• International Journal of Fluid Machinery and Systems
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• v.7 no.3
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• pp.86-93
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• 2014

This paper describes performance enhancement of a regenerative blower used for a 20 kW fuel cell system. Two design variables, bending angle of an impeller and blade thickness of an impeller tip, which are used to define an impeller shape, are introduced to enhance the blower performance. Internal flow of the regenerative blower has been analyzed with three-dimensional Navier-Stokes equations to obtain the blower performance. General analysis code, CFX, is introduced in the present work. SST turbulence model is employed to estimate the eddy viscosity. Throughout the numerical analysis, it is found that the thickness of impeller tip is effective to increase the blower efficiency in the present blower. Pressure is successfully increased up to 2.8% compared to the reference blower at the design flow condition. And efficiency is also enhanced up to 2.98 % compared to the reference one. It is noted that low velocity region disturbs to make strong recirculation flow inside the blade passages, thus increases local pressure loss. Detailed flow field inside the regenerative blower is also analyzed and compared.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.135-140
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• 2010

An important goal in diesel engine research is the development of a means to reduce the emissions of nitrogen oxides (NOX). The use of a cooled exhaust gas recirculation (EGR) system is one of the most effective techniques currently available for reducing nitrogen oxides. Since Particular Matter (PM) fouling reduces the efficiency of an EGR cooler, a trade-off exists between the amount of NOX and PM emissions, especially at high engine loads. In the present study, engine dynamometer experiments have been performed to investigate the heat exchange characteristics of the stack-type EGR coolers with wave fin pitches of 3.6 and 4.6 mm. The results show that the heat exchange effectiveness is decreased as surface area decrease with pitch of 4.6 mm due to PM fouling. As surface area increase at pitch of 3.6 mm, super-cooling happens in the recirculated exhaust gas.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.42-47
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• 2004

Air-fuel mixing and flame-holding are two important factors that have to be considered in the design of an injection system. Different injection strategies have been proposed with particular concern for rapid air-fuel mixing and flame-holding. Two representative injection techniques can be applied in a supersonic combustor. One of the simplest approaches is a transverse(normal) injection. The cavity flame holder, an integrated fuel injection/flame-holding approach, has been proposed as a new concept for flame holding and air-fuel mixing in a supersonic combustor. This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of a model scramjet engine combustor, where hydrogen is injected into a supersonic cross flow and a cavity. The combustion phenomena in a model scramjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, were observed around the separation region of the transverse injector upstream and the inside cavity. The results show that this flow separation generates recirculation regions which increase air-fuel mixing. Self-ignition occurs in the separation-freestream and cavity-fteestream interfaces.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.766-774
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• 2017

Software has been developed for simulating particle dispersion in a circular pipe with sudden-expansion, which models the fuel feeding system of a combustor that uses metal powder like aluminum as fuel. The Lagrangian based discrete tracer point method was employed for a plug flow of particles that satisfies local turbulent velocity fluctuations. A radial velocity component was created to improve the flow turning outwards in the recirculation zone. The particle distribution patterns from both with and without the component were directly compared with the experiments near the reattachment.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.1
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• pp.121-126
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• 2016

Hydraulic performance of a micro-bubble pump has been analyzed by numerical simulation and experimental measurements. Flow recirculation apparatus between the pump inlet and outlet reserviors has been adopted to measure pump performance according to flow conditions sequentially. To analyze three-dimensional flow field in the micro-bubble pump, general analysis code, CFX, is employed. SST turbulence model is employed to estimate the eddy viscosity and compared the pump performance to k-${\varepsilon}$ model. Unstructured grids are used to represent a composite grid system including blade, casing and inlet casing. It is found that the numerical model used in the present study is effective to evaluate the pump performance. From the numerical simulation, low velocity region due to pressure loss is decreased where pump efficiency has maximum value. Detailed flow field inside the micro-bubble pump is also analyzed and compared.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.25-31
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• 2006

Controlled Auto Ignition(CAI) combustion has great potential in achieving significant increase in engine efficiency, while simultaneously reducing exhaust emissions. The process itself involves the auto ignition and subsequent simultaneous combustion of a premixed charge. In this study, NVO(Negative Valve Overlap) system was applied to a CAI engine in order to use residual gas. The fuel was injected directly to the cylinder under the high temperature condition resulting from heating the intake port to initiate CAI combustion. This paper introduced the valve timing strategy and experimental set-up. From this study, the effect of engine speed and valve timing on CAI combustion and exhaust emissions was clarified. In addition, stratified charge method was used to extend CAI operating region.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.6
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• pp.608-614
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• 2015

Nitrogen oxide(NOx) emission reductions are required to meet the strict emission regulations for environmental protection. Most of the Exhaust Gas Recirculation(EGR) system applied to a diesel engine can relatively decrease the NOx at a low cost, but it has a disadvantage in that the PM generation is promoted due to the hot intake air temperature. Thus, high heat exchange efficiency of the EGR cooler is required for an effective removal of NOx. In this study, heat exchange efficiency for various types of heat exchangers used in EGR cooler was measured under same conditions, and determined best heat exchange performance shape depending on type of heat exchanger.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.4
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• pp.104-111
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• 2016

The flame stabilization is one of the topics which have to be solved for the airbreathing propulsion systems, using the entering air which is supersonic velocity as an oxygen sources. Making a recirculation zone with an eddy flow, installed the reducing velocity devices such as the bluff body, is the typical method of the flame stabilization. Recently using a cavity flame stabilization at the wall is an emerging technique as an effective method which extends the stabilization zone, and the related research papers have been published on the flow separation and reattachment, pressures and oscillations including length/depth ratios in the cavities. Even though, still there are lots of topics to study more in the cavity flame stabilization field as the preceding techniques, as well as the research and the development of the airbreathing propulsion system itself.

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.4003-4013
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• 2021

During the long-term cooling (LTC) phase of a loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR), water is supplied from the containment sump to the reactor coolant system (RCS) by the flooded sump water to the Reactor Vessel (RV) through the broken pipes. As part of the technical efforts for resolving GSI-191 [( Reid and Crytzer, May. 2007) 1, consideration is needed for the consequences of debris penetrating the sump screen and propagating downstream into the RV. Injection of debris (fiberglass) into the RV during the LTC recirculation phase needs special attention to assure that reactor core cooling is maintained. The point of concern is the potential for debris to adversely affect the reactor core flow paths or heat transfer [2]. However, all the experiments for proving the coolability of RV have been done with the assumption of the most of debris would be transferred to the RV and the bottom nozzle of the FAs. The purpose of the tests is to quantify the amount of the debris that would be accumulated at the lower plenum and the debris that passes through the FAs since non-conservatism of other researches assumptions that have been used in the past experimental or analytical programs.

• Journal of Microbiology and Biotechnology
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• v.33 no.4
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• pp.419-429
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• 2023

Ultraviolet C (UV-C, 200-280 nm) light has germicidal properties that inactivate a wide range of pathogenic and spoilage microorganisms. UV-C has been extensively studied as an alternative to thermal decontamination of fruit juices. Recent studies suggest that the efficacy of UV-C irradiation in reducing microorganisms in fruit juices is greatly dependent on the characteristics of the target microorganisms, juice matrices, and parameters of the UV-C treatment procedure, such as equipment and processing. Based on evidence from recent studies, this review describes how the characteristics of target microorganisms (e.g., type of microorganism/strain, acid adaptation, physiological states, single/composite inoculum, spore, etc.) and fruit juice matrices (e.g., UV absorbance, UV transmittance, turbidity, soluble solid content, pH, color, etc.) affect the efficacy of UV-C. We also discuss the influences on UV-C treatment efficacy of parameters, including UV-C light source, reactor conditions (e.g., continuous/batch, size, thickness, volume, diameter, outer case, configuration/arrangement), pumping/flow system conditions (e.g., sample flow rate and pattern, sample residence time, number of cycles), homogenization conditions (e.g., continuous flow/recirculation, stirring, mixing), and cleaning capability of the reactor. The collective facts indicate the immense potential of UV-C irradiation in the fruit juice industry. Existing drawbacks need to be addressed in future studies before the technique is applicable at the industrial scale.