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B J Matkowsky - One of the best experts on this subject based on the ideXlab platform.
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maximal energy accumulation in a superadiabatic filtration combustion wave
Combustion and Flame, 1999Co-Authors: A P Aldushin, I E Rumanov, B J MatkowskyAbstract:Abstract The ability of energy to be concentrated in the front of a coflow (forward) filtration combustion (FC) wave in a porous solid is analyzed. Combustion is due to the exothermic reaction between the fuel in the porous solid and oxidizer contained in the Gas flowing through the solid. Coflow filtration refers to the fact that the Gaseous oxidizer flows to the reaction site through the product region, so that energy accumulation occurs due to the recovery of heat stored in the product. The Gas flowing through the burned region transfers heat from the product region to the reaction site, and, even more importantly to the unburned fuel region. This results, primarily in preheating the fresh mixture, and consequently in strong overheating of the reaction zone where the temperature far exceeds the thermodynamic combustion temperature. This is the superadiabatic effect. The paper focuses on the mode of FC wave propagation corresponding to the most pronounced superadiabatic effect. We show that for this case, in the absence of heat losses, the temperature grows as l where l is the distance traveled by the reaction front. The ratio lT/l, where lT is the width of the high temperature zone into which the energy is gathered, decreases as l−1/2, showing that the efficiency of energy accumulation increases as the wave propagates. In addition, it was previously shown that there exist both reaction leading and reaction trailing traveling wave (TW) structures, which occur when a parameter δ, which is proportional to the ratio of the specific heats of the Gas and solid and to the ratio of the initial concentrations of the solid fuel and the Gaseous oxidizer, is greater than or less than 1, respectively. The case δ = 1 which separates the two structures corresponds to the most pronounced superadiabatic effect, and to a combustion temperature Tb which is infinite. Thus, the TW analysis breaks down when δ = 1, indicating that TW solutions are no longer possible. For this case (δ = 1) we therefore investigate the full time-dependent problem to determine the structure of the FC wave, to determine whether Tb actually becomes infinite and if so, its rate of approach to infinity. Though the combustion temperature in a FC wave experiment is, in fact, bounded, the ratio (Tb − T0)/q may be extremely large. Here, q, which characterizes the effect of the caloricity of the medium, is small when either the amount of fuel in the solid or the heat release in the reaction, is small. Thus, for any given q, no matter how small, FC wave propagation can always be realized by enhancing the energy accumulation. Heat losses to the environment bound the temperature growth at a level depending on the rate of heat exchange with the environment and the rate of Incoming Gas flux. Increasing the heat loss above the critical level causes extinction. The extinction limit may be overcome by increasing the Gas influx.
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forced forward smolder combustion
Combustion and Flame, 1996Co-Authors: D A Schult, B J Matkowsky, V A Volpert, A C FernandezpelloAbstract:Abstract We consider porous cylindrical samples closed to the surrounding environment except at the ends, with Gas forced into the sample through one of the ends. A smolder wave is initiated at that end and propagates in the same direction as the flow of the Gas. We employ asymptotic methods to find smolder wave solutions with two different structures. Each structure has two interior layers, i.e., regions of relatively rapid variation in temperature separated by longer regions in which the temperature is essentially constant. One layer is that of the combustion reaction, while the other is due to heat transfer between the solid and the Gas. The layers propagate with constant, though not necessarily the same, velocity, and are separated by a region of constant high temperature. A so-called reaction leading wave structure occurs when the velocity of the combustion layer exceeds that of the heat transfer layer, while a so-called reaction trailing wave structure is obtained when the combustion layer is slower than the heat transfer layer. The former (latter) occurs when the Incoming oxygen concentration is sufficiently high (low). Reaction trailing structures allow for the possibility of quenching if the Gas mass influx is large enough; that is, incomplete conversion can occur due to cooling of the reaction by the Incoming Gas. For each wave structure there exist stoichiometric, and kinetically controlled solutions in which the smolder velocity is determined, respectively, by the rate of oxygen supply to the reaction site and by the rate of consumption in the reaction, i.e., by the kinetic rate. Stoichiometric (kinetically controlled) solutions occur when the Incoming Gas flux is sufficiently low (high). For each of the four solution types, we determine analytical expressions for the propagation velocities of the two layers, the burning temperature, and the final degree of solid conversion. We also determine analytical expressions for the spatial profiles of temperature, Gas flux, and oxygen concentration. Gravitational forces are considered and are shown to have a minimal effect provided the ambient pressure is large compared to the hydrostatic pressure drop. The solutions obtained provide qualitative theoretical descriptions of various experimental observations of forward smolder. In particular, the reaction trailing stoichiometric solution corresponds to the experimental observations of Ohlemiller and Lucca, while the reaction leading stoichiometric solution corresponds to the experimental observations of Torero et al.
Endah Palupi Aisyah - One of the best experts on this subject based on the ideXlab platform.
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SIMULASI ALIRAN Gas-SOLID-LIQUID DALAM BIOREATOR MEMBRAN TERENDAM
'University of Pembangunan Nasional Veteran Jawa Timur', 2012Co-Authors: Endah Palupi AisyahAbstract:Hydrodynamics characteristic for the mixing of Gas-solid-liquid in membrane bioreactorsubmerged (MBRs) and its influence on mass transfer was studied computationally at various solid concentration, Incoming Gas rate, and the baffle distance. Computational method was conducted by using software GAMBIT 2.1.6. for the making of the grid which represents the calculation domain and conduct the simulation using CFD software FLUENT commercial code 6.2.16. The calculation result was recorded after the iteration reach the certain convergence level.Multiphase flow in reactor was simulated with mixture model, while to model the turbulence characteristic of the flow standard k-ε model was used. The geometric system studied is bioreactor in the form of box with flat bottom, 2 baffles, submerged hollow fiber membrane and air passage at the bottom of the reactor. For the membrane modeling, it is used two approachesthat is membrane as black box and membrane as porous media. The liquid used is water, and the solid is activated sludge, and air acts as Gas phase. The result indicates that Gas-solid-liquid system with the nearest baffle location from the membrane cause, the liquid dispersion process goes faster, so that fluid in the tank can be mixed perfectly and it can increase the Gas-liquid mass transfer rate and the flux at MBRs.The increase of the solid concentration does not significantly affect the change of Gasliquid mass transfer rate and flux through the membrane, but the increase of air flow rate can increase the Gas-liquid mass transfer and the flux. Porous media approach give the prediction of the Gas hold up distribution more over all than black box approach. The position of baffle 9 cm from tank wall is the best position viewed from the balance between the of air flow with the circulating fluid flow. Considered from the solid distribution, double inlet MBRs is better compared to that of single inlet. Flux obtained does not show significant difference. From both approaches of the membrane model, membrane model as porous media give the simulation results closer to the experimental data.Keyword:MBRs, hydrodynamic, simulation CFD, Gas-solid-liqui
Palupi A. E. - One of the best experts on this subject based on the ideXlab platform.
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Simulasi Aliran Gas-solid-liquid Dalam Bioreator Membran Terendam
Universitas Pembangunan Nasional "Veteran" Jawa Timur, 2009Co-Authors: Palupi A. E.Abstract:Hydrodynamics characteristic for the mixing of Gas-solid-liquid in membrane bioreactorsubmerged (MBRs) and its influence on mass transfer was studied computationally at various solid concentration, Incoming Gas rate, and the baffle distance. Computational method was conducted by using software GAMBIT 2.1.6. for the making of the grid which represents the calculation domain and conduct the simulation using CFD software FLUENT commercial code 6.2.16. The calculation result was recorded after the iteration reach the certain convergence level.Multiphase flow in reactor was simulated with mixture model, while to model the turbulence characteristic of the flow standard k-ε model was used. The geometric system studied is bioreactor in the form of box with flat bottom, 2 baffles, submerged hollow fiber membrane and air passage at the bottom of the reactor. For the membrane modeling, it is used two approachesthat is membrane as black box and membrane as porous media. The liquid used is water, and the solid is activated sludge, and air acts as Gas phase. The result indicates that Gas-solid-liquid system with the nearest baffle location from the membrane cause, the liquid dispersion process goes faster, so that fluid in the tank can be mixed perfectly and it can increase the Gas-liquid mass transfer rate and the flux at MBRs.The increase of the solid concentration does not significantly affect the change of Gasliquid mass transfer rate and flux through the membrane, but the increase of air flow rate can increase the Gas-liquid mass transfer and the flux. Porous media approach give the prediction of the Gas hold up distribution more over all than black box approach. The position of baffle 9 cm from tank wall is the best position viewed from the balance between the of air flow with the circulating fluid flow. Considered from the solid distribution, double inlet MBRs is better compared to that of single inlet. Flux obtained does not show significant difference. From both approaches of the membrane model, membrane model as porous media give the simulation results closer to the experimental data
Changho Park - One of the best experts on this subject based on the ideXlab platform.
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effects of Gas flow rate inlet concentration and temperature on biofiltration of volatile organic compounds in a peat packed biofilter
Journal of Bioscience and Bioengineering, 2002Co-Authors: Inkil Yoon, Changho ParkAbstract:The effects of Incoming Gas concentration, empty bed residence time (EBRT), and column temperature on the removal efficiency of volatile organic compounds (isoprene, dimethyl sulfide, chloroform, benzene, trichloroethylene, toluene, m-xylene, o-xylene and styrene) were studied for 101 d in a biofilter comprising two glass columns (I.D. 5.0 cm × height 62 cm) packed with peat. At an EBRT of 3 min the removal efficiency increased up to 90% 34 d after start up at both 25°C and 45°C when the Incoming Gas concentration was raised stepwise to 65 g · m−3. When the Incoming Gas concentration increased to 83 g · m−3, the removal efficiency was 93% at 25°C, but dropped to 74% at 45°C. At an Incoming Gas concentration of 92 g · m−3 and an EBRT of 1.5 min, the removal efficiencies were 91% and 94% at 25°C and 32°C, respectively. However, at 1 min of EBRT, the removal efficiencies decreased to 68% and 81% at 25°C and 32°C, respectively. The removal rate per unit time and per unit volume of the biofilter was proportional to the Incoming Gas rate up to 3483 g VOC · m−3 · h−1. Further increase of the Incoming Gas rate lowered the removal rate as compared to that predicted by the proportionality. The maximum removal rate was 3977 g · m−3 · h−1 at 32°C. At an EBRT of 1.5 min, the removal efficiency was highest for isoprene (93%), and lowest for chloroform (84%). Aromatic compounds (benzene, toluene, and xylene) were removed by 93–94%. The cell concentration increased 100-fold from the initial value, and reached 1.12 × 108 cells · (g of dry peat)−1. At 32°C, 67% of the Incoming VOC was removed in the first quarter of the column.
Minking K Chyu - One of the best experts on this subject based on the ideXlab platform.
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optimization of the hole distribution of an effusively cooled surface facing non uniform Incoming temperature using deep learning approaches
International Journal of Heat and Mass Transfer, 2019Co-Authors: Li Yang, Minking K ChyuAbstract:Abstract External cooling technologies such as transpiration cooling and effusion cooling are ideal thermal protection strategies for hot section components. Conventional cooling structures were not capable to adaptively fit non-uniform Incoming temperature loads due to the limit in modelling and designing tools. The present study established an optimization workflow to adjust the hole distribution of an effusively cooled porous plate. A Conditional Generative Adversarial Neural Network model was developed to model the high dimensional and non-linear mapping between the surface profile and the surface temperature of a series of effusively cooled plates. Computational Fluid Dynamics was utilized to provide data samples for the training of the model. With careful testing and validation of the trained model, the neural network model was integrated with Genetic Algorithms to search for optimal structures that can uniformly cool the plate to a proper temperature level. Results obtained from the modeling efforts indicated a good capability of the neural network model to reconstruct the cooling effectiveness distribution on the external surface of the porous plates. Integrated with this low cost machine learning model, the GA approach successfully identified several optimized structures which fit well with the thermal loads induced by non-uniform Incoming Gas temperate. Surface temperature variation of the porous plates was reduced by around 50% as compared to the structure with a regular hole array. These attempts of introducing deep learning to external cooling in the present study were successful and future work could further focus on generalization of the modelling and enhancement of the robustness of the optimization approach.
