Maintaining IAQ (Internal Air Quality) and thermal comfort of occupants in buildings have been a challenge to overcome satisfying the two ends: criteria for sustainability and cost effectiveness. Although there was a movement for mechanical ventilation systems in the recent past, in addition to the cost involved, they are found to not deliver the desired air quality, lead to social consequences such as sick building syndrome, contribute to environmental consequences related to ozone-depleting substances with increasing energy consumption, generate noise and having difficulties in cleaning and maintaining. These consequences compelled research on natural ventilation systems, which were used in ancient buildings. Although it has been found that natural ventilation of buildings can become a substantial architectural design tool that leads to “breathing architecture,” fluctuations in indoor temperature and air quality makes depending entirely on natural ventilation less effective. The combination of natural and mechanical ventilation, the hybrid ventilation or mixed-mode ventilation, systems utilizes advantages and eliminates drawbacks from both mechanical and entirely dependent natural ventilation systems. Hybrid ventilation systems, which have been utilized in historical buildings, with less investment cost and reduction of energy usage have been found to be a solution to provide acceptable standards of IAQ and thermal comfort through natural air circulation in buildings. This research study was carried out to verify the effectiveness of a hybrid ventilation system in an auditorium built around 60 years back for its effectiveness as a provider of thermal comfort to its occupants. Computational Fluid Dynamic (CFD) modeling was carried out on a Finite Element (FE) model owing to its capability of offering a wide range of flexible analytical solutions, lower realization time and comparative cost effectiveness to experimental methods of modeling. This verification of the system has revealed that hybrid ventilation systems could provide effective thermal comfort in buildings designed specifically to allow circulation of air through the system. The results of the study were in agreement with measured data and the expected flow of air through the building when the thermal load due to metabolism of occupants was not included in the analysis. In addition, the expected results complied with similar studies on natural/hybrid ventilation systems. With the addition of the thermal load, as a uniform heat flux from the flow of the auditorium, it was observed that the conditioning of the air throughout the space was better than the without thermal load scenario. In the case modeling people as cylinders, with a convective heat flux, it was observed that the air flow direction changes and the seating level of the auditorium do not get sufficient air flow to maintain a comfortable air quality.  Ineffective simulation of the inlet louver was assumed to be the primary reason for this scenario and other reasons such as the seating arrangement modeling too could have effects on the result. As conclusions of the study it was found that the whole building system properties have to be selected, as the control component to produce operating commands, to circulate air through the building in accordance with the air flow: both velocity and patterns, required to maintain thermal comfort of all occupants. Air inflow could be through windows as acquisition components to collect indoor and outdoor climatic parameters and air outflow could be mechanically controlled through exhausted fans turning on or off as the operating component in the system. The result of the study ensures the method of solutions through CFD to be utilized to provide effective and less costly path to verify systems such as natural or hybrid air flow systems through buildings.  The whole system studied could be applied with suitable contextual modifications to any new location, with similar cost effective modeling, to produce less fuel consuming building systems leading to sustainability of built environment.

The triboelectrification of particles by contact or frictional charging is known to be an operational challenge in the polyolefin industry. Particularly in polyethylene production, gas-solid fluidized bed reactors are known to be susceptible to electrostatic charging due to the rigorous mixing of polyethylene and catalyst particles in a dry environment. The presence of charged particles coupled with a highly exothermic polymerization reaction results in sheet formation on the reactor walls. This behaviour can decrease reactor performance and obstruct the system, consequently forcing a shutdown for reactor maintenance. The generation of electrostatic charge in fluidized beds has been widely studied throughout the years; however, limited attention has been paid to the simulation and modeling of this phenomenon. Since it is difficult to accurately quantify the charge generation in industrial fluidized beds, developing an electrostatic model based on material properties would considerably aid in providing insight on this occurrence and its effects. A computational fluid dynamics (CFD) model that incorporates this electrostatic model can then be used as a predictive tool in research and development. Simulating electrostatic charging in gas-solid fluidized beds would be a cost-effective alternative to running experiments on them, especially for industrial-scale test runs. In this thesis, an electrostatic charging model was developed to be used in conjunction with an Euler-Euler Two-Fluid CFD model to simulate triboelectrification and its effects in gas-solid flows. The electrostatic model was first established for mono-dispersed gas-particle flows and was validated using past experimental findings of particle charging for gas-solid fluidization runs. With the goal of providing a realistic representation of gas-solid fluidization of polyethylene resins with a wide particle-size distribution, the electrostatic model was extended to consider bi-dispersed particulate flow systems. Simulation results using this model show the prediction of bipolar charging when the particles have different sizes, even though they are made of the same material. This phenomenon is analyzed and is shown to be driven by the electric field produced by the charge accumulated on the particles. Experimental studies of particle-wall and particle-particle contact charging were performed to investigate the electrostatic and mechanical parameters that are crucial for modeling the magnitude and direction of charge transfer in gas-solid flow systems. Particle-wall contact charging due to single and repeated collisions were tested with various particles, including commercial linear low-density polyethylene, to determine their rates of charging as well as their charge saturation limits when colliding with a metal surface. Plotting the charge saturation value of the particles against their respective surface areas revealed a linear trend which could be used to calculate the charge saturation of the particle for a given particle size. Additional particle-wall charging studies include the effect of initial charge, collision frequency, particle type, impact angle, impact velocity and the presence of impurities on particle charging. To study particle-particle contact charging, a novel apparatus was designed, built, and tested to determine the magnitude and direction of charge transfer due to the individual particle-particle collisions of insulator particles. This apparatus was the first of its kind, and it ensured that the measured charge transfer for each experimental trial was solely due to the binary collision between the particles. It was observed that the direction of charge transfer in identical particle collisions is not dictated by the net initial charges of the particles, but the localized charge difference at the particles’ contacting surface. Moreover, particle-particle collisions of nylon particles of varying sizes confirmed the bipolar charging phenomena, where the direction of charging was dictated by the relative size of the colliding particles. These findings, among others, contradict the charge transfer behavior predicted by electrostatic charging models currently proposed for particle-particle collisions. As such, it was concluded that an empirically accurate charge transfer model needs to be established to simulate the electrostatic charging of particles in poly-dispersed gas-solid flow systems.

Polymers used in enhanced oil recovery (EOR) help to control the mobility ratio between oil and aqueous phases and as a result, polymer flooding improves sweep efficiency in reservoirs. However, the conventional wisdom is that polymer flooding does not have considerable effect on pore-level displacement because pressure forces would not be enough to overcome trapping caused by capillary forces. Recently, both coreflood experiments and field data suggest that injecting viscoelastic polymers, such as hydrolyzed polyacrylamide (HPAM), can result in lower residual oil saturation. The hypothesis is that the polymer elasticity provides several pore-level mechanisms for oil mobilization that are generally not significant for purely-viscous fluids. Both experiments and modeling need to be performed to investigate the effect of polymer elasticity on residual oil saturation. Pore-scale modeling and micro-fluidic experiments can be used to investigate pore-level physics, and then used to upscale to the macro-scale. The objective of this work is to understand the effect of polymer elasticity on apparent viscosity and residual oil saturation in porous media. Single- and multi-phase pore-level computational fluid dynamics (CFD) modeling for viscoelastic polymer flow is performed to investigate the dominant mechanisms at the pore level to mobilize trapped oil. Several interesting results are found from the CFD results. First, the elasticity of the polymer results in an increase in normal stress at the pore-level; therefore, the normal stresses exerted on a static oil droplet are significant and not negligible as for a purely-viscous fluid. The CFD results show that viscoelastic fluid exerts additional forces on the oil-phase which may help mobilize trapped oil out of the porous medium. Second, due to the elasticity of polymer, the viscoelastic polymer has some level of pulling effect; while passing above a dead-end pore it can pull out the trapped oil phase and then mobilize it. However, both CFD modeling and micro-fluidic experiments show the pulling-effect is not likely the main mechanism to reduce oil saturation at pore-level. Third, dynamic CFD simulations show less deformation of the oil phase while viscoelastic polymer is displacing fluid compared to purely viscous fluid. It may justify the hypothesis that polymer elasticity resists against snap-off mechanism. As a result, when viscoelastic polymer displaces the oil ganglia, the oil phase does not snap off, and the oil phase remains connected, and therefore easier to move in porous media compared to disconnected oil. For single phase flow, a closed-form flow equation has been developed based on CFD modeling in converging/diverging ducts representative of pore throats. The pore-level equations were substituted into a pore-network model and validated against experimental data. Good agreement is observed. This study reveals important findings about the effect of polymer elasticity to reduce the residual oil saturation; however, more experiments and simulations are recommended to fully-understand the mobilization mechanisms and take advantage of them to optimize the polymer-flooding process in the field. / text

Biomass, as a renewable energy resource, can be utilized to generate chemicals, heat, and electricity. Compared with biomass combustion, biomass gasification is more eco-friendly because it generates less amount of green gas (CO2) and other polluting gases (NOx and SO2). This research is focused on biomass gasification using a circulating fluidized bed. In the gasifier, fully fluidized biomass particles react with water vapor and air to generate syngas (CO and H2). A comprehensive model, consisting of three modules, hydrodynamics, mass transfer and energy transfer modules, is built to simulate this process using ANSYS Fluent software and C programming language. In the hydrodynamics module, the k-epsilon turbulence equations are coupled with the fluctuating energy equation to simulate gas-particle interaction in the turbulent flows occurring in the riser. In the mass transfer and energy transfer modules, heat transfer and mass transfer in turbulent flows are simulated to solve for the profiles of temperature and species concentration in the gasifier. The impacts of thermal radiation, water gas shift reaction (WGS), equivalence ratio (ER), and char combustion product distribution coefficient are also investigated to gain deeper understanding of biomass gasification process.

abstract: Buildings and other structures, all components and cladding thereof, shall be designed and constructed to resist the wind loads are required in all wind codes. Simple quasi-static treatment of wind loads, which is universally applied to design of low to medium-rise structures, can be either overly conservative or erroneous under-estimated for design of high-rise structures. Dynamic response, vortex, wind directionality, and shedding from other structures are all complicated key factors suppose to be considered in design. Meanwhile, wind tunnel testing is expansive, difficult and sometimes inaccurate even if it is a widely used method in simulation of aerodynamic response. Computational Fluid dynamics (CFD), historically, were two-dimensional (2D) method using conformal transformations of the flow about a cylinder to the flow about an airfoil were developed in the 1930s. A number of three-dimensional (3D) codes were developed, leading to numerous commercial packages, which is more accessible and economical for wind load analysis. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2014

Carefully engineered mine ventilation is critical to the safe operation of underground longwall mines. Currently, there are several options for simulation of mine ventilation. This research was conducted to rapidly simulate an underground longwall mine, especially for the use of tracer gas in an emergency situation. In an emergency situation, limited information about the state of mine ventilation system is known, and it is difficult to make informed decisions about safety of the mine for rescue personnel. With careful planning, tracer gases can be used to remotely ascertain changes in the ventilation system. In the meantime, simulation of the tracer gas can be conducted to understand the airflow behavior for improvements during normal operation. Better informed decisions can be made with the help of both tracer gas technique and different modeling approaches. This research was made up of two main parts. One was a field study conducted in an underground longwall mine in the western U.S. The other one was a simulation of the underground longwall mine with different approaches, such as network modeling and Computational Fluid Dynamics (CFD) models. Networking modeling is the most prevalent modeling technique in the mining industry. However, a gob area, which is a void zone filled with broken rocks after the longwall mining, cannot be simulated in an accurate way with networking modeling. CFD is a powerful tool for modeling different kinds of flows under various situations. However, it requires a significant time investment for the expert user as well as considerable computing power. To take advantage of both network modeling and CFD, the hybrid approach, which is a combination of network modeling and CFD was established. Since tracer gas was released and collected in the field study, the tracer gas concentration profile was separately simulated in network modeling, CFD model, and hybrid model in this study. The simulated results of airflow and tracer gas flow were analyzed and compared with the experimental results from the field study. Two commercial network modeling software packages were analyzed in this study. One of the network modeling software also has the capability to couple with CFD. A two-dimensional (2D) CFD model without gob was built to first analyze the accuracy of CFD. More 2D CFD models with gob were generated to determine how much detail was necessary for the gob model. Several three-dimensional (3D) CFD models with gob were then created. A mesh independence study and a sensitivity study for the porosity and permeability values were created to determine the optimal mesh size, porosity and permeability values for the 3D CFD model, and steady-state simulation and transient simulations were conducted in the 3D CFD models. In the steady-state simulation, a comparison was made between the 3D CFD models with and without taking the diffusivity of SF6 in air into account. Finally, the different simulation techniques were compared to measured field data, and assessed to determine if the hybrid approach was considerably simpler, while also providing results superior to a simple network model. / Master of Science

Dust is a detrimental, but unavoidable, consequence of any mining process. It is particularly problematic in underground coal mining, where respirable coal dust poses the potential health risk of coal workers’ pneumoconiosis (CWP). Float dust, if not adequately diluted with rock dust, also creates the potential for a dust explosion initiated by a methane ignition. Furthermore, recently promulgated dust regulations for lowering a miner’s exposure to respirable coal dust will soon call for dramatic improvements in dust suppression and capture. Computational fluid dynamics (CFD) results are presented for a research project with the primary goal of applying a flooded-bed dust scrubber, with high capture and cleaning efficiencies, to a Joy 7LS longwall shearer operating in a 7-ft (2.1 m) coal seam. CFD software, Cradle is used to analyze and evaluate airflow patterns and dust concentrations, under various arrangements and conditions, around the active mining zone of the shearer for maximizing the capture efficiency of the scrubber.

There is a lack of fundamental studies by means of state of the art numerical and scale modeling techniques scrutinizing the theoretical and technical aspect of air table separators as well as means to comprehend and improve the efficiency of the process. The dissertation details the development of a workable empirical model, a numerical model and a scale model to demonstrate the use of a laboratory air table unit. The modern air-based density separator achieves effective density-based separation for particle sizes greater than 6 mm. Parametric studies with the laboratory scale unit using low rank coal have demonstrated the applicability with regards to finer size fractions of the range 6 mm to 1 mm. The statistically significant empirical models showed that all the four parameters, i.e, blower and table frequency, longitudinal and transverse angle were significant in determining the separation performance. Furthermore, the tests show that an increase in the transverse angle increased the flow rate of solids to the product end and the introduction of feed results in the dampening of airflow at the feed end. The higher table frequency and feed rate had a detrimental effect on the product yield due to low residence time of particle settlement. The research further evaluated fine particle upgrading using various modeling techniques. The numerical model was evaluated using K-Epsilon and RSM turbulence formulations and validated using experimental dataset. The results prove that the effect of fine coal vortices forming around the riffles act as a transport mechanism for higher density particle movement across the table deck resulting in 43% displacement of the midlings and 29% displacement of the heavies to the product side. The velocity and vector plots show high local variance of air speeds and pressure near the feed end and an increase in feed rate results in a drop in deshaling capability of the table. The table was further evaluated using modern scale-modeling concepts and the scaling laws indicated that the vibration velocity has an integral effect on the separation performance. The difference between the full-scale model and the scaled prototype was 3.83% thus validating the scaling laws.

Incorporating insulation material with phase change materials (PCMs) could help enhance the insulation capability for a refrigerator system. The phase change material can absorb or release large amount of latent heat of fusion depending on surrounding temperatures for efficient thermal management. This research focuses on how incorporating PCM to the conventional PU foam insulation affects the inside temperatures of the refrigerator system and in-turn helps in conserving energy by reducing the compressor run time. It was found that only 0.25-inch-thick PCM layer in insulation can certainly benefit the refrigerators by reducing the amount of electricity consumption and thus increasing the total energy savings through the numerical study results via COMSOL Multiphysics in this study. This work aims to investigate a PCM-incorporated insulation material to accomplish the enhancement of thermal insulation performance for refrigerators.

Escalating energy and environmental issues are driving researchers and industries throughout the world to study gas separation. Being common toxic gases, volatile organic compounds (VOCs) must be removed from the atmosphere. When compared to the conventional adsorption process, e.g. packed bed to separate VOC, the adsorbent hollow fibre has exhibited advantages in low-pressure drop, easy operation and lower capital cost with high adsorption performance. This research investigates the optimisation and development of single and multi-channel adsorbent hollow fibres to improve the mechanical properties, flexibility, adsorbent loading and enhance adsorption capacity. These fibres are made up of an adsorbent (13X zeolite, HiSiv 1000 zeolite powder and HiSiv 3000 zeolite powder) held together with a polymer (polyethersulfone) binder through wet/wet spinning followed by a phase inversion process. Single adsorbent hollow fibres were optimised by changing the ratio of adsorbent to the polymer, the viscosity of polymer/adsorbent/solvent mixtures, the pre-treatment temperature and by adding a pore former. This optimal recipe of polymer/adsorbent/solvent mixtures was then used to fabricate tri-lobe and hexagonal multi-channel adsorbent hollow fibre. The adsorption performance and mechanical properties of these multi-channel fibres were compared to those of the single adsorbent hollow fibres. Dynamic adsorption challenges were carried out using n-butane as the VOC model gas to provide breakthrough curves using a flame ionisation detector (FID) hydrocarbon analyser. Scanning electron microscopy (SEM) was used to characterise the surface and porous structures of the different adsorbent hollow fibres formation. Adsorption isotherm experiments were also used to measure the surface area of adsorbent hollow fibres. In order to understand the transport mechanism of gases through adsorbent hollow fibres, single and multi-channel fibres were modelled using a computational fluid dynamics (CFD) using COMSOL software 5.2, thus enabling the prediction of breakthrough time and mass transfer for the new geometries of adsorbent hollow fibre.