Measurement of sliding bubble behavior on a horizontal heated tube using a stereoscopic image processing technique

Kim, Yu-Na,Kim, Jae Soon,Park, Goon Cherl,Cho, Hyoung Kyu Elsevier 2017 International journal of multiphase flow Vol.94 No.-

<P><B>Abstract</B></P> <P>The significance of the sliding bubble effect on boiling heat transfer has been reported by a number of precedent studies through experiments and numerical analyses. However, the experimental data and mechanistic boiling heat transfer models considering sliding bubbles on horizontal tube outer surfaces are insufficient. In the present study, therefore, the behavior of sliding bubbles on a horizontal tube heater is measured at nearly saturation temperature and atmospheric pressure for various flow conditions; liquid velocity (14.7–27.6mm/s), wall heat flux (67–129kW/m<SUP>2</SUP>), and the location of nucleation site (45° and 90° from the bottom of the heater). A thin film heater with a narrow heating strip was proposed to generate boiling bubbles in a restricted region on a horizontal heater. This improved the quality of the visualization of the sliding bubbles. Two synchronized high-speed cameras were used to capture the behavior of the bubbles from two perpendicular measurement angles. The configurations of the bubbles were identified by an image processing method based on shadowgraphy from the two images, and the results of the image processing elicited various boiling bubble parameters, such as the bubble diameter transient, bubble velocity, bubble frequency, etc. In particular, the volume of the nonspherical bubble was measured by a three-dimensional reconstruction method which defines a specific cross-section configuration at each elevation using stereoscopic images. Two verification steps confirmed that the reconstruction method has allowable errors and also indicated the limitation of the monoscopic visualization method for deformed bubble measurement. According to the result of this measurement, the location of the nucleation site is a principal factor affecting the life cycle of a sliding bubble on a horizontal tube. Under the present experimental conditions, a bubble generated on the lower half of the tube showed the lift-off from the heating surface twice during its life cycle; the first is due to the contact pressure force and the inertia of the surrounding liquid caused by bubble shape change shortly after the nucleation, and the second is mainly due to the lift force after being accelerated by the sliding motion. In contrast, bubbles occurring at the side of the tube did not show sliding motion, but rather rose without confinement by the wall after the lift-off. The effects of the bulk liquid velocity and wall heat flux on bubble behavior were investigated and the results are discussed in this paper. This experimental observation can be used to improve understanding of the boiling heat transfer mechanism on a horizontal tube and the bubble dynamics of a sliding bubble on a downward heating surface.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The visualization technique for sliding bubble on a horizontal tube was devised. </LI> <LI> Various bubble parameters were measured with the visualization method. </LI> <LI> Advantage of the proposed method for a deformed bubble has been quantified. </LI> <LI> The life cycle of boiling bubble was elucidated based on the experimental data. </LI> </UL> </P>

Finite-Element Analysis on the Stability of Geotextile Tube-Reinforced Embankments under Scouring

Kim, Hyeong-Joo,ASCE, A.M.,Won, Myoung-Soo,Jamin, Jay C. CRC Press, LLC 2015 International journal of geomechanics Vol.15 No.2

<P> Scouring is a significant problem on river bank and coastal protection systems. Severe scouring can cause damaging consequences to geotextile tube embankment structures. In this study, five case scenarios of an embankment system supported by stacked geotextile tubes were analyzed using a commercially available finite-element analysis software. These case scenarios include (1) conventional geotextile tube stacking on ground base foundation; (2) geotextile tube stacking on gravel bedding foundation; (3) geotextile tube stacking on excavated foundation; (4) geotextile tube stacking on excavated foundation with gravel bedding; and (5) fortification of stacked geotextile tubes by riprap protection. Each case scenario is simulated under normal loading and critical loading conditions with and without scouring at the base toe of the embankment system. Results suggest that the potential problems that occur during scouring and critical states of the embankment system instigate failures that could destabilize the geotextile tube retaining structure. Among all the case scenarios considered, additional fortification by riprap increases the performance and global stability of the geotextile tube embankment system. </P>

The experimental investigation of tube’s diameter and inclination angle in a separate effect PAFS test facility for APR+

Shin, Chang Wook,NO, Hee Cheon,Yun, Bong Yo,Jeon, Byong Guk Elsevier 2015 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.86 No.-

<P><B>Abstract</B></P> <P>Experiments on high pressure steam condensation inside a nearly horizontal tube were performed for application into Passive Auxiliary Feedwater System (PAFS) of Advanced Power Reactor Plus (APR+). At KAIST, a Single-tube COndensation experiment facility of PAFS (SCOP) was constructed. The one-through type open loop test, where steam circulation is driven by pressure difference between the steam generator and the venting valve, was conducted in order to compensate for insufficiency of the heater power. We found out that the open loop test produced the same condensation heat transfer coefficients as those of the closed loop within 1% difference. Using the open loop, we were able to generate the higher steam flow rate by three times than that done by the heater power. Sensitivity studies were performed to validate the heat transfer performance of the PAFS in regard to the pressure effect, the diameter effect and the angle effect. The operating range of experiments are 1–7MPa (pressure), 50.4mm (reference tube) and 33.4mm (comparing tube) (tube outer diameter) and 2–4° (tube angle). The comparing tube gave 30% higher heat transfer coefficients over the reference tube. In our tests, the slug flow was not observed. Compared with the reference case with the inclined angle of 3°, the case with the inclined angle of 2° showed just a bit lower heat capacity without any transition into slug flow.</P>

A study on the lift-off diameter of bubbles generated on horizontal tube

Ryu, Sung Uk,Kim, Seok,Euh, Dong-Jin Elsevier 2018 Annals of nuclear energy Vol.111 No.-

<P><B>Abstract</B></P> <P>In this study, experiments and a theoretical analysis on the lift-off diameter of bubbles generated on a horizontal tube were conducted. A force balance analysis in the direction normal to the heated surface at the moment of the bubble lift-off was performed to develop the model. According to the developed model, the bubble lift-off diameter strongly depends on the azimuthal position of the horizontal tube, the relative velocity between a bubble and the surrounding liquid, and the properties of the bubble and liquid. To validate the prediction performance of the proposed model, the dynamics of the bubble growth and sliding process was visualized using a high-speed digital video camera. The proposed model agrees well with the experimental data within an averaged relative deviation of 19.6%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A theoretical correlation for the bubble lift-off diameter on a horizontal tube. </LI> <LI> Growth and lift-off phenomena of bubbles generated on a horizontal tube. </LI> <LI> Bubble lift-off diameter depends on the azimuthal position of the horizontal tube. </LI> </UL> </P>

소수성 코팅된 수평관내에서의 적응축 유도를 통한 응축 열전달 성능 증진

강주원(Joo Won Kang),황경원(Kyung Won Hwang),박현선(Hyun Sun Park),Moriyama Kiyofumi,김무환(Moo Hwan Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

We measured how the condensation heat transfer coefficient h inside a horizontal tube changes by hydrophobic coating on the condensing surface. We built horizontal test sections in which steam flows inside a tube and coolant flows outside as counter flow. The 2-meter-long stainless steel tubes were used as condensing tubes, which were two types: one as purchased and the other tube coated internally with polytetrafluoroethylene (PTFE). The outer diameter of the tubes was 50.8 mm, and the inner diameter was 47 mm. Steam at saturation temperature was supplied to the test section with maximum mass flux of 12.2 kg/m2/s at a pressure 1.5 bar. Tube outer wall temperatures, coolant temperature difference between inlet/outlet, and coolant mass flow rate were measured for calculation of h. The value of h was 53% increased in the PTFE-coated tube than in the normal tube. This result shows usefulness of the present method for the improvement of the efficiency of heat exchangers.

초소수성 코팅 튜브에서의 비응축가스 영향에 대한 응축 열전달 연구

지대윤(Dae-Yun Ji),김대호(Daeho Kim),이권영(Kwon-Yeong Lee) 한국산학기술학회 2018 한국산학기술학회논문지 Vol.19 No.4

본 연구의 목표는 수평 관외 초소수성 튜브에서 비응축가스(NCG)의 영향을 관찰하고, 이를 일반 알루미늄 튜브의 응축 현상과 비교하는 것이다. 초소수성 튜브 제작을 위해 Self-Assembled Monolayer(SAM) 코팅으로 알루미늄 튜브의 외부를 표면개질 했다. 응축 성능을 나타내기 위해 총합 열전달계수를 사용하였고, 이 값으로 응축 성능을 비교 검토하였다. 본 연구의 주요 변수는 비응축가스 질량 분율로, 0.08에서 0.45의 범위에서 실험을 진행하였다. 응축 실험을 통해 비응축가스 질량 분율이 낮아질수록 응축 성능이 SAM 튜브와 일반 튜브에서 모두 향상되는 것을 확인했다. SAM 튜브에서 적응축 열전달 성능은 일반 튜브 대비하여 평균 약 1.9배에서 2.5배 정도 큰 것을 관찰하였다. SAM 튜브에서 비응축가스 질량 분율이 낮아지면서 응축 성능 상승폭이 감소하게 되는데, 이는 Flooded 응축 현상이 발현되었기 때문이다. 응축이 더 활발하게 진행되면 SAM 튜브에서 막응축이 일어나는 것을 관찰하였고, 이 때 성능은 일반 알루미늄 튜브보다도 저하된 성능을 보였다. SAM 알루미늄 튜브에서 Flooded 응축과 막응축이 일어나는 원인으로 표면에서의 Pinning 효과를 이용하여 설명하였다. 결론적으로, SAM 튜브를 실제 응축기에 적용해 표면개질로 인한 응축 성능 개선 효과를 얻기 위해서는 적응축 또는 Flooded 응축이 일어나는 조건으로 응축기 내 환경 조성을 해야 한다. This purpose of this research is to observe the influence of non-condensable gas (NCG) on a horizontal super-hydrophobic aluminum tube and compare it with a bare aluminum tube. To achieve super-hydrophobic characteristics, an aluminum tube was coated with a Self-Assembled Monolayer (SAM). The overall heat transfer coefficient U was used to represent the condensation performance. The NCG mass fraction was the main variable, and its range was 0.08 to 0.45. The condensation performance of the SAM tube and bare tube increased with decreasing mass fraction of NCG. The SAM tube showed 1.9 to 2.5 times larger dropwise condensation performance than the bare tube. When the mass fraction of NCG decreased in the SAM tube, the rate of increase of the SAM tube was lower because flooded condensation occurred. In addition, filmwise condensation occurred in the SAM tube when more active condensation was generated, and its performance was lower than that of the bare aluminum tube. The flooded and filmwise condensation in the SAM tube is explained by the pinning effect. In conclusion, controlling the condition of the condenser is necessary to improve the condensation performance by surface modification a SAM.

가연성 냉매의 외부 응축 열전달에 관한 연구

배동수,하종철,유길상,정동수 대한설비공학회 2004 설비공학 논문집 Vol.16 No.6

In this study, external condensation heat transfer coefficients (HTCs) of flammable refrigerants of propylene, propane, isobutane, butane, DME, and HFC32 were measured on a horizontal plain tube, 26 fpi low fin tube, and Turbo-C tube. All data were taken at the temperature of 39℃ with a wall subcooling of 3∼8℃. Test results showed a typical trend that condensation HTCs of flammable refrigerants decrease with increasing wall subcooling. HFC32 had the highest HTCs among the tested refrigerants showing 44% higher HTCs than those of HCFC22 while DME showed 28% higher HTCs than those of HCFC22. HTCs of propylene and butane were similar to those of HCFC22 while those of propane and isobutane were similar to those of HFC134a. Based upon the tested data, Nusselt's equation is modified to predict the plain tube data within a deviation of 3%. For 26 fpi low fin tube, Beatty and Katz equation predicted the data within a deviation of 7.3% for all flammable refrigerants tested. The heat transfer enhancement factors for the 26 fpi low fin and Turbo-C tubes were 4.6∼5.7 and 4.7∼6.9 respectively for the refrigerants tested indicating that the performance of Turbo-C tube is the best among the tubes tested.

Analysis of running depth and study of combined tubing of drill-grinding string in horizontal wells

Wenkang Chen,Chuanjun Han,Liangliang Ding 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.12

To solve the difficulty of running drill-grinding string in oilfields, the joining pattern of two-line weight tubing combination is used to increase the running depth of drill-grinding string. There are currently few theoretical bases and systematic researches on the combined tubing. Thus, a calculation model of the combined tubing was established. Meanwhile, an experimental study of running drill-grinding string was conducted. The accuracy of the calculation model was discussed based on the experimental results. The field application of the calculation model was discussed. Finally, the combined characteristics and sensitivity analysis were studied. The results indicate that the critical condition for the optimal combination proportion of twoline weight tubing is a well depth of 1.236 rad deviated angle. The parameters affect running drill-grinding string, including frictional coefficient, running velocity, liquid density, and inner diameter. The work presented provides an effective solution and theoretical evidence for solving this difficulty.

수평관내 HC계 냉매의 증발 압력강하 특성

최준혁(Choi Jun Hyuk),이호생(Lee Ho Saeng),김재돌(Jae-Dol Kim),윤정인(Yoon Jung-In) 한국마린엔지니어링학회 2006 한국마린엔지니어링학회 학술대회 논문집 Vol.2006 No.-

Chracteristics on evaporating pressure drop of HCs refrigerants inside a horizontal tube were studied experimentally. Experimental results were presented for pressure drops of hydrocarbon refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 inside a horizontal double pipe heat exchanger. Three tubes with a tube diameter of 12.70㎜, 9.52㎜ and 6.35㎜ were used for this study. Hydrocarbon refrigerants showed higher evaporating pressure drop than that of R-22 in all tubes. The highest pressure drop was founded in R-600a. The highest evaporating perssure drop of all refrigerants was shown in a tube diameter of 6.35㎜ with same mass flux. The results can be used as the basic data for the design of heat exchanger using hydrocarbon refrigerants as an alternatives.

Connections between RC beam and square tubed-RC column under axial compression: Experiments

Xu-Hong Zhou,Bin-Yang Li,Dan Gan,Jie-Peng Liu,Y. Frank Chen 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.4

The square tubed-reinforced concrete (TRC) column is a kind of special concrete-filled steel tube (CFST) columns, in which the outer thin-walled steel tube does not pass through the beam-column joint, so that the longitudinal steel reinforcing bars in the RC beam are continuous through the connection zone. However, there is a possible decrease of the axial bearing capacity at the TRC column to RC beam connection due to the discontinuity of the column tube, which is a concern to engineers. 24 connections and 7 square TRC columns were tested under axial compression. The primary parameters considered in the tests are: (1) connection location (corner, exterior and interior); (2) dimensions of RC beam cross section; (3) RC beam type (with or without horizontal haunches); (4) tube type (with or without stiffening ribs). The test results show that all specimens have relatively high load-carrying capacity and satisfactory ductility. With a proper design, the connections exhibit higher axial resistance and better ductility performance than the TRC column. The feasibility of this type of connections is verified.