• 한국자기학회지
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• 제15권4호
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• pp.236-240
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• 2005

본 연구에서는 페로스카이트 구조를 갖고 있는 란타늄 망간산화물인 $La_{1-x}Pb_{x}MnO_{3}$(x=0.1, 0.2, 0.3) 합금에 대한 연구를 수행하였다. 무엇보다도 이들 재료는 다른 계열의 재료에 비해 낮은 자기열량효과를 보이나 제조하기 쉬운 산화물이라는 것과 가격이 매우 저렴하다는 장점을 갖고 있어 유용한 자기냉각소재로서 기대가 되어지고 있는 물질이다. $LaMnO_3$ 합금에서 La을 Pb로 치환할 때 치환량에 따른 자기적 특성과 자기열량효과를 측정하였다. 자기적인 특성을 측정하기 위하여 진동시료형 자력계(VSM) 를 이용하여 자기이력곡선과 자기모멘트의 온도의존성을 측정하였고 자기열량효과의 간접적인 측정방법인 자기엔트로피변화를 측정하기 위하여 큐리온도 근처에서 외부자기장의 변화에 따른 자기모멘트의 변화를 측정하였다. 자기열랑효과의 직접적인 측정방법인 단열온도변화를 측정하기 위하여 제작한 cryostat을 이용하여 큐리온도 근처에서 외부자기장의 변화에 따른 $LaPbMnO_3$ 합금의 단열온도변화를 측정하였다. 특히, 본 연구에서는 Pb 치환량이 증가함에 따라 쌍교환작용(double-exchange interaction)이 작게 변화하여 자기엔트로피 변화를 크게 함을 알 수 있었다.

• 설비공학논문집
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• 제17권11호
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• pp.1028-1034
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• 2005

The objective of this paper is to study the effects of the cooling air mass flow rate and the heat input variation by the simulation and the experiment. An air-cooled $NH_3/H_2O$ absorption chiller is tested in the present study. The nominal cooling capacity of the single effect machine is 17.6 kW (5.0 USRT). The overall conductance (UA) of each component, the cooling capacity, coefficient of performance and each state point are measured with the variation of the cooling air mass flow rate and the heat input. It is found that the COP and cooling capacity increase and then decreases with increasing the heat input. It is also found that the COP and the cooling capacity increase and keep constant with increasing the cooling air mass flow rate. The maximum COP is estimated as 0.51 and the optimum cooling air mass flow rate is $217\;m^3/min$ from the present experiment.

• 설비공학논문집
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• 제29권10호
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• pp.551-557
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• 2017

Most European economies, Japan, and many governments have made it a major policy to expand the green business by disseminating heat pump technology, which has a large $CO_2$ reduction effect. The heat pump of all heat sources has been recognized as renewable energy and the policy to encourage has been implemented. In the recently revised Renewable Energy Law, the hydrothermal source (surface sea water) heat pump was newly included in renewable energy. In addition, the scope of application of heat pumps has expanded in the mandatory installation of renewable energy for new buildings, remodeling buildings, and reconstructed buildings based on this law. However application to heat pumps using all natural energy as heat source has been put off. In this revision, the ratio of renewable energy to the total energy produced by the heat pump was fixed at 73%, which depends on coefficient of performance of heat pump. The ratio of renewable energy is $1-1.8/COP_H$, and should be calculated including the coefficient of performance of the heat pump. Using a high efficiency heat pump or a high-temperature heat source increases the coefficient of performance and also reduces $CO_2$ emissions. It is necessary to expand the application of heat pumps as renewable energy equipment and to improve the correct calculation of renewable energy production.

• 설비공학논문집
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• 제8권4호
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• pp.463-472
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• 1996

Experiments were carried out to study the operation characteristics of a regenerator with a thermo-syphon pump and a surface-flame burner for a lithium bromide (LiBr)-water absorption heat pump. A cylindrical-shape metal-fiber burner and commercial grade propane were used. The emission of carbon monoxide and nitric oxide was measured by a combustion gas analyzer. Ther regeneration rate of water vapor as a refrigerant was measured. It could be as a reference value showing the performance of the regenerator. The circulation rate of the LiBr-water solution was also measured from both the tanks for the weak-and the strong-solution. Using a refractometer, the LiBr concetration in the solution was calculated from the measured refractory index of the solution. Temperature of the solution and the condensed water was recorded at several points in the experimental apparatus with thermocouples, using a personal computer. This data collecting system for measuring temperature was calibrated with a set of standard thermometers. The generating rate of water vapor as refrigerant increased linearly with heat supplied. It was about 4.0g/s with the heat supplied at a rate of 16,500kcal/h. The circulation rate of LiBr solution also increases with the heat supplied. The difference in LiBr concentrations between the weak and the strong solution was in the range of 1 to 5% when the concentration of the strong solution was about 60%. It was dependent upon both the heat supplied and the circulation rate of the solution. The initial concentration and the level of the LiBr solution in the regenerator were measured and recorded before experiments. The effect of them on the generating rate of water vapor and the circulation rate of the solution was also studied. The generating rate of water vapor was not strongly dependent upon both the level of the LiBr solution and the initial LiBr concentration. However, the concentration difference of the solution increases with the initial level of the LiBr solution.

• 설비공학논문집
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• 제7권2호
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• pp.184-195
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• 1995

A theoretical one-dimensional model for the charging process in stratified thermal storage tanks is established presuming that the fluid ensuing from the tank inlet creates a perfectly mixed, layer above the thermocline. Both the generic and asymptotic closed-form solutions are obtained via the Laplace transformation. The asymptotic solution describes the nature of the charging pertaining to the case of no thermal diffusion, whereas the generic solution is of practical importance to understand the role of operating parameters on the stratification. The present model is validated through comparison with available experimental data, where they agree well with each other within a reasonable limit. An interpretation of the exact solution entails two important features associated with the charging process. The first is that an in-crease in the mixing depth $h_m$ causes a relatively slow temperature rise in the perfectly mixed region, but on the other hand it results in a faster decay of the overall temperature gradient across the thermocline. Next is the predominance of the mixing depth in the presence of the prefectly mixed region. In such a case the effect of the Peclet number is marginal and there-fore the thermal characteristics are solely dependent on the mixing depth paticularly for large $h_m$. The Peclet number affects significantly only for the case without mixing. Variation of the storage efficiency in response to the change in the mass flow rate agrees favorably with the published experimental results, which confirms the utility of the present study.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권8호
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• pp.404-410
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• 2006

Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 40[K] should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. In order to take advantage of a greater critical current density of high temperature superconducting (HTS) and considerably reduce the size and weight of the system, conduction-cooled HTS superconducting magnetic energy storage (SMES) at temperatures well below 40[K] should be investigated. This work focuses on the breakdown and flashover phenomenology of dielectrics exposed in air and/or vacuum for temperatures ranging from room temperature to cryogenic temperature. Firstly, we summarize the insulation factors of the magnet for the conduction cooled HTS SMES. And Secondly a surface flashover as well as volume breakdown in air and/or vacuum with two kind insulators has been investigated. Finally, we will discuss applications for the HTS SMES including aging studies on model coils exposed in vacuum at cryogenic temperature. The commercial application of many conduction-cooled HTS magnets, however, requires refrigeration at temperatures below 40[K], in order to take advantage of a greater critical current density of HTS and reduce considerably the size and weight of the system. The magnet is driven in vacuum condition. The need to reduce the size and weight of the system has led to the consideration of the vacuum as insulating media. We are studying on the insulation factors of the magnet for HTS SMES. And we experiment the spacer configure effect in the dielectric flashover characteristics. From the results, we confirm that our research established basic information in the insulation design of the magnet.

• 설비공학논문집
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• 제19권8호
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• pp.563-568
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• 2007

The air-side particulate fouling in the heat exchangers of HVAC applications degrades the performances of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. An empirical modeling equation has been derived from the experimental results using accelerated tests and it showed good predictions of the fouling characteristics of the slitted finned tube heat exchangers. However the modeling equation predicts only the fouling characteristics of new heat exchangers and it can not predicts fouling characteristics obtained from actual field data which contains the effect of hydrophilicity deterioration. Therefore an modified modeling equation is proposed and it shows good predictions of the actual fouling characteristics of finned-tube heat exchangers.

• 한국산학기술학회논문지
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• 제11권2호
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• pp.449-454
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• 2010

본 논문은 균질유동모델을 적용하여 단열 모세관내 R600a의 유동 특성을 이론적으로 조사하였다. 이 모델은 시뮬레이션 해석에 필요한 기본적인 질량, 에너지, 운동량 방정식에 근거하고 있다. 또한 2개의 마찰인자와 점성계수모델을 이용하여 유동특성을 조사하였다. R600a의 열역학 및 전달 물성치는 EES 물성치 코드를 이용하여 계산하였다. 작동변수들에 대한 기초 설계자료를 제공하고자 단열 모세관내 R600a의 유동 특성을 분석하였다. 본 연구의 작동변수에는 응축온도, 증발온도, 과냉각도, 모세관의 직경이 있다. 주요 결과를 요약하면 다음과 같다. R600a용 단열 모세관내 응축온도, 증발온도, 과냉각도, 관직경은 모세관 전체길이에 영향을 준다. 즉 R600a용 모세관 전체길이는 식(15)와 같은 상관식으로 나타낸다.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1440-1446
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• 2012

본 논문은 수평 마이크로핀관내 초임계 $CO_2$와 PAG 혼합물의 열전달과 압력강하 특성에 대해서 실험적으로 연구한 것이다. $CO_2$와 PAG 혼합물의 열전달계수는 압력이 10 MPa이고, 질량유속은 520 kg/$m^2s$이며, PAG 오일 농도는 0.06~2.26%에서 측정하였다. PAG 오일농도가 0.3%인 경우, $CO_2$와 PAG 혼합물의 열전달계수와 압력강하는 순수 $CO_2$ 냉매의 열전달계수와 동일한 경향을 나타내었다. 그리고 PAG 질량농도가 2.26%인 경우, 초임계 온도근처에서 측정한 열전달계수는 순수 $CO_2$의 열전달계수 보다 약 50%정도 낮게 나타났다. 마찰압력강하는 $60^{\circ}C$의 $CO_2$ 평균온도에서 순수 $CO_2$의 압력강하보다 약 1.6배 더 높게 나타났다.

• 설비공학논문집
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• 제10권6호
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• pp.773-783
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• 1998

The heating system for apartment complex may be classified as old systems including central system with steam boiler(S1), gas engine driven heat pump system(S2), system using waste heat(S3) and new systems including mechanical vapor re-compression system with flashing heat exchangers(S4), system using methanol(S5), system using metal hydride (S6). The purpose of the present study is to suggest optimal heating system by technically, economically and environmentally evaluating old and new heating systems of apartment complex from 500 to 3,000 households. Economic evaluation based on the technical evaluation results which estimated heat transfer area of heat exchangers and capacity of equipments was estimated initial investment cost, annual operating cost and relative payback period by considering annual increasing rates of energy cost and interest. Environmental evaluation provided annual generation rate of carbon dioxide. Initial investment cost was cheap in the order of S6, S5, S3, S2, S4, S1, annual operating cost was cheap in the order of S1, S2, S4, S5 and relative payback period was short in the order of S6, S5, S2, S3 and S4. Relative payback period was within 8 years for all scenarios of 3,000 households, and was increased as annual increasing rates of energy cost and interest were increased. As transportation pipe length was increased twice, payback period was increased by 1.4~2.6 time. The effect of temperatures of waste gas and waste water on the relative payback period was small within 0.8 years. The annual generation rate of carbon dioxide was big in the order of S4, S2 and S1. S4 was the most economic system among whole scenarios when S1 was replaced with other scenarios.