건식 3채널 초음파 유량측정 방법에 대한 연구

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.

Flow visualization and noise measurement of R410A two-phase flow near electric expansion valve for heating cycle of multi-split air-source heat pump

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>

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.

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 Visualization of Oscillation Characteristics of Liquid and Vapor Flow in the Oscillating Capillary Tube Heat Pipe

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.

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.

Tailored RF 경자사계방향 (TRFGE} 자기공명영상(MRI)에서 유체에 의한 영상신호 변화 : 유체유입효과와 영상면내를 흐르는 유체의 효과에 대하여

문치웅,김상태,노용만,임태환,조장희,Mun, Chi-Ung,Kim, Sang-Tae,No, Yong-Man,Im, Tae-Hwan,Jo, Jang-Hui 대한의용생체공학회 1997 의공학회지 Vol.18 No.3

본 연구에서는 유체보상 경사자장 기법(flow-compensation-gradient of gradient-moment nulling method)을 이용하지 않은 Tailored RF를 이용한 TRFGE(tailored rf gradient echo) 영상에는 유체유입효과(in-flow effect)가 나타나지 않지만 절편(slice)내에서 판독경사자장(reading gradient)과 같은 방향으로 흐르는 유체는 신호가 강조가 됨을 이론과 실험으로 보였다. 절편 내에서 판독경사자장과 같은 방향으로 흐르는 유체의 신호가 TRFGE 영상에서 강조되는 이유를 이론적으로 설명하였으며 이 이론을 뒷받침 할 실험을 위해 유체 모형을 제작하였다. 원통 모양의 물 모형 중앙으로 유체 관을 통해 식염수(saline)가 주자장(B$B_0$)와 평행인 z 축 방향으로 흐를 수 있도록 하였다. 유체가 흐를 때와 흐르지 않을 때 CGE(conventional gradient echo) 영상과 TRFGE 영사을 얻어 각각 비교하였다. 유체 유입효과를 관찰하기 위해서는 횡단면(axial)의 영상을 얻었고 절편 내에서 판독경사자장과 같은 방향으로 흐르는 유체의 영상신호를 관찰하기 위해서 시상면(sagittal) 영상을 얻었다. In this paper, we have reported two interesting flow effects arising in the TRFGE sequence using water flow phantom. First, we have shown that the TRFGE sequence is indeed not affected by "in-flow" effect from the unsaturated spins flowing into the imaging slice. Second, the enhancement of "in-plane flow" signal in the readout gradient direction was observed when the TRFGE sequence was used without flow compensation. These two results have many interesting applications in MR imaging other than fMRI. Results obtained were also compared with the results obtained by the conventional gradient echo(CGE) imaging. Experiments were performed at 4.7T MRI/S animal system (Biospec, BRUKER, Switzerland). A cylindrical phantom was made using acryl and a vinyl tube was inserted at the center(Fig. 1). The whole cylinder was filled with water doped with $MnCl_2$ and the center tube was filled with saline which flows in parallel to the main magnetic field along the tube. Tailored RF pulse was designed to have quadratic ($z^2$) phase distribution in slice direction(z). Imaging parameters were TR/TE = 55~85/10msec, flip angle = $30^{\circ}$, slice thickness = 2mm, matrix size = 256${\times}$256, and FOV= 10cm. In-flow effect : Axial images were obtained with and without flow using the CGE and TRFGE sequences, respectively. The flow direction was perpendicular to the image slice. In-plane flow : Sagittal images were obtained with and without flow using the TRGE sequence. The readout gradient was applied in parallel to the flow direction. We have observed that the "in-flow" effect did not affect the TRFGE image, while "in-plane flow" running along the readout gradient direction enhanced the signal in the TRFGE sequence when flow compensation gradient scheme was not used.

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.

해양스포츠 현장에서의 몰입(Flow) 탐색

황희성,황선환,이유진 한국융합과학회 2024 한국융합과학회지 Vol.13 No.2

연구목적 이 연구는 Csikszentmihalyi의 몰입(Flow)이론을 근거로 하여 기존 이론을 발전시키고자 하였으며, 연구를 통해 변인들을 정량화하여 몰입을 수준별로 파악하고자 하였다. 변인 수준별로 군집을 구성하여몰입 수준의 채널을 확인하고, 변수 수준에 따른 몰입 수준을 기존 3채널 이론과 비교, 분석하고자 한다. 연구방법 이 연구의 전체 표본수는 스쿠버다이빙 392명, 서핑 421명으로 총 813명이다. 자료처리방법으로SPSS 27.0 version을 활용하여 빈도분석과 기술통계 분석, 신뢰도분석, K-평균 군집분석, 일원배치분산분석을 실시하였다. 모든 통계치에 대한 유의수준은 5%로 설정하였다. 결과 첫째, 기술수준과 도전수준이높아질수록 몰입수준도 높아지는 양상을 보였다. 둘째, 기존 3채널 이론과 마찬가지로 기술수준과 도전수준이 일치하는 구간에서 높은 기술수준과 높은 도전수준 일치 구간일수록 몰입수준이 높은 것으로 나타났다. 하지만, 가장 높은 몰입수준 구간은 기존 3채널 이론과 일치하지 않았다. 결론 이 연구에서 해양스포츠 참가자들의 높은 몰입 수준은 기존의 몰입 3채널 이론의 몰입 분포와 다르게 나타났으나 기술과 도전이 균형을이루는 구간이 커질수록 몰입 수준은 커졌다. 몰입은 감정의 영역이기에 기술과 도전이라는 두 가지 요인만으로 설명하기에는 어려운 부분이 있다. 기존의 몰입(Flow)이론은 주로 보편적인 일상의 상황들을 기준으로연구되었기에, 이 연구에서와 같이 특정 종목별 연구를 통해 몰입과 감정을 다양한 채널을 통하여 다차원적으로 확인할 필요가 있다. 향후 도전적인 스포츠를 비롯한 다양한 스포츠 종목의 종목별 특징이 충분히 고려된 연구가 이루어져야 할 것이며, 감정을 설명하기 위한 추가 변인을 통해 몰입과 몰입외 다른 감정들의채널 분포와 수준을 확인할 필요가 있다. Purpose This study aims to develop the existing theory based on Csikszentmihalyi's Flow theory, and throughthe study, we tried to understand flow by level by quantifying variables. By organizing clusters by variable level, we want to check the channel of flow level and compare and analyze the level of flow according to the variablelevel with the existing three channels theories. Method The total number of samples in the Survey was 813, with392 scuba divers and 421 surfers. As a data processing method, frequency analysis, descriptive statisticsanalysis, reliability analysis, K-means cluster analysis, and one-way analysis of variance were conductedusing SPSS 27.0 version. The significance level for all statistics was set to 5%. Result First, we saw a trend ofhigher flow levels as the skill levels and challenge levels increased. Second, consistent with the traditionalthree-channels theory, higher skill and challenge levels are associated with higher levels of flow in the highskill and high challenge matching sectors. However, the highest level of flow was not consistent with thetraditional three-channels theory. Conclusion In this study, the high levels of flow among marine sportsparticipants differed from the flow distribution in traditional three-channels theory of flow, but higher levels ofbalanced skill and challenge were associated with higher flow. As flow is an feelings domain, it is difficult toexplain it with only two factors: skill and challenge. As the existing flow theories are mainly based on universaleveryday situations, in future study, it is necessary to expand flow and feelings to various channels in a multidimensional manner through study on specific sports as in this study. In the future, research on varioussports, including challenging sports, is needed, and the characteristics of each sport should be fullyconsidered. In the future, studies that fully consider the characteristics of various sports events, includingchallenging sports, should be conducted, and it is necessary to check the channel distribution and level ofFeelings other than flow and flow through additional variables to explain Feelings.

Effects of plate angle on flow bifurcations and heat transfer characteristics in a channel with inclined plates

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>