• 제목/요약/키워드: U-tube

검색결과 384건 처리시간 0.026초

Simulations of fluidelastic forces and fretting wear in U-bend tube bundles of steam generators: Effect of tube-support conditions

  • Hassan, Marwan;Mohany, Atef
    • Wind and Structures
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    • 제23권2호
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    • pp.157-169
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    • 2016
  • The structural integrity of tube bundles represents a major concern when dealing with high risk industries, such as nuclear steam generators, where the rupture of a tube or tubes will lead to the undesired mixing of the primary and secondary fluids. Flow-induced vibration is one of the major concerns that could compromise the structural integrity. The vibration is caused by fluid flow excitation. While there are several excitation mechanisms that could contribute to these vibrations, fluidelastic instability is generally regarded as the most severe. When this mechanism prevails, it could cause serious damage to tube arrays in a very short period of time. The tubes are therefore stiffened by means of supports to avoid these vibrations. To accommodate the thermal expansion of the tube, as well as to facilitate the installation of these tube bundles, clearances are allowed between the tubes and their supports. Progressive tube wear and chemical cleaning gradually increases the clearances between the tubes and their supports, which can lead to more frequent and severe tube/support impact and rubbing. These increased impacts can lead to tube damage due to fatigue and/or wear at the support locations. This paper presents simulations of a loosely supported multi-span U-bend tube subjected to turbulence and fluidelastic instability forces. The mathematical model for the loosely-supported tubes and the fluidelastic instability model is presented. The model is then utilized to simulate the nonlinear response of a U-bend tube with flat bar supports subjected to cross-flow. The effect of the support clearance as well as the support offset are investigated. Special attention is given to the tube/support interaction parameters that affect wear, such as impact and normal work rate.

수평 평활관 및 전열촉진관내 대체 냉매 R-407C의 응축 열전달 특성에 관한 연구 (Heat Transfer Characteristics of R-407C During Condensing Inside Horizontal Smooth and Micro-Fin Tubes)

  • 노건상;오후규
    • 대한기계학회논문집B
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    • 제23권2호
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    • pp.210-217
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    • 1999
  • This paper reports the experimental results on heat transfer characteristics of R-22 and R-407C(HFC-32/125/134a 23/25/52 wt%) condensing inside horizontal smooth and finned tubes. The test condensers used In the study are double pipe heat exchangers of 7.5 mm ID, 9.5 mm OD smooth tube, and 60 finned micro-fin tube with 8.53 mm ID, 9.53 mm OD. Each of these tubes was 4 000 mm long tubes connected with an U-bend. These U type two-path test tubes are divided In 8 local test sections for the identification of the local condensing heat transfer characterisitcs and pressure drop, U-bend effects on condensing flows. Inlet quality is maintained 1.0, and refrigerant mass velocity is varied from 102.0 to $301.0kg/m^2{\cdot}s$. From the results, it was found that the pressure drop of the R-407C Increased, and heat transfer coefficient decreased compared to those of R-22. In comparison condensing heat transfer characteristics of micro-fm tube with those of smooth tube, increasing of condensing heat transfer coefficient was found outstanding compared to the increasing ratio of pressure drop. Furthermore, pressure drop In U-bend showed at most a 30 % compared to the total pressure drop in the test section.

지열원 물대공기 멀티 히트펌프의 냉방 운전 특성에 관한 실증 연구 (Verification Experiment of a Ground Source Multi-heat Pump at Cooling Mode)

  • 최종민;강신형;최재호;임효재;문제명;권영석;권형진;김록희
    • 설비공학논문집
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    • 제21권5호
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    • pp.297-304
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    • 2009
  • The aim of this study is to investigate the cooling performance of ground source multi-heat pump systems with a vertical single U-tube GLHX(U-tube system) and a vertical double tube GLHX(double tube system), which were installed in a school building located in Cheonan. All systems were operated in a part load conditions for all day, and the maximum COP of the single U-tube system and the double tube system were 6.2 and 5.2 at cooling mode, respectively. The double tube GLHX designed by the GLHEPRO, commercial program, was estimated to have the same performance as the U-tube GLHX, because the inlet temperatures of each outdoor unit heat exchanger for the former was similar to the latter. However, it is needed to prove the long tenn performance. It is suggested that the new algorithms to control the flow rate of secondary fluid for GLHX according to load variation have to be developed in order to enhance the performance of the system.

이중 진공관형 태양열 집열기의 집열관 내부 형상과 운전 조건이 성능 변화에 미치는 영향 (Effects of Absorber Tube Shape and Operating Conditions on Thermal Performance of All-Glass Evacuated Tube Solar Collectors)

  • 최은용;김용;서태범
    • 한국태양에너지학회 논문집
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    • 제25권1호
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    • pp.19-25
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    • 2005
  • All-glass evacuated tube solar collectors consist of glass evacuated tubes and absorber tubes. Solar thermal energy from the sun is transferred to the working fluid through the glass evacuated tube and the absorber tube. Several collectors which have different absorber tubes are tested to find the effects of the absorber tube shapes and the operating conditions such as the incident heat flux and the flow rate. As the results, the efficiency of the collector which has a finned tube U tube is about $2{\sim}5%$ higher than that of the others in all cases on an average. And the collector has a finned U tube has the highest efficiency at the high flow rate and the low incident heat flux. In this condition, the outlet mean temperature is low and the heat loss becomes small. Also, it is known that the fin effect is greater than the shade effect.

A SIMPLIFIED METHOD TO PREDICT FRETTING-WEAR DAMAGE IN DOUBLE $90^{\circ}$ U-BEND TUBES

  • Choi, Seog-Nam;Yoon, Ki-Seok;Choi, Taek-Sang
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 추계학술대회
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    • pp.616-621
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    • 2003
  • Fluid-elastic instability is believed to be a cause of the large-amplitude vibration and resulting rapid wear of heat exchanger tubes when the flow velocity exceeds a critical value. For sub-critical flow velocities, the random turbulence excitation is the main mechanism to be considered in predicting the long-term wear of steam generator tubes. Since flow-induced interactions of the tubes with tube supports in the sub-critical flow velocity can cause a localized tube wear, tube movement in the clearance between the tube and tube support as well as the normal contact force on the tubes by fluid should be maintained as low as possible. A simplified method is used for predicting fretting-wear damage of the double $90^{\circ}$U-bend tubes. The approach employed is based on the straight single-span tube analytical model proposed by Connors, the linear structural dynamic theory of Appendix N-1300 to ASME Section III and the Archard's equation for adhesive wear. Results from the presented method show a similar trend compared with the field data. This method can be utilized to predict the fretting-wear of the double $90^{\circ}$U-bend tubes in steam generators.

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CE형 원전 증기발생기 전열관의 유동유발진동 해석 (Flow-induced Vibration of the CE-type Steam Generator Tube)

  • 유기완;박치용
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집D
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    • pp.828-833
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    • 2001
  • In this study, an analysis tool to assess the susceptibility of steam generator tubes due to the flow-induced vibration was developed. The fluid-elastic instability analysis of the U-tube bundle for CE-type steam generator was accomplished. The effective mass distribution along the U-tube was obtained to calculate the natural frequency and dynamic mode shape. Finally, stability ratios for selected tubes are obtained.

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증기발생기 전열관의 유체탄성불안정성 및 난류가진 특성 연구 (Study on the Fluid-elastic Instability and Turbulence Excitation for the Steam Generator Tube)

  • 유기완;박치용;박수기;이종호
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2001년도 추계학술대회논문집 II
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    • pp.1400-1405
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    • 2001
  • In this study, an analysis program to assess the susceptibility of steam generator tubes due to the flow-induced vibration was developed. Analysis of fluid-elastic instability and random turbulence excitation for the U-tube bundle in CE-type steam generator was accomplished. The effective mass distribution along the U-tube was obtained to calculate the natural frequency and dynamic mode shape. Finally, stability ratios and rms vibration amplitude for selected tubes are obtained.

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손마사지가 폐엽 절제술 환자의 흉관 제거시 통증과 불안에 미치는 영향 (The Effect of Hand Massage on Pain and Anxiety Related to Chest Tube Removal in Patients with a Lobectomy)

  • 송영숙
    • 기본간호학회지
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    • 제9권1호
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    • pp.27-44
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    • 2002
  • The main purpose of this study was to identify the effect of hand massage on pain and anxiety related to chest tube removal in patients with a lobectomy. The research design of this study was a nonequivalent control group non-synchronized design. Of the twenty nine adult subjects, fourteen were assigned to the experimental group and fifteen to the control group. The data were obtained over 3 months from a medical center in Seoul. The instruments used to assess trait state anxiety was the Spielberger Trait-State anxiety Inventory. For pain and psychological anxiety. The Visual Analogue Scale was used. Hiko analogue sphygmo-manometer(2001) was used to check blood pressure and pulse rate as indicators of physiological anxiety Subjects in the experimental group received hand massage for 5 minutes just before chest tube was removed, and subjects assigned to the control group did not receive hand massage. Data were analysed with $x^2$-test and Mann-Whitney U test using the SPSSWIN 10.0 program. The results of the study are as follows : 1. Hypothesis 1: 'there will be a significant difference between two groups in the level of pain after chest tube removal' was supported (u = 23.00, p < 0.001). 2. Hypothesis 2: 'there will be a significant difference between the two groups in the level of psychological anxiety after chest tube removal' was supported (u = 3.00, p < 0.001). 3. Hypothesis 3: 'there will be a significant difference between the two groups in physiological anxiety(systolic, diastolic blood pressure and pulse rate) after chest tube removal' was supported(u =55.50, p = 0.01 ; u = 41.50, p = 0.01 ; u = 20.50, p < 0.001, relatively). The findings of this study indicate that hand massage is effective for pain and anxiety related to chest tube removal in patients with lobectomy. Therefore, hand massage is recommended as an effective nursing intervention for relieving pain and anxiety in patients undergoing chest tube removal. Further research is needed to identify the proper duration and timing to achieve the optimal effect of hand massage. A larger subject population is required to apply the current findings to the general population. Further research is also needed to assess the effects of hand massage in other patient subsets. Finally, it would be interesting to see if the effects of hand massaging would be attenuated when performed by a non-medical specialist.

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편심압출굽힘가공법에 의한 사각형 단면을 가진 중공 튜브제품의 U형굽힘가공에 관한 연구 (A Study on the U-bending of Rectangular Hollow Tube by the Eccentric Extrusion and Bending Process)

  • 김진훈;진인태
    • 소성∙가공
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    • 제7권5호
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    • pp.496-504
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    • 1998
  • The eccentric extrusion and bending process for the forming of the curved rectangular hollow tube is newly developed. Generally the bending process of hollow tube is the secondary process followed by the extrusion process of the hollow tube from the round billet. So many defects such as wrinkling and the difference of wall thickness can be happened during the secondary bending process. In order to avoid the defects the new process named as "the eccentric extrusion and bending process" is suggested and applied to the U-bending of rectangular hollow tube. In this paper the kinematically admissible velocity field between the dies surface and the internal plug boundary surface s developed for the curving velocity. By the using of this curving velocity field the curvature of extruded products can be calculated with the parameters such as eccentricity dies length friction constant aspect ratio.

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