• Nuclear Engineering and Technology
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• 제31권5호
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• pp.486-497
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• 1999

The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate, A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side has a shape of annulus around vertical tube and the lost heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 11 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348∼3.282kg/hr, of inlet air mass fraction 11.8∼55.0%. The investigation of the flooding is preceded to find the upper limit of the reflux condensation. Onset of flooding is lower than that of Wallis' correlation. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the increase of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed by 165 data of the local heat transfer. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7% between the results by the experiment and by the correlation.

• 콘크리트학회논문집
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• 제24권6호
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• pp.737-744
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• 2012

강재형 댐퍼는 주로 철골구조에서 많이 사용되어 왔으나 최근에 들어 철근콘크리트 건물에도 사용빈도가 증가하는 추세이다. 철근콘크리트 건물에 강재이력댐퍼를 적용하기 위해서는 댐퍼의 접합부재가 댐퍼의 지지능력을 보 및 벽체로 전달하기에 적합한 강도와 강성을 지녀야만 한다. 하지만 균열로 인한 철근콘크리트 요소의 손상은 부득이한 것으로, 댐퍼로부터 지지부재로의 하중전달 메커니즘과 댐퍼 지지부재 이력특성의 규명은 이러한 댐퍼의 거동을 평가하는데 매우 중요하다. 이에 이 연구에서는 EaSy 댐퍼와 같은 강재판형 이력댐퍼의 지지부재와 RC벽체와의 접합상세를 대상으로 실험을 실시하였다. 실험 결과 전단과 관련된 균열의 양과 패턴을 제외하고는 모든 실험체의 파괴패턴은 거의 동일한 것으로 나타났으며, 잘 분산된 균열을 지닌 HD-3 실험체가 에너지소산능력, 강성저하 그리고 강도저하 측면에서 좋은 거동을 보여주었다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1999년도 춘계학술발표회요약집
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• pp.104-104
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• 1999

The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side is installed in the form of coolant block around vertical tube and the heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 15 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348 -3.282kg/hr, of inlet air mass fraction 11.8 -55.0%. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the decrease of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed represented with the 165 sets of local heat transfer data. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17. 7% between the results by the experiment and by the correlation.

• 설비공학논문집
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• 제2권1호
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• pp.37-48
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• 1990

The drag and heat transfer reduction phenomena and degradation effects of drag reducing polymer solutions which are known as the viscoelastic fluids are investigated experimentally for the turbulent circular tube flows. Two stainless steel tubes are used for the experimental flow loops. Aqueous solutions of Polyacrylamide Separan AP-273 with concentrations from 300 to 1000 wppm are used as working fluids. Flow loops are set up to measure the friction factors and heat transfer coefficients of test tubes in the once-through system and the recirculating flow system. Test tubes are heated by power supply directly to apply constant heat flux boundary conditions on the wall. Capillary tube viscometer and falling ball viscometer are used to measure the viscous characteristics of fluids and the characteristic relaxation time of a fluid is determined by the Powell-Eyring model. The order of magnidude of the thermal entrance length of a drag reducing polymer solution is close to the order of magnitude of the laminar entrance length of Newtonian fluids. Dimensionless heat transfer coefficients of the viscoelastic non-Newtonian fluids may be represented as a function of flow behavior index n and newly defined viscoelastic Graetz number. As degradation continues viscosity and the characteristic relaxation time of the testing fluids decrease and heat transfer coefficients increase. The characteristic relaxation time is used to define the Weissenberg number and variations of friction factors and heat transfer coefficients due to degradation are presented in terms of the Weissenberg number.

• 비파괴검사학회지
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• 제28권5호
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• pp.407-415
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• 2008

원전 발전소 터빈계통을 구성하는 열교환기 튜브는 일반적으로 구리합금, 스테인리스강, 탄소강, 티타늄합금 등의 재질로 제작된다. 이들 재질중에서 페라이트계 type-439 스테인리스강은 자성 재질로서 오스테나이트계보다 더 높은 열전달율 가지며, 부식에 의해 유발되는 결함에 대해 더 높은 저항성을 가진다. 페라이트계 스테인리스강은 보통 발전소 열교환기의 저압급수가열기와 습분분리재열기에 사용된다. 저압급수가열기는 일반적으로 두께가 얇은 type-439 스테인리스강을 이용하는 반면에 습분분리재열기는 더 두꺼운 핀튜브를 사용한다. 이와 같이 터빈 습분분리재열기 튜브로 사용되는 type-439 스테인리스강 핀튜브는 터빈계통의 운전으로 인하여 손상이 발생할 수 있다. 손상에 의한 가장 대표적인 결함은 진동에 의해 발생할 수 있는 마모, 피로균열 등이며 마모성 결함은 일반적으로 튜브-튜브지지판에서 발생되는 것으로 보고되고 있다. 본 연구에서는 type-439 스테인리스강 자성체 튜브에 발생할 수 있는 결함을 검출하고 크기를 측정할 수 있는 자기포화 와전류탐상검사 기법의 능력을 평가하였다.

• Nuclear Engineering and Technology
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• 제27권3호
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• pp.281-291
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• 1995

이 연구의 목적은 수동형 격납용기 냉각계통의 용기 바깥표면이 건조 및 습한 조건일때 격납용기 내, 외벽에서 일어나는 열전달과정에 대한 실험적 자료를 얻는데 있다. 시험모델은 AP 600구조에 근거하여 격납용기의 둘레중 60$^{\circ}$부분만을 취하였다. 시험모델의 주요치수는 원형의 값을 대략 10분의 1로 축소한 것이다. 붕괴열을 모의하기 위하여 전기적으로 가열되는 증기발생기를 시험모델내에 설치하였다. 최대열유속은 8.91 kW/$m^2$ 이었다. 두 가지 형식의 시험이 수행되었다. 하나는 수막유동없이 공기만의 자연대류에 관한 시험이고 다른 하나는 수막유동과 공기의 자연대류가 동반된 증발열전달 시험이다. 시험결과 수막유동이 없는 경우 공기만의 자연대류 열전달 능력은 약 1.48 kW/$m^2$ 열유속에서 제한되고 있음을 알게 되었다 또한 수막유동과 공기의 자연대류가 동시에 일어나는 시험에서 열제거 능력은 현저히 향상됨을 알게 되었다 이들 열전달 측정치들을 기존 관계식들과 비교하였다.

• 한국멀티미디어학회논문지
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• 제23권2호
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• pp.255-261
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• 2020

As the accidents of cargo and passenger carrying ships occur, the stress faced by the vessel users is increasing. The risk factors for accident deterioration in remote marine area are stronger than those in road accidents, and therefore the need for safety control is greatly emphasized. To overcome such issue, a lot of effort has been made in terms of conducting research and development of the passengers and freights location tracking system. However, the inner bulkhead structures are made of aluminum/steel which is a difficult material to transfer location information through. This study aims to measure the receiving rate of LoRaWAN signal inside the aluminum/steel bulkhead structures with variation in reception strength and distance. The test was taken place at platforms with 6T and 8T enclosures to reflect the same conditions found in fishery patrol boats. The receiving rate of through-the-wall communication at 10M distance turned out to be 86% in case of using two 6T enclosures, and 73% in case of using one 8T enclosure. The result showed that the receiving rate was more affected by the thickness rather than the number of enclosures.

• 한국수정란이식학회지
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• 제12권2호
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• pp.211-218
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• 1997

This experiment was carried out to develop the anesthetic methods for ultrasonography and a new simplified disposable needle guidance device for ovum pick-up(OPU) in cows. Three different anesthetic methods were applied as. 1) epidural analgesia only with 2% lidocaine(20~30 ml), 2) epidural analgesia with 2% under general sedation with xylazine, 3) epidural analgesia with 2% lidocaine under general sedation with detomidine. We evaluated the anesthetic effects with items such as relaxation of anal sphincter, tail movement and rectal wall, retractability of both ovaries, additional anesthesia and possibility of OPU. Through this experiment, the above three anesthetic methods were applicable to OPU, but the epidural anlagesia under general sedation with detomldine was most effective for OPU. We developed a new disposable needle guidance device with stainless steel tube. With this, disposable needles can be easily attatchable to any other intravaginal probes. And also, it was found to he practical, economic and effective for OPU with the recovery rate of 51.2%.

• 한국태양에너지학회 논문집
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• 제29권4호
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• pp.22-27
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• 2009

This study focus on verification of the thermal efficiency of volumetric receiver with 5k Wth Dish-type solar thermal system. Spiral flow path shaped on receiver and working fluid(steam) flow along with this flow path. Porous material for radiation-thermal conversion used in former researches are substituted with the stainless steel wall installed along the spiral flow path. Numerical analysis for the flow path and temperature distributions are carried out. Numerical results are compared with experimental data. Using the numerical model, the heat transfer characteristics of spiral type receiver for dish-type solar thermal systems are known and the thermal performance of the receiver can be estimated.

• 설비공학논문집
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• 제13권8호
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• pp.674-681
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• 2001

An experiment is conducted to investigate the effect of the inclination angle on convective boiling heat transfer of a uniformly heated tube. The test section used is a stainless steel tube with10.7mm in inner diameter. The hating length is 3m and is heated directly by an AC current. The test fluid is R-113. Experiment are carried out with mass flow rates of 300, 500 and $700\;kg/m^{2}s$, and heat fluxes varying from 5 to 65 kW/$m^2$. The inclination angles of the tube are $0^{\circ},\;5^{\circ},\;11^{\circ}\;and\;25^{\circ}$. the circumferential temperature variation at low quality region and the location of dryout at high quality region are mainly observed. Circumferential anisothermality occurring at low mass flow rate and low quality conditions is gradually reduced with the increase in the inclination angle and finally disappears at the inclination angle of $25^{\circ}$. Critical quality where dryout is initiated is seriously influenced by the inclination angle. Wall temperature after critical quality is also affected by the inclination angle.