This article analyzes a published formulation of the Navier–Stokes equations cast into surface-fo... more This article analyzes a published formulation of the Navier–Stokes equations cast into surface-following coordinates and provides some additional mathematical background to follow the article. Ubiquitous in the paint shops of automotive plants around the world, a high-speed rotary bell is succinctly described as a rapidly spinning concave axisymmetric surface with liquid paint supplied from a port coinciding with the center of rotation. The spinning surface transfers momentum to the paint film causing it to flow outward. Upon reaching the bell periphery, it is flung off, subsequently forming an atomized spray transferred to an automotive body through advection and electrostatics. Common analytical frameworks of rotating films were spherical or cylindrical coordinate systems where the wetted surface profile of the bell was constrained to follow a coordinate axis. This led to solutions for films modeled with conical, disk-like, or partial hemispherical profiles. An alternative was a m...
In this second part of a two part exploration of dynamic behavior observed in wildland fires, tim... more In this second part of a two part exploration of dynamic behavior observed in wildland fires, time scales differentiating convective and radiative heat transfer is further explored. Scaling laws for the two different types of heat transfer considered: Radiation-driven fire spread, and convection-driven fire spread, which can both occur during wildland fires. A new interpretation of the inertial forces introduced a downstream, time-dependent frequency, ω, which captures the dynamic, vortex shedding behavior of flames due to the unstable nature of the turbulent flow created in the wake of the fire. Excelsior and paper strip experiments suggest wildland fire is a falls into the convection-driven spread regime. Nomenclature the fuel bed angle temperature rise of air and gas temperature rise of fuel pi-number gas density
Laboratory fires spreading through laser-cut cardboard fuel beds were instrumented and analyzed f... more Laboratory fires spreading through laser-cut cardboard fuel beds were instrumented and analyzed for physical processes associated with spread. Flames in the span-wise direction appeared as a regular series of peaks-andtroughs that scaled directly with flame length. Flame structure in the stream-wise direction fluctuated with the forward advection of coherent parcels that originated near the rear edge of the flame zone. Thermocouples arranged longitudinally in the fuel beds revealed the frequency of temperature fluctuations decreased with flame length but increased with wind speed. The behaviors are remarkably similar to those of boundary layers, suggesting a dominant role for buoyancy in determining wildland fire spread.
Despite progress in laser-based and computational tools, an accessible model that relies on funda... more Despite progress in laser-based and computational tools, an accessible model that relies on fundamentals and offers a reasonably accurate estimation of droplet size and velocity is lacking, primarily due to entangled complex breakup mechanisms. Therefore, this study aims at using the integral form of the conservation equations to create a system of equations by solving which, the far-field secondary atomization can be analyzed through predicting droplet size and velocity distributions of the involved phases. To validate the model predictions, experiments are conducted at ambient conditions using water, methanol, and acetone as model fluids with varying formulation properties, such as density, viscosity, and surface tension. Droplet size distribution and velocity are measured with laser diffraction and a high-speed camera, respectively. Finally, an attempt is made to utilize non-scaled parameters to characterize the atomization process, useful for extrapolating the sensitivity analys...
International Journal of Heat and Mass Transfer, 2021
Despite the wide-spread applications of spray drying in the production of chemicals, food, and ph... more Despite the wide-spread applications of spray drying in the production of chemicals, food, and pharmaceuticals, accurate control and development of this unit remains an elusive task because of the complex interactions of variables and phenomena. In this paper, we offer the development of a computationally efficient closed-loop system with a model predictive controller (MPC) where a computational fluid dynamics (CFD) process model is utilized to represent the process behavior. In particular, we present the development of an MPC and its implementation within the CFD model of a lab-scale spray dryer. Dynamic model is created with an adopted CFD model based on a 2D axisymmetric dryer, and Reaction Engineering Approach (REA)- as the drying kinetic method. Then, an MPC control strategy is designed using a linear approximation of a data-driven dynamic model and implemented within the CFD simulation as a user-defined function (UDF). We demonstrate the application of the developed MPC within...
Live foliage for some tree and shrub species can support flaming fire spread at much higher moist... more Live foliage for some tree and shrub species can support flaming fire spread at much higher moisture content than dead fuel materials. However, the role of live fuels in forest fires has been controversial in the past decades. Although ignition and spread statistical data for live and dead fuels exist in the literature, a clear understanding of the fundamental difference in the burning behavior is missing. To illuminate the role of live fuel on forest fire spreading, a laboratory ignition experiment was designed to examine the burning behavior of live Norway spruce needles. A Schlieren-Infrared combined measurement apparatus was developed with a spatial resolution of 0.75 mm and a time resolution of 0.0025 s, to visualize/measure the ignition behavior of live fuels. Schlieren and IR images revealed that the ejection of live fuel volatiles can alter the flame direction and induce previously unaccounted heating of the nearby fuel. Depending on the conditions, these interferences could...
Cable-stayed bridges are being constructed more frequently due to their architectural appeal, eas... more Cable-stayed bridges are being constructed more frequently due to their architectural appeal, ease of construction, and lower cost and environmental footprint in comparison to other bridge types. On some more recent bridges of that type built in the past 10-20 years, the stay-cables are comprised of greased-and-sheathed, stranded steel wires enclosed in high density polyethylene (HDPE) pipes with the interstices filled with a cementatious grout. This design is susceptible to voids in the grout, which can possibly promote cracking in the HDPE piping and reduce the ability of the corrosion protection to safeguard the wires. Several non-destructive techniques have been used to detect defects (voids) in stay cables. In this work, voids in stay cables are studied using passive infrared thermography during solar irradiation over days from sunrise to sunset. Effects of stay cable material properties, time of day, solar orientation and void sizes on the capacity of passive infrared thermogr...
In this work, small-scale experiments of fire whirl were conducted to study the spinning fire phe... more In this work, small-scale experiments of fire whirl were conducted to study the spinning fire phenomenon and to gain comprehensive understandings of fire tornadoes and the factors that affect their behavior. High speed imaging was used to track the flames at both temporal and spatial scales. This allowed us to better understand the role of the near-ground height in creating a boundary layer flow profile that, in turn contributes to formation of vortices around the fire, and consequent fire whirls. Based on the results obtained from these observations, we were able to spot the differences in the fuel burning rate of the fire itself as a function of a newly defined specific non-dimensional near-ground height. Based on our observations, there is a cutoff non-dimensional height, beyond which a normal fire can be turned into a fire whirl. Additionally, the results showed that the fire burning rate decreases by moving the fire to a height higher than the ground level. These effects were j...
Wind tunnel laboratory fires spreading through laser-cut cardboard fuel beds were instrumented an... more Wind tunnel laboratory fires spreading through laser-cut cardboard fuel beds were instrumented and analyzed for physical processes associated with spread. Flames in the span-wise direction appeared as a regular series of peaks-and-troughs that scaled directly with flame length. Flame structure in the stream-wise direction fluctuated with the forward advection of coherent parcels that originated near the rear edge of the flame zone. Thermocouples arranged longitudinally in the fuel beds revealed the frequency of these temperature fluctuations decreased with flame length but increased with wind speed. The downstream extent of these fluctuations scaled with Froude number and flame zone depth. These behaviors are remarkably similar to those of boundary layers, suggesting a dominant role for buoyancy in determining wildland fire spread.
Many developing countries suffer from high energy-import dependency and inadequate electrificatio... more Many developing countries suffer from high energy-import dependency and inadequate electrification of rural areas, which aggravates the poverty problem. In this work, Al-Tafilah in Jordan was considered as a case study, where the technical, economic, and environmental benefits of a decentralized hybrid renewable energy system that can match 100% of the city demand were investigated. A tri-hybrid system of wind, solar, and hydropower was integrated with an energy storage system and optimized to maximize the match between the energy demand and production profiles. The optimization aimed at maximizing the renewable energy system (RES) fraction while keeping the levelized cost of electricity (LCOE) equal to the electricity purchase tariff. The techno-economic analysis showed that the optimal system in Al-Tafilah comprises a 28 MW wind system, 75.4 MW PV, and 1 MW hydropower, with a 259 MWh energy storage system, for which a RES fraction of 99% can be achieved, and 47,160 MtCO2 are avoid...
Abstract Spray drying as a primary powder synthesis tool is not designed to separate particles du... more Abstract Spray drying as a primary powder synthesis tool is not designed to separate particles during the process. Here we report on the simulation, optimization, and development of a customized multi-bin cyclone for a lab-scale spray dryer to segregate particles based on their sizes. Two criteria were chosen to optimize the number of bins, cutoff size, and pressure drop. Accordingly, a non-dimensional factor describing cyclone performance was introduced by investigating which five bins of powder collection were found to render a compromise between competing factors. Spray-dried powders were administered to the cyclone, and deposition of the particles in the bins was recorded. The cyclone could segregate particles with a size resolution as low as 4 μm. For each bin, the data on particle size, morphology, pore attributes, BET surface, and moisture content showed that even within a single batch, there is a broad span of particle properties.
Recently, remarkable developments have taken place, leading to significant improvements in microf... more Recently, remarkable developments have taken place, leading to significant improvements in microfluidic methods to capture subtle biological effects down to single cells. As microfluidic devices are getting sophisticated, design optimization through experimentations is becoming more challenging. As a result, numerical simulations have contributed to this trend by offering a better understanding of cellular microenvironments hydrodynamics and optimizing the functionality of the current/emerging designs. The need for new marketable designs with advantageous hydrodynamics invokes easier access to efficient as well as time-conservative numerical simulations to provide screening over cellular microenvironments, and to emulate physiological conditions with high accuracy. Therefore, an excerpt overview on how each numerical methodology and associated handling software works, and how they differ in handling underlying hydrodynamic of lab-on-chip microfluidic is crucial. These numerical mean...
In this study, we evaluated the fundamental physical behavior during droplet formation and flow f... more In this study, we evaluated the fundamental physical behavior during droplet formation and flow from a rotary bell spray in the absence of an electrostatic field. The impact of a wide range of operating parameters of the rotary bell sprayer, such as flow rates, rotational speeds, and spatial positioning, on droplet sizes and size distributions using a three-dimensional (3-D) mapping was studied. The results showed that increasing the rotational speed caused the Sauter mean diameter of the droplets to decrease while increasing flow rate increased the droplet sizes. The rotational speed effect, however, was dominant compared to the effect of flow rate. An increase in droplet size radially away from the cup was noted in the vicinity of the cup, nevertheless, as the lateral distances from the cup and rotational speed were increased, the droplet sizes within the flow field became more uniform. This result is of importance for painting industries, which are looking for optimal target dist...
This brief paper explains the slight differences in governing equations for a fluid film in a spi... more This brief paper explains the slight differences in governing equations for a fluid film in a spinning cone, and the mechanism that reduces the order of a solution. Spinning cones with a centrally supplied fluid that spreads over its inner surface as a thin film have been the subject of interest for many years. Though often cast as a mathematical analysis, understanding this process is important, especially in the application of automotive painting. The analysis consists of a system of equations obtained from the Navier–Stokes equations along with simple boundary conditions that describe radial and tangential momentum conservation. Solutions to this system of equations are shown using several techniques. The connection between these techniques is slightly subtle. However, the conditions that enable reduction of order are clear once they are exposed. Directional velocity profiles in the film can be a combination of four roots in the complex plane. This system of roots also contains t...
This article analyzes a published formulation of the Navier–Stokes equations cast into surface-fo... more This article analyzes a published formulation of the Navier–Stokes equations cast into surface-following coordinates and provides some additional mathematical background to follow the article. Ubiquitous in the paint shops of automotive plants around the world, a high-speed rotary bell is succinctly described as a rapidly spinning concave axisymmetric surface with liquid paint supplied from a port coinciding with the center of rotation. The spinning surface transfers momentum to the paint film causing it to flow outward. Upon reaching the bell periphery, it is flung off, subsequently forming an atomized spray transferred to an automotive body through advection and electrostatics. Common analytical frameworks of rotating films were spherical or cylindrical coordinate systems where the wetted surface profile of the bell was constrained to follow a coordinate axis. This led to solutions for films modeled with conical, disk-like, or partial hemispherical profiles. An alternative was a m...
In this second part of a two part exploration of dynamic behavior observed in wildland fires, tim... more In this second part of a two part exploration of dynamic behavior observed in wildland fires, time scales differentiating convective and radiative heat transfer is further explored. Scaling laws for the two different types of heat transfer considered: Radiation-driven fire spread, and convection-driven fire spread, which can both occur during wildland fires. A new interpretation of the inertial forces introduced a downstream, time-dependent frequency, ω, which captures the dynamic, vortex shedding behavior of flames due to the unstable nature of the turbulent flow created in the wake of the fire. Excelsior and paper strip experiments suggest wildland fire is a falls into the convection-driven spread regime. Nomenclature the fuel bed angle temperature rise of air and gas temperature rise of fuel pi-number gas density
Laboratory fires spreading through laser-cut cardboard fuel beds were instrumented and analyzed f... more Laboratory fires spreading through laser-cut cardboard fuel beds were instrumented and analyzed for physical processes associated with spread. Flames in the span-wise direction appeared as a regular series of peaks-andtroughs that scaled directly with flame length. Flame structure in the stream-wise direction fluctuated with the forward advection of coherent parcels that originated near the rear edge of the flame zone. Thermocouples arranged longitudinally in the fuel beds revealed the frequency of temperature fluctuations decreased with flame length but increased with wind speed. The behaviors are remarkably similar to those of boundary layers, suggesting a dominant role for buoyancy in determining wildland fire spread.
Despite progress in laser-based and computational tools, an accessible model that relies on funda... more Despite progress in laser-based and computational tools, an accessible model that relies on fundamentals and offers a reasonably accurate estimation of droplet size and velocity is lacking, primarily due to entangled complex breakup mechanisms. Therefore, this study aims at using the integral form of the conservation equations to create a system of equations by solving which, the far-field secondary atomization can be analyzed through predicting droplet size and velocity distributions of the involved phases. To validate the model predictions, experiments are conducted at ambient conditions using water, methanol, and acetone as model fluids with varying formulation properties, such as density, viscosity, and surface tension. Droplet size distribution and velocity are measured with laser diffraction and a high-speed camera, respectively. Finally, an attempt is made to utilize non-scaled parameters to characterize the atomization process, useful for extrapolating the sensitivity analys...
International Journal of Heat and Mass Transfer, 2021
Despite the wide-spread applications of spray drying in the production of chemicals, food, and ph... more Despite the wide-spread applications of spray drying in the production of chemicals, food, and pharmaceuticals, accurate control and development of this unit remains an elusive task because of the complex interactions of variables and phenomena. In this paper, we offer the development of a computationally efficient closed-loop system with a model predictive controller (MPC) where a computational fluid dynamics (CFD) process model is utilized to represent the process behavior. In particular, we present the development of an MPC and its implementation within the CFD model of a lab-scale spray dryer. Dynamic model is created with an adopted CFD model based on a 2D axisymmetric dryer, and Reaction Engineering Approach (REA)- as the drying kinetic method. Then, an MPC control strategy is designed using a linear approximation of a data-driven dynamic model and implemented within the CFD simulation as a user-defined function (UDF). We demonstrate the application of the developed MPC within...
Live foliage for some tree and shrub species can support flaming fire spread at much higher moist... more Live foliage for some tree and shrub species can support flaming fire spread at much higher moisture content than dead fuel materials. However, the role of live fuels in forest fires has been controversial in the past decades. Although ignition and spread statistical data for live and dead fuels exist in the literature, a clear understanding of the fundamental difference in the burning behavior is missing. To illuminate the role of live fuel on forest fire spreading, a laboratory ignition experiment was designed to examine the burning behavior of live Norway spruce needles. A Schlieren-Infrared combined measurement apparatus was developed with a spatial resolution of 0.75 mm and a time resolution of 0.0025 s, to visualize/measure the ignition behavior of live fuels. Schlieren and IR images revealed that the ejection of live fuel volatiles can alter the flame direction and induce previously unaccounted heating of the nearby fuel. Depending on the conditions, these interferences could...
Cable-stayed bridges are being constructed more frequently due to their architectural appeal, eas... more Cable-stayed bridges are being constructed more frequently due to their architectural appeal, ease of construction, and lower cost and environmental footprint in comparison to other bridge types. On some more recent bridges of that type built in the past 10-20 years, the stay-cables are comprised of greased-and-sheathed, stranded steel wires enclosed in high density polyethylene (HDPE) pipes with the interstices filled with a cementatious grout. This design is susceptible to voids in the grout, which can possibly promote cracking in the HDPE piping and reduce the ability of the corrosion protection to safeguard the wires. Several non-destructive techniques have been used to detect defects (voids) in stay cables. In this work, voids in stay cables are studied using passive infrared thermography during solar irradiation over days from sunrise to sunset. Effects of stay cable material properties, time of day, solar orientation and void sizes on the capacity of passive infrared thermogr...
In this work, small-scale experiments of fire whirl were conducted to study the spinning fire phe... more In this work, small-scale experiments of fire whirl were conducted to study the spinning fire phenomenon and to gain comprehensive understandings of fire tornadoes and the factors that affect their behavior. High speed imaging was used to track the flames at both temporal and spatial scales. This allowed us to better understand the role of the near-ground height in creating a boundary layer flow profile that, in turn contributes to formation of vortices around the fire, and consequent fire whirls. Based on the results obtained from these observations, we were able to spot the differences in the fuel burning rate of the fire itself as a function of a newly defined specific non-dimensional near-ground height. Based on our observations, there is a cutoff non-dimensional height, beyond which a normal fire can be turned into a fire whirl. Additionally, the results showed that the fire burning rate decreases by moving the fire to a height higher than the ground level. These effects were j...
Wind tunnel laboratory fires spreading through laser-cut cardboard fuel beds were instrumented an... more Wind tunnel laboratory fires spreading through laser-cut cardboard fuel beds were instrumented and analyzed for physical processes associated with spread. Flames in the span-wise direction appeared as a regular series of peaks-and-troughs that scaled directly with flame length. Flame structure in the stream-wise direction fluctuated with the forward advection of coherent parcels that originated near the rear edge of the flame zone. Thermocouples arranged longitudinally in the fuel beds revealed the frequency of these temperature fluctuations decreased with flame length but increased with wind speed. The downstream extent of these fluctuations scaled with Froude number and flame zone depth. These behaviors are remarkably similar to those of boundary layers, suggesting a dominant role for buoyancy in determining wildland fire spread.
Many developing countries suffer from high energy-import dependency and inadequate electrificatio... more Many developing countries suffer from high energy-import dependency and inadequate electrification of rural areas, which aggravates the poverty problem. In this work, Al-Tafilah in Jordan was considered as a case study, where the technical, economic, and environmental benefits of a decentralized hybrid renewable energy system that can match 100% of the city demand were investigated. A tri-hybrid system of wind, solar, and hydropower was integrated with an energy storage system and optimized to maximize the match between the energy demand and production profiles. The optimization aimed at maximizing the renewable energy system (RES) fraction while keeping the levelized cost of electricity (LCOE) equal to the electricity purchase tariff. The techno-economic analysis showed that the optimal system in Al-Tafilah comprises a 28 MW wind system, 75.4 MW PV, and 1 MW hydropower, with a 259 MWh energy storage system, for which a RES fraction of 99% can be achieved, and 47,160 MtCO2 are avoid...
Abstract Spray drying as a primary powder synthesis tool is not designed to separate particles du... more Abstract Spray drying as a primary powder synthesis tool is not designed to separate particles during the process. Here we report on the simulation, optimization, and development of a customized multi-bin cyclone for a lab-scale spray dryer to segregate particles based on their sizes. Two criteria were chosen to optimize the number of bins, cutoff size, and pressure drop. Accordingly, a non-dimensional factor describing cyclone performance was introduced by investigating which five bins of powder collection were found to render a compromise between competing factors. Spray-dried powders were administered to the cyclone, and deposition of the particles in the bins was recorded. The cyclone could segregate particles with a size resolution as low as 4 μm. For each bin, the data on particle size, morphology, pore attributes, BET surface, and moisture content showed that even within a single batch, there is a broad span of particle properties.
Recently, remarkable developments have taken place, leading to significant improvements in microf... more Recently, remarkable developments have taken place, leading to significant improvements in microfluidic methods to capture subtle biological effects down to single cells. As microfluidic devices are getting sophisticated, design optimization through experimentations is becoming more challenging. As a result, numerical simulations have contributed to this trend by offering a better understanding of cellular microenvironments hydrodynamics and optimizing the functionality of the current/emerging designs. The need for new marketable designs with advantageous hydrodynamics invokes easier access to efficient as well as time-conservative numerical simulations to provide screening over cellular microenvironments, and to emulate physiological conditions with high accuracy. Therefore, an excerpt overview on how each numerical methodology and associated handling software works, and how they differ in handling underlying hydrodynamic of lab-on-chip microfluidic is crucial. These numerical mean...
In this study, we evaluated the fundamental physical behavior during droplet formation and flow f... more In this study, we evaluated the fundamental physical behavior during droplet formation and flow from a rotary bell spray in the absence of an electrostatic field. The impact of a wide range of operating parameters of the rotary bell sprayer, such as flow rates, rotational speeds, and spatial positioning, on droplet sizes and size distributions using a three-dimensional (3-D) mapping was studied. The results showed that increasing the rotational speed caused the Sauter mean diameter of the droplets to decrease while increasing flow rate increased the droplet sizes. The rotational speed effect, however, was dominant compared to the effect of flow rate. An increase in droplet size radially away from the cup was noted in the vicinity of the cup, nevertheless, as the lateral distances from the cup and rotational speed were increased, the droplet sizes within the flow field became more uniform. This result is of importance for painting industries, which are looking for optimal target dist...
This brief paper explains the slight differences in governing equations for a fluid film in a spi... more This brief paper explains the slight differences in governing equations for a fluid film in a spinning cone, and the mechanism that reduces the order of a solution. Spinning cones with a centrally supplied fluid that spreads over its inner surface as a thin film have been the subject of interest for many years. Though often cast as a mathematical analysis, understanding this process is important, especially in the application of automotive painting. The analysis consists of a system of equations obtained from the Navier–Stokes equations along with simple boundary conditions that describe radial and tangential momentum conservation. Solutions to this system of equations are shown using several techniques. The connection between these techniques is slightly subtle. However, the conditions that enable reduction of order are clear once they are exposed. Directional velocity profiles in the film can be a combination of four roots in the complex plane. This system of roots also contains t...
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Papers by Nelson Akafuah