Experimental Study of Transition and Stability in Taylor-Couette Flow

Xin Cheng Tu,Dong Liu,Hyoung-Bum Kim(김형범) 한국가시화정보학회 2010 한국가시화정보학회 학술발표대회 논문집 Vol.2010 No.11

The confined fluid flow in a gap between an inner rotating cylinder and an outer stationary cylinder wasexperimentally investigated by using digital particle image velocimetry. Based on the analysis of velocity fields by DPIV, we observed the flow change of the transition zone from circular Couette flow (CCF) to Taylor vortex flow (TVF). The proper orthogonal decomposition (POD) technique was applied to detect the onset of transition process and dominant flow structure in the transition zone. The quantitative characteristics of transition zone were proposed by processing the oscillation characteristics of vortices.

Quantitative investigation of the transition process in Taylor-Couette flow

Xin Cheng Tu,Dong Liu,김형범 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.2

The transition process from circular Couette flow to Taylor vortex flow regime was experimentally investigated by measuring the instantaneous velocity vector fields at the annular gap flow region between two concentric cylinders. The proper orthogonal decomposition method, vorticity calculation, and frequency analysis were applied in order to analyze the instantaneous velocity fields to identify the flow characteristics during the transition process. From the results, the kinetic energy and corresponding reconstructed velocity fields were able to detect the onset of the transition process and the alternation of the flow structure. The intermittency and oscillation of the vortex flows during the transition process were also revealed from the analysis of the instantaneous velocity fields. The results can be a measure of identifying the critical Reynolds number of the Taylor-Couette flow from a velocity measurement method.

Improvement of two-phase flow distribution in the header of a plate-fin heat exchanger

Tu, Xin-Cheng,Wu, Yuting,Kim, Hyoung-Bum Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.123 No.-

<P><B>Abstract</B></P> <P>The two-phase (liquid and gas) flow distribution in the header of a plate-fin heat exchanger was experimentally investigated. Small mass fractions of the liquid phase in the liquefaction process of natural gas were considered in this study. The liquid and gas flow velocity were measured using optical methods such as PIV/PTV/LIF. The flow maldistribution of liquid and gas flows was quantified and addressing this problem by attaching a porous baffle or modifying the inlet nozzle configuration was studied. The results showed that a vane swirler with a diffuser enhanced the flow distribution of both the liquid and gas phases fluid.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two-phase flow distribution in the header of plate-fin heat exchanger was quantified. </LI> <LI> The effect of porous baffle and other passive jet modifiers was investigated. </LI> <LI> Vane swirler and diffuser improves the two-phase flow distribution. </LI> </UL> </P>

원통-다관형 열교환기의 다관측 입출구 유동 특성의 실험적 연구

도흔승(Xin Cheng Tu),왕개(Kai Wang),박승하(Seung-Ha Park),김형범(Hyoung-Bum Kim) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.7

본 논문에서는 원통-다관형 열교환기의 다관측 유량의 분배도 향상을 위해 다공성 배플 유무에 따른 입구 및 출구부의 유동 특성을 실험적으로 연구하였다. 원통 및 다관측 유량의 분배성능은 원통-다관형 열교환기의 성능에 직간접적인 영향을 준다. 실험 연구를 위하여 원형 크기의 1/3로 축소한 실험 모델을 제작하였고, 60, 80, 90 LPM의 유량 조건에서 다공성 배플의 유무에 따른 다관측의 분배 성능을 입자화상속도기법을 이용한 입구 및 출구부의 속도장 측정을 통해 확인하였다. 연구로부터 절대 불균일 분배도를 계산하여 정량적으로 다공성 배플이 유량의 분배도에 주는 영향을 확인하였다. 측정 결과로부터 유량에 상관없이 배플을 설치하였을 경우 74%의 절대 불균일 분배도의 감소 효과를 가졌다. The inlet/outlet flow in the tube-side of the shell and tube heat exchanger was experimentally measured to investigate the effect of the porous baffle on uniform flow distribution. A 1/3rd scale-downed model of a heat exchanger was used and particle image velocimetry was applied for measuring the instantaneous velocity vector fields. The absolute errors in the flow rate were calculated and compared for the tube-side with and without the porous baffle, by varying the flow rate from 60 to 90 LPM. The results revealed that the porous baffle can improve flow uniformity and reduce the absolute error in the flow rate of the model with the baffle by about 74%, compared to that without the baffle. This result can be used for improving the performance and design of the shell and tube heat exchanger.

고주파수 초음파 영상기법을 이용한 불투명 유동 측정

도흔승(Xin-Cheng Tu),차재은(Jae-Eun Cha),김형범(Hyoung-Bum Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10

The noninvasive measurement technique that combines particle image velocimetry and ultrasound brightness (B)-mode image of scattering particles, referred as Echo-PIV method, was applied to analyze the flow structure of a pump system inside the nuclear reactor model. The fundamental characteristic of the ultrasound image system was quantified using phantom test. The spatial resolution of the ultrasound image system was determined by tracking the movement of a wire phantom along the axial and lateral direction. The conventional PIV method was used to process the consecutive ultrasound images to obtain the 2D instantaneous velocity fields of downstream region of the impeller. The flow rate comparison between the bulk flow rate measurement and Echo-PIV method were performed. This study demonstrated the feasibility of Echo-PIV method for investigating the opaque flow in fluid machinery.

원심 블로어 출구 유동의 정량적 가시화 연구

도흔승(Xin Cheng Tu),김성준(Sung-Jun Kim),박승하(Seung Ha Park),김형범(Hyoung-Bum Kim) 한국가시화정보학회 2014 한국가시화정보학회지 Vol.12 No.1

The outlet flow of the centrifugal blower were quantitatively visualized using particle image velocimetry. Because the centrifugal blower is one of the key parts of electric vehicle battery cooling system, the quantitative information of centrifugal blower is necessary to design and optimize the cooling system. The effect of different inlet flow condition to the outlet flow was investigated in this study. Two different inlet ducts were used. One is the straight inlet and the other is a bended one. The results clearly showed the outlet flow asymmetry in both inlet ducts. When the blower has the bended inlet, the flow rate decreases due to the increase of the head loss.

Optimal design of porous baffle to improve the flow distribution in the tube-side inlet of a shell and tube heat exchanger

Wang, Kai,Tu, Xin-Cheng,Bae, Chan-Hyo,Kim, Hyoung-Bum Elsevier 2015 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.80 No.-

<P><B>Abstract</B></P> <P>An optimization study of a porous plate to improve the flow distribution in the tube side of a shell and tube heat exchanger was performed using numerical and experimental methods. The first assumption in the design stage of multichannel heat exchangers is that there is an even flow distribution along the multi channels. However, this assumption is generally not upheld in real situations. An experimental study was first performed to confirm the effectiveness of a porous baffle in improving the flow distribution in the tube side of a shell and tube heat exchanger. The results showed that the baffle can largely decrease maldistribution. We then performed numerical optimization of the porous baffle shape. The optimized curvature of a porous plate and the distribution of circular holes in the baffle were determined using the numerical method. The optimization results showed that the area-weighted averaged absolute error of the flow rate of the optimized baffle decreased to one-third that of the proto-type baffle model. For validation of the numerical optimization, the flow field with the optimized baffle was measured. Although there were some differences between the experimental and the numerical results, the results showed that the flow distribution using the optimized model was largely improved compared with that of the proto-type porous baffle.</P>

Visualization of resin impregnation through opaque reinforcement textiles during the vacuum-assisted resin transfer molding process using ultrasound

Liu, Hai Long,Tu, Xin-Cheng,Lee, Joon Oh,Kim, Hyoung-Bum,Hwang, Wook Ryol SAGE Publications 2014 Journal of composite materials Vol.48 No.9

<P>In this study, an ultrasound visualization system has been set up for in-situ monitoring of the resin flow impregnating through opaque carbon fiber reinforcements during the vacuum-assisted resin transfer molding. The flow front advancement through the carbon fabrics covered by a bagging film can be identified and visualized by the high frequency B (brightness) mode ultrasound imaging technique. The resin advancement in the opaque carbon fabrics has turned out to form a non-uniform plug flow along the pressure gradient direction and the potential void formation can be observed from the mesoscopic resin flow behavior: the inter-tow regions have been preferentially filled by the resin fluid and the fiber tow region behaves as a sink that probably remain as a void defect. The local unsaturated transient velocity of the resin flow has been also evaluated, which is particularly important in understanding saturation behaviors in dual-scale fabrics and is hardly measurable by other means. In spite of the hardware limitations on the resolution, the proposed ultrasound visualization system can provide a less expensive and portable visualization tool to understand the microstructure of opaque reinforcements and monitor the resin flow behavior during the vacuum-assisted resin transfer molding process in the industrial composite manufacturing environment.</P>

원심 블로어 입구 유동의 정량적 가시화 연구

정태식(Tae-Sik Jeong),도흔승(Xin Cheng Tu),김성준(Sung-Jun Kim),장환영(Hwan-Young Jang),김진광(Jin-Kwang Kim),김형범(Hyoung-Bum Kim) 한국가시화정보학회 2013 한국가시화정보학회지 Vol.11 No.2

The inlet flow of centrifugal blower were quantitatively visualized using particle image velocimetry. Because the centrifugal blower system is one of the key parts of EV battery cooling system, the quantitative information of flow field of centrifugal blower is important to design and optimize the cooling system. Two types of inlet parts were used in this study. One is the straight inlet and the other is a bended one. The results showed the flow asymmetry exists in the straight model due to the pressure difference in the blower. In case of the bended one, the separation bubble and the increase of head loss appeared compared with the straight model.

Study of Different Radial Temperature Gradient Effect on Taylor-Couette Flow Instability

차재은(Jae-Eun Cha),류동(Dong Liu),도흔승(Xin Cheng Tu),김형범(Hyoung-Bum Kim) 한국가시화정보학회 2010 한국가시화정보학회지 Vol.8 No.3

We have investigated different radial temperature gradient effect on the stability of Taylor-Couette flow. The radius ratio and aspect ratio of the model was 0.825 and 48, respectively. Two heating exchangers were used for generating different temperature gradient along the radial direction. The change of flow regime in the Taylor-Couette flow was studied by increasing the Reynolds number. The results showed that: as Gr is increased in helical vortex flow regime, the vortices with the same direction of convection flow increased in size, and the vortex moving velocity also increased. It is also shown that the presence of temperature gradient obviously increased the flow instability when the Richardson number is larger than 0.0045