• 정보저장시스템학회논문집
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• 제8권2호
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• pp.72-77
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• 2012

The demand for the laptop computer has been increased day by day and most of users ask quiet computer and devices to work in comfortable environment. One of the devices which generate acoustic noise is an external ODD. Unlike the internal ODD, the external ODD is easy to emit noise because it runs outside of the computer and also it is packed with a thin plastic covers. As the disk rotates, vortex flow is generated inside of the cavity due to various and complicated mold parts of the cover. In addition, there is a gap between the disk tray and the upper/lower cases, through which the air flows as well as the noise leaks. In this study, we have proposed how to reduce the acoustic noise of an external ODD using numerical and experimental analysis. The pressure fluctuations and turbulent kinetic energy distributions are calculated for the developed model. The results show that the sound pressure level is reduced by 2.3dB through simple modifications of ribs of the top cover, which remove or suppress flow instabilities inside of the cavity.

• Wind and Structures
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• 제11권6호
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• pp.479-496
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• 2008

In this paper, computer simulation of wind flow around a single cooling tower with louver support at the base in the KAZERUN power station in south part of IRAN is presented as a case study. ANSYS FLOTRAN, an unstructured finite element incompressible flow solver, is used for numerical investigation of wind induced pressure load on a single cooling tower. Since the effects of the wind ribs on external surface of the cooling tower shell which plays important role in formation of turbulent flow field, an innovative relation is introduced for modeling the effects of wind ribs on computation of wind pressure on cooling tower's shell. The introduced relation which follows the concept of equivalent sand roughness for the wall function is used in conjunction with two equations ${\kappa}-{\varepsilon}$ turbulent model. In this work, the effects of variation in the height/spacing ratio of external wind ribs are numerically investigated. Conclusions are made by comparison between computed pressure loads on external surface of cooling tower and the VGB (German guideline for cooling tower design) suggestions.

• Membrane and Water Treatment
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• 제2권2호
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• pp.75-89
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• 2011

The predicting equations for mass transfer rate in cross-flow rectangular dialyzers with double flow and recycle, have been derived by mass balances. The recycling operation has two conflicting effects. One is the desirable effect of the increase in fluid velocity, resulting in an increased mass transfer coefficient. The other is the undesirable effect of the reduction in concentration difference due to remixing, resulting in decreased mass-transfer driving force. In contrast a single-pass device without recycling, considerable improvement in mass transfer is achieved if the cross-flow rectangular dialyzer of same size is operated with double pass and external recycling. It is concluded that recycle can enhance mass transfer, especially for larger reflux ratio.

• 한국해양공학회지
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• 제10권3호
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• pp.105-116
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• 1996

In this paper, we report the experimental results for the flow pattern and the material transport around a cavity subject to a sinusoidal external flow at the far region to ward the open side of the cavity. A tilting mechanism is used to generate a oscillatory flow inside a shallow rectangular container having a cavity at one side. The surface flow visualization is performed to obtain the unsteady behavior of vortices generated at two edges situated at the entrance of the cavity. It was found that at the period 4.5 sec., the behavior of the vortices is asymmetric, and there exists a steady residual flow in the cavity. The bottom flow patterns are also visualized. There are two regions outside of the cavity where the bottom fluid particles concentrate. The material transport in this flow model is very peculiar; fluid particles in the cavity flows outward through the passage along the walls starting from the edges, and particles in the outer region approach the cavity from the central region.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1999년도 추계학술발표회요약집
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• pp.190-190
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• 1999

CHF (Critical heat flux) on the external surface of the reactor vessel lower head is major key in the evaluation on the feasibility of IVR-EVC (In-Vessel Retention through External Vessel Cooling) concept. To identify the CHF on the external surface, considerable works have been performed. Through the review on the previous works related to the CHF on the external surface, liquid subcooling, induced flow along the external surface, ICI (In-Core Instrument) nozzle and minimum gap are identified as major parameters. According to the present analysis, the effects of the ICI nozzle and minimum gap on CHF are pronounced at the upstream of test vessel: on the other hand, the induced flow considerably affects the CHF at downstream of test vessel. In addition, the subcooling effect is shown at all of test vessel, and decreases with the increase in the elevation of test vessel. In the real application of the IVR-EVC concept, vertical position is known as a limiting position, at which thermal margin is the minimum. So, it is very important to precisely predict the CHF at vertical position in a viewpoint of gaining more thermal margins. However, the effects of the liquid subcooling and induced flow do not seem to be adequately included in the CHF correlations suggested by previous works, especially at the downstream positions.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.304-309
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• 1997

A method to mitigate the thermal stratification flow of a horizontal pipe line is proposed by heating external bottom of the pipe with electrical heat tracing. Unsteady two dimensional model has been used to numerically investigate an effect of the external Denting to the thermally stratified flow. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature distribution, streamline profile and Nusselt numbers of fluids and pipe walls with time are analyzed in case of externally heating condition. no numerical result of this study shows that the maximum dimensionless temperature difference between the hot and the cold sections of pipe inner wall is 0.424 at dimensionless time 1,500 ann the thermal stratification phenomena is disappeared at about dimensionless time 9,000. This result means that external heat tracing can mitigate the thermal stratification phenomena by lessening $\Delta$ $T_{ma}$ about 0.1 and shortening the dimensionless time about 132 in comparison with no external heat tracing.rnal heat tracing.

• 한국가시화정보학회지
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• 제9권3호
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• pp.44-50
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• 2011

In this study, we propose a method for characterizing fluid-mechanical properties of a fluid surface, such as surface dilatational and shear viscosity, by matching the flow visualization and the numerical simulation for a Stokes flow in a three-dimensional cavity. The surface flow is driven by shear stress exerted on the free surface by an external gas flow. The external gas flow is simulated by using a commercial code, while the Stokes flow is calculated by an in-house code. We have found that the surface flow is very sensitive to the surface tension and other properties. The qualitative feature of the surface flow can be reproduced by the parameter tuning.

• 한국통신학회논문지
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• 제30권2B호
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• pp.1-10
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• 2005

빠른 데이터 처리를 위하여 기존에는 소프트웨어방식으로 구현되었던 TCP/IP를 고속의 하드웨어로 구현함에 있어, TCP/IP 하드웨어와 외부 블록간의 통신을 중계하는 블록인 Host Interface를 구현하였다. Host Interface는 TCP/IP 하드웨어와 외부 블록의 중간에 위치하여 외부 블록과의 통신을 위해 AMBA AHB 규약을 따른다. Host Interface는 내부의 Command/Status Register를 통하여 CPU와 TCP/IP 하드웨어 간의 명령, 상태, 헤더 정보 등을 전달하는데 이 때에는 AMBA AHB의 Slave로서 동작한다. Data Flow를 위해서 Host Interface는 AMBA AHB의 Master로서 동작하는데, 데이터 흐름의 방향에 따라 Data flow는 데이터를 수신하는 Receive flow와 데이터를 패킷으로 만들어 보내는 Transmit Flow로 나된다. Rx Flow의 경우, UDP 블록이나 TCP Buffer로부터 받은 데이터를 내부의 작은 RxFIFO를 통해 외부 RxRAM에 써서 CPU가 읽어갈 수 있도록 하고, Tx Flow의 경우에는 외부 TxRAM에서 전송할 데이터를 읽어 와서 TxFIFO를 거쳐 UDP Buffer나 TCP Buffer에 씀으로써 패킷을 만들어 보내도록 한다. 외부 RAM의 액세스에는 Command/Status Register에 위치한 Buffer Descriptor의 정보를 이용하게 된다. Host Interface는 이러한Data Flow의 원활한 흐름을 위해서 여러 세부 기능들을 수행하게 된다. Host Interface의 기능을 검증하기 위하여 여러 testcase들이 수행되었으며, 0.18 마이크론 기술을 사용하여 synthesis한 결과, 내부의 Command/Status Register와 FIFO를 모두 포함하여 약 173K 게이트가 소요됨을 보았다.

• Nuclear Engineering and Technology
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• 제49권5호
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• pp.979-988
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• 2017

The feasibility of cooling in a pressurized heavy water reactor after a large break loss-of-coolant accident has been analyzed using Multidimensional Analysis of Reactor Safety-KINS Standard code during the recirculation phase. Through evaluation of sensitivity of the fuel channel temperature to various effective recirculation flow areas, it is determined that proper cooling of the fuel channels in the broken loop is feasible if the effective flow area remains above approximately 70% of the nominal flow area. When the flow area is reduced by more than approximately 25% of the nominal value, however, incipience of boiling is expected, after which the thermal integrity of the fuel channel can be threatened. In addition, if a dramatic reduction of the recirculation flow occurs, excursions and frequent fluctuations of temperature in the fuel channels are likely to be unavoidable, and thus damage to the fuel channels would be anticipated. To resolve this, emergency coolant supply through the newly installed external injection path can be used as one alternative means of cooling, enabling fuel channel integrity to be maintained and permanently preventing severe accident conditions. Thus, the external injection flow required to guarantee fuel channel coolability has been estimated.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.80-83
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• 2004

This experiment has been carried out to measure the process of droplet formation between water phase fluid$(PVA\;3\%)$ and organic phase fluid(oil), Internal and External flow fields measured by a Dynamic Micro-PIV method Water-in-oil(W/O) droplets successfully generated at a cross junction and Y junction. Internal and external flow fields were measured when the droplet grew up, stretched and separated.