• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.642-647
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• 2008

The boiler structure is determined by combustion characteristics and construction costs in the combustion chamber of a large commercial boiler. The heat transfer in boiler is composed of the radiation and the convection. The convective heat transfer has happened to back-pass heating surface. The combustion gas sequentially passes through the reheater tube, 1st economizer tube, and 2nd economizer tube. In case of being lowered in boiler height, we have to install additional tube bundle in back-pass heating surface for increasing the heat transfer of boiler, which causes the noise and vibration from combustion gas. When the combustion gas passes through the back-pass tube bundle in specified load of commercial boiler, this paper analyzes the acoustic characteristics between vortex-shedding frequency and natural frequency in tube bundle cavity. The case study reduce the resonance by changing natural frequency characteristics of tube-bundle cavity using a way to install ant-noise baffle in the direction of combustion gas flow.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.33-41
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• 2012

The component cooling water heat exchangers are critical components in a nuclear power plant. As the operation years of the heat exchanger go by, the maintenance costs required for continuous operation also increase. Most heat exchangers have carbon steel shells, tube support plates and flow baffles. The titanium tube is susceptible to flow induced vibration. The damage on carbon steel tube support rod and titanium tube around cooling water entrance area is inevitable. Therefore, analysis of internal flow around the component cooling water entrance and tube channel is a good opportunity to seek for failure prevention practice and maintenance method. The numerical study was carried out by FLUENT code to find out the causes of tube failure and its location.

• Progress in Superconductivity and Cryogenics
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• v.1 no.1
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• pp.42-47
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• 1999

Enthalpy transport in a pulse tube was investigated by two-dimensional analysis of mass. momentum an energy equations of the gas as well as energy conservation of the tube wall. The mean temperature of the gas and the tube wall was obtained directly by assuming that the outer surface of a pules tibe wall is adiabatic. Axial profile of mean temperature is small. but it deviates significantly from linear profile when the dimensionless frequency is large. Effect of operating frequency. tube wall thickness, velocity ratio and velocity phase angle between both ends of a pulse tube on net enthalpy flow were shown.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.1
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• pp.20-24
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• 2015

Steam generator(S/G) tubes in pressurized water reactor (PWR's) are subject to several types of degradation. This degradation includes denting, pitting, intergranular attack(IGA), intergranular stress corrosion cracking(IGSCC), fatigue, fretting and wear. Degradation can be derived from either the primary side(inside) or the secondary side(outside) of the tube. Recent issue for tube degradation in domestic steam generator is the tube end cracking on seal weld region. The seal weld region at the tube end and tube itself is regarded as a pressure boundary between the primary side and the secondary side. One of the Westinghouse Model-F S/G has experienced tube end cracking and its number of plugging approximately becomes to the operating limit up to 5% due to tube end cracking which was reported as SAI/MAI(single/multiple axial indication) or SCI/MCI(Single/multiple circumferential indication) from the results of eddy current testing. Eddy current mock-up test was carried out to determine the origin of cracking whether it is from weld zone area or parent tube. This result was helpful to analyze crack location on ECT data. Correct action on this problem was the installation of tube-end sleeve. Last year, after removing 340 installed plugs from tubes, selected 269 tubes took tube-end sleeve installation. Tube-end sleeve brought pressure boundary from parent tube to installed sleeve tube. Tube-end sleeve has the benefit of reducing outage period and increasing more revenue than replacing S/G. This paper is provided to assist interest parties in effectively understanding this issue.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1264-1274
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• 1994

Heat transfer performance of integral-fin tube which is used in recipro turbo refrigerator or high compact heat exchangers is studied. Eight tubes with trapezoidal shaped integral-fins having fin densities from 748 to 1654 fpm and 10, 30 internal grooves are tested. A plain tube having the same(inner and outer) diameter as the fin tubes is also tested for comparison. Pool boiling heat transfer of R-11 is investigated experimentally and theoretically on single tube arrangement. The refrigerant evaporates at saturation state of 1 bar on the outside tube surface and heat is supplied by not water which circulates inside of the tube. From the result of eight fin tubes and one plain tube tested, a tube having 1299 fpm-30 grooves shows the best performance. A maximum overall heat transfer coefficient of this tube is about 4000 $W/m^{2}K$ at 2.8m/s of water velocity. The maximum heat transfer enhancement (i.e., the ratio of overall heat transfer coefficients of finned to plain tubes)is about 2.1.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.552-558
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• 2009

An experimental study using the combustor with branch tube was conducted in order to model the industry combustor with FGR (flue gas recirculation) system and to study a thermo-acoustic instability generated by a branch tube. The branch tube is a structure used to modify a system geometry and then to change its pressure field, and the thermo-acoustic instability, usually occurs in a confined geometry, can result in serious problems on industrial combustors. Thus understanding of the instability created by modifying geometry of combustor is necessary to design and operate combustor with FGR system. Pressure fluctuation in the combustion chamber was observed according to diameter and length of branch and it was compared with the solution of 1-D wave equation. It was found that branch tube affects the pressure field in the combustion chamber, and the pressure fluctuation in the combustion chamber was reduced to almost zero when phase difference between an incipient wave in the combustion chamber and a reflected wave in the branch tube is $\pi$ at the branch point. Also, the reduction of pressure fluctuation is irrespective of the installed height of branch tube if it is below $h^*=0.9$ in the close-open tube and open-open tube.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.3
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• pp.174-180
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• 2006

Steam generator (SG) tubes are expanded inside tubesheet holes by using explosive or hydraulic methods to be fixed in a tubesheet. In the tube expansion process, it is important to minimize the crevice gap between expanded tube and tube sheet. In this paper, absolute and differential signals are computed by a numerical method for several different locations of tube expansion inside and outside a tubesheet and signal variations due to tubesheet, tube expansion and operating frequencies are observed. Results show that low frequency is good for detecting tubesheet location in both types of signals and high frequency is suitable for sizing of tube diameter as well as the detection of transition region. Also learned is that the absolute signal is good for measuring tube diameter, while the differential signal is good for locating the top of tubesheet and both ends of the transition region. In the case of mingled anomaly with tube expansion and tubesheet, low frequency inspection is found to be useful to analyze the mixed signal.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.2
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• pp.63-68
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• 2015

The fin and tube type heat exchangers widely used in air conditioners have been developed to improve on the heat transfer performance and compactness. This study presents the new type of tube for the heat exchanger to improve the heat transfer performance by increasing the heat transfer area per unit volume in the air-conditioner heat exchanger. The new type tube can be used for mechanical expansion facility, due to the two-port copper tube. Numerical calculation shows that the heat exchanger using the two-port copper tube outperforms the conventional heat-exchanger using a circular copper tube, in terms of the increased heat transfer coefficient and higher pressure drop. The calculation results were experimentally validated and are in agreement with the experimental results. Compared to the heat exchanger using a conventional circular tube, the heat exchanger with a two-port tube increased the heat transfer coefficient up to 21%, and the pressure dropped up to 16%.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.4 no.4
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• pp.275-284
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• 1975

By the experiment of a model Ondol heating system gas flow characteristics in a briquette flue tube was investigated. As a heat source electric heater was used, which renders steady flow condition of air. working fluid. It was observed that the flow augumentation may be obtained by increasing the vertial elevation of the flue tube, namely increase in the tube length or increase in the tube inclination, and the gas temperature at the tube entrance Among several factors which augument the flow rate slope of the flue tube has the most striking effect and then the temperature of gas entering the tube. Increase in length of the tube also auguments the flow but the rate of augumentation is so small that it gives little assistance to improvement of the flow The flow in a briguette flue gas does not essentially satisfy the one dimensional steady flow assumption. It is also observed that the flow begins to accompany irregular velocity fluctuation as inclination of the tube increases.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.269-275
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• 2000

The fretting wear characteristics of TiN coated Zircaloy-4 tube were investigated experimentally The fretting wear experiment was performed using TiN coated Zircaloy-4 tube as the fuel rod cladding material and uncoated Zircaloy-4 tube as one of grids. TiN coating is probably one of the most frequently and successfully used PVD coatings for the mitigation of fretting wear. In this study, TiN coating by PVD was employed for improvement of Zircaloy-4 tube fretting characteristics. The fretting tester was designed and manufactured for this experiment. TiN coated Zircaloy-4 tube was used as the moving specimen, uncoated ZircaBoy-4 tube as the stationary one. The number of cycles, slip amplitude and normal load were selected as main factors of fretting wear. The results of this research showed that the wear volume of TiN coated Zircaloy-4 tube increased as number of cycles, normal load and slip amplitude increase but the quantity of volume was lower than the case of uncoated Zircaloy-4 tube pairs.