• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.477-482
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• 2001

An experimental study on the performance evaluation of a brazed plate heat-exchanger with 10RT of normal cooling capacity has been carried out. In the present study, a brazed type plate heat exchanger was tested at a chevron angle $25^{\circ}$ with refrigerant R-22. Mass flux was ranged from $23\;to\;58kg/m^{2}s$ in condensation, and from $22\;to\;53kg/m^{2}s$ in evaporation. The heat transfer coefficient and pressure drop increased with the mass flux increases. The water side pressure drop increased with the cooling water flow rate and chilled water flow rate increases, while mass flux has little affect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

• 설비공학논문집
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• 제14권1호
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• pp.83-90
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• 2002

An experimental study on the performance evaluation of a brazed plate heat exchanger with 10USRT of normal cooling capacity has been carried out. In the present study, a brazed plate heat exchanger was tested at a chevron angle $25^{\circ}$with refrigerant R-22. Refrigerant mass flux was ranged from 23 to 58 kg/$m^2$s in condensation, and from 22 to 53 kg/$m^2$s in evaporation. The heat transfer coefficients and pressure drops are increased as the mass flux increases. The water side pressure drop is increased as the cooling water flow rate and chilled water flow rate increase, while mass flux has little effect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1689-1696
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• 2008

Heat pumps transfer heat by circulating a substance called a refrigerant through a cycle of evaporation and condensation. But Heat pumps system by only using heat-source is not efficient. Because the mean temperature of North Korean winter season is low, economy of air heat-source heat pump descend. This paper is practiced the simulation on evaluation criteria for Heat pump heating and cooling systems to Rolling Stock. Efficiency of the heat pump in order improving from certainly the development of the technique will be able to prevent a freezing actual condition must proceed. As a result, Below $-10^{\circ}C$ used heating and cooling systems of heat pump format even in cold winter season and is serviceable confirmed with heat source supply circle of the Rolling Stock.

• 생물환경조절학회지
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• 제22권2호
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• pp.138-145
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• 2013

최근 국내에 많이 보급되고 있는 이류체 포그 냉방시스템의 효율적인 제어알고리즘을 개발하기 위하여 다양한 조건의 분무사이클을 설정하여 토마토재배 온실에서 냉방실험을 실시하였다. 냉방효과는 평균 $1.2{\sim}4.0^{\circ}C$를 보였고, 냉방효율은 평균 8.2~32.9%로 나타났다. 분무간격에 따른 실험에서 90초 분무사이클의 냉방효율이 가장 높았고, 대체로 분무시간이 길수록, 정지시간이 짧을수록 냉방효율이 높게 나타났다. 이류체 포그시스템의 분무량이 증가할수록 냉방효율이 높아지는 경향을 찾을 수 있었다. 그러나 분무량을 증가시키더라도 내부공기가 포화상태에 가까워지면 더 이상 증발이 일어나지 않으므로 내부공기가 포화상태에 도달하기 전까지 분무량을 증대시키는 방법으로 냉방효율을 높일 수 있을 것으로 판단된다. 냉방효율이 증가함에 따라 실내공기의 포차는 감소하였고 실내외 절대습도 차이는 증가하는 경향을 보였다. 포그의 증발량이 증가할수록 실내와 실외의 절대습도 차이는 커지고, 이에 따라 환기에 의한 수증기 배출이 잘 되어 다시 증발효율을 상승시키므로 냉방효율이 높아지는 순환구조를 갖게 되는 것으로 판단된다. 분무시간과 정지시간에 따른 실내공기의 포차변화를 회귀분석한 결과 $10g{\cdot}kg^{-1}$의 포차 변화에 필요한 분무시간은 120초, 정지시간은 60초로 나타났다. 그러나 온도의 진동폭을 줄이고 냉방효율을 높이기 위해서는 포차의 변동범위를 $5g{\cdot}kg^{-1}$으로 설정하여 60초 분무, 30초 정지가 더 적당할 것으로 판단된다. 이류체 포그시스템의 제어방식을 컴퓨터 제어시스템과 현재 보급되고 있는 간편제어시스템으로 분류하여 제어알고리즘을 유도하였다. 자연환기 온실에서 간편 제어시스템을 사용한다면 분무사이클을 60초 on, 30초 off로 설정하고 온도하한은 30~$30{\sim}32^{\circ}C$, 습도상한은 85~90%로 설정할 것을 제안한다.

• 설비공학논문집
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• 제12권12호
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• pp.1098-1125
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• 2000

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 1998 and 1999 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. 1) A review of the recent studies on fluid flow, turbomachinery and pipe-network shows that many experimental investigations are conducted in applications of impingement jets. Researches on turbulent flows, pipe flows, pipe-networks are focused on analyses of practical systems and prediction of system performance. The results of noise reduction in the turbomachinery are also reported. 2) A review of the recent studies on heat transfer analysis and heat exchanger shows that there were many papers on the channel flow with the application to the design of heat exchanger in the heat transfer analysis. Various experimental and numerical papers on heat exchanger were also published, however, there were few papers available for the analysis of whole system including heat exchanger. 3) A review of the recent studies on heat pump system have focused on the multi-type system and the heat pump cycle to utilize treated sewage as the heat source. The defrosting and the frosting behaviors in the fin-tube heat exchanger is experimentally examined by several authors. Several papers on the ice storage cooling system are presented to show the dynamic simulation program and optimal operation conditions. The study on the micro heat pipes for the cooling of high power electronic components is carried out to examine the characteristics of heat and mass transfer processed. In addition to these, new type of separate thermosyphon is studied experimentally. 4) The recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. New systems operating with natural refrigerants are drawing lots of attention. In addition to these, evaporation and condensation heat transfer characteristics of traditional and new refrigerants are investigated for plain tubes and also for microfin tubes. Capillary tubes and orifice are main topics of research as expansion devices and studies on thermophysical properties of new refrigerants and refrigerant/oil mixtures are widely carried out. 5) A review of the recent studies on absorption cooling system shows that numerous experimental and analytical studies on the improvement of absorber performance have been presented. Dynamic analysis of compressor have been performed to understand its vibration characteristics. However research works on tow-phase flow and heat transfer, which could be encountered in the refrigeration system and various phase-change heat exchanger, were seemed to be insufficient. 6) A review of recent studies on duct system shows that the methods for circuit analysis, and flow balancing have been presented. Researches on ventilation are focused on the measurement of ventilation efficiency, and variation of ventilation efficiency with ventilation methods by numerous experimental and numerical studies. Furthermore, many studies have been conducted in real building in order to estimate indoor thermal environments. Many research works to get some information for cooling tower design have been performed but are insufficient. 7) A review on the recent studies on architectural thermal environment and building mechanical systems design shows that thermal comfort analysis is sitting environment, thermal performance analysis of Korean traditional building structures., and evaluation of building environmental load have been performed. However research works to improve the performance of mechanical system design and construction technology were seemed to be insufficient.

• 생물환경조절학회지
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• 제10권1호
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• pp.10-14
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• 2001

포그냉방시스템의 냉방효과는 온실 내부의 상대습도, 공기유동과 밀접한 관계가 있다. 냉방설계용 VETH선도에서 냉발효율은 환기회수의 증가와 그에 상응하는 분무수량의 증가로 인하여 개선될 수 있다. 시간제어방식을 이용한 무차광 실험온실에서 분당 환기회수가 평균 0.77회, 분무수량이 2,009g 일 때 온실 내부의 기온이 31$^{\circ}C$로 외부기온과 거의 같게 나타났으며, 이 때의 증발효율은 82%이다. 분당 환기회수가 평균 0.26회, 분무수량이 1.256g인 경우 무냉방 온실의 기온과 비슷한 37.1$^{\circ}C$였다. 차광율 70%인 실험온실의 분당 환기환수가 평균 2.59회, 분무수량이 2,009g 일 때, 내부의 상대습도는 증가하나 기온은 하강하지 못했다. 그러나 분당 환기회수가 평균 2.33회, 분무수량이 2,009g인 경우 내부의 기온이 31.4$^{\circ}C$로 이 때 온실의 유입구 풍속은 최고 1.9m.s$^{-1}$였다. 시간제어의 경우 일정간격으로 일정한 수량을 분무하기 때문에 분무입자가 모두 증발하지 못하고 온실 내부에 누적되어 온실 내부의 상대습도를 증가시켜 냉방효율을 감소 시키는 원인이 되고 차광망이 온실내부의 공기흐름을 차단하여 증발효율을 감소시키는 것으로 나타났다. 포그냉방시스템의 냉방효율을 높이기 위해서는 온실 내부의 상대습도에 의한 제어방식과 내부 공기의 순환에 대한 연구가 필요하다.

• 대한기계학회논문집B
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• 제21권5호
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• 한국추진공학회지
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• 제17권2호
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• pp.114-121
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• 2013

미세채널을 갖는 증발형 열교환기의 효율을 평가하기 위하여, 공기의 온도와 물의 온도와 같은 열교환기의 상태값들을 계산하기위한 관계식들이 문제를 단순화하기 위한 몇 가지 가정을 적용한 Navier-Stokes 방정식으로부터 유도되었다. 미세채널내부는 물의 상태에 따라 3가지 영역으로 나누었다. 이 연구의 결과로써, 미세유로를 갖는 증발형 열교환기의 증발시작시점과 건조완료점을 계산하는 방정식이 제시되었다. 본 연구결과는 증발효과를 이용하는 미세채널형 열교환기의 설계, 성능예측 및 시험결과 분석 등에 효과적으로 활용될 수 있을 것으로 기대된다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권4호
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• pp.459-465
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• 2009

This paper considers the influence of internal heat exchangers to the efficiency of a refrigerating system. These internal heat exchangers(liquid-suction or suction-line heat exchangers) can, in some cases, yield improved system performance while in other cases they degrade system performance. A steady state mathematical model is used to analysis the performance characteristics of refrigeration system with internal heat exchanger. The influence of operating conditions, such as gas cooler pressure and evaporation temperatures, superheat in the evaporator and temperature of gas cooler outlet, to optimal dimensions of the heat exchanger is also analyzed in the paper. The main results were summarized as follows : the mass flowrate of R744, inner diameter tube and length of internal heat exchanger, and effectiveness have an effect on the cooling capacity, compressor work and RCI(Relative capacity index) of this system. With a thorough grasp of these effect, it is necessary to design the R744 compression refrigeration cycle using internal heat exchanger.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권2호
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• pp.44-50
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• 2008

This study presents test results of a mobile air-conditioning system using a potential alternative refrigerant, R152a. A series of performance tests have been carried out and cycle characteristics such as cooling capacity, energy efficiency ratio, suction and discharge pressures, and temperatures are presented, compared to those for the baseline R134a system. Tests were conducted with evaporation temperature of $5^{\circ}C$, condensation temperature of $45^{\circ}C$, subcooling temperature of $5^{\circ}C$, superheating temperature of $5^{\circ}C$, and compressor speed of 500-1500 rpm. The performance of R152a system with readjustment of an expansion valve showed better than those of R134a. The effect of oil on the pressure drop in the evaporator was also addressed.