RESUMEN

A dissolved air flotation (DAF) system is one of the water treatment processes that purifies contaminants through a buoyancy effect by attaching the moiety of micro-bubbles on their free surface. Since the DAF system was first used in the drinking water treatment in the 1960s, it has been recognized as an effective treatment for the water purification process. Most previous works laid great emphasis on the internal flow behaviors of fluid to improve the purification efficiency of the DAF system. Nevertheless, the practical implementation with a pilot plant indeed revealed some technical incompleteness for the DAF system. To circumvent for the technical incompleteness, numerical simulation based on computational fluid dynamics (CFD) has been carried out to understand the in-depth knowledge on internal flow phenomena in the DAF system. However, the standard k-ε turbulence model has been conventionally used in the most studies without any proper consideration process. Accordingly, the objectives of this study were to investigate the major effects on the internal flow behaviors for an efficient numerical simulation of DAF when a different turbulence model and micro-bubble parameters are used. As a result, the present study found that the standard k-ε model would be not proper for the internal flow simulation of the DAF process and a careful consideration would be required for a more accurate prediction. In addition, the present study examined a desirable internal flow pattern with various operating conditions of the micro-bubble. Consequently, the main findings of this study are expected to provide realistic information to related researchers for designing the DAF system with the optimal operating parameters.

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RESUMEN

An exhaust plume gas flow from a bipropellant thruster has been recognized as a potential source of a load, heat, and contamination on the exposed satellite components which can especially degrade the optical properties and performance of solar panel. Therefore, accurate predictions of a bipropellant thruster plume gas flow and assessments of its influences should be considered at the design phase of a satellite. The objective of the present study is to investigate the plume gas flow behavior of a small bipropellant thruster and to evaluate its influence on the solar array of a GEO satellite numerically. To deal with complex plume flow regimes efficiently, the combined approach of computational fluid dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) was applied depending on the flow characteristic conditions. Throughout the numerical results of the present study, the influences of the plume gas flow exhausted from a single bipropellant thruster were considered for the disturbance, heat, and contamination of the three-dimensional satellite configuration equipped with a large solar array.

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RESUMEN

A space propulsion system is important for the normal mission operations of a spacecraft by adjusting its attitude and maneuver. Generally, a mono- and a bipropellant thruster have been mainly used for low thrust liquid rocket engines. But as the plume gas expelled from these small thrusters diffuses freely in a vacuum space along all directions, unwanted effects due to the plume collision onto the spacecraft surfaces can dramatically cause a deterioration of the function and performance of a spacecraft. Thus, aim of the present study is to investigate and compare the major differences of the plume gas impingement effects quantitatively between the small mono- and bipropellant thrusters using the computational fluid dynamics (CFD). For an efficiency of the numerical calculations, the whole calculation domain is divided into two different flow regimes depending on the flow characteristics, and then Navier-Stokes equations and parallelized Direct Simulation Monte Carlo (DSMC) method are adopted for each flow regime. From the present analysis, thermal and mass influences of the plume gas impingements on the spacecraft were analyzed for the mono- and the bipropellant thrusters. As a result, it is concluded that a careful understanding on the plume impingement effects depending on the chemical characteristics of different propellants are necessary for the efficient design of the spacecraft.

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RESUMEN

In general, a space propulsion system has a crucial role in the normal mission operations of a spacecraft. Depending on the types and number of propellants, a monopropellant and a bipropellant thrusters are mostly utilized for low thrust liquid rocket engines. As the plume gas flow exhausted from these small thrusters expands freely in a vacuum space environment along all directions, adverse effects of the plume impingement onto the spacecraft surfaces can dramatically reduce the function and performance of a spacecraft. Thus, the purpose of the present study is to investigate and compare the major differences of the plume gas flow behaviors numerically between the small monopropellant and bipropellant thrusters. To ensure efficient numerical calculations, the whole physical domain was divided into three different subdomains depending on the flow conditions, and then the appropriate numerical methods were combined and applied for each subdomain sequentially. With the present analysis results, the plume gas behaviors including the density, the overall temperature and the separation of the chemical species are compared and discussed between the monopropellant and the bipropellant thrusters. Consequently, the present results are expected to provide useful information on selecting the appropriate propulsion system, which can be very helpful for actual engineers practically during the design process.

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RESUMEN

CO2 adsorption measurement at 273 K was employed to see if the porous material has either micropore or mesopore dominantly. The adsorption isotherm of CO2 on microporous solid such as zeolite A and Y was the typical Langmuir type while on SBA-15, silica gel and polymer, the adsorption isotherm was proportional to the applied pressure, following the Henry's law. Such distinctive difference between the adsorption isotherms provided the reasonable basis to discriminate the pore characteristics otherwise it was difficult to obtain it. Also, it was possible to get the surface property of polymer due to the pretreatment using CO2 adsorption measurement at 273 K while the N2 adsorption isotherm measurement at 77 K did not give the meaningful data.