• 대한기계학회논문집B
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• 제23권10호
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• pp.1347-1354
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• 1999

Recently, the markets of the air conditioner are enlarging. The market size will reach 2.0 billion won in 2000. Electric heat pumps have been utilized as main residential air conditioners. especially in Korea. They cause a surge up electric power demand during summer. Moreover, the use of HCFCs and HFCs causes serious problem to the global environment such as global warming and ozone layer destruction. Absorption chiller and heater could solve such problems. It was built and tested for analyzing the performance of the generator for absorption chiller and heater. Experiment was done with a high temperature generator, a low temperature generator, heat exchangers, a condenser and a solution tank. It was tested that the double effect series flow cycle with two kinds of solution cycle. Solution cycle B showed better than solution cycle A. Two kinds of heat exchanger were used, where one's heat transfer area is bigger than the other. Bigger one increased a little performance of absorption chiller and heater. But it was not economical. From this study, we got that the coefficient of performance(COP) is 0.82 and the capacity is 7.24 kW for an absorption chiller and heater.

• 한국추진공학회지
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• 제16권1호
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• pp.64-71
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• 2012

환경조절장치는 일반적으로 냉각기계와 열교환기를 주요 구성품으로 한다. 그런데, 본 연구에서는 환경조절장치의 천이성능 향상을 위하여 상변화 열교환기를 추가하는 새로운 개념을 제시하였다. 그 효과는 상변화 열교환기를 포함하는 환경조절장치의 모델링 프로그램을 개발하여 이륙, 기동, 순항, 착육 등과 같은 다양한 비행조건에 대하여 평가되었다. 다양한 조건에서의 시뮬레이션 결과, 회수되는 공기의 온도가 $80^{\circ}C$ 이내를 유지하는 것이 확인되어, 상변화 열교환기를 포함하는 새로운 환경조절장치의 개념이 성공적으로 검증되었다.

• 열처리공학회지
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• 제19권3호
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• pp.156-162
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• 2006

The aim of this study is to investigate the full annealing parameter for A3003 Al alloy welded tubes. The A3003 Al alloy tubes with 34 mm in external diameter and 1.3 mm in thickness for OPC drum were manufactured by high frequency induction welding with the V shaped convergence angle $6.7^{\circ}$ and power input 50 kW. The tensile and yield strength decreased with increasing the annealing temperature and time remarkably, but elongation increased remarkably. Vickers hardness in welds and base metal decreased with increasing the annealing temperature and time remarkably. In a certain experimental condition, the welds line in A3003 alloys disappeared at $520^{\circ}C$ for 4hr because of the same mechanical properties and structures between welds and base metal.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.255-262
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• 2008

The simulation of refrigeration cycle is important since the experimental approach is too costly and time-consuming. The present simulation focuses on the effect of capillary tube-suction line heat exchangers (CT-SLHX), which are widely used in small vapor compression refrigeration systems. The simulation of steady states is based on fundamental conservation equations of mass and energy. These equations are solved simultaneously through iterative process. The non-adiabatic capillary tube model is based on homogeneous two-phase model. This model is used to understand the refrigerant flow behavior inside the non-adiabatic capillary tubes. The simulation results show that both of the location and length of heat exchange section influence the coefficient of performance (COP). These results can be used in either design calculation of capillary tube length for refrigeration cycle or effect of suction line heat exchanging on refrigeration cycle.

• Nuclear Engineering and Technology
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• 제47권6호
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• pp.647-661
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• 2015

The supercritical $CO_2$ (S-$CO_2$) Brayton cycle has recently been gaining a lot of attention for application to next generation nuclear reactors. The advantages of the S-$CO_2$ cycle are high efficiency in the mild turbine inlet temperature region and a small physical footprint with a simple layout, compact turbomachinery, and heat exchangers. Several heat sources including nuclear, fossil fuel, waste heat, and renewable heat sources such as solar thermal or fuel cells are potential application areas of the S-$CO_2$ cycle. In this paper, the current development progress of the S-$CO_2$ cycle is introduced. Moreover, a quick comparison of various S-$CO_2$ layouts is presented in terms of cycle performance.

• 설비공학논문집
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• 제4권1호
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• pp.33-47
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• 1992

Experimental investigation on the performance of a heat pump system using refrigerant mixtures is done. The condenser and the evaporator are double pipe heat exchangers of counter flow type and the compressor is driven by a variable speed motor. The refrigerant mixture used in the experiment is R22/R142b. Experiments are performed by changing the compressor speed, composition on ratio of mixture, and the average temperatures of condenser and evaporator. The compressor work, heating capacity and the coefficient of performance are calculated. Results show that the heating capacity can be changed by varying the mass flow rate of refrigerant mixtures to meet the heating load. It is shown that the capacity control by changing the composition ratio is more effective than by changing the compressor speed. Under the condition where the external conditions are fixed and the heating loads are equal, the coefficient of performance has its maximum value near 50 : 50 mass fraction of the refrigerant mixture in this study.

• 한국수소및신에너지학회논문집
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• 제31권2호
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• pp.234-241
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• 2020

This paper presents a thermodynamic performance analysis of a combined cycle consisting of regenerative organic Rankine cycle (ORC) and liquefied natural gas (LNG) Rankine cycle to recover low-grade heat source and the cold energy of LNG. The mathematical models are developed and the system performances are analyzed in the aspect of thermodynamics. The effects of the turbine inlet pressure and the working fluid on the system performance such as the mass flow rates, heat transfers at heat exchangers, power productions at turbines, and thermal efficiency are systematically investigated. The results show that the thermodynamic performance of ORC such as net power production and thermal efficiency can be significantly improved by the regenerative ORC and the LNG cold energy.

• 한국산학기술학회논문지
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• 제9권3호
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• pp.587-592
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• 2008

이산화탄소 냉매 시스템용 내부 열교환기의 성능을 조사하기 위하여 4종류의 내부 열교환기를 사용하여 냉방운전조건에서 실험을 수행하였다. 내부 열교환기의 길이, 관 개수, 운전조건, 형상 변화에 대한 영향이 연구되었다. 내부 열교환기 길이가 증가할수록 능력과 효율은 향상되었다. 압력강하는 고압측보다 저압측에서 더 크게 나타났다. 가스쿨러의 온도가 높아질수록 능력과 효율은 선형적으로 증가하였으며, 증발기의 운전조건은 과열도보다는 이상영역을 설정하면 효율증대 효과 측면에서 유리하였다. 마이크로 채널의 경우가 튜브보다 능력과 효율이 크게 우수하였지만 압력강하 측면에서는 크게 불리하였다.

• 설비공학논문집
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• 제17권12호
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• pp.1132-1138
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• 2005

Recently, production and use of freon substances are restrained due to depletion of ozone layer and global warming. In this aspect of environmental problems, the best solution is to use the natural refrigerant such as ammonia. Thus, this study is to find the optimal operating conditions by comparing the performance between the shell and tube type and shell and disk type heat exchangers using the ammonia refrigerant, and to verify the superiority of the shell and disk type heat exchanger that is not used in field of refrigeration and air conditioning. Finally, this study shows that the shell and disk type heat exchanger is applicable to the ammonia refrigeration system, and this system minimizes the refrigerant charge and installation space.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.3140-3153
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• 2022

A numerical feasibility study was conducted to investigate the thermal-hydraulic characteristics of a steam generator with corrugated plates for a small modular reactor. Accordingly, a one-dimensional thermal-hydraulic analysis code was developed based on the existing state-of-the-art thermal-hydraulic models and correlations for corrugated plate heat exchangers. Subsequently, the pressure loss, heat transfer, and instability characteristics of the steam generator with corrugated plates were investigated according to the chevron angle and mass flux. Additionally, the characteristics of rectangular and disk-type corrugated plate steam generators with equivalent heat transfer areas were analyzed. The steam generator with disk-type corrugated plates exhibited better performance in terms of pressure loss and heat transfer rate than the rectangular type. In addition, when the mass flux decreased from the onset of boiling points, reverse gradients of the total pressure change were observed in both types. Thus, it was confirmed that Ledinegg instability could occur in the steam generator with corrugated plates. However, it was dependent on the chevron angle, and the optimal chevron angle to minimize instability was 45° under the conditions of the present analysis.