• 한국연소학회지
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• 제20권2호
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• pp.46-53
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• 2015

The relationship between mass transfer and reaction within the washcoat is investigated in a monolith type micro-scale Pt-catalytic combustor. Nondimensionalized balance equation of butane is applied in a simplified washcoat geometry having the shape of slab. Both Thiele modulus and effectiveness factor are considered to compare reaction rate and diffusion rate according to the operation temperature and the diameter of alumina nano-pores. The effect of reaction becomes stronger as the temperature increases, while the effect of diffusion becomes relatively dominant as the diameter of nano-pores increases. From the analysis of butane distribution within the washcoat, design criterion for the thickness of washcoat is discussed.

• 한국가시화정보학회지
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• 제9권1호
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• pp.49-54
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• 2011

An investigation has been made of a viscous incompressible flow in a circular cylindrical tank. The flow is driven by the spinning bottom disk of tank together with/without central injection and radial uniform-ejection through the sidewall. Numerical solutions of steady and unsteady flows to 3-dimensional Navier-Stokes equation were obtained for several cases of injection strength. In a moderate flow rate of injection, the mass transfer occurs through the boundary layers but, as the flow rate increases, the inner region far from the container walls takes part in mass transfer.

• KSBB Journal
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• 제8권3호
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• pp.243-255
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• 1993

In this study, it was observed that hydrogen Productivity varied with stirrer speed, bead radius, input glucose concentration and dilution rate in a continuous stirred tank reactor in which immobilized R. rubrum KS-301 was used as a hydrogen-producing bacterium The mass transfer resistance due to cell immobilization was also studied. In order to estimate an effectiveness factor, Des of glucose was first obtained, which was subsequently represented by the correlation equation between Dos and Xb, As a result external mass transfer resistance could be neglected for stirrer speeds greater than 400rpn With bead radius increasing, the hydrogen productivity and internal effectiveness factor decreased. With input 91ucose concentration increasing, the hydrogen productivity and interval and external effectiveness factor increased. Although an Internal effectiveness factor was not affected, hydrogen productivity Increased with dilution rate increasing. An overall effectiveness factor remained nearly constant for the dilution rates investigate4 but increased with input 91ucose concentration increasing.

• Journal of Biosystems Engineering
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• 제20권1호
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• pp.66-72
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• 1995

A numerical study for a two dimensional multi-impingement jet with crossflow of the spent fluid has been carried out. To study the flow characteristics especially in the jet flow region, three different distributions of mass flow rate at 5-jet exits were assumed. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Calculations drew the following items as conclusion. 1) A periodical fully developed flow was observed from the third protrusion. This was also observed from previous experimentally by Whidden at al. The Nessult number at the protrusion surface increased mildly as going downstream. 2) The low Reynolds number turbulence model of Launder and Sharma was found to be adequate for the prediction of fluid flow and heat transfer characteristics of two dimensional multi-jet configuration. 3) The Nusselt number at the protrusion surface was nearly proportional to the square root of the Reynolds number.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.240-245
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• 2001

Phenomena of direct contact condensation (DCC) heat transfer between steam and water are characterized by the transport of heat and mass through a moving steam/water interface. Application of the phenomena of DCC heat transfer to the engineering industries provides some advantageous features in the viewpoint of enhanced heat transfer. This study proposes a simple condensation model on the steam jets discharging into subcooled water from a single horizontal pipe for the prediction of the steam jet shapes. The analysis model was derived from the mass, momentum and energy equations as well as a thermal balance equation with condensing characteristics at the steam/water interface for the axi-symmetric coordinates. The extremely large heat transfer rate at the steam/water interface was reflected in the effective thermal conductivity estimated from the previous experimental results. The analysis results were compared with the experimental ones. The analysis model predicted that the steam jet shape (i. e. radius and length) was increasing as the steam mass flux and the pool temperature were increasing, which was similar in trend to that observed in the experiment.

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.20-25
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• 2011

This work focuses on the behavior of the overpotential increase due to a utilization rise in a molten carbonate fuel cell. The behavior is generally explained by Nernst loss, which is a kind of voltage loss due to the thermodynamic potential gradients in a polarization state due to the concentration distribution of reactant species through the gas flow direction. The evaluation of Nernst loss is carried out with a traditional experimental method of constant gas utilization (CU). On the other hand, overpotential due to the gas-phase mass-transport resistance at the anode and cathode shows dependence on the utilization, which can be measured using the inert gas step addition (ISA) method. Since the Nernst loss is assumed to be due to the thermodynamic reasons, the voltage loss can be calculated by the Nernst equation, referred to as a simple calculation (SC) in this work. The three values of voltage loss due to CU, ISA, and SC are compared, showing that these values rise with increases in the utilization within acceptable deviations. When we consider that the anode and cathode reactions are significantly affected by the gas-phase mass transfer, the behavior strongly implies that the voltage loss is attributable not to thermodynamic reasons, namely Nernst loss, but to the kinetic reason of mass-transfer resistance in the gas phase.

• 동력기계공학회지
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• 제21권3호
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• pp.93-101
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• 2017

In conventional adsorption chamber, adsorbent is embedded in between heat exchanger fins by wire mesh. This method impedes heat and mass transfer efficiency. So in this study, to improve the heat transfer performance of heat exchanger, a fin-tube exchanger was coated with FAPO (Ferroaluminophosphate) zeolite adsorbent. The fin-tube heat exchanger has a fin pitch of 1.8 mm with a variation of adsorbent coating thickness of about 0.1 mm, 0.15 mm and 0.2 mm. By varying cooling water temperature and chilled water temperature respecively, heat transfer rate and overall heat transfer coefficient were investigated. As a result, the heat transfer rate and overall heat transfer coefficient increase with decreasing cooling water temperature and increasing chilled water temperature. Under the basic conditions, the heat transfer rate of heat exchanger with 0.2 mm coating thickness is 11% and 43% higher than that of 0.1 mm and 0.15 mm, respectively. The overall heat transfer coefficient is $189.1W/m^2{\cdot}^{\circ}C$, it is two times lager than that of 0.1 mm.

• 한국기계가공학회지
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• 제21권2호
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• pp.94-100
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• 2022

A study was conducted to significantly increase the heat transfer area by simultaneously burying the excel pipe in the floor and wall of a container house, thereby greatly reducing the initial heating time. In addition, a small hot water boiler suitable for the heating load of a small container house with a maximum area of 6 m² was studied. A wall-mounted hot water boiler was developed as a result of the study. When a hot water boiler is installed outdoors for heating, heat radiation energy is lost in winter from the hot water boiler and hot water pipe due to the low temperature. We propose an approach through which the energy loss was greatly reduced and the temperature of hot water increased in proportion to the operating time. Moreover, as the mass flow rate of the hot water flowing inside the excel pipe increased, the temperature of the hot water decreased. The temperature of the wall and floor surfaces of the container house increased in proportion to the increase in the mass flow rate of hot water flowing inside the excel tube. Natural convection heat transfer was realized from the wall and floor surfaces of the container house, and the heat transfer area was increased by a factor of 3 with respect to heat transfer area limited to the floor by the existing hot water panel. As a result, the initial temperature increase rate was much higher because of the larger heat transfer area.

• 천문학회보
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• 제45권1호
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• pp.42.3-42.3
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• 2020

We investigate the observational properties of Wolf-Rayet stars, suggest the constraint of their mass-loss rate and apply our results to the observed progenitor candidates of Type Ib/Ic supernovae (iPTF13bvn and SN 2017ein). For this purpose, we adopt the WR star models with various mass-loss rates and wind terminal velocities. We obtain the high resolution spectra of those models at the pre-supernova phase using the radiative transfer code CMFGEN. We verify the optically faint property of SN Ic progenitors and show that the optical faintness is mainly originated by the high effective temperature at the photosphere. We also show that a simple analytic model for WR winds using a constant opacity can roughly predict the photospheric parameters. We show that the change of the mass-loss rate and the terminal wind velocity critically affects the optical luminosity. We find the optical luminosities of SN Ic progenitor models with our fiducial mass-loss rate prescription are fainter than the detection limits. We also suggest the mass-loss rate of WR stars may not exceed 2 times of our fiducial value by comparing our predictions with the detection limit of SN Ib/Ic progenitors. The directly observed progenitor candidate of iPTF13bvn can be explained by our SN Ib progenitor models. We find that the SN 2017ein progenitor candidate is too bright and too blue to be a SN Ic progenitor.

• 대한환경공학회지
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• 제33권12호
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• pp.868-873
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• 2011

산소전달률은 음폐수, 축산폐수 그리고 매립지 침출수와 같은 고농도 폐수처리를 호기성 공정으로 처리할 시 그 성과를 결정하는 아주 중요한 요소이다. 본 논문에서는, Jet Loop Reactor (JLR)를 이용하여 공기유량과 동력량을 운전조건의 변수로 두고 미생물의 농도에 따른 산소소비율(Oxygen uptake rate, OUR)과 물질전달계수(Volumetric mass transfer coefficient, $K_L{\cdot}a$)를 측정하였으며, 산출된 $K_L{\cdot}a$ 값의 결과를 가지고 통계학적인 분석을 통하여 비선형 회귀 모형을 제안하여 보았다. 연구 결과, 미생물 농도를 높게 유지시켜야 하는 고농도 폐수를 적용할 경우에는, 동력량과 공기량은 산소전달률의 중요한 인자이며, 마지막으로 최종 비선형 회귀모형을 동력량과, 공기량 그리고 점성계수의 함수로 나타내보았다.