• 대한기계학회논문집B
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• 제24권12호
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• pp.1635-1643
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• 2000

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1467-1472
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• 2003

Fouling of heat exchangers is generated by water-borne deposits, commonly known as foulants including particulate matter from the air, migrated corrosion produces; silt, clays, and sand suspended in water; organic contaminants; and boron based deposits in plants. This fouling is known to interfere with normal flow characteristics and reduce thermal efficiencies of heat exchangers. This paper focuses on fouling analyses for six heat exchangers of two primary systems in two nuclear power plants; the regenerative heat exchangers of the chemical and volume control system and the component cooling water heat exchangers of the component cooling water system. To analyze the fouling for heat exchangers, fouling factor was introduced based on the ASME O&M codes and TEMA standards. Based on the results of the fouling analyses, the present thermal performances and fouling levels for the six heat exchangers were predicted.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.595-600
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• 1993

The heat of reaction has been estimated from heat balance relationships around the reactor. The heat balance equations were formulated with the assumptions that the reactor temperature is uniformly distributed and the jacket temperatures are axially distributed. We have obtained the temperature distribution of jacket contents by FDM. And then, we have rearranged the heat balance equations so that the heat of reaction can be estimated from the finite number of temperature measurements, i.e., temperatures of the reactor contents, at the jacket inlet and outlet, respectively. The proposed method for reaction heat estimation on were applied to industrial batch reactors ; one is ABS polymerization reactor and the other is SAN polymerization reactor. We have also examined the variation of overall heat transfer coefficients for the reactors during reaction.

• 한국가스학회:학술대회논문집
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• 한국가스학회 2005년도 추계학술발표회 논문집
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• pp.123-127
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• 2005

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1388-1395
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• 2017

The Helically coiled tube Once-Through Steam Generator (H-OTSG) is a key piece of equipment for compact small reactors. The present study developed and verified a thermal-hydraulic design and performance analysis computer code for a countercurrent H-OTSG installed in a small pressurized water reactor. The H-OTSG is represented by one characteristic tube in the model. The secondary side of the H-OTSG is divided into single-phase liquid region, nucleate boiling region, postdryout region, and single-phase vapor region. Different heat transfer correlations and pressure drop correlations are reviewed and applied. To benchmark the developed physical models and the computer code, H-OTSGs developed in Marine Reactor X and System-integrated Modular Advanced ReacTor are simulated by the code, and the results are compared with the design data. The overall characteristics of heat transfer area, temperature distributions, and pressure drops calculated by the code showed general agreement with the published data. The thermal-hydraulic characteristics of a typical countercurrent H-OTSG are analyzed. It is demonstrated that the code can be utilized for design and performance analysis of an H-OTSG.

• 설비공학논문집
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• 제17권9호
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• pp.789-798
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• 2005

This paper is a numerical study concerning how the interactions between a pair of the vortices effect flow field and heat transfer. The flow field (common flow down) behind a vortex generator is modeled by the information that is available from studies on a half-delta winglet. Also, the energy equation and the Reynolds-averaged Wavier-Stokes equation for three-dimensional turbulent flows, together with a two-layer turbulence model to resolve the near-wall flow, are solved by the method of AF-ADI. The present results predict that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it Is directed away from the wall. Although some discrepancies are observed near the center of the vortex core, the overall performance of the computational model is found to be satisfactory.

• 대한기계학회논문집B
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• 제31권10호
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• pp.823-831
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• 2007

This paper presents the experimental and simulation study of a loop heat pipe (LHP) that can be applied to present electronics, space missions and thermal control systems. The present experimental study was carried out employing sintered alumina ceramic wick ($d=2.96\;{\mu}m$, ${\phi}=0.61$). High purity R-134a, R-22 and water were also used as alternative working fluids in addition to ammonia. The experimental study showed that the maximum heat transfer performance for the test LHP in the vertical top heating mode was over 100 Watts when ammonia was used as the working fluid. The simulation results have been compared with the experimental results to validate a simulation model based on the thermal resistance network that was developed to evaluate the performance of LHPs, focusing on their prospective applications in electronics. The simulation model is based on the loop overall energy, mass, and momentum balance. The simulation program can predict the effects of various parameters which affect the performance of LHP within 5% compared with the experimental results.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.1096-1101
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• 2005

In this study, the experiment of thermal performance about closed-type hybrid cooling tower was conducted. A closed type cooling tower is a device similar to a general cooling tower, but with cooling tower replaced by a heat exchanger. The test section for this experiment has the process that the cooling water flows from top part of heat exchanger to bottom side in the inner side of tube, and spray water flows gravitational direction in the outer side of it. Air contacts of tube outer side are counterflow. The heat transfer pipe used in this experiment is a bare type tube having an outside diameter of 15.88mm. In this experiment, heat performances of the cooling tower are calculated such as overall heat transfer coefficient of between the process fluid and air, cooing capacity and pressure drop.

• 설비공학논문집
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• 제19권7호
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• pp.512-520
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• 2007

The design of a ground-source heat pump system includes specifications for a ground loop heat exchanger where the heat transfer rate depends on the effective thermal conductivity of the ground and the effective thermal resistance of the borehole. To evaluate these heat transfer properties, in-situ thermal response tests on four vertical test boreholes with different grouting materials were conducted by adding a monitored amount of heat to circulating water. The line-source method is applied to the temperature rise in an in-situ test and extended to also give an estimate of borehole effective thermal resistance. The effect of increasing thermal conductivity of the grouting materials from 0.818 to $1.104W/m^{\circ}C$ resulted in overall increases in effective thermal conductivity by 15.8 to 56.3% and reductions in effective thermal resistance by 13.0 to 31.1%.

• Journal of Advanced Marine Engineering and Technology
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• 제40권6호
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• pp.453-457
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• 2016

발전 플랜트, 석유 화학 플랜트, 단위 공장과 같은 다양한 산업 플랜트에서, 사용 후 스팀이나 잉여 스팀을 이용하여 온수나 급탕수를 만드는 시스템의 수요가 증가하고 있다. 스팀을 사용하여 온수를 제조하는 장치인 컴팩트 스팀 유닛(Compact Steam Unit, 이하 CSU)가 에너지 재활용 측면에서 좋은 대안이 되고 있다. 본 연구에서는 고압 CSU 개발을 위한 기초 연구로서, CSU의 핵심 부품인 열교환기로 기존 판형 열교환기 대신 하이브리드 열교환기를 적용하여 위해, 실험적인 방법으로 하이브리드 열교환기의 전열 특성을 파악하고자 하였다. 실험 결과, 온수측과 냉수측 사이의 열 평형은 ${\pm}5%$ 이내를 만족하였다. 레이놀즈 수가 증가함에 따라, 총괄 열전달 계수는 선형적으로 증가하였으며, 채널 유속 0.5 m/s 이상에서 총괄 열전달 계수는 개발 목표치인 $5,524W/m^2K$를 초과하였다. 레이놀즈 수가 증가함에 따라, 압력 강하 또한 증가하였으며, 단위 길이당 압력 강하값은 유속 0.5 m/s에서 50 kPa/m 이하였다.