Nanoparticles of zeolitic imidazolate framework-7 (nZIF-7) were blended with poly(ether imide) (P... more Nanoparticles of zeolitic imidazolate framework-7 (nZIF-7) were blended with poly(ether imide) (PEI) to fabricate a new mixed-matrix membrane (nZIF-7/PEI). nZIF-7 was chosen in order to demonstrate the power of postsynthetic modification (PSM) by linker exchange of benzimidazolate to benzotriazolate for tuning the permeability and selectivity properties of a resulting membrane (PSM-nZIF-7/PEI). These two new membranes were subjected to constant volume, variable pressure gas permeation measurements (H 2 , N 2 , O 2 , CH 4 , CO 2 , C 2 H 6 , and C 3 H 8), in which unique gas separation behavior was observed when compared to the pure PEI membrane. Specifically, the nZIF-7/PEI membrane exhibited the highest selectivities for CO 2 /CH 4 , CO 2 /C 2 H 6 , and CO 2 /C 3 H 8 gas pairs. Furthermore, PSM-nZIF-7/PEI membrane displayed the highest permeabilities, which resulted in H 2 /CH 4 , N 2 /CH 4 , and H 2 /CO 2 permselectivities that are remarkably well-positioned on the Robeson upper bound curves, thus, indicating its potential applicability for use in practical gas purifications.
ABSTRACT Reasonably high oxygen permeation fluxes, similar to 4 x 10(-2) mu mol.cm(-2).s(-1), wer... more ABSTRACT Reasonably high oxygen permeation fluxes, similar to 4 x 10(-2) mu mol.cm(-2).s(-1), were obtained from surface decoration with La0.8Sr0.2CoO3-delta (LSC113) or LaSrCoO4 +/-delta (LSC214) on La0.8Sr0.2Ga0.8Mg0.115Co0.085O3-delta (LSGMC) and Ce0.8Sm0.2O2-delta (SDC) membranes at 700 degrees C. Promoting surface exchange kinetics at the feed side of LSGMC and SDC membranes, which was found rate-limiting, is needed to further enhance oxygen permeation of these membranes. This work demonstrates the possibility of reducing the amount of noble metal usage for membranes based on the concept of short-circuited ion conductors and shows promise for the development of noble-metal-free permeation membranes.
Various nutritional values are more influenced by cooking than others. This study compared the ef... more Various nutritional values are more influenced by cooking than others. This study compared the effects of microwave heating with conventional cooking method of fresh Potato (Solanum tuberosum). The moisture and ash content in raw potato were 76.60% and 0.40%, respectively. After conventional cooking moisture and ash content were 78.00% and 0.50%, respectively and after microwave heating it saw the values were 77.20% and 0.60%, respectively. The fat and carbohydrate content in raw potato were 0.70% and 20.46%, respectively. After conventional cooking those values were 0.80% and 19.40%, respectively and in microwave heating it showed the values were 0.50% and 20.08%, respectively. Total protein content was also changed by those cooking methods. In microwave heating it reduced the vitamin-C content to some extent but the conventional cooking completely destroyed the vitamin-C contents.
This paper presents a computational study of an energy-efficient technique for post-combustion CO... more This paper presents a computational study of an energy-efficient technique for post-combustion CO 2 capture using novel material, namely, Mg-MOF-74, using pressure swing adsorption (PSA) processes. A detailed one-dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multicomponent mass diffusion. The PSA model has been further extended by incorporating a heat regenerating process to enhance CO 2 sequestration. The heat dissipated during adsorption is stored in packed sand bed and released during desorption step for heating purpose. The model has been implemented on a MATLAB program using second-order discretization. Validation of the model was performed using a complete experimental data set for CO 2 sequestration using zeolite 13X. Simulation of the PSA experiment on fixed bed has been carried out to evaluate the capacity of Mg-MOF-74 for CO 2 capture with varying feed gas temperature of 28 and 100°C, varying pressurization and purge times and heat regeneration. It was discovered that the PSA process with heat regeneration system might be advantageous because it achieves equivalent amount of CO 2 sequestration in fewer PSA cycles compared with PSA without heat regeneration system. Based on the simulated conditions, CO 2 recovery with Mg-MOF-74 gives high percentage purity (above 98%) for the captured CO 2 .
Boiler swing rate, which is the rate at which the boiler load is changed, has significant influen... more Boiler swing rate, which is the rate at which the boiler load is changed, has significant influence on the parameters of the boiler operating conditions such as drum water pressure and level, steam quality in the riser tubes, wall temperatures of riser tubes, and the associated thermal stresses. In this paper, the thermal stresses developed in boiler tubes due to elevated rates of heat transfer and friction are presented versus thermal stresses developed in tubes operated under normal conditions. The differential equations comprising the nonlinear model and governing the flow inside the boiler tubes were formulated to study different operational scenarios in terms of resulting dynamic response of critical variables. The experimental results and field data were obtained to validate the present nonlinear dynamic model. The calculations of the heat flux and the allowable steam quality were used to determine the maximum boiler swing rates at different conditions of riser tube of frictio...
This research paper investigates the effects of boiler swing and firing rate of power plant boile... more This research paper investigates the effects of boiler swing and firing rate of power plant boilers on NO emissions. For this purpose, a nonlinear state space dynamic model has been developed on the basis of collected field experimental data to relate the NO emissions of drum boilers with other state variables. The collected experimental field data were used to determine the model coefficients. The NO formation computations were conducted using a Matlab program, and model response was validated with experimental data obtained from the literature. The current model results are in good agreement with the experimental data from the literature. The NO formation was obtained as a result of four steam flow rate perturbation schemes: (i) eight steps of 5%/min, (ii) four steps of 10%/min, (iii) two steps of 20%/min, and (iv) one step of 40%/min. The research results reflect that the total NO formation over a period of time decay with lower swing rates and the magnitude of the total formed NO over a period of time increase as the swing rate increases. The model was then implemented to predict the NO emission variations from boiler field data.
Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presente... more Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presented. The flow field in the inlet and return headers was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The effects of the number of nozzles, nozzle location,
In the present study, large-eddy simulation (LES) is utilized to analyze lean-premixed propaneair... more In the present study, large-eddy simulation (LES) is utilized to analyze lean-premixed propaneair flame stability in a backward-step combustor over a range of equivalence ratio. The artificially thickened flame approach coupled with a reduced reaction mechanism is incorporated for modeling the turbulence-combustion interactions at small scales. Simulation results are compared to high-speed particle image velocimetry (PIV) measurements for validation. The results show that the numerical framework captures different topological flow features effectively and with reasonable accuracy, for stable flame configurations, but some quantitative differences exist. The recirculation zone (RZ) is formed of a primary eddy and a secondary eddy and its overall size is significantly impacted by the equivalence ratio. The temperature distribution inside the recirculation zone is highly non-uniform, with much lower values observed close to the backward step and the bottom wall. The mixture distribution inside the RZ is also non-uniform because of mixing with reactants and heat loss to the walls. The flame is stabilized closer to the backward step as the equivalence ratio increases. At lower fuel fractions, the flame lifts off the step starting at equivalence ratio of 0.63 and the lift off distance is increased while the equivalence ratio is lowered.
Journal of Petroleum Exploration and Production Technology, 2019
The phenomenon of two-phase flows is characterized by its wide range of presence in nature and in... more The phenomenon of two-phase flows is characterized by its wide range of presence in nature and industrial applications. In gas and oil production, the simultaneous two-phase flow of gases and liquids often occurs in gas wells. The produced gases flow rate decreases over the years until reaching a critical flow rate when they lose their ability to lift the associated liquids upward and the liquid film reverses direction, which triggers liquid loading. Liquid loading causes the produced liquids to accumulate in the bottom of the wellbore, which causes a high back pressure that reduces the well production rate till production is ceased eventually. The critical gas velocity exists in the churn flow regime which is mainly characterized by the oscillatory behavior of the liquids flow field. This study employs CFD techniques to model the churn flow in a 3-inchdiameter vertical pipe near the critical gas flow rate for different liquid flow rates. This work utilizes the two-fluid Eulerian model along with the RNG (Re-Normalization Group) k-ε turbulence model to investigate the behavior of the flow field in a two-dimensional axisymmetric computational domain. Simulations were carried out using the commercial software ANSYS Fluent 18.2 with air and water as the two working fluids. The model results showed a good agreement with the experimental data and proved the mesh and time independence of the model. Oscillatory behaviors of the liquid film flow rate, shear stress, and pressure were observed along with the formation of interfacial waves. Detailed information about the velocity, shear stress, and pressure behaviors is presented. Accordingly, recommendations are suggested for future considerations.
instead of air, resulting in a flue gas that consists mainly of CO 2 and water (H 2 O). The latte... more instead of air, resulting in a flue gas that consists mainly of CO 2 and water (H 2 O). The latter can be separated easily via condensation, while removing other contaminants leaving pure CO 2 for storage. However, fuel combustion in pure O 2 results in uncontrollable combustion temperatures. In order to provide the dilution effect of the absent nitrogen (N 2) and to moderate the furnace/combustor temperatures, part of the flue gas is recycled Contents lists available at ScienceDirect
Journal of Materials Engineering and Performance, 2014
ABSTRACT In this paper, the erosion behavior of commonly used stainless steels (AISI 310S, AISI 3... more ABSTRACT In this paper, the erosion behavior of commonly used stainless steels (AISI 310S, AISI 316), carbon steel (AISI 1020), and Aluminum 6060 were experimentally investigated. The effect of hardness on erosion rates and on the morphologies of eroded surfaces has been evaluated. The experiments were carried out using an air jet erosion tester and utilizing angular alumina as erodent with 50 lm particle size. The samples were tested at six different impact angles (15�, 30�, 45�, 60�, 75�, and 90�) using three different impact velocities (30, 60, and 100 m/s). The eroded surfaces were analyzed using a scanning electron microscope (SEM) for the evaluation of material degradation. The erosion rates were found to increase with the increase of the alloy bulk hardness and Aluminum 6060 showed maximum erosion resistance. For all specimens, the erosion rates were found to increase with the increase of impact velocity and the maximum erosion rate was found to occur between 15� and 30� impact angles. The obtained results were found to correlate very well with Oka et al. (Wear, 259:95–101, 2005) erosion model.
In this study, swing rates of drum boilers are investigated in regard to maintaining proper drum ... more In this study, swing rates of drum boilers are investigated in regard to maintaining proper drum level limits. The nonlinear boiler model employed in study investigations was validated by comparing simulated results against literature data. Experimental field data was recorded for variations in firing, steam, and feedwater flow rates in addition to drum pressure and water level were obtained from a Saudi Aramco power plant. The experimental results were used also for tuning the water level control loop and finding the proportional and integral gains of the boiler model that was simulated using matlab. Influence of steam demand perturbations on water drum levels was tested using four different perturbation schemes and in all cases the levels were found to be within the allowable limits. The time variation of drum water level in response to 40% ramp increase in steam demand occurring at the four different input perturbations was obtained. The considered values of swing rates of steam ...
Erosion is one of the most serious problems in various gas and liquid flow passages such as flow ... more Erosion is one of the most serious problems in various gas and liquid flow passages such as flow in pipes, pumps, turbines, compressors and many other devices. Sand presence causes loss of pipe wall thickness that can lead to pipe erosion, frequent failures and loss of expensive production time. The importance of this problem is mainly due to many related engineering applications, viz. heat exchangers. In order to reduce the frequency of such pipe erosions, caps in the form of replaceable pipes are protruded in the sudden contraction regions which are exposed to most of the serious erosion rates. In the present work, numerical investigation of the erosion of a pipe protruded in a sudden contraction is presented. The turbulent, steady, 2-D axi-symmetric flow inside an axi-symmetric abrupt contraction pipe with a pipe protrusion embedded in it was solved by steady-state time averaged conservation equations of mass and momentum along with two equation model for turbulence. Particles are tracked using Lagrangian particle tracking. An erosion model was employed to investigate the erosion phenomena for the given geometry. The influence of the different parameters such as the inlet flow velocity (3-10 m/s), the particle diameter (10-400 mm), the protruded pipe geometry (thickness T ¼ 1-5 mm and depth H ¼ 2-5 mm) and the pipe contraction ratio (Cr ¼ 0.25-0.5) on the erosion of pipe protrusion was investigated. Correlations for the influence of inlet flow velocity, depth and thickness of the protruded pipe on the erosion rate are presented.
Tangentially fired furnaces are vortex-combustion burners preferably used for oxy-fuel combustion... more Tangentially fired furnaces are vortex-combustion burners preferably used for oxy-fuel combustion in order to minimize the CO 2 emission and control the boiler temperature. The objective of the present study is to investigate numerically the combustion and emission characteristics of oxy-fuel combustion of turbulent reacting flows in a three-dimensional model furnace of a 600 MW tangentially fired boiler. Numerical calculations of the flow field and thermal fields as well as the species concentrations for the oxy-fuel combustion in the furnace of a gaseous fuel tangentially fired boiler were conducted. Three cases of oxy-fuel combustion were investigated. These were 73%, 79%, and 65% of volumetric inlet CO 2 while the remaining inlet volume was O 2. The results of these three oxy-fuel cases are compared to the air-fired combustion. In the present model, the radiation heat transfer was solved by the weighted sum gray gases approach, whereas the chemical reaction model was facilitated by a simple lumped reaction model. The results show that the oxy-fuel case of 79% CO 2 can preferably minimize the combustion temperature for highly sustainable materials. However, the 65% CO 2 oxy-fuel case generates high temperature values for improving the heat characteristics. The 73% CO 2 oxy-fuel and the air-fired cases are fairly close to each other in thermal behavior.
The critical heat flux look-up table was applied to a large diameter tube, namely 67 mm inside di... more The critical heat flux look-up table was applied to a large diameter tube, namely 67 mm inside diameter tube, to predict the occurrence of the phenomenon for both vertical and horizontal uniformly heated tubes. Water was considered as coolant. For the vertical tube, a diameter correction factor was directly applied to the 1995 critical heat flux look-up table. To predict the occurrence of critical heat flux in horizontal tube, an extra correction factor to account for flow stratification was applied. Both derived tables were used to predict the effect of high heat flux and tube blockage on critical heat flux occurrence in boiler tubes. Moreover, the horizontal tube look-up table was used to predict the safety limits of the operation of boiler for 50% allowable heat flux.
Steady, laminar, mixed convection in the fully developed region of horizontal concentric annuli h... more Steady, laminar, mixed convection in the fully developed region of horizontal concentric annuli has been investigated numerically for the case of non-uniform circumferential heating. Two heating conditions were studied, one in which a 180 arc encompassing the top half of
Nanoparticles of zeolitic imidazolate framework-7 (nZIF-7) were blended with poly(ether imide) (P... more Nanoparticles of zeolitic imidazolate framework-7 (nZIF-7) were blended with poly(ether imide) (PEI) to fabricate a new mixed-matrix membrane (nZIF-7/PEI). nZIF-7 was chosen in order to demonstrate the power of postsynthetic modification (PSM) by linker exchange of benzimidazolate to benzotriazolate for tuning the permeability and selectivity properties of a resulting membrane (PSM-nZIF-7/PEI). These two new membranes were subjected to constant volume, variable pressure gas permeation measurements (H 2 , N 2 , O 2 , CH 4 , CO 2 , C 2 H 6 , and C 3 H 8), in which unique gas separation behavior was observed when compared to the pure PEI membrane. Specifically, the nZIF-7/PEI membrane exhibited the highest selectivities for CO 2 /CH 4 , CO 2 /C 2 H 6 , and CO 2 /C 3 H 8 gas pairs. Furthermore, PSM-nZIF-7/PEI membrane displayed the highest permeabilities, which resulted in H 2 /CH 4 , N 2 /CH 4 , and H 2 /CO 2 permselectivities that are remarkably well-positioned on the Robeson upper bound curves, thus, indicating its potential applicability for use in practical gas purifications.
ABSTRACT Reasonably high oxygen permeation fluxes, similar to 4 x 10(-2) mu mol.cm(-2).s(-1), wer... more ABSTRACT Reasonably high oxygen permeation fluxes, similar to 4 x 10(-2) mu mol.cm(-2).s(-1), were obtained from surface decoration with La0.8Sr0.2CoO3-delta (LSC113) or LaSrCoO4 +/-delta (LSC214) on La0.8Sr0.2Ga0.8Mg0.115Co0.085O3-delta (LSGMC) and Ce0.8Sm0.2O2-delta (SDC) membranes at 700 degrees C. Promoting surface exchange kinetics at the feed side of LSGMC and SDC membranes, which was found rate-limiting, is needed to further enhance oxygen permeation of these membranes. This work demonstrates the possibility of reducing the amount of noble metal usage for membranes based on the concept of short-circuited ion conductors and shows promise for the development of noble-metal-free permeation membranes.
Various nutritional values are more influenced by cooking than others. This study compared the ef... more Various nutritional values are more influenced by cooking than others. This study compared the effects of microwave heating with conventional cooking method of fresh Potato (Solanum tuberosum). The moisture and ash content in raw potato were 76.60% and 0.40%, respectively. After conventional cooking moisture and ash content were 78.00% and 0.50%, respectively and after microwave heating it saw the values were 77.20% and 0.60%, respectively. The fat and carbohydrate content in raw potato were 0.70% and 20.46%, respectively. After conventional cooking those values were 0.80% and 19.40%, respectively and in microwave heating it showed the values were 0.50% and 20.08%, respectively. Total protein content was also changed by those cooking methods. In microwave heating it reduced the vitamin-C content to some extent but the conventional cooking completely destroyed the vitamin-C contents.
This paper presents a computational study of an energy-efficient technique for post-combustion CO... more This paper presents a computational study of an energy-efficient technique for post-combustion CO 2 capture using novel material, namely, Mg-MOF-74, using pressure swing adsorption (PSA) processes. A detailed one-dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multicomponent mass diffusion. The PSA model has been further extended by incorporating a heat regenerating process to enhance CO 2 sequestration. The heat dissipated during adsorption is stored in packed sand bed and released during desorption step for heating purpose. The model has been implemented on a MATLAB program using second-order discretization. Validation of the model was performed using a complete experimental data set for CO 2 sequestration using zeolite 13X. Simulation of the PSA experiment on fixed bed has been carried out to evaluate the capacity of Mg-MOF-74 for CO 2 capture with varying feed gas temperature of 28 and 100°C, varying pressurization and purge times and heat regeneration. It was discovered that the PSA process with heat regeneration system might be advantageous because it achieves equivalent amount of CO 2 sequestration in fewer PSA cycles compared with PSA without heat regeneration system. Based on the simulated conditions, CO 2 recovery with Mg-MOF-74 gives high percentage purity (above 98%) for the captured CO 2 .
Boiler swing rate, which is the rate at which the boiler load is changed, has significant influen... more Boiler swing rate, which is the rate at which the boiler load is changed, has significant influence on the parameters of the boiler operating conditions such as drum water pressure and level, steam quality in the riser tubes, wall temperatures of riser tubes, and the associated thermal stresses. In this paper, the thermal stresses developed in boiler tubes due to elevated rates of heat transfer and friction are presented versus thermal stresses developed in tubes operated under normal conditions. The differential equations comprising the nonlinear model and governing the flow inside the boiler tubes were formulated to study different operational scenarios in terms of resulting dynamic response of critical variables. The experimental results and field data were obtained to validate the present nonlinear dynamic model. The calculations of the heat flux and the allowable steam quality were used to determine the maximum boiler swing rates at different conditions of riser tube of frictio...
This research paper investigates the effects of boiler swing and firing rate of power plant boile... more This research paper investigates the effects of boiler swing and firing rate of power plant boilers on NO emissions. For this purpose, a nonlinear state space dynamic model has been developed on the basis of collected field experimental data to relate the NO emissions of drum boilers with other state variables. The collected experimental field data were used to determine the model coefficients. The NO formation computations were conducted using a Matlab program, and model response was validated with experimental data obtained from the literature. The current model results are in good agreement with the experimental data from the literature. The NO formation was obtained as a result of four steam flow rate perturbation schemes: (i) eight steps of 5%/min, (ii) four steps of 10%/min, (iii) two steps of 20%/min, and (iv) one step of 40%/min. The research results reflect that the total NO formation over a period of time decay with lower swing rates and the magnitude of the total formed NO over a period of time increase as the swing rate increases. The model was then implemented to predict the NO emission variations from boiler field data.
Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presente... more Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presented. The flow field in the inlet and return headers was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The effects of the number of nozzles, nozzle location,
In the present study, large-eddy simulation (LES) is utilized to analyze lean-premixed propaneair... more In the present study, large-eddy simulation (LES) is utilized to analyze lean-premixed propaneair flame stability in a backward-step combustor over a range of equivalence ratio. The artificially thickened flame approach coupled with a reduced reaction mechanism is incorporated for modeling the turbulence-combustion interactions at small scales. Simulation results are compared to high-speed particle image velocimetry (PIV) measurements for validation. The results show that the numerical framework captures different topological flow features effectively and with reasonable accuracy, for stable flame configurations, but some quantitative differences exist. The recirculation zone (RZ) is formed of a primary eddy and a secondary eddy and its overall size is significantly impacted by the equivalence ratio. The temperature distribution inside the recirculation zone is highly non-uniform, with much lower values observed close to the backward step and the bottom wall. The mixture distribution inside the RZ is also non-uniform because of mixing with reactants and heat loss to the walls. The flame is stabilized closer to the backward step as the equivalence ratio increases. At lower fuel fractions, the flame lifts off the step starting at equivalence ratio of 0.63 and the lift off distance is increased while the equivalence ratio is lowered.
Journal of Petroleum Exploration and Production Technology, 2019
The phenomenon of two-phase flows is characterized by its wide range of presence in nature and in... more The phenomenon of two-phase flows is characterized by its wide range of presence in nature and industrial applications. In gas and oil production, the simultaneous two-phase flow of gases and liquids often occurs in gas wells. The produced gases flow rate decreases over the years until reaching a critical flow rate when they lose their ability to lift the associated liquids upward and the liquid film reverses direction, which triggers liquid loading. Liquid loading causes the produced liquids to accumulate in the bottom of the wellbore, which causes a high back pressure that reduces the well production rate till production is ceased eventually. The critical gas velocity exists in the churn flow regime which is mainly characterized by the oscillatory behavior of the liquids flow field. This study employs CFD techniques to model the churn flow in a 3-inchdiameter vertical pipe near the critical gas flow rate for different liquid flow rates. This work utilizes the two-fluid Eulerian model along with the RNG (Re-Normalization Group) k-ε turbulence model to investigate the behavior of the flow field in a two-dimensional axisymmetric computational domain. Simulations were carried out using the commercial software ANSYS Fluent 18.2 with air and water as the two working fluids. The model results showed a good agreement with the experimental data and proved the mesh and time independence of the model. Oscillatory behaviors of the liquid film flow rate, shear stress, and pressure were observed along with the formation of interfacial waves. Detailed information about the velocity, shear stress, and pressure behaviors is presented. Accordingly, recommendations are suggested for future considerations.
instead of air, resulting in a flue gas that consists mainly of CO 2 and water (H 2 O). The latte... more instead of air, resulting in a flue gas that consists mainly of CO 2 and water (H 2 O). The latter can be separated easily via condensation, while removing other contaminants leaving pure CO 2 for storage. However, fuel combustion in pure O 2 results in uncontrollable combustion temperatures. In order to provide the dilution effect of the absent nitrogen (N 2) and to moderate the furnace/combustor temperatures, part of the flue gas is recycled Contents lists available at ScienceDirect
Journal of Materials Engineering and Performance, 2014
ABSTRACT In this paper, the erosion behavior of commonly used stainless steels (AISI 310S, AISI 3... more ABSTRACT In this paper, the erosion behavior of commonly used stainless steels (AISI 310S, AISI 316), carbon steel (AISI 1020), and Aluminum 6060 were experimentally investigated. The effect of hardness on erosion rates and on the morphologies of eroded surfaces has been evaluated. The experiments were carried out using an air jet erosion tester and utilizing angular alumina as erodent with 50 lm particle size. The samples were tested at six different impact angles (15�, 30�, 45�, 60�, 75�, and 90�) using three different impact velocities (30, 60, and 100 m/s). The eroded surfaces were analyzed using a scanning electron microscope (SEM) for the evaluation of material degradation. The erosion rates were found to increase with the increase of the alloy bulk hardness and Aluminum 6060 showed maximum erosion resistance. For all specimens, the erosion rates were found to increase with the increase of impact velocity and the maximum erosion rate was found to occur between 15� and 30� impact angles. The obtained results were found to correlate very well with Oka et al. (Wear, 259:95–101, 2005) erosion model.
In this study, swing rates of drum boilers are investigated in regard to maintaining proper drum ... more In this study, swing rates of drum boilers are investigated in regard to maintaining proper drum level limits. The nonlinear boiler model employed in study investigations was validated by comparing simulated results against literature data. Experimental field data was recorded for variations in firing, steam, and feedwater flow rates in addition to drum pressure and water level were obtained from a Saudi Aramco power plant. The experimental results were used also for tuning the water level control loop and finding the proportional and integral gains of the boiler model that was simulated using matlab. Influence of steam demand perturbations on water drum levels was tested using four different perturbation schemes and in all cases the levels were found to be within the allowable limits. The time variation of drum water level in response to 40% ramp increase in steam demand occurring at the four different input perturbations was obtained. The considered values of swing rates of steam ...
Erosion is one of the most serious problems in various gas and liquid flow passages such as flow ... more Erosion is one of the most serious problems in various gas and liquid flow passages such as flow in pipes, pumps, turbines, compressors and many other devices. Sand presence causes loss of pipe wall thickness that can lead to pipe erosion, frequent failures and loss of expensive production time. The importance of this problem is mainly due to many related engineering applications, viz. heat exchangers. In order to reduce the frequency of such pipe erosions, caps in the form of replaceable pipes are protruded in the sudden contraction regions which are exposed to most of the serious erosion rates. In the present work, numerical investigation of the erosion of a pipe protruded in a sudden contraction is presented. The turbulent, steady, 2-D axi-symmetric flow inside an axi-symmetric abrupt contraction pipe with a pipe protrusion embedded in it was solved by steady-state time averaged conservation equations of mass and momentum along with two equation model for turbulence. Particles are tracked using Lagrangian particle tracking. An erosion model was employed to investigate the erosion phenomena for the given geometry. The influence of the different parameters such as the inlet flow velocity (3-10 m/s), the particle diameter (10-400 mm), the protruded pipe geometry (thickness T ¼ 1-5 mm and depth H ¼ 2-5 mm) and the pipe contraction ratio (Cr ¼ 0.25-0.5) on the erosion of pipe protrusion was investigated. Correlations for the influence of inlet flow velocity, depth and thickness of the protruded pipe on the erosion rate are presented.
Tangentially fired furnaces are vortex-combustion burners preferably used for oxy-fuel combustion... more Tangentially fired furnaces are vortex-combustion burners preferably used for oxy-fuel combustion in order to minimize the CO 2 emission and control the boiler temperature. The objective of the present study is to investigate numerically the combustion and emission characteristics of oxy-fuel combustion of turbulent reacting flows in a three-dimensional model furnace of a 600 MW tangentially fired boiler. Numerical calculations of the flow field and thermal fields as well as the species concentrations for the oxy-fuel combustion in the furnace of a gaseous fuel tangentially fired boiler were conducted. Three cases of oxy-fuel combustion were investigated. These were 73%, 79%, and 65% of volumetric inlet CO 2 while the remaining inlet volume was O 2. The results of these three oxy-fuel cases are compared to the air-fired combustion. In the present model, the radiation heat transfer was solved by the weighted sum gray gases approach, whereas the chemical reaction model was facilitated by a simple lumped reaction model. The results show that the oxy-fuel case of 79% CO 2 can preferably minimize the combustion temperature for highly sustainable materials. However, the 65% CO 2 oxy-fuel case generates high temperature values for improving the heat characteristics. The 73% CO 2 oxy-fuel and the air-fired cases are fairly close to each other in thermal behavior.
The critical heat flux look-up table was applied to a large diameter tube, namely 67 mm inside di... more The critical heat flux look-up table was applied to a large diameter tube, namely 67 mm inside diameter tube, to predict the occurrence of the phenomenon for both vertical and horizontal uniformly heated tubes. Water was considered as coolant. For the vertical tube, a diameter correction factor was directly applied to the 1995 critical heat flux look-up table. To predict the occurrence of critical heat flux in horizontal tube, an extra correction factor to account for flow stratification was applied. Both derived tables were used to predict the effect of high heat flux and tube blockage on critical heat flux occurrence in boiler tubes. Moreover, the horizontal tube look-up table was used to predict the safety limits of the operation of boiler for 50% allowable heat flux.
Steady, laminar, mixed convection in the fully developed region of horizontal concentric annuli h... more Steady, laminar, mixed convection in the fully developed region of horizontal concentric annuli has been investigated numerically for the case of non-uniform circumferential heating. Two heating conditions were studied, one in which a 180 arc encompassing the top half of
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