. The predictions of the OWM show an excellent agreement with the results of the analytical solutions. Compared to Murthy’s pixelation method, the OWM method provides better accuracy with lower computational cost. Finally, the sensitivity of the OWM method to uniform and non-uniform directional discretizations, used in the finite volume solution of the radiative heat transfer, is investigated.

ACS Style

Farid Alinejad; Hadi Bordbar; Simo Hostikka. The ordinate weighting method for solving radiative heat transfer through a Fresnel interface. Journal of Quantitative Spectroscopy and Radiative Transfer 2021, 270, 107685 .

AMA Style

Farid Alinejad, Hadi Bordbar, Simo Hostikka. The ordinate weighting method for solving radiative heat transfer through a Fresnel interface. Journal of Quantitative Spectroscopy and Radiative Transfer. 2021; 270 ():107685.

Chicago/Turabian Style

Farid Alinejad; Hadi Bordbar; Simo Hostikka. 2021. "The ordinate weighting method for solving radiative heat transfer through a Fresnel interface." Journal of Quantitative Spectroscopy and Radiative Transfer 270, no. : 107685.

Journal article
Published: 31 March 2021 in International Journal of Heat and Mass Transfer
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The effect of total pressure of gas mixture is included in the development of new coefficients for the weighted-sum-of-gray-gases model (WSGG). The WSGG formulation previously reported by Bordbar et al. (combustion and Flame 2014, V. 161, pp. 2435–2445), which accounts for variations of molar fraction ratio of H2O to CO2, was employed here to obtain a new total pressure-dependent WSGG model. Hence, the new model includes both the effect of total pressure and variation of molar fraction ratio. High-resolution absorption spectra of gases produced by line-by-line (LBL) calculations using the HITEMP2010 spectral database are used to produce the total emissivity databases needed for the WSGG model development and also to produce the benchmark solution of one-dimensional slab problems used for validation of the new model. The performance of the new WSGG model is studied through several test cases representing various conditions of total pressure, inhomogeneity of temperature, concentration of gas species and molar fraction ratios. In all cases, the new model exhibits a good agreement with the LBL solutions. The new WSGG coefficients allow the model to efficiently solve the spectral thermal radiation in both sub- and super-atmospheric combustion systems.

ACS Style

Hadi Bordbar; Felipe R. Coelho; Guilherme C. Fraga; Francis H.R. França; Simo Hostikka. Pressure-dependent weighted-sum-of-gray-gases models for heterogeneous CO2-H2O mixtures at sub- and super-atmospheric pressure. International Journal of Heat and Mass Transfer 2021, 173, 121207 .

AMA Style

Hadi Bordbar, Felipe R. Coelho, Guilherme C. Fraga, Francis H.R. França, Simo Hostikka. Pressure-dependent weighted-sum-of-gray-gases models for heterogeneous CO2-H2O mixtures at sub- and super-atmospheric pressure. International Journal of Heat and Mass Transfer. 2021; 173 ():121207.

Chicago/Turabian Style

Hadi Bordbar; Felipe R. Coelho; Guilherme C. Fraga; Francis H.R. França; Simo Hostikka. 2021. "Pressure-dependent weighted-sum-of-gray-gases models for heterogeneous CO2-H2O mixtures at sub- and super-atmospheric pressure." International Journal of Heat and Mass Transfer 173, no. : 121207.

Journal article
Published: 25 July 2020 in Journal of Quantitative Spectroscopy and Radiative Transfer
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A numerical model is presented for spectral characteristics of radiation coming from a pool fire flame. The case studies are 1.75 m × 1.75 m and 2.5 m × 2.5 m Kerosene pool fires. Transient heat and mass transfer of the system was solved using a CFD model of a 4 m × 4 m × 5 m rectangular domain built in Fire Dynamic Simulator (FDS) with LES of turbulence and a two-step combustion reaction. Transient profiles of gas compositions, soot concentration and temperature along a line of sight of an imaginary sensor were collected from the CFD simulations, and instantaneous solutions of the thermal radiation along the line were calculated using high-resolution LBL spectral absorption profiles of combustion gases together with a model for soot absorption coefficient, based on spectrally dependant complex index of refraction. The transient spectra, consisting of numerous instantaneous intensity solutions, were then averaged and compared against the similar experimentally measured data. The line of sight and other settings of the model were carefully checked to be consistent with the experiments performed for the same system. The modelling results revealed the strong absorption effect of cold atmospheric gases while the emission peak of hot CO2 at ~2200 cm−1 in fire is still quite distinguishable from the spectral profile of hot blackbody even at 23 m away from the centre of the flame. This emission peak can be therefore used for detection of the fire. The spectral changes of the spectrum are explained and a sensitivity analysis is performed to study the effects of the sensor's distance from the pool, pool size, and modelling and operational conditions, such as relative humidity and radiative fraction.

ACS Style

Hadi Bordbar; Simo Hostikka; Pascal Boulet; Gilles Parent. Numerically resolved line by line radiation spectrum of large kerosene pool fires. Journal of Quantitative Spectroscopy and Radiative Transfer 2020, 254, 107229 .

AMA Style

Hadi Bordbar, Simo Hostikka, Pascal Boulet, Gilles Parent. Numerically resolved line by line radiation spectrum of large kerosene pool fires. Journal of Quantitative Spectroscopy and Radiative Transfer. 2020; 254 ():107229.

Chicago/Turabian Style

Hadi Bordbar; Simo Hostikka; Pascal Boulet; Gilles Parent. 2020. "Numerically resolved line by line radiation spectrum of large kerosene pool fires." Journal of Quantitative Spectroscopy and Radiative Transfer 254, no. : 107229.

Journal article
Published: 17 July 2020 in Fuel
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Gas-solid fluidized beds have heterogeneous flow structures, which affect the reactions due to uneven distribution and limited mixing of reactants. Some model approaches neglect these heterogeneous structures and use a homogeneous assumption instead. This work demonstrates the effects of neglecting this heterogeneity. Eulerian multiphase modeling is utilized to model fuel conversion in a fluidized bed riser. The effects of the chemical reactivity of the fuel, the amount of fuel in the reactor and the fluidization regime are investigated. The model data are time- and space-averaged into 1D results and compared with a 1D modelling which assumes homogeneous distributions in radial direction. Based on this study, the negligence of the heterogeneous flow structures leads to significantly higher local and overall reaction rates and conversion in the system.

ACS Style

Markku Nikku; Hadi Bordbar; Kari Myöhänen; Timo Hyppänen. Effects of heterogeneous flow on carbon conversion in gas-solid circulating fluidized beds. Fuel 2020, 280, 118623 .

AMA Style

Markku Nikku, Hadi Bordbar, Kari Myöhänen, Timo Hyppänen. Effects of heterogeneous flow on carbon conversion in gas-solid circulating fluidized beds. Fuel. 2020; 280 ():118623.

Chicago/Turabian Style

Markku Nikku; Hadi Bordbar; Kari Myöhänen; Timo Hyppänen. 2020. "Effects of heterogeneous flow on carbon conversion in gas-solid circulating fluidized beds." Fuel 280, no. : 118623.

Journal article
Published: 30 June 2020 in International Journal of Heat and Mass Transfer
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In this paper, full spectrum correlated k-distribution (FSCK) models are developed for several liquid fuels including decane, ethanol, ethylene glycol, heptane, and toluene. The models were built using high-resolution absorption spectra, collected from the literature. To validate the novel FSCK models, they were used to solve radiative heat transfer within liquid pools assuming three temperature profiles (i.e. constant temperature, linear and nonlinear temperature profiles) and the calculated transmissivity and radiative heat source of FSCK were compared with those of using high resolution absorption spectra and the gray models implementing Planck mean absorption coefficient. The sensitivity analysis was performed for the accuracy of the FSCK results with number of quadrature points for different fuels. Using seven quadrature points for FSCK model has been found to be sufficient for providing good accuracy of spectral radiative heat transfer within the liquid fuels with a reasonable computational cost. Moreover, we studied the effect of the reference temperature used in FSCK model and found out that for the pool fire scenario, the FSCK provides its best accuracy if an equivalent temperature representing the radiation feedback from the flame is used as the reference temperature. Comparison of computational costs of high-resolution spectral radiation calculations and FSCK method revealed a significant computational gain by use of FSCK model.

ACS Style

Farid Alinejad; Hadi Bordbar; Simo Hostikka. Development of full spectrum correlated k-model for spectral radiation penetration within liquid fuels. International Journal of Heat and Mass Transfer 2020, 158, 119990 .

AMA Style

Farid Alinejad, Hadi Bordbar, Simo Hostikka. Development of full spectrum correlated k-model for spectral radiation penetration within liquid fuels. International Journal of Heat and Mass Transfer. 2020; 158 ():119990.

Chicago/Turabian Style

Farid Alinejad; Hadi Bordbar; Simo Hostikka. 2020. "Development of full spectrum correlated k-model for spectral radiation penetration within liquid fuels." International Journal of Heat and Mass Transfer 158, no. : 119990.

Journal article
Published: 14 March 2020 in Energy
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A numerical framework was carefully developed to simulate the combustion of heavy-fuel-oil (HFO) in a large-scale boiler. The present numerical solutions were compared with the measured data of a laboratory benchmark test and on-site operational data of the chosen HFO-fired boiler. Next, the developed framework was used to perform sensitivity analyses aiming to reduce the NO emission from the HFO-fired boiler without any adverse effect on its combustion performance. Practically, this study focused on re-adjustments of 24 working burners, which could control combustion in the HFO-fired boiler. The early outcome showed that the boiler NO emission and its combustion performance could be controlled via proper adjustments of air distributions within the three burners’ stages and the swirl intensity. Although bigger mean droplet sizes and higher injection velocities reduced the NO emission considerably, it adversely led to much lower boiler’s combustion efficiency. The present study eventually arrived at an optimal adjustment for the burners by reconsideration of the air distributions within the three burners’ stages, the flame swirl intensity magnitude, and the fuel injection quality. The achieved optimal adjustment reduced the amount of NO emission by 30%, while the combustion efficiency would remain unaffected.

ACS Style

Masoud Darbandi; Ali Fatin; Hadi Bordbar. Numerical study on NOx reduction in a large-scale heavy fuel oil-fired boiler using suitable burner adjustments. Energy 2020, 199, 117371 .

AMA Style

Masoud Darbandi, Ali Fatin, Hadi Bordbar. Numerical study on NOx reduction in a large-scale heavy fuel oil-fired boiler using suitable burner adjustments. Energy. 2020; 199 ():117371.

Chicago/Turabian Style

Masoud Darbandi; Ali Fatin; Hadi Bordbar. 2020. "Numerical study on NOx reduction in a large-scale heavy fuel oil-fired boiler using suitable burner adjustments." Energy 199, no. : 117371.

Journal article
Published: 13 March 2020 in Journal of Quantitative Spectroscopy and Radiative Transfer
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Oxy-fuel combustion is a modern carbon capture and storage (CCS) technique that improves the combustion process and reduces the environmental penalty of many combustion systems. Evidently, the accurate radiative calculation of oxy-fuel combustion is very important to arrive at more improved combustion system designs with less environmental drawbacks. In the present study, a small scale unconfined turbulent bluff-body flame is numerically simulated to calculate the gas radiative properties using three different approaches of ignoring radiation, applying a modified version of the weighted sum of gray gases (WSGG) model, and employing the spectral line based weighted sum of gray gases (SLW) model. First, the selected bluff-body flame is validated against experimental data. The early outcome is that the simulation results of three chosen approaches are very close if there is no oxygen enrichment. Next, the effect of oxygen enrichment is carefully investigated imposing the aforementioned spectral radiation approaches. The achieved results indicate that the predicted gas temperature becomes more sensitive to the implemented radiative approach as the oxygen concentration in the oxidizer increases. In very high oxygen enrichment case, the gas temperature predicted by SLW model shows up to 155 K differences with that of ignoring radiation approach. The simulation results also show that the oxygen enrichment would raise the CO2 and H2O volume fractions in the flame zone. Therefore, the non-grayness of gases becomes more significant in such cases and the accurate radiative calculation becomes more essential. This is investigated carefully in this study.

ACS Style

M. Darbandi; M.B. Barezban; A. Fatin; Hadi Bordbar. Effect of oxygen enrichment in spectral thermal radiation in an unconfined turbulent bluff-body flame. Journal of Quantitative Spectroscopy and Radiative Transfer 2020, 247, 106958 .

AMA Style

M. Darbandi, M.B. Barezban, A. Fatin, Hadi Bordbar. Effect of oxygen enrichment in spectral thermal radiation in an unconfined turbulent bluff-body flame. Journal of Quantitative Spectroscopy and Radiative Transfer. 2020; 247 ():106958.

Chicago/Turabian Style

M. Darbandi; M.B. Barezban; A. Fatin; Hadi Bordbar. 2020. "Effect of oxygen enrichment in spectral thermal radiation in an unconfined turbulent bluff-body flame." Journal of Quantitative Spectroscopy and Radiative Transfer 247, no. : 106958.

Journal article
Published: 13 January 2020 in Journal of Heat Transfer
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Nongray gas radiation calculations are conducted for four three-dimensional benchmarks using line-by-line (LBL) integration with the up-to-date high-resolution spectroscopic database HITEMP 2010. The radiative transfer equation (RTE) is solved using the finite volume method (FVM) over each wavenumber interval of the spectrum. A detailed mesh quality analysis assured the mesh independence of the solution. Accurate results for distributions of volumetric radiative heat source term and wall radiative heat flux are provided for four cases: (i) an isothermal pure water vapor medium at 1000 K; (ii) an isothermal and nonhomogeneous H2O–N2 mixture at 1000 K; (iii) a nonisothermal and homogeneous CO2–H2O–N2 mixture; and (iv) a nonisothermal and nonhomogeneous CO2–H2O–N2 mixture. These data can be useful to assess the accuracy of gas radiative property models.

ACS Style

Guilherme C. Fraga; Hadi Bordbar; Simo Hostikka; Francis H. R. França. Benchmark Solutions of Three-Dimensional Radiative Transfer in Nongray Media Using Line-by-Line Integration. Journal of Heat Transfer 2020, 142, 1 .

AMA Style

Guilherme C. Fraga, Hadi Bordbar, Simo Hostikka, Francis H. R. França. Benchmark Solutions of Three-Dimensional Radiative Transfer in Nongray Media Using Line-by-Line Integration. Journal of Heat Transfer. 2020; 142 (3):1.

Chicago/Turabian Style

Guilherme C. Fraga; Hadi Bordbar; Simo Hostikka; Francis H. R. França. 2020. "Benchmark Solutions of Three-Dimensional Radiative Transfer in Nongray Media Using Line-by-Line Integration." Journal of Heat Transfer 142, no. 3: 1.

Journal article
Published: 09 December 2019 in International Communications in Heat and Mass Transfer
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All published weighted sum of gray gases models (WSGGM) were either developed for a limited number of molar fraction ratios, MR, or include MR as a variable in their formulations. Either way, they are not able to adequately support moisture-rich regions of combustion environments, such as the outer regions of unwanted fires, fires during water-based suppression, and some air-injection regions of furnaces. In this article, we provide an extension to a previously published WSGGM by coupling it to a new accurate set of WSGGM coefficients for pure carbon dioxide and water vapor. The coupling follows a linear interpolation methodology, which is justified by a detailed analysis of the line-by-line (LBL) absorption spectra and by plotting the total emissivity of CO2 ‐ H2O mixtures with large and small values of MR for various temperatures and path lengths. The proposed model is discussed and validated in four benchmarks, using a solution obtained by LBL integration as reference. The results indicate that, while the previously available WSGGMs either have excessive computational costs or yield inaccurate results in the regions of large MR, the new model can be safely used for all gas compositions in a computationally efficient manner.

ACS Style

Hadi Bordbar; Guilherme Fraga; Simo Hostikka. An extended weighted-sum-of-gray-gases model to account for all CO2 ‐ H2O molar fraction ratios in thermal radiation. International Communications in Heat and Mass Transfer 2019, 110, 104400 .

AMA Style

Hadi Bordbar, Guilherme Fraga, Simo Hostikka. An extended weighted-sum-of-gray-gases model to account for all CO2 ‐ H2O molar fraction ratios in thermal radiation. International Communications in Heat and Mass Transfer. 2019; 110 ():104400.

Chicago/Turabian Style

Hadi Bordbar; Guilherme Fraga; Simo Hostikka. 2019. "An extended weighted-sum-of-gray-gases model to account for all CO2 ‐ H2O molar fraction ratios in thermal radiation." International Communications in Heat and Mass Transfer 110, no. : 104400.

Journal article
Published: 17 November 2018 in Applied Energy
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To develop an efficient and practical spectral radiation model for CFD simulations, a banded approach is proposed for a mixture of carbon dioxide and water vapor in varying thermodynamic states. Using a previously reported band dividing scheme, a statistical narrow band model is implemented to provide gray band absorption coefficient databases. The databases were then approximated by certain simple correlations, which can be readily used in CFD calculations of RTE solvers. The correlations were validated in several 1D and 3D benchmarks representing various combustion conditions. The accuracy and CPU cost of the proposed banded approach were studied and compared with those of other similar methods. The results demonstrated that the new approach is an efficient and accurate method that can be conveniently applied in a commercial CFD code for spectral radiation; moreover, it can handle non-gray walls. As a practical case study, the proposed approach was used to simulate radiative heat transfer within a back pass channel of a CFB boiler. The effect of combustion scenarios, i.e., air- and oxygen-fired, boiler load, inlet flow conditions, and wall material, was analyzed by the CFD model. The predictions of two different RTE solvers, i.e., P1 and DO, and the required CPU time were compared for gray and non-gray models.

ACS Style

Hadi Bordbar; Alexander Maximov; Timo Hyppänen. Improved banded method for spectral thermal radiation in participating media with spectrally dependent wall emittance. Applied Energy 2018, 235, 1090 -1105.

AMA Style

Hadi Bordbar, Alexander Maximov, Timo Hyppänen. Improved banded method for spectral thermal radiation in participating media with spectrally dependent wall emittance. Applied Energy. 2018; 235 ():1090-1105.

Chicago/Turabian Style

Hadi Bordbar; Alexander Maximov; Timo Hyppänen. 2018. "Improved banded method for spectral thermal radiation in participating media with spectrally dependent wall emittance." Applied Energy 235, no. : 1090-1105.

Conference paper
Published: 14 November 2018 in Journal of Physics: Conference Series
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The radiative transfer mechanisms in a volatile hydrocarbon pool fire were investigated by solving the transmittance of infrared radiation through fuel (n-heptane) layers of different depths. The incoming radiation was assumed to have the same relative amounts of different wavelengths as a spectrum obtained experimentally for a 2 meter pool fire, and the transmittances were calculated by integrating either the single-ray Lambert-Beer formula, the two-flux (Schuster-Schwarzschild) method solution or the analytical plane-parallel monochromatic/gray solution of the radiative transfer equation over wavelength, using the liquid absorption coefficients from several sources. The obtained transmittances were compared to earlier heat flux measurements, and the possibility of calculating them with significantly less computation time by using a k-distribution method was investigated. The results managed to replicate the measured heat flux values at depths over 1 mm in the liquid with reasonable accuracy, and the use of the k-distribution, more known and used in gas phase thermal radiation calculations, significantly speeds up the calculations.

ACS Style

Teemu Isojärvi; Hadi Bordbar; Simo Hostikka. Calculation of radiation transmittance through n-heptane in a pool fire. Journal of Physics: Conference Series 2018, 1107, 042002 .

AMA Style

Teemu Isojärvi, Hadi Bordbar, Simo Hostikka. Calculation of radiation transmittance through n-heptane in a pool fire. Journal of Physics: Conference Series. 2018; 1107 (4):042002.

Chicago/Turabian Style

Teemu Isojärvi; Hadi Bordbar; Simo Hostikka. 2018. "Calculation of radiation transmittance through n-heptane in a pool fire." Journal of Physics: Conference Series 1107, no. 4: 042002.

Journal article
Published: 30 August 2018 in International Journal of Heat and Mass Transfer
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The radiative heat transfer in a volatile hydrocarbon pool fire was investigated by obtaining the transmittance of infrared radiation through fuel (n-heptane) layers of different depths. The incident radiation spectrum was assumed to be either the same as a spectrum obtained experimentally for a 2 meter pool fire, or to be a Planck distribution corresponding to the approximate flame temperature. The transmittances were calculated by integrating either the single-ray Lambert–Beer formula, the two-flux method or the analytical plane-parallel monochromatic/gray solution of the radiative transfer equation over wavelength, using the liquid spectral absorption coefficients found in literature. The obtained results are validated against earlier measurements, and the possibility of calculating them with significantly less computation time by using a k-distribution method was investigated. The results managed to replicate the measured heat flux values in the liquid with a fractional error of only about 5% being attainable even with a 3-point quadrature method. The use of the k-distribution, more known and used in gas phase thermal radiation calculations, significantly speeds up the calculations. It was found out that in the calculation of total transmitted fractions of radiation, the flame spectrum can be approximated with a Planck distribution of an appropriate temperature.

ACS Style

Teemu Isojärvi; Hadi Bordbar; Simo Hostikka. Spectrally resolved calculation of thermal radiation penetration into liquid n-heptane in pool fires. International Journal of Heat and Mass Transfer 2018, 127, 1101 -1109.

AMA Style

Teemu Isojärvi, Hadi Bordbar, Simo Hostikka. Spectrally resolved calculation of thermal radiation penetration into liquid n-heptane in pool fires. International Journal of Heat and Mass Transfer. 2018; 127 ():1101-1109.

Chicago/Turabian Style

Teemu Isojärvi; Hadi Bordbar; Simo Hostikka. 2018. "Spectrally resolved calculation of thermal radiation penetration into liquid n-heptane in pool fires." International Journal of Heat and Mass Transfer 127, no. : 1101-1109.

Journal article
Published: 14 July 2018 in International Journal of Heat and Mass Transfer
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The banded approach or box model is a method to include the non-grayness of combustion gases in radiation heat transfer calculations. However, the determination of the correct limits for the bands and the effective band absorption coefficients is still something of a black art. In this study, the line by line (LBL) spectral absorption coefficient profile has been implemented to obtain the effective number of bands, and bands’ limits for pure H2O, pure CO2 and a H2O-CO2 gas mixture. A mathematical technique has been used to smooth the LBL profiles of pure gases in atmospheric pressure in order to be used for identifying the gray bands. The optimization for selecting the bands is done by analyzing the radiative heat transfer in several one-dimensional benchmarks. After obtaining the optimal band dividing scheme, a set of correlations for the pressure based gray band absorption coefficient of pure gases is found by integrating the line by line spectral absorption coefficient weighted by the corresponding black body intensity along the bands. In contrary to the previous similar works, by using the LBL data for pressure based gray absorption coefficient of the bands, the current correlations are independent of gas concentration and path length. The present approach could successfully support the non-gray walls. The method has been validated using several benchmarks and exhibited comparable accuracy with other available models.

ACS Style

Hadi Bordbar; Timo Hyppänen. Line by line based band identification for non-gray gas modeling with a banded approach. International Journal of Heat and Mass Transfer 2018, 127, 870 -884.

AMA Style

Hadi Bordbar, Timo Hyppänen. Line by line based band identification for non-gray gas modeling with a banded approach. International Journal of Heat and Mass Transfer. 2018; 127 ():870-884.

Chicago/Turabian Style

Hadi Bordbar; Timo Hyppänen. 2018. "Line by line based band identification for non-gray gas modeling with a banded approach." International Journal of Heat and Mass Transfer 127, no. : 870-884.

Journal article
Published: 01 March 2015 in Applied Thermal Engineering
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ACS Style

Mohammad Hadi Bordbar; Timo Hyppänen. The correlation based zonal method and its application to the back pass channel of oxy/air-fired CFB boiler. Applied Thermal Engineering 2015, 78, 351 -363.

AMA Style

Mohammad Hadi Bordbar, Timo Hyppänen. The correlation based zonal method and its application to the back pass channel of oxy/air-fired CFB boiler. Applied Thermal Engineering. 2015; 78 ():351-363.

Chicago/Turabian Style

Mohammad Hadi Bordbar; Timo Hyppänen. 2015. "The correlation based zonal method and its application to the back pass channel of oxy/air-fired CFB boiler." Applied Thermal Engineering 78, no. : 351-363.

Journal article
Published: 01 February 2015 in Applied Thermal Engineering
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ACS Style

Mohammad Hadi Bordbar; Kari Myöhänen; Timo Hyppänen. Coupling of a radiative heat transfer model and a three-dimensional combustion model for a circulating fluidized bed furnace. Applied Thermal Engineering 2015, 76, 344 -356.

AMA Style

Mohammad Hadi Bordbar, Kari Myöhänen, Timo Hyppänen. Coupling of a radiative heat transfer model and a three-dimensional combustion model for a circulating fluidized bed furnace. Applied Thermal Engineering. 2015; 76 ():344-356.

Chicago/Turabian Style

Mohammad Hadi Bordbar; Kari Myöhänen; Timo Hyppänen. 2015. "Coupling of a radiative heat transfer model and a three-dimensional combustion model for a circulating fluidized bed furnace." Applied Thermal Engineering 76, no. : 344-356.

Journal article
Published: 01 September 2014 in Combustion and Flame
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Mohammad Hadi Bordbar; Gabriel Węcel; Timo Hyppänen. A line by line based weighted sum of gray gases model for inhomogeneous CO2–H2O mixture in oxy-fired combustion. Combustion and Flame 2014, 161, 2435 -2445.

AMA Style

Mohammad Hadi Bordbar, Gabriel Węcel, Timo Hyppänen. A line by line based weighted sum of gray gases model for inhomogeneous CO2–H2O mixture in oxy-fired combustion. Combustion and Flame. 2014; 161 (9):2435-2445.

Chicago/Turabian Style

Mohammad Hadi Bordbar; Gabriel Węcel; Timo Hyppänen. 2014. "A line by line based weighted sum of gray gases model for inhomogeneous CO2–H2O mixture in oxy-fired combustion." Combustion and Flame 161, no. 9: 2435-2445.

Feature articles
Published: 01 January 2013 in Heat Transfer Engineering
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In this article, a numerical method for the simulation of radiative heat transfer is presented. The multiscale radiative exchange method (MREM) calculates the radiative source terms in a mesh structure that is coarser than the structures that are typically used in computational fluid flow calculations. To consider the effects of smaller scales on the overall predictions of the model, two dimensionless exchange factors are defined. An accurate simulation of self-extinction and rescattering in coarse volume cells is achieved if the exchange factors are used in the radiative energy balance. According to the location and size of each pair of coarse cells, integration elements of different sizes are used for the calculation of exchange factors. Therefore, the MREM takes into account the effects of a wide range of optical scales in its prediction. On the other hand, the MREM considers the radiative interaction between all of the geometric points in a quick and accurate manner. To improve the accuracy and the performance of the model, a mesh size analysis is performed and some sizes for various mesh structures are suggested for use in the MREM calculations. The model is verified by comparing it against some benchmarks. The predictions and computational cost of the method are compared to the results of other numerical methods, and the effects of different spatial scales on the accuracy of the method are addressed.

ACS Style

Mohammad Hadi Bordbar; Timo Hyppänen. Multiscale Numerical Simulation of Radiation Heat Transfer in Participating Media. Heat Transfer Engineering 2013, 34, 54 -69.

AMA Style

Mohammad Hadi Bordbar, Timo Hyppänen. Multiscale Numerical Simulation of Radiation Heat Transfer in Participating Media. Heat Transfer Engineering. 2013; 34 (1):54-69.

Chicago/Turabian Style

Mohammad Hadi Bordbar; Timo Hyppänen. 2013. "Multiscale Numerical Simulation of Radiation Heat Transfer in Participating Media." Heat Transfer Engineering 34, no. 1: 54-69.