Handbook of Environmental Degradation of Materials, 2005
Under the premise of ensuring the protective effect, it is of great significance to design the op... more Under the premise of ensuring the protective effect, it is of great significance to design the optimal protective suit. In this paper, under the premise of analyzing the basic temperature distribution, the optimal thickness of the protective clothing is optimized. First, a temperature distribution model based on the heat transfer equation. The partial differential equations of temperature, time and spatial position are written for fabric layers I, II, III and air layer IV respectively. The initial and boundary conditions are given according to the measured external temperature and thermodynamic laws of skin. The finite difference method is used to numerically solve the partial differential equations to obtain the temperature distribution at different time and space. It was found that the human skin temperature increased with time and reached a steady state at time t=1645s. Then the optimal thickness is solved. Under the condition of meeting the basic safety requirements, the constraint optimization model with the optimal II layer thickness (ie the thinnest and the lowest cost) as the objective function is established. Then use the particle swarm optimization algorithm based on dynamic target method to solve. The optimum layer thickness was found to be 6.2 mm. Finally, the model was tested. Using the finite element heat transfer analysis of ANSYS workbanch to simulate the temperature distribution in the actual material, the similarity is high, which proves that the temperature distribution model is more accurate. This model can be extended to other heat transfer related clothing and container optimal thickness design.
A skin burn model using variable thermophysical properties as a function of water content is stud... more A skin burn model using variable thermophysical properties as a function of water content is studied as it is subjected to a heat flux at the skin surface. The model employs the finite element method to solve Pennes' [1] bio-heat equation as it is subjected to heat fluxes modeled from actual sensor test data. The model assesses burn damage using the burn integral of Henriques [2] using burn-threshold criteria Ω at both the epidermal-dermal and dermal-subcutaneous tissue interface. The model's times-to-degree burn, cumulative burn damage Ω, and peak temperatures are studied as the blood perfusion rate and water contents for the respective layers of skin are separately and arbitrarily varied. Results from the variable- and constant-property Pennes' models are compared.
In this project, a numerical model of heat and moisture transport in firefighter protective cloth... more In this project, a numerical model of heat and moisture transport in firefighter protective clothing during a flash fire exposure is presented. A mathematical model is constructed to study transient heat and moisture transport through multi-layer fabric assemblies. The model accounts for changes in thermodynamic and transport properties of the fabric due to the presence of moisture. Numerical simulations are performed to study heat and moisture transport through wet fabrics when subjected to intensive flash fire exposure. The numerical model is compared with experimental data from different garment configurations. The distributions of temperature and moisture content in the fabric during the exposure to the flash fire as well as during the cooldown period are calculated. The numerical solutions are further analyzed to provide a detailed physical understanding of the transport processes. Moisture in the fabric vaporizes starting from the outside to the inside during heating, and then...
In this paper the filament winding process was analyzed to relate process variables to structural... more In this paper the filament winding process was analyzed to relate process variables to structural parameters. An analytical model has been developed for a filament wound preform by determining the necessary geometric and kinematic conditions. An equation of motion of winding was developed to predict layer by layer geometry using the mandrel shape as the initial boundary condition. This model provides the laws of motion of the traverse stroke relative to the mandrel to ensure that the filament laydown is of the predetermined geodesic path over the mandrel, that the winding density is distributed over the mandrel in the prearranged manner, and that the winding build is being formed to reproduce the preassigned shape or contour of the preform. From this analysis, the winding process parameters can be controlled accordingly to produce any given shape. The analytical model was used to produce computer simulation of the winding process. The dynamic simulation of the winding process visual...
The hydrodynamic stability of the growing conduction layer in an extensive fluid above a horizont... more The hydrodynamic stability of the growing conduction layer in an extensive fluid above a horizontal surface has been investigated both analytically and experimentally. The analysis involved a study of the stability of convective flows in the vicinity of a horizontal surface suddenly generating a spatially uniform and time independent heat flux in an extensive fluid. The transport phenomenon occurring next to such a horizontal flat surface is formalized herein in terms of new hydrodynamic stability equations, which constitute a two-point-boundary-value eigenvalue problem. These equations were derived using conservation laws and by assuming that periodic small disturbances are superimposed on a base flow. A simple new dimensionless parameter arose. These stability equations are stiff and were integrated using a computer code designed for especially precise solutions of two-point-value problems. Associated measurements using color Schlieren photography and a data acquisition system wer...
Technologies for color removal of a highly colored industrial waste stream were evaluated. A mixe... more Technologies for color removal of a highly colored industrial waste stream were evaluated. A mixed stream with specific concentration and peak absorbance values exceeding 500 absorbs was the target for this experi- mental study. Combined ultraviolet light and hydrogen peroxide, carbon adsorp- tion, ion exchange, and ozone were assessed for their efficiency in treating the waste stream. Initial bench scale testing indicated that ozone was the only viable technology. A pilot scale unit was developed and used to determine ozone dosages necessary to treat the waste stream. Ozonation was run in a batch reactor using a venturi injector with ozone generation from air. The effects of pH and dilution on color removal of the waste steam were evalu- ated. Biological toxicity of the ozonated deodorized waste stream to an existing activated sludge treatment process was determined.
From theoretical considerations, a custom slug calorimeter heat flux transducer was developed for... more From theoretical considerations, a custom slug calorimeter heat flux transducer was developed for experimental use in the measurement of heat fluxes transferred through layers of fabric to the surface of a human mannequinduring simulated flash fire conditions. This paper describes the determination of the transducer's physical size, its limitations and heat loss considerations, a computer simulation of transducer operation and the evaluation of transient heat flux measurements. The transducer's loss factors were predicted numerically and determined experimentally. The overall performance of the transducer was also examined under varying simulated applied heat flux input.
A higher amount of post industrial and post consumer fiber waste has been accumulated, due to the... more A higher amount of post industrial and post consumer fiber waste has been accumulated, due to the growth in world population, overall improvement of living standards and global fiber consumption. General descriptions of fibrous waste, statistics, material characteristics (compositions) and sources in the world were provided. The state-of-the-art of textile wastes recycling has been presented. Varied recycling technologies have been developed so as to maximize the use of the fibrous waste collected. Prevailing recycling technologies, including reusing, recycling, incineration, and landfill, are reviewed. Some promising recycling techniques, such as dissolution and deploymerization, which are applicable to valuable PET or nylon, were focused upon in this paper. The summary on some selected recycling technologies and products from the recycling processes was also offered. Different combinations of incineration, materials recycling, and biological treatment of biodegradable waste, or la...
ABSTRACT A novel type of hybrid membrane has been fabricated by incorporating superacidic sulfate... more ABSTRACT A novel type of hybrid membrane has been fabricated by incorporating superacidic sulfated zirconia (S-ZrO2) fibers into recast Nafion for proton exchange membrane fuel cells (PEMFCs). With the introduction of electrospun superacidic fiber mats, a large amount of protogenic groups aggregated in the interfacial region between S-ZrO2 fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had high proton conductivities, which were controlled by selectively adjusting the fiber diameter and fiber volume fraction. Consequently, the superacidic S-ZrO2 electrospun fibers are promising filler materials and hybrid membranes containing S-ZrO2 fiber mats can be potentially used in high-performance fuel cells.
ABSTRACT The presence of voids is one of the major problems associated with resin infiltration te... more ABSTRACT The presence of voids is one of the major problems associated with resin infiltration techniques when using 3-D woven preforms. Efforts to reduce the voids invariably result in the creation of microcracks. In this paper, the use of PEEK fibers intermingled with carbon fibers into a multi-layer preform is discussed. Influence of processing parameters, such as temperature, pressure, and consolidation time, on the composite properties is presented. One of the issues emphasized is the effect of pressure on buckling of the Z-reinforcement fibers and the bending behavior.
Handbook of Environmental Degradation of Materials, 2012
Fabric systems that include all clothing and other textile-based goods are altered when exposed t... more Fabric systems that include all clothing and other textile-based goods are altered when exposed to intense heat or flames; however, the characteristics of these changes are vastly different depending on the fiber type, cloth structure, the nature of finish applied, amount of moisture trapped within the garment, and the compactness of its various components. Burning of fabric swatches, an old trade method for quick fibers identification, would illustrate that cloth composition and fiber compactness dictates the effortless motion of gases within a structure. Loosely woven knitted light fabric or nonwoven mats promote a propagation of fire within the material in a much faster procession than a tight heavy fabric structure would support. Cloth system flammability is also affected by the surface morphology of the fabric as well as the moisture trapped within the structure or absorbed by the fiber materials. A high amount of free fiber ends extending beyond the plane of the fabric would also support a prompt fire spread throughout the cloth. Fire-retardant chemical additives are usually applied to natural fibers to essentially delay the combustion onset and, therefore, provide additional time to control or attenuate the flames.
This paper describes research on the effects of absorbed moisture on the thermal protective perfo... more This paper describes research on the effects of absorbed moisture on the thermal protective performance of the fire fighter turnout materials exposed to thermal assaults lower than flashover conditions. A thermal testing platform and sensor are used to measure thermal protective performance of turnout systems exposed to a sub flashover heat flux range 6.3 kw/m2 (0.15 cal/ cm2 s). The effects of moisture level on predicted second-degree burn injury for turnout systems having different moisture vapor permeability and total heat loss are discussed. Heat transfer analysis and experimental results show that, for selected test conditions, moisture negatively impacts protective performance most severely when the amount of added moisture is at a comparatively low level (15–20% of turnout system weight).
This research developes a numerical model to predict skin burn injury resulting from heat transfe... more This research developes a numerical model to predict skin burn injury resulting from heat transfer through a protective garment worn by an instrumented manikin exposed to laboratory-controlled flash fire exposures. This model incorporates characteristics of the simulated flash fire generated in the chamber and the heat-induced changes in fabric thermophysical properties. The model also accounts for clothing air layers between the garment and the manikin. The model is validated using an instrumented manikin fire test system. Results from the numerical model help contribute to a better understanding of the heat transfer process in protective garments exposed to intense flash fires, and to establishing systematic methods for engineering materials and garments to produce optimum thermal protective performance.
The influence of fibers on the fatigue cracking resistance of asphalt concrete is investigated us... more The influence of fibers on the fatigue cracking resistance of asphalt concrete is investigated using fracture energy. Nylon, a popular facing yarn of carpets, is used for the actual recycled carpet fibers in asphalt pavement. The experimental program is designed with two phases: the single fiber pull-out test and the indirect tension strength test. Through pull-out tests of 15-denier single nylon fibers, the critical fiber embedded length is determined to be 9.2 mm. As for indirect tension strength tests, samples of asphalt concrete mixed with nylon fibers of two lengths, 6 and 12 mm, based on results of the pull-out tests (critical embedded length) and three volume fractions, 0.25, 0.5, and 1%, are prepared and tested. Asphalt concrete samples fabricated with fibers of 1% and 12 mm results in 85% higher fracture energy than non-reinforced specimens, showing improved fatigue cracking resistance. Although an optimized asphalt mix design with fibers has not been developed for this stu...
Page 1. JON P. RUST HECHMI HAMOUDA ELIZABETH R. HEWITT Department of Textile Engineering, Chemist... more Page 1. JON P. RUST HECHMI HAMOUDA ELIZABETH R. HEWITT Department of Textile Engineering, Chemistry and Science North Carolina State University JAMES W. SHELNUTT Department of Engineering Technology ...
International Journal of Heat and Mass Transfer, 1991
ABSTRACT The hydrodynamic stability considered here is formulated in terms of a two-point boundar... more ABSTRACT The hydrodynamic stability considered here is formulated in terms of a two-point boundary-value, eigenvalue problem derived by assuming periodic small disturbances superimposed on a time-dependent base-state which is the quiescent growing conduction layer resulting from a step in surface heat flux. Since the local heat flux field is similar, a dimensionless similarity parameter arises. The assumed disturbance form is guided by previous stability investigations. The stiff equations are integrated to obtain the neutral stability curve with an extreme at Gr = 202.19, alpha = 1.151, and C(r) = 0.0. Although the postulated disturbance form allowed for time-dependent periodic oscillation, the computed disturbance wave velocity is found to be identically zero for the entire curve. Thus, it is presumed that the assumed oscillatory component of the perturbation is not time dependent, during the instability onset, at least for the calculated range (202 less-than-or-equal-to Gr less-than-or-equal-to 1000). Thus, unlike analyses for steady base-states, these results prohibit 'tracking' disturbances along constant frequency paths. Nevertheless, experimental results suggest that the wave number should decrease with increasing Gr as the neutral curve is crossed by the perturbation.
This study describes an approximate theoretical analysis of drying a moving wet fabric exposed to... more This study describes an approximate theoretical analysis of drying a moving wet fabric exposed to constant radiant heat and hot air blown normal to its surface. By considering the problem as a combination of heat and mass transfer processes, the governing dimensionless groups are identified and their influence on the residence time is established. These groups are then utilized in
Novel conductive inorganic fiber/polymer hybrid proton exchange membranes (PEMs) were obtained by... more Novel conductive inorganic fiber/polymer hybrid proton exchange membranes (PEMs) were obtained by taking advantage of sulfated zirconia (S-ZrO 2) fibers made by electrospinning and post-electrospinning processes. Induced by electrospun inorganic fibers, long-range ionic channels were formed by agglomerating functional groups, which served as continuous hopping pathways for protons and significantly improved the proton conductivity of PEMs.
A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) ele... more A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) electrospun fibers into Nafion for the application in proton exchange membrane fuel cells. With the introduction of S-PS fiber mats, a large amount of sulfonic acid groups in Nafion aggregated onto the interfaces between S-PS fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had higher proton conductivities than that of recast Nafion, and the conductivities were controlled by selectively adjusting the fiber diameters. Consequently, hybrid membranes fabricated by ionomers, such as Nafion, incorporated with ionic-conducting nanofibers established a promising strategy for the rational design of high-performance proton exchange membranes.
The effects of various process and material parameters on fabric roll making have been discussed ... more The effects of various process and material parameters on fabric roll making have been discussed in the earlier parts of this series. A number of theoretical models have been proposed to better understand the roll-making process and its effects on the state of stress in a fabric roll. In this analysis, the influence of varying winding tension is investigated. If winding tension can be controlled as a function of fabric properties, undesirable levels of stress in the fabric can be minimized. The principles demonstrated here can be used to develop a process control system.
Handbook of Environmental Degradation of Materials, 2005
Under the premise of ensuring the protective effect, it is of great significance to design the op... more Under the premise of ensuring the protective effect, it is of great significance to design the optimal protective suit. In this paper, under the premise of analyzing the basic temperature distribution, the optimal thickness of the protective clothing is optimized. First, a temperature distribution model based on the heat transfer equation. The partial differential equations of temperature, time and spatial position are written for fabric layers I, II, III and air layer IV respectively. The initial and boundary conditions are given according to the measured external temperature and thermodynamic laws of skin. The finite difference method is used to numerically solve the partial differential equations to obtain the temperature distribution at different time and space. It was found that the human skin temperature increased with time and reached a steady state at time t=1645s. Then the optimal thickness is solved. Under the condition of meeting the basic safety requirements, the constraint optimization model with the optimal II layer thickness (ie the thinnest and the lowest cost) as the objective function is established. Then use the particle swarm optimization algorithm based on dynamic target method to solve. The optimum layer thickness was found to be 6.2 mm. Finally, the model was tested. Using the finite element heat transfer analysis of ANSYS workbanch to simulate the temperature distribution in the actual material, the similarity is high, which proves that the temperature distribution model is more accurate. This model can be extended to other heat transfer related clothing and container optimal thickness design.
A skin burn model using variable thermophysical properties as a function of water content is stud... more A skin burn model using variable thermophysical properties as a function of water content is studied as it is subjected to a heat flux at the skin surface. The model employs the finite element method to solve Pennes' [1] bio-heat equation as it is subjected to heat fluxes modeled from actual sensor test data. The model assesses burn damage using the burn integral of Henriques [2] using burn-threshold criteria Ω at both the epidermal-dermal and dermal-subcutaneous tissue interface. The model's times-to-degree burn, cumulative burn damage Ω, and peak temperatures are studied as the blood perfusion rate and water contents for the respective layers of skin are separately and arbitrarily varied. Results from the variable- and constant-property Pennes' models are compared.
In this project, a numerical model of heat and moisture transport in firefighter protective cloth... more In this project, a numerical model of heat and moisture transport in firefighter protective clothing during a flash fire exposure is presented. A mathematical model is constructed to study transient heat and moisture transport through multi-layer fabric assemblies. The model accounts for changes in thermodynamic and transport properties of the fabric due to the presence of moisture. Numerical simulations are performed to study heat and moisture transport through wet fabrics when subjected to intensive flash fire exposure. The numerical model is compared with experimental data from different garment configurations. The distributions of temperature and moisture content in the fabric during the exposure to the flash fire as well as during the cooldown period are calculated. The numerical solutions are further analyzed to provide a detailed physical understanding of the transport processes. Moisture in the fabric vaporizes starting from the outside to the inside during heating, and then...
In this paper the filament winding process was analyzed to relate process variables to structural... more In this paper the filament winding process was analyzed to relate process variables to structural parameters. An analytical model has been developed for a filament wound preform by determining the necessary geometric and kinematic conditions. An equation of motion of winding was developed to predict layer by layer geometry using the mandrel shape as the initial boundary condition. This model provides the laws of motion of the traverse stroke relative to the mandrel to ensure that the filament laydown is of the predetermined geodesic path over the mandrel, that the winding density is distributed over the mandrel in the prearranged manner, and that the winding build is being formed to reproduce the preassigned shape or contour of the preform. From this analysis, the winding process parameters can be controlled accordingly to produce any given shape. The analytical model was used to produce computer simulation of the winding process. The dynamic simulation of the winding process visual...
The hydrodynamic stability of the growing conduction layer in an extensive fluid above a horizont... more The hydrodynamic stability of the growing conduction layer in an extensive fluid above a horizontal surface has been investigated both analytically and experimentally. The analysis involved a study of the stability of convective flows in the vicinity of a horizontal surface suddenly generating a spatially uniform and time independent heat flux in an extensive fluid. The transport phenomenon occurring next to such a horizontal flat surface is formalized herein in terms of new hydrodynamic stability equations, which constitute a two-point-boundary-value eigenvalue problem. These equations were derived using conservation laws and by assuming that periodic small disturbances are superimposed on a base flow. A simple new dimensionless parameter arose. These stability equations are stiff and were integrated using a computer code designed for especially precise solutions of two-point-value problems. Associated measurements using color Schlieren photography and a data acquisition system wer...
Technologies for color removal of a highly colored industrial waste stream were evaluated. A mixe... more Technologies for color removal of a highly colored industrial waste stream were evaluated. A mixed stream with specific concentration and peak absorbance values exceeding 500 absorbs was the target for this experi- mental study. Combined ultraviolet light and hydrogen peroxide, carbon adsorp- tion, ion exchange, and ozone were assessed for their efficiency in treating the waste stream. Initial bench scale testing indicated that ozone was the only viable technology. A pilot scale unit was developed and used to determine ozone dosages necessary to treat the waste stream. Ozonation was run in a batch reactor using a venturi injector with ozone generation from air. The effects of pH and dilution on color removal of the waste steam were evalu- ated. Biological toxicity of the ozonated deodorized waste stream to an existing activated sludge treatment process was determined.
From theoretical considerations, a custom slug calorimeter heat flux transducer was developed for... more From theoretical considerations, a custom slug calorimeter heat flux transducer was developed for experimental use in the measurement of heat fluxes transferred through layers of fabric to the surface of a human mannequinduring simulated flash fire conditions. This paper describes the determination of the transducer's physical size, its limitations and heat loss considerations, a computer simulation of transducer operation and the evaluation of transient heat flux measurements. The transducer's loss factors were predicted numerically and determined experimentally. The overall performance of the transducer was also examined under varying simulated applied heat flux input.
A higher amount of post industrial and post consumer fiber waste has been accumulated, due to the... more A higher amount of post industrial and post consumer fiber waste has been accumulated, due to the growth in world population, overall improvement of living standards and global fiber consumption. General descriptions of fibrous waste, statistics, material characteristics (compositions) and sources in the world were provided. The state-of-the-art of textile wastes recycling has been presented. Varied recycling technologies have been developed so as to maximize the use of the fibrous waste collected. Prevailing recycling technologies, including reusing, recycling, incineration, and landfill, are reviewed. Some promising recycling techniques, such as dissolution and deploymerization, which are applicable to valuable PET or nylon, were focused upon in this paper. The summary on some selected recycling technologies and products from the recycling processes was also offered. Different combinations of incineration, materials recycling, and biological treatment of biodegradable waste, or la...
ABSTRACT A novel type of hybrid membrane has been fabricated by incorporating superacidic sulfate... more ABSTRACT A novel type of hybrid membrane has been fabricated by incorporating superacidic sulfated zirconia (S-ZrO2) fibers into recast Nafion for proton exchange membrane fuel cells (PEMFCs). With the introduction of electrospun superacidic fiber mats, a large amount of protogenic groups aggregated in the interfacial region between S-ZrO2 fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had high proton conductivities, which were controlled by selectively adjusting the fiber diameter and fiber volume fraction. Consequently, the superacidic S-ZrO2 electrospun fibers are promising filler materials and hybrid membranes containing S-ZrO2 fiber mats can be potentially used in high-performance fuel cells.
ABSTRACT The presence of voids is one of the major problems associated with resin infiltration te... more ABSTRACT The presence of voids is one of the major problems associated with resin infiltration techniques when using 3-D woven preforms. Efforts to reduce the voids invariably result in the creation of microcracks. In this paper, the use of PEEK fibers intermingled with carbon fibers into a multi-layer preform is discussed. Influence of processing parameters, such as temperature, pressure, and consolidation time, on the composite properties is presented. One of the issues emphasized is the effect of pressure on buckling of the Z-reinforcement fibers and the bending behavior.
Handbook of Environmental Degradation of Materials, 2012
Fabric systems that include all clothing and other textile-based goods are altered when exposed t... more Fabric systems that include all clothing and other textile-based goods are altered when exposed to intense heat or flames; however, the characteristics of these changes are vastly different depending on the fiber type, cloth structure, the nature of finish applied, amount of moisture trapped within the garment, and the compactness of its various components. Burning of fabric swatches, an old trade method for quick fibers identification, would illustrate that cloth composition and fiber compactness dictates the effortless motion of gases within a structure. Loosely woven knitted light fabric or nonwoven mats promote a propagation of fire within the material in a much faster procession than a tight heavy fabric structure would support. Cloth system flammability is also affected by the surface morphology of the fabric as well as the moisture trapped within the structure or absorbed by the fiber materials. A high amount of free fiber ends extending beyond the plane of the fabric would also support a prompt fire spread throughout the cloth. Fire-retardant chemical additives are usually applied to natural fibers to essentially delay the combustion onset and, therefore, provide additional time to control or attenuate the flames.
This paper describes research on the effects of absorbed moisture on the thermal protective perfo... more This paper describes research on the effects of absorbed moisture on the thermal protective performance of the fire fighter turnout materials exposed to thermal assaults lower than flashover conditions. A thermal testing platform and sensor are used to measure thermal protective performance of turnout systems exposed to a sub flashover heat flux range 6.3 kw/m2 (0.15 cal/ cm2 s). The effects of moisture level on predicted second-degree burn injury for turnout systems having different moisture vapor permeability and total heat loss are discussed. Heat transfer analysis and experimental results show that, for selected test conditions, moisture negatively impacts protective performance most severely when the amount of added moisture is at a comparatively low level (15–20% of turnout system weight).
This research developes a numerical model to predict skin burn injury resulting from heat transfe... more This research developes a numerical model to predict skin burn injury resulting from heat transfer through a protective garment worn by an instrumented manikin exposed to laboratory-controlled flash fire exposures. This model incorporates characteristics of the simulated flash fire generated in the chamber and the heat-induced changes in fabric thermophysical properties. The model also accounts for clothing air layers between the garment and the manikin. The model is validated using an instrumented manikin fire test system. Results from the numerical model help contribute to a better understanding of the heat transfer process in protective garments exposed to intense flash fires, and to establishing systematic methods for engineering materials and garments to produce optimum thermal protective performance.
The influence of fibers on the fatigue cracking resistance of asphalt concrete is investigated us... more The influence of fibers on the fatigue cracking resistance of asphalt concrete is investigated using fracture energy. Nylon, a popular facing yarn of carpets, is used for the actual recycled carpet fibers in asphalt pavement. The experimental program is designed with two phases: the single fiber pull-out test and the indirect tension strength test. Through pull-out tests of 15-denier single nylon fibers, the critical fiber embedded length is determined to be 9.2 mm. As for indirect tension strength tests, samples of asphalt concrete mixed with nylon fibers of two lengths, 6 and 12 mm, based on results of the pull-out tests (critical embedded length) and three volume fractions, 0.25, 0.5, and 1%, are prepared and tested. Asphalt concrete samples fabricated with fibers of 1% and 12 mm results in 85% higher fracture energy than non-reinforced specimens, showing improved fatigue cracking resistance. Although an optimized asphalt mix design with fibers has not been developed for this stu...
Page 1. JON P. RUST HECHMI HAMOUDA ELIZABETH R. HEWITT Department of Textile Engineering, Chemist... more Page 1. JON P. RUST HECHMI HAMOUDA ELIZABETH R. HEWITT Department of Textile Engineering, Chemistry and Science North Carolina State University JAMES W. SHELNUTT Department of Engineering Technology ...
International Journal of Heat and Mass Transfer, 1991
ABSTRACT The hydrodynamic stability considered here is formulated in terms of a two-point boundar... more ABSTRACT The hydrodynamic stability considered here is formulated in terms of a two-point boundary-value, eigenvalue problem derived by assuming periodic small disturbances superimposed on a time-dependent base-state which is the quiescent growing conduction layer resulting from a step in surface heat flux. Since the local heat flux field is similar, a dimensionless similarity parameter arises. The assumed disturbance form is guided by previous stability investigations. The stiff equations are integrated to obtain the neutral stability curve with an extreme at Gr = 202.19, alpha = 1.151, and C(r) = 0.0. Although the postulated disturbance form allowed for time-dependent periodic oscillation, the computed disturbance wave velocity is found to be identically zero for the entire curve. Thus, it is presumed that the assumed oscillatory component of the perturbation is not time dependent, during the instability onset, at least for the calculated range (202 less-than-or-equal-to Gr less-than-or-equal-to 1000). Thus, unlike analyses for steady base-states, these results prohibit 'tracking' disturbances along constant frequency paths. Nevertheless, experimental results suggest that the wave number should decrease with increasing Gr as the neutral curve is crossed by the perturbation.
This study describes an approximate theoretical analysis of drying a moving wet fabric exposed to... more This study describes an approximate theoretical analysis of drying a moving wet fabric exposed to constant radiant heat and hot air blown normal to its surface. By considering the problem as a combination of heat and mass transfer processes, the governing dimensionless groups are identified and their influence on the residence time is established. These groups are then utilized in
Novel conductive inorganic fiber/polymer hybrid proton exchange membranes (PEMs) were obtained by... more Novel conductive inorganic fiber/polymer hybrid proton exchange membranes (PEMs) were obtained by taking advantage of sulfated zirconia (S-ZrO 2) fibers made by electrospinning and post-electrospinning processes. Induced by electrospun inorganic fibers, long-range ionic channels were formed by agglomerating functional groups, which served as continuous hopping pathways for protons and significantly improved the proton conductivity of PEMs.
A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) ele... more A novel type of hybrid membrane was fabricated by incorporating sulfonated polystyrene (S-PS) electrospun fibers into Nafion for the application in proton exchange membrane fuel cells. With the introduction of S-PS fiber mats, a large amount of sulfonic acid groups in Nafion aggregated onto the interfaces between S-PS fibers and the ionomer matrix, forming continuous pathways for facile proton transport. The resultant hybrid membranes had higher proton conductivities than that of recast Nafion, and the conductivities were controlled by selectively adjusting the fiber diameters. Consequently, hybrid membranes fabricated by ionomers, such as Nafion, incorporated with ionic-conducting nanofibers established a promising strategy for the rational design of high-performance proton exchange membranes.
The effects of various process and material parameters on fabric roll making have been discussed ... more The effects of various process and material parameters on fabric roll making have been discussed in the earlier parts of this series. A number of theoretical models have been proposed to better understand the roll-making process and its effects on the state of stress in a fabric roll. In this analysis, the influence of varying winding tension is investigated. If winding tension can be controlled as a function of fabric properties, undesirable levels of stress in the fabric can be minimized. The principles demonstrated here can be used to develop a process control system.
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