• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.83-88
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• 2001

This paper presents modelling and analyzing method of centrifugal chiller which has a rated capacity of 200 RT(703 kW) through on-site performance test. Field data of chiller installed in the clean-room building of KIST have been collected, Simple models were developed for predicting the heat exchangers and system performances by regression of chiller operation data during 5 days in August. The models proposed here account for the effect of variations of cooling capacity, temperatures and flow rates of secondary fluids. The models are consistent with real performance data from June to September within ${\pm}5%$ error. The COP of centrifugal chiller are estimated under the standard rating conditions and reduced mass flow rate of chilled and cooling water.

• Nuclear Engineering and Technology
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• 제44권8호
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• pp.831-846
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• 2012

KAERI has developed a two-phase CFD code, CUPID, for a refined calculation of transient two-phase flows related to nuclear reactor thermal hydraulics, and its numerical models have been verified in previous studies. In this paper, the CUPID code is validated against experiments on the downcomer boiling and moderator flow in a Calandria vessel. Physical models relevant to the validation are discussed. Thereafter, multi-scale thermal hydraulic analyses using the CUPID code are introduced. At first, a component-scale calculation for the passive condensate cooling tank (PCCT) of the PASCAL experiment is linked to the CFD-scale calculation for local boiling heat transfer outside the heat exchanger tube. Next, the Rossendorf coolant mixing (ROCOM) test is analyzed by using the CUPID code, which is implicitly coupled with a system-scale code, MARS.

• 대한기계학회논문집A
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• 제29권8호
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• pp.1043-1050
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• 2005

Condenser tube is a component of the heat exchanger in automobile and air conditioning apparatus. It is generally made from the 1000 or 3000 series Al alloys that have good heat efficiency. In the case of 3000 series, these have high strength and hardness but have the disadvantage of low extruability. The development of extruding process in condenser tube with 3000 series Al alloys is studied in this paper. A study on extrusion process is performed through the 3D FE simulation in non-steady state and extrusion experimentation. Also, nano-indentation test is employed to estimate the weldability of tubes. Especially, An evaluation of the weldability using the nano-indentation is accomplished as compared with nano-hardness of welded part and the others in cross-section of tube.

• 동력기계공학회지
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• 제9권1호
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• pp.82-88
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• 2005

This paper presents numerical study on dynamic characteristics of evaporator to control evaporator superheat and compressor capacity with optimum condition in refrigeration system. It is very important to reduce energy consumption and to keep room temperature within a very restricted range with minimum oscillation in some special applications of the refrigeration system. Heat exchange is mainly happened in the evaporator. So, making mathematical model of evaporator and analyzing evaporator characteristics are necessary in order to control the superheat and the capacity of the system. A mathematical model based on the one dimensional partial differential equations representing mass and energy conservation and a tube-wall energy is described. A set of ordinary differential equation is formulated by integrating separately over the two regions(two-phase and vapor) generally presented in a heat exchanger.

• 소음진동
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• 제4권2호
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• pp.199-208
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• 1994

Two-phase cross-flow exists in many shell-tube heat exchangers such as nuclear steam generators, condensers and reboilers. An understanding of damping and of flow-induced vibration excitation mechanisms in necessary to avoid problems due to excessive tube vibration. In this paper, we present the results of experiments on normal-triangular tube bundles of pitch to tube diameter ratio, p/d, 1.22, 1.32 and 1.47. The bundle were subjected to air-water mixtures to simulate realistic mass fluxes and vapour qualities corresponding to void fractions from 5 to 99%. Damping, fluidelastic instability and turbulence- induced excitation are discussed. The behaivior of damping and two vibration mechanisms are different for intermittent flows from for bubbly flows. The effect of pitch to tube diameter ratio and void fraction is dominant on damping and fluidelastic instability.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1454-1459
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• 2024

Researchers have applied theoretical and CFD models for years to analyze the fluidelastic instability (FEI) of tube arrays in steam generators and other heat exchangers. The accuracy of each approach has typically been evaluated using the discrepancy between the experimental critical flow velocity and the predicted value. In the best cases, the predicted critical flow velocity was within an order of magnitude comparable to the measured one. This paper revisits the quasi-steady approach for damping controlled FEI in a normal triangular array with a pitch ratio of P/d = 1.375. The method addresses the fluidelastic frequency at the stability threshold as an input parameter for the approach. The excellent agreement between the estimated stability thresholds and the equivalent experimental results suggests that the fluidelastic frequency must be included in the quasi-steady analysis, which requires minimal computing time and experimental data. In addition, the model allows a simple time delay analysis regarding flow convective and viscous effects.

• 한국지열·수열에너지학회논문집
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• 제7권1호
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• pp.1-9
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• 2011

Storing and transferring heat in soils is governed by the soil thermal properties and these properties are therefore needed in many engineering applications, including horizontal ground heat exchanger for ground-coupled heat pumps. This paper presents the evaluation results of the ground subsurface temperature and apparent thermal diffusivity of soils by using ground temperature data collected at the depths of 0.5 m, 1.0 m, 1.5 m, 3.0 m, and 5.0 m at four sites. The existing correlation assuming that the soil was homogeneous and of constant thermal diffusivity was applied to calculate the subsurface temperature and two analytical equations, amplitude and phase equation, were also used to evaluate the soil apparent thermal diffusivity. Comparison of the estimated and of the measured values of the subsurface temperature has shown that the empirical correlation predicts quite accurately the ground temperature at various depths. Based on the one-dimensional heat conduction equation, the apparent thermal diffusivity can be estimated by the two equations.

• 한국수소및신에너지학회논문집
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• 제24권6호
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• pp.510-517
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• 2013

The ammonia-water based power generation cycle utilizing liquefied natural gas (LNG) as its heat sink has attracted much attention, since the ammonia-water cycle has many thermodynamic advantages in conversion of low-grade heat source in the form of sensible energy and LNG has a great cold energy. In this paper, we carry out thermodynamic performance analysis of a combined power generation cycle which is consisted of an ammonia-water regenerative Rankine cycle and LNG power generation cycle. LNG is able to condense the ammonia-water mixture at a very low condensing temperature in a heat exchanger, which leads to an increased power output. Based on the thermodynamic models, the effects of the key parameters such as source temperature, ammonia concentration and turbine inlet pressure on the characteristics of system are throughly investigated. The results show that the thermodynamic performance of the ammonia-water power generation cycle can be improved by the LNG cold energy and there exist an optimum ammonia concentration to reach the maximum system net work production.

• 동력기계공학회지
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• 제11권4호
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• pp.32-37
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• 2007

Regarding the need of energy in advance and the depletion of fossil fuel energy, all researches around the world now are trying to extract energy from many alternative sources especially the renewable one. Solar, ocean tidal, wind and geothermal energy are renewable energy fields which many researches are focused on. This paper explains about effort to replace electric pump used in solar water heating system by bubble pump. The utilization of bubble pump in this system is very efficient since it needs heat energy for its operation that can be obtained easily. In addition, it can also simplify the construction of the system. Bubble pump also functions as a controller to circulate water inside the system. Before the installation of bubble pump, the special quality and performance of bubble pump should be analyzed. The result got from the analysis could show the fluctuation of water flow rate occurred because it sensitively reacts to the heat quantity. Here the heat quantity is taken from the solar that, as we know, is not stable in a whole day. Problems often occurred are the flow rate in this system is very low moreover it could be stop if the pressure exceeds the limit.

• 대한기계학회논문집B
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• 제34권5호
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• pp.531-537
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• 2010

본 연구에서는 옵셋 스트립 휜 열교환기에서 휜 형상에 대한 최적화를 수행하였다. 압력강하량은 감소시키고 열전달량을 증가시키기 위해 이 둘을 동시에 나타낼 수 있는 j/f, $j/f^{1/3}$, JF 등의 성능 인자가 고려되었다. STDQAO, PQRSM, MGA 등의 최적화 기법이 사용되었으며, MGA 를 통해 기존 옵셋 스트립 휜보다 JF 인자는 36%, 열전달 성능은 280% 향상된 최적화된 휜 형상을 제안하였다.