• 설비공학논문집
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• 제11권1호
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• pp.48-60
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• 1999

An experimental study on the performance enhancement of a screw-compressor-type chiller with 100kW of nominal cooling capacity has been carried out. Performance test facility was developed to investigate the effects of a partial modification from the existing chiller on the performance. By replacing the existing shell-and -tube heat exchangers with plate heat exchangers, the cooling capacity is increased by 15~18% and the COP is also increased by 19~21% depending on the operation temperature range. Charging mixed refrigerant R22/R142b(80 : 20) instead of R22 into the chiller with plate heat exchangers improves the cooling capacity by 4% and the COP very largely by 30%. Each contribution of the plate evaporator, plate condenser, and mixed refrigerant to the performance enhancement is examined by analyzing the refrigeration cycle and the heat transfer processes. It is also shown that the chiller performance can be improved by adapting 2-stage-compression cycle using an economizer.

• Composites Research
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• 제36권1호
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• pp.53-58
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• 2023

PIC 설계 방법은 선행 유한요소해석을 통해 하중 유형을 나누어, 각 구간마다 하중 유형에 강한 복합재료의 적층 각도 순서를 배치하는 방법이다. 기존 연구에서는 효율적으로 구간을 나누기 위하여 PIC 설계 방법에 머신 러닝이 적용되었으며, 학습 데이터는 선행 유한요소해석 결과 값을 통해 전체 요소의 일부인 참조 요소에서의 인장, 압축 그리고 전단과 같은 하중 유형으로 나누어 라벨링 되었다. 하지만 좌굴에 대해 고려되지 않아서 좌굴 발생 시, 적절한 하중 유형으로 나눌 수 없기 때문에 이를 해결하기 위한 방법이 필요하다. 본 연구에서는 좌굴이 고려되기 위한 새로운 하중 유형 분석 방법을 기존의 PIC 설계에 적용하는 기법(PIC-NTL)이 제안되었다. 좌굴의 하중 분석은 각 플라이(Ply)별 응력 3축 특성을 통해 진행되었으며, 요소의 두께 방향으로 동일한 크기의 두 영역으로 나누어진 판단 영역 내에서 결정된 하중 유형을 통해 대표 하중 유형이 지정되었다. 학습 데이터의 특성 값은 참조 요소의 좌표, 라벨(Label)은 각 판단 영역의 대표 하중 유형으로 구성되었으며, 이 데이터를 통해 머신 러닝 모델이 학습되었다. 머신 러닝 모델의 성능에 영향을 미치는 하이퍼파라미터는 베이지안 알고리즘을 통하여 최적 값으로 튜닝되었다. 튜닝 된 머신 러닝 모델의 중 SVM 모델이 가장 높은 예측률과 ROC-AUC로 나타났으며, 해당 모델을 통해 예측된 데이터가 유한요소 모델에 매핑되었다. 기존에 제안된 PIC 설계 방법과 비교하기 위하여 사각관 형태의 모델을 압축시키는 유한요소해석이 진행되었으며, 본 연구에서 제안된 설계 방법이 강도와 에너지 흡수율에서 더 우수함이 검증되었다.

• 한국가스학회지
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• 제7권2호
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• pp.22-32
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• 2003

Al-황동은 기계적 특성 및 열전도성이 우수하고 해수 중에서 표면 보호피막을 형성하므로 부식저항성이 높아 해수를 냉각수로 사용하는 선박용 열교환기의 세관재로 널리 사용되고 있다 Al-황동 세관은 실제 사용 환경에서 굽힘 등에 의한 소성변형된 상태로 사용되는 경우가 많다. 이와 같은 소성변형에 의한 Al-황동 세관의 균열 파손사례는 선박의 오일탱크 내의 가열코일, 각종 열교환기의 세관 등에서 흔히 찾아 볼 수 있다. 또한 세관의 확관에 의한 밀봉 방법에 따라 세관의 변형에 의한 잔류응력 및 어패류 혼입에 의한 해수 유입부의 국부적인 유속증가 등에 기인하여 Al-황동 세관의 균열 및 침식 등의 파손사례가 보고되고있다. 본 연구에서는 $3.5\%$ NaCl. + $0.1\%\;NH_4OH$ 수용액을 시험편 표면에 5 m/s로 액분사하의 가속실험에서 Al-황동 세관의 응력부식균열 거동에 미치는 응력의 영향에 대하여 고찰하였다.

• 동력기계공학회지
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• 제21권2호
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• pp.64-69
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• 2017

The purpose of this study is to investigate the performance characteristics of seawater cooling system for a fishing vessel. The circulation amount of refrigerant, condensation capacity, evaporation capacity, compression work and coefficient of performance(COP) were analyzed as the heat source temperature changed. The experimental setup consisted of an open-type compressor, a shell&tube type condenser, an evaporator and an expansion valve. The heat source was controlled by a constant temperature chamber. The main results of this study are summarized as follows. The condensation capacity increased with increasing heat source temperature, and it was confirmed that the effect of circulating amount of refrigerant was dominant. The amount of heat for vaporization was almost constant even though the temperature of the heat source increased. On the other hand, the compression power was increased. This is because the compression ratio increases as the condensation pressure, the enthalpy difference between inlet and outlet, the amount of circulating refrigerant increases. The performance coefficient of this system showed a tendency decreasing with increasing heat source temperature. Therefore, the basic data of the seawater cooling system for the maintenance of the catch line of the shore fishing boats was acquired through this study, and it is considered that it will be sufficient for the actual design.

• Journal of Advanced Marine Engineering and Technology
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• 제32권6호
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• pp.893-900
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• 2008

The heat exchangers in the ships have been changed from the conventional shell & tube type to the plate type due to some merits as a compactness, a high thermal efficiency and a light-weight. In recent. it is reported that the vacuum phenomena were occurred in the seawater outlet piping of a main central cooler (MCC) on the ships. From the viewpoints of a common sense, the vacuum pressure in the seawater piping is rare event and difficult to be convinced because the seawater is pumped into the piping by a seawater pump with a high discharge head. However, the occurrence of a vacuum pressure in the seawater line of an MCC is real situation and often gives a severe damage to a rubber gasket of an MCC with a plate type heat transfer area. In this study, we analyzed the vacuum pressure in the seawater line of an MCC by using the simpl Bernoulli's equation and found that the vacuum pressure in the seawater line of an MCC is inevitable untill the installation postion of an MCC is not lowered.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.630-635
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• 2008

A dynamic model has been developed to investigate the operability of a single and double-effect solar energy assisted parallel type absorption chiller. In the study, main components and fluid transport mechanism have been modeled. Flow discharge coefficients of the valves and the pumps were optimized for the double-effect mode with solar-heated water circulated. The model was run for the single mode with solar energy supply only and the solar/gas driving double effect mode. And the cases of the double mode with and without the solar energy were compared. From the simulation results, it was found that the present configuration of the chiller is not capable of regulating solution flow rates according to variable solar energy input. And the single mode utilizing the solar energy only is not practical. It is suggested to operate the system in the double mode and the flow rate control system adaptive to variable solar energy input has to be developed.

• 한국태양에너지학회 논문집
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• 제30권3호
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• pp.33-38
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• 2010

The evaporative desalination system using solar thermal energy would be the efficient and attractive method to get fresh water from brine due to low carbon dioxide generation. In this research the solar desalination system as a heating source of refrigerant R123 in the evaporator was considered. The circulation of refrigerant in the evaporator can reduce the energy consumption of the system, because of using the latent heat of the refrigerant 123 instead of the sensible heat of present hot water. The system was comprised of the single-stage fresh water production unit on the capacity of 1ton/day with shell and tube type evaporator, heaters instead of solar collector to supply the proper heat to refrigerant, and refrigerant and brine circulation systems. Various operating flowrate and temperature ranges were varied in the experiments to get the optimum design data. The results showed that the optimum flow rate of brine feed rate to evaporator was 1.2Liter/min, and the yield of fresh water was increased as higher temperature of feed brine. It was confirmed that the circulation flowrate of heating source of refrigerant was decrease of one fifth of the present warm water system, and very efficient system for solar desalination.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1002-1007
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• 2009

The research are performed to check the characteristics of the ice slurry transport system for the district cooling. The system are installed at the 1st floored building which is as large as the $1204\;m^2$ ($86\;m{\times}14\;m$). Three kinds of heat exchanger are selected, such as, plate, spiral and shell & tube type, to apply to the ice slurry systems. Experiment was done in the two cases. The first case, circulation water flow fixed at the design conditions for the state to change the flow of the supply of ice slurry. The second case, Ice slurry flow fixed at the design conditions for the state to change the flow of circulation water. Both side of Energy balance was calculated. The performance of plate heat exchanger is higher than others and it's enthalpy effectiveness is higher too.

• 한국공작기계학회논문집
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• 제14권4호
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• pp.69-74
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• 2005

Nowadays CFC and HCFC refrigerants are restricted because they causes to depletion of ozone layer. Accordingly, an experiment is apply to the $NH_3$ gas for refrigerant to study the performance characteristic and to improve the energy efficiency. An experiment are carried out for the condensed pressure in a range from 14.5bar to 16bar and for degree of superheat in a range from 0 to $10^{\circ}C$ at each condensed pressure. As the result of experiment, when degree of superheat is $1^{\circ}C$ and condensed pressure is 14.5bar, the refrigeration system showed the high performance.

• 한국자동차공학회논문집
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• 제14권5호
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• pp.100-106
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• 2006

NiTi alloy known as its shape memory effect also has superelastic characteristic, which makes it possible to be elastic under large deformation. Since the tensile strength of the alloy is very high and density is low compared to carbon steel, it can be applied to lightweight structural design. In order to design structures with shape memory alloy, finite element analysis is used and a constitutive algorithm based on Aurrichio's model is added to LS-DYNA as a user subroutine. Explicit time integration and shell element formulation are used to simulate thin-walled structures. The algorithm uses Drucker-Prager type loading condition to calculate martensite volume fraction during the transformation. The implemented algorithm is verified in uni-axial loading condition and martensite phase transformation can be detected well with the algorithm. In this study, as a energy absorbing structure, thin-walled tube is modeled with finite elements and the deformation behavior is studied. Simulation results has shown that the martensite transformation was generated in loading condition. After plastic deformation reached, the load decreases linearly without reverse martensite transformation.