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Kim, Jong-Soo,Kim, Ju-Won,Jung, Hyun-Seok The Korean Society of Mechanical Engineers 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.10
The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.
Zhan, Yinxiao,Park, Tae Seon Elsevier 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.97 No.-
<P><B>Abstract</B></P> <P>Oscillatory flows and heat transfer characteristics in a channel with inclined plates have been numerically investigated. For the fully developed channel flow of 10 ⩽ Re ⩽ 800 , the inclined plates as a vortex generator are installed at the upper wall. To examine the effects of inclined plates on flow bifurcation and attendant heat transfer rates, unsteady simulations are performed for various plate conditions. The resulting flows are classified into three vortical structures of recirculation bubble (RB), standing vortex (SV), and traveling vortices (TV) depending on the Reynolds number and geometrical conditions. The variation of flow pattern is closely related to the spectral characteristics of steady state, periodic state, and quasi-periodic state. Based on these flow patterns and unsteady features, the transition scenario is proposed with increasing the plate angle. The flow is evolved from the steady state to the periodic and quasi-periodic state, and the frequency-locking phenomenon is observed for specific Reynolds numbers at a certain range of plate angle. In addition, the heat transfer enhancement is discussed with flow patterns and unsteady characteristics. The Nusselt numbers continuously increases from the steady state of RB to the periodic state of SV, while their variations are discontinuous when the periodic state of SV is changed into the quasi-periodic state of TV. The flow analyses show that these discontinuities are related to the supercritical Hopf bifurcation and the additional appearances of fundamental frequency. Also, the frequency-locking state before the development of quasi-periodic state with multiple frequencies brings about a jump increase of heat transfer. The disturbed flows by the inclined plates exhibit the logarithmic variation and Nusselt number correlation similar to the transition flow.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oscillatory flows are characterized by three vortical structures. </LI> <LI> The discontinuous variation of <I>Nu</I> is strongly related to the quasi-periodic state. </LI> <LI> The frequency-locking phenomenon depends on the flow development with multiple frequencies. </LI> <LI> The disturbed flows exhibit Nusselt number correlations similar to the transition flow. </LI> </UL> </P>
몰입(flow) 기능의 재구성: 몰입과 행복 관계에 대한 타인맥락의 조절효과를 중심으로
장훈아,한성열 한국사회및성격심리학회 2010 한국심리학회지 사회 및 성격 Vol.24 No.4
The purpose of the present study was to investigate the function of flow in relational context. Previous studies on the function of flow suggested that flow has a positive effect on personal growth and happiness. However, Previous studies were only focused on individual context and aspect of flow. However it was supposed that the function of flow could be changed according to the contexts, the present study focused relational function of flow. In study 1, moderate effects were found that significant other's approval/disapproval, regulation with significant other and self conscious emotion moderated relationship between on flow and happiness. In study 2, the reasons of disapproval on person's flow were that flow activities were not socially valuable and flow pursuing frequently violated relational expectancy. The Results of present studies suggested that the functions of flow could be changed and reconstructed along the contexts. Results of the present research had a valuable implication in that it is not sufficient to conduct a research on individual happiness and positivity only in individual context. Instead, It is necessary that individual positive concepts should be reappraised carefully in relational, interdependent, moral context. 기존 몰입연구는 개인적인 경험측면과 몰입경험이 개인에게 어떠한 긍정적 기능이 있는지 밝히는데 주안점을 두었다. 하지만 본 연구는 몰입경험과 경험의 기능적 측면을 통합적으로 이해하기 위해서 몰입경험에 대한 중요타인의 평가, 중요타인의 평가에 따른 몰입의 심리적 결과물이 어떻게 달라지는지 알아보았다. 이를 위해 연구 1에서는 중요타인의 개인몰입에 대한 동의여부, 몰입으로 인한 자의식 유무, 타인과 의견공유 여부가 몰입과 행복의 관계를 어떻게 조절하는지 알아보았다. 연구 결과, 개인몰입에 대한 중요 타인의 동의여부, 몰입자의식, 의견조율은 몰입수준과 상호작용하여 몰입의 결과물에 영향을 주는 것으로 나타났다. 동의여부, 자의식은 동일한 패턴의 조절효과를 보였고, 의견공유는 반대 패턴의 조절효과를 보였다. 이와 관련해서는 논의부분에 논의 하였다. 연구 2에서는 무엇 때문에 개인의 몰입에 타인이 동의/비동의를 하는지 알아보았다. 연구 결과, 사회적으로 가치 없는 활동, 다른 활동에 지장을 주는 활동에 몰입하는 경우 중요타인은 개인의 몰입에 동의하지 않았고, 사회적 가치가 있는 영역에 몰입하는 것에 동의하는 것으로 나타났다. 이러한 결과를 종합해보면, 타인이 인정할 수 없는 활동에 몰입할 경우, 타인은 개인의 몰입에 대해 부정적인 태도를 취하고, 이는 다시 개인의 몰입의 결과물에 영향을 줄 수 있다고 추론되었다. 이와 관련된 문제를 추가적으로 논의하였다.
Assessment of combined V/Z clamp-on ultrasonic flow metering
전세종,윤병로,강웅,권휴상 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6
Clamp-on ultrasonic flow metering can provide a non-invasive and portable means for flow measurement. However, it indicates flowrates with low measurement accuracy at low flow velocity in pipe flows. Typical accuracy of the clamp-on ultrasonic flow meteringamounts as low as ±1% if the flow velocity in a pipe is greater than 0.5 m/s. The accuracy can be increased greater than ±2% if the flowvelocity is lowered smaller than 0.5 m/s. Inner pipe diameter can be also an influential factor in flow metering when the exact value ofthe inner diameter is not known. The inner pipe diameter cannot be found if the pipe is too large to measure or if there are erosions oradhesions on the inner pipe surface due to small particles in the flow. These shortcomings of the clamp-on ultrasonic flow metering canbe overcome by combining two transit times along a Z-shaped and a V-shaped ultrasonic path. This technique is termed combined V/Zclamp-on ultrasonic flow metering. With the water flow standard system in KRISS, this combined technique exhibited intermediate performancebetween the two flow metering techniques along the Z-shaped and the V-shaped ultrasonic paths. Notably, the combined techniqueshowed better performance (expanded uncertainty less than 0.76%, k = 2) than the two flow metering techniques (1.61% and1.17%, k = 2) in the flow range of (100 ~ 400) m3/h with pipe diameter of 250 mm.
Forces and flow around three side-by-side square cylinders
Qinmin Zheng,Md. Mahbub Alam,S. Rehman,D.K. Maiti 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.1
A numerical investigation on forces and flow around three square cylinders in side-by-side arrangement is conducted at a Reynolds number Re = 150 with the cylinder center-to-center spacing ratio L/W = 1.1 ~ 9.0, where W is the cylinder side width. The flow at this Re is assumed to be two-dimensional, incompressible, and Newtonian. The flow simulation is conducted by using ANSYS-Fluent. The flow around the three side-by-side cylinders entails some novel flow physics, involving the interaction between the gap and free-stream side flows as well as that between the two gap flows. An increase in L/W from 1.1 to 9.0 leads to five distinct flow regimes, viz., base-bleed flow (L/W < 1.4), flip-flopping flow (1.4 < L/W < 2.1), symmetrically biased beat flow (2.1 < L/W < 2.6), non-biased beat flow (2.6 < L/W < 7.25) and weak interaction flow (7.25 < L/W < 9.0). The gap flow behaviors, time-averaged and fluctuating fluid forces, time-averaged pressure, recirculation bubble, formation length, and wake width in each flow regime are discussed in detail.
유량변화에 따른 판형열교환기의 압력강하와 내부유동 가시화에 관한 실험적 연구
황주원(Ju Won Hwang),김덕규(Deok Gyu Kim),박창용(Chang Yong Park) 대한설비공학회 2019 대한설비공학회 학술발표대회논문집 Vol.2019 No.-
This study was carried out to measure the pressure drop and visualize the flow in the flow path between the chevron corrugated two plates in a heat exchanger. A test section was made to visualize the flow characteristics in the flow channels formed by a metal real heat exchanger plate and transparent replica of the counterpart plate. A simple closed loop test facility was made to do the experiment with the change of volume flow rate. The visualization was performed by a high speed camera with 800 fps and air bubbles were injected in the flow to visualize the flow distribution in the channels on the two plates. The measured pressure drop agreed well with the general trend of the pressure drop change with the increase of flow rate. The visualized flow patterns showed that the flow was not evenly distributed in the channels between the two plates, due to the left-sided inlet and outlet location od the flow. The flow visualization with air bubbles showed the limitation to visualize the actual flow velocity distribution on the two plates because Buoyant effect was dominant under upward flow conditions.
Kim, Gangjune,Lee, Jaehong,Park, Junhong,Song, Simon Pergamon 2019 Applied thermal engineering Vol. No.
<P><B>Abstract</B></P> <P>Multi-split air-source heat pumps (ASHPs) have been widely used for both heating and cooling. An electric expansion valve (EEV) is frequently positioned in the indoor unit (IDU), leading to an increase in the two-phase flow noise of the refrigerant. In this study, we experimentally investigated the two-phase flow patterns and flow-induced noise of R410A refrigerant near the EEV in an IDU during the heating cycle of a multi-split ASHP with four IDUs. The flow-induced noise and two-phase flow patterns of horizontal and vertical pipe layouts near the EEV were simultaneously measured under a transient operation condition of temperature (24–38 °C), pressure (1.7–2.7 MPa), and mass flowrate (6.2–41.9 kg/h). The big noise near the EEV was generated for an intermittent flow and a churn/slug flow pattern at the EEV inlet for both horizontal and vertical pipe layouts, respectively. Unlike refrigerators and cooling air-conditioners, a vertical pipe layout has two-phase flow patterns that are advantageous for noise reduction near the EEV because of the high operating mass flux and pressure for R410A of a heating cycle of a multi-split ASHP. The two-phase flow-induced noise of the refrigerant near the EEV was strongly affected by the flow patterns at the EEV’s inlet and outlet. The present study indicates that the flow patterns affected by pipe layout, phase properties, and operating conditions should be considered as one of the important factors in designing a refrigerant system of reduced noise.</P> <P><B>Highlights</B></P> <P> <UL> <LI> R410A two-phase flow of multi-split air-source heat pump cycle was studied. </LI> <LI> Two-phase flow visualization and noise measurement were simultaneously performed. </LI> <LI> Vertical pipe layout resulted in 3 dB lower noise level than horizontal layout. </LI> <LI> Effect of flow pattern on two-phase flow noise overwhelmed those of pipe layout. </LI> </UL> </P>
전세종(Sejong Chun),윤병로(Byung-Ro Yoon),강웅(Woong Kang),권휴상(Hyu-Sang Kwon) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Clamp-on ultrasonic flow metering can provide a non-invasive and portable means for flow measurement. However, the clamp-on ultrasonic flow metering indicates flow rates with low measurement accuracy at low flow velocity in pipe flows. Typical accuracy of the clamp-on ultrasonic flow metering amounts as low as ±1 % if the flow velocity in a pipe is greater than 0.5 m/s. The accuracy can be greater than ±2 % if the flow velocity is lowered smaller than 0.5 m/s. These shortcomings of the clamp-on ultrasonic flow metering can be overcome by combining two transit times along a Z-shaped and a V-shaped ultrasonic path. This technique is named as combined V/Z clamp-on ultrasonic flow metering. With the water flow standard system in KRISS, this combined technique exhibited intermediate performance between the two flow metering techniques along the Z-shaped and the V-shaped ultrasonic paths.
광역 토사재해 물리적 취약성 평가를 위한 Flow-R 모델의 매개변수 분석
강효섭(Kang, Hyo-Sub),김윤태(Kim, Yun-Tae) 한국방재학회 2017 한국방재학회논문집 Vol.17 No.4
This study analyzed effects of input parameters (maximum velocity and travel angle) of Flow-R model on debris flow mobility and deposition, which are essential to evaluate physical vulnerability of debris flow disasters in regional scale. The characteristics of debris flow spreading area and the maximum kinetic energy were analyzed through sensitivity analysis according to input parameters. Back analysis was carried out using total 11 cases of debris flow disasters in 2011, and the reasonable values of input parameters were determined through a comparison with investigated debris flow spreading areas. The results of numerical analysis showed that debris flow spreading area and kinetic energy increased with an increase in maximum velocity, but they converged to asymptote values at critical maximum velocity. The debris flow spreading area decreases with an increase in travel angle. Several case studies showed that travel angles of the 11 debris flow disaster regions were ranged from 10° to 22°, with an average of 15°, and the maximum velocities from 11 m/s to 35 m/s, with an average value of 22 m/s. The estimated travel angle and maximum velocity were compared with the results of previous researches. 본 연구는 광역 토사재해 물리적 취약성 평가를 위해 필요한 Flow-R 입력 매개변수(토석류 최대속도, 이동각)가 토석류의 거동특성에 미치는 영향에 대한 분석을 수행하였다. 입력 매개변수에 따른 민감도 분석을 통해 토석류 확산면적과 최대 운동에너지 변화 특성을 분석하였다. 2011년에 발생한 총 11개 토석류 재해 사례에 대해 Flow-R 모델을 이용하여 역해석을 수행하였고, 조사된 토석류 재해영역과의 비교를 통해 합리적인 입력 매개변수를 산정하였다. 최대속도가 증가함에 따라 토석류 확산범위가 증가하는 것으로 나타났으며, 한계 최대속도 이상에서는 토석류 확산범위가 수렴하는 것으로 나타났다. 이동각이 증가함에 따라 토석류 확산면적은 감소하는 것으로 나타났다. 사례 분석을 통해 산정된 총 11개 토석류 재해지역의 이동각은 10°~22°범위를 나타내며, 평균값은 약 15°로 분석되었다. 역해석을 통해 얻어진 한계 최대속도 값은 11 m/s에서 35 m/s범위를 나타내며, 평균 값은 약 22 m/s로 분석되었다. 산정된 이동각과 최대속도를 기존 연구결과와 비교하였다.
Flow-Aware Network에서 QoS제어를 위해 Flow 특성에 따른 대역할당 방법과 특성
김재홍(Jae-Hong Kim),한치문(Chimoon Han) 대한전자공학회 2008 電子工學會論文誌-TC (Telecommunications) Vol.45 No.9
오늘날 인터넷에서는 실시간 및 비실시간 등 다양한 멀티미디어 서비스가 존재하고 있으며, 이러한 개개의 서비스 특성을 만족 시키는 데는 한계가 있다. 따라서 서비스의 QoS를 보장하기 위한 한 방법으로 flow-aware 네트워킹 개념을 갖는 네트워크를 제안하고 있다. 인터넷에서 네트워크 이용율 향상과 통계적으로 서비스 보장을 위해 MBAC(Measurement-Based Admission Control) 방식이 연구되었다. 대부분의 MBAC 방식은 집합 flow에 대해 적용하는 총체적 MBAC 알고리즘이며, 입력 flow에 적용하는 per-flow MBAC 알고리즘이 최근 연구되기 시작하고 있다. 본 논문에서는 per-flow MBAC 알고리즘 기반 시스템에서 flow를 특성에 따라 그룹핑하고, 각 그룹핑된 flow에서 먼저 입력되는 flow에 우선순위를 주는 DPS(Dynamic Priority Scheduling)알고리즘 적용한다. 그리고 각 그룹핑된 그룹에 일정대역을 고정 할당한 다음에 그룹 인접대역간 대역폭차용이 가능한 우선등급 하위대역 차용방식과 각 그룹핑된 flow에 그룹핑된 flow 특성에 따라 대역을 동적으로 할당하는 동적대역할당 방식을 제안한다. 제안한 두 방식을 시뮬레이션을 통해 서비스 지속성, 링크 이용율, 지연 특성을 평가 분석한다. 그 결과 제시한 방식이 기존의 방식보다 우수하고, 다양한 멀티미디어 환경에서 더 효율적 방식이라는 것을 분명히 한다. Recently, many multimedia services have emerged in Internet, such as real-time and non- real time services. However, in this Internet environment, we have some limitations to satisfy each service feature. To guarantee the service features in Measurement-Based Admission Control(MBAC) based system on the flow-aware network, there is the method applying Dynamic Priority Scheduling(DPS) algorithm that gives a higher priority to an earlier incoming flow in all of the link bandwidth. This paper classifies all flows under several groups according to flow characteristics on per-flow MBAC algorithm based system. In each flow group, DPS algorithm is applied. This paper proposes two methods that are a DPS based bandwidth borrowing method and a bandwidth dynamic allocation method. The former is that if low priority class has available bandwidths, the flow of high priority class borrows the bandwidth of low priority class when high priority flow has insufficient bandwidth to connect a flow call. The later is that the each group has a minimum bandwidth and is allocated the bandwidth dynamically according to the excess rate for available bandwidth. We compare and analyze the characteristics of the two proposed methods through the simulation experiments. As the results of the experiment, the proposed methods are more effective than existing DPS based method on the packet loss and delay characteristics. Consequently the proposed two methods are very useful in various multimedia network environments.