• 제목/요약/키워드: Refrigerator cycle

검색결과 102건 처리시간 0.025초

터보기기용 포일 저널 베어링 개발 (Development of Foil Journal Bearing for Turbo Machinery)

  • 김경수;이기호;김승우
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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    • pp.475-481
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    • 2001
  • Foil bearings have been successfully used for small high speed rotors, such as ACM(Air Cycle Machine), turbo charger, turbo compressor, high speed motor, etc. Recently advanced researches are concentrated on the high load capacity and the extreme temperature foil bearings to extend the application boundary. Some bearings are already adopted into cryogenic machines and micro gas turbines. In this paper, a foil journal bearing designed for high load capacity, which is under development, is introduced. The bearing is for the turbo refrigerator which has a rotor of 18${\~}$25 kgf rotating at 23,000${\~}$38,000 rpm. This application is well beyond conventional spectrum of foil bearings because the rotor is relatively heavy and the rotational speed is low. Therefore, the development is challenging. The foil bearing is a bump type, the size is 60mm in diameter and 50mm in length, the operating fluid is air and rotational speed is 26,000 rpm. In-house software was developed and used for bearing design. Tested maximum load capacity is 80kgf, 0.62 in terms of load capacity coefficient, and testing is being continued.

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Thermodynamic Analysis of Hydrogen Lquefaction Systems Using Gifford-McMahon Cryocooler

  • Chang, Ho-Myung;Park, Dae-Jong;Kang, Byung-Ha
    • International Journal of Air-Conditioning and Refrigeration
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    • 제8권2호
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    • pp.39-50
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    • 2000
  • Thermodynamic cycle analysis is presented to estimate the maximum liquefaction rate of hydrogen for various systems using a Gifford-McMahon(GM) cryocooler. Since the present authors` previous experiments showed that the gaseous hydrogen was liquefied approximately at the rate of 5.1 mg/s from the direct contact with a commercial two-stage GM refrigerator, this study has been proposed to predict how much the liquefaction rate can be increased in different configurations using the GM cooler and with improved heat exchangers. The optimal operating conditions have been analytically sought with real properties of normal hydrogen for the Linde-Hampson(L-H) system precooled by single-stage GM, the direct-contact system with two-stage GM, the L-H system precooled by two-stage GM, and the direct-contact system with helium GM-JT (Joule-Thomson). The maximum liquefaction rate has been predicted to be only about 7 times greater than the previous experiment, even though the highly effective heat exchangers may be employed. It is concluded that the liquefaction rate is limited mainly because of the cooling capacity of the commercially available GM cryocoolers and a practical scale of hydrogen liquefaction is possible only if the GM cooler has a greater capacity at 70-100 K.

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저온용 R502 대체 냉매의 이론 및 실험적 평가 (Theoretical and Experimental Evaluation of R502 Alternatives in Low Temperature Applications)

  • 권승림;박윤범;정동수;김종보;강득주
    • 설비공학논문집
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    • 제7권4호
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    • pp.654-666
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    • 1995
  • R502 has been extensively used as a working fluid in transport refrigerating vehicles and low temperature refrigerating machines but is to be phased out by the end of 1995 due to ozone layer depletion problem. In this study, both theoretical cycle analysis and experiments were carried out to examine the best substitutes for R502. Theoretical results indicate that the alternatives available in the market today may replace R502 without significant changes in the system without suction line heat exchanger(SLHX). When the system contains a SLHX, however, COPs of the alternatives increase up to approximately 15~20% than those without the SLHX. But simultaneously, the discharge temperatures of the compressor also increrease significantly with the SLHX. Actual test results obtained from the experiment with a transport vehicle's refrigerator indicate the similar trend as those of the theoretical results. Especially, HFCs and their mixtures show lower discharge temperature than those of R502, which is one of the desirable features. Further research is needed to study the effect of the SLHX on the performance of the real machine as well as on the oil return for reliability of the system.

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설비공학 분야의 최근 연구 동향 : 2013년 학회지 논문에 대한 종합적 고찰 (Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2013)

  • 이대영;김사량;김현정;김동선;박준석;임병찬
    • 설비공학논문집
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    • 제26권12호
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    • pp.605-619
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    • 2014
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2013. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and relative parts including orifices, dampers and ducts, fuel cells and power plants, cooling and air-conditioning, heat and mass transfer, two phase flow, and the flow around buildings and structures. Research issues dealing with home appliances, flows around buildings, nuclear power plant, and manufacturing processes are newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for general analytical model for desiccant wheels, the effects of water absorption on the thermal conductivity of insulation materials, thermal properties of Octadecane/xGnP shape-stabilized phase change materials and $CO_2$ and $CO_2$-Hydrate mixture, effect of ground source heat pump system, the heat flux meter location for the performance test of a refrigerator vacuum insulation panel, a parallel flow evaporator for a heat pump dryer, the condensation risk assessment of vacuum multi-layer glass and triple glass, optimization of a forced convection type PCM refrigeration module, surface temperature sensor using fluorescent nanoporous thin film. In the area of pool boiling and condensing heat transfer, researches on ammonia inside horizontal smooth small tube, R1234yf on various enhanced surfaces, HFC32/HFC152a on a plain surface, spray cooling up to critical heat flux on a low-fin enhanced surface were actively carried out. In the area of industrial heat exchangers, researches on a fin tube type adsorber, the mass-transfer kinetics of a fin-tube-type adsorption bed, fin-and-tube heat exchangers having sine wave fins and oval tubes, louvered fin heat exchanger were performed. (3) In the field of refrigeration, studies are categorized into three groups namely refrigeration cycle, refrigerant and modeling and control. In the category of refrigeration cycle, studies were focused on the enhancement or optimization of experimental or commercial systems including a R410a VRF(Various Refrigerant Flow) heat pump, a R134a 2-stage screw heat pump and a R134a double-heat source automotive air-conditioner system. In the category of refrigerant, studies were carried out for the application of alternative refrigerants or refrigeration technologies including $CO_2$ water heaters, a R1234yf automotive air-conditioner, a R436b water cooler and a thermoelectric refrigerator. In the category of modeling and control, theoretical and experimental studies were carried out to predict the performance of various thermal and control systems including the long-term energy analysis of a geo-thermal heat pump system coupled to cast-in-place energy piles, the dynamic simulation of a water heater-coupled hybrid heat pump and the numerical simulation of an integral optimum regulating controller for a system heat pump. (4) In building mechanical system research fields, twenty one studies were conducted to achieve effective design of the mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, and renewable energies in the buildings. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment is mostly focused on indoor environment and building energy. The main researches of indoor environment are related to infiltration, ventilation, leak flow and airtightness performance in residential building. The subjects of building energy are worked on energy saving, operation method and optimum operation of building energy systems. The remained studies are related to the special facility such as cleanroom, internet data center and biosafety laboratory. water supply and drain system, defining standard input variables of BIM (Building Information Modeling) for facility management system, estimating capability and providing operation guidelines of subway station as shelter for refuge and evaluation of pollutant emissions from furniture-like products.

구성주의 과학교사를 만들기 위한 장기적인 현직 교육의 한 예 (One Year Long In-Service Education to Help Become a Constructivist Science Teacher)

  • 조정일;윤수미
    • 한국과학교육학회지
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    • 제22권3호
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    • pp.632-648
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    • 2002
  • 이 연구에서는 2000년 여름부터 2001년 여름까지 1년여 동안 실시된 순환학습/STS 과학교사 현직 교육을 받은 한 과학교사의 수업 지도안 개발 과정을 기술하고, 그 과정에서 구성주의와 일치하는 방향으로 그 교사의 과학, 과학 학습, 과학 수업 관점의 변화를 알아보았다. 참여 교사는 개념에 기초한 실험 중심의 수업 지도안에서 실생활을 적극 반영한 학생 활동 중심으로 수업 내용을 바꾸어 갔다. 동기 부여 측면에서 학생들이 쉽게 경험할 수 있는 실생활의 소재를 활용하였고, 학생들의 오개념을 반영한 수업을 위해 간단한 실험에서 학생들의 의견을 많이 듣고 개념 변화로서의 학습을 고려하였다. 그 교사의 이러한 구성주의적 반응은 현직 교육 기간 동안에 긍정적인 방향으로 증가하였다. 실제 수업 지도안에 반영된 변화는 면담을 통해서 그 교사가 과학, 과학 수업, 과학 학습 등에서 확인되었다. 특히 7차 교육과정이 학생 활동을 강조하는 방향으로 개편된 점을 감안할 때 순환학습과 STS에 기초한 수업 지도안 개발은 현장에서 더욱 요구되는 사항으로 생각된다.

혼합 냉매를 이용한 극저온 J-T 냉동기 관한 실험적 연구 (An Experimental Study of The J-T Cryocooler with Mixed Refrigerant)

  • 이경수;정상권
    • 한국초전도ㆍ저온공학회논문지
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    • 제3권1호
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    • pp.64-68
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    • 2001
  • An experimental study on the Joule-Thomson cryocooler with the mixed refrigerant (MR) is described in this paper, J-T refrigeration experiment was performed with a single stage regular air-conditioning compressor The mixed refrigerant in the experiment was composed of 75% mol fraction of $N_2$. 30% moi fraction of CH$_4$. 30% moi fraction of $C_2$H$_{6}$. 10% mot fraction of $C_3$H$_{8}$ and 15% mot fraction of iso-C$_4$H$_{10}$. Oil mist in the MR stream could be eliminated completely by the glass microfiber filter. Since a single stage compressor that had been designed thor R22 is not appropriate for high Pressure ratio of the mixed refrigerant especially during the transient period. two modifications were incorporated to regular J-T refrigeration cycle. First. a Portion of the MR was by-passed at the inlet of the heat exchanger and transferred directly to 7he suction of the compressor in the modified system. Second, a buffer volume was Prepared to change the mass flow rate of refrigerant. The pressure ratio in J-T expansion device was relieved at the beginning of the operation due to the by-Pass scheme. but it gradually decreased during the transient Process as some of the MR component condensed at low temperature. The buffer volume at the suction side was used to increase the MR gas density in the system after the transient cool-down period. Form the experiment with the modified system, the refrigerator could reach the lowest temperature of -152$^{\circ}C$ without cooling load. and about -15$0^{\circ}C$ with 5 W of cooling load . . . .

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두개의 증발기가 장착된 소프트 아이스크림 제조기의 성능 해석 (Performance Analysis of the Soft Ice-cream Maker Having Two Evaporators Operating at Different Temperatures)

  • 김정식;김내현
    • 한국산학기술학회논문지
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    • 제14권2호
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    • pp.517-522
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    • 2013
  • 아이스크림제조기는 원액통과 냉각통의 증발온도가 $4^{\circ}C$$-8^{\circ}C$로 각각 다르므로 다수의 모세관을 이용하는데 이 경우 서로 냉매 유량에 영향을 주므로 냉동사이클 설계가 복잡하다. 본 연구에서는 증발온도가 서로 다른 두개의 증발기(냉장 및 냉동)가 장착된 소프트 아이스크림 제조기의 성능을 해석하였다. 압축기 해석에는 효율모델을 적용하였고, 모세관은 1차원 유동으로 간주하여 해석하였으며, 응축기와 증발기는 UA-LMTD법을 적용하여 해석하였다. 요소부품에서의 엔탈피, 압력 및 질량의 평형을 적용하여 냉동사이클 시뮬레이션 프로그램을 개발하였고 R404A를 사용하는 아이스크림 제조기에 적용한 결과, 냉장과 냉동 증발기의 온도를 $3^{\circ}C$ 이내로 예측하여 측정치와 대체로 일치하였다.

대학생 대상 급식시설의 김밥 생산과정에 따른 계절별 미생물적 품질평가 (The Seasonal Microbiological Quality Assessment of Kimbap(seaweed roll) Production flow in Foodservice facilities for Univ. students - HACCP model -)

  • 이혜상;류승연
    • 한국식품조리과학회지
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    • 제14권4호
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    • pp.367-374
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    • 1998
  • The purpose of this study was to evaluate the microbiological quality of, and to assure the hygienic safety of, the kimbap production in the university foodservice facilities in accordance with the HACCP (Hazard Analysis Critical Control Point) Program. The time-temperature relationship and the microbiological quality (specifically, total plate count and coliform bacteria count) were assessed to find the critical control point (CCP) during each of the production phases. The average of the daily longest duration time of the kimbap at the facilities was 23.4 hours in summer, while 29.6 hours in winter. In the purchasing phase of the raw materials, the microbiological quality of laver, fish paste, carrot and cucumber in summer was not at an acceptable level according to the standard set by the Natick research center, especially the number of TPC and the coliform level of laver was higher than the threshold level. In the refrigerator storage phase, the temperature of the carrot was 7.4$^{\circ}C$. This temperature is far exceeding the standard so that the microbiological counts was increased by the 2 log cycle during the average storage time of 17 hours or more. In the preparation phase, the temperature of the blanching is too low compared to the standard. In the holding phase before serving, its time-temperature relationship was out of the FDA food code standard both in winter and summer. In the sewing phase, the number of microbiological count was higher than the threshold level in summer while that in winter was up to standard. According to the Harrigan and McCance standard, the number of microbiological count of the utensils was higher than the threshold level in summer while that in winter was up to standard.

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세포 배양액의 연속 공급기 제작을 통한 심근세포의 성숙개선에 관한 연구 (A study on the maturation of cardiomyocytes by continuous supply of culture media)

  • 권우진;김근우;정운선;김종윤;이동원
    • 센서학회지
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    • 제30권2호
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    • pp.109-113
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    • 2021
  • In this study, an automated culture media replacement system was developed to analyze changes in the contraction characteristics of cardiomyocytes according to the state of the culture media. For the long-term storage of culture media, a Peltier refrigerator with a temperature of 5 to 8℃ was provided and a pH of 7.4 was maintained. The cell culture media of the cardiomyocytes was continuously replaced using interlocking pumps at a flow rate of 0.83 μl/h. The cardiomyocytes in which the culture media was replaced automatically demonstrated lower heartbeats per minute compared to samples in which there was no replacement. However, these cardiomyocytes moved more uniformly and produced greater displacement in one heartbeat cycle. It was observed that the sarcomere length of the cardiomyocytes increased due to the automated culture media replacement system. These cardiomyocytes were found to demonstrate better maturation compared to the control group. The maturation of cardiomyocytes was verified through staining images. The proposed automated culture media replacement system generates a uniform heart rate and improvements in contraction force. Based on the study, patient-specific drug toxicity assessments can be conducted using differentiated cardiomyocytes in induced pluripotent stem cells.

Environment-wide association study of elevated liver enzymes: results from the Korean National Environmental Health Survey 2018-2022

  • Youngchan Chi;Jong-Tae Park;Sewhan Na;Kyeongmin Kwak
    • Annals of Occupational and Environmental Medicine
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    • 제35권
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    • pp.27.1-27.12
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    • 2023
  • Background: Environmental exposure is characterized by low concentration, chronic, and complex exposure. Traditional epidemiological studies show limitations in reflecting these characteristics since they usually focus on a single or very limited number of exposure factors at a time. In this study, we adopted the methodology of environment-wide association study (EWAS) to figure out the association of human liver function with various environmentally hazardous substances. Methods: We analyzed 2,961 participants from the Korean National Environmental Health Survey Cycle 4 (2018-2020). Using generalized linear model (GLM) analysis, we analyzed the association of 72 variables with 3 liver function indices (aspartate aminotransferase [AST], alanine aminotransferase [ALT], and gamma glutamyl transferase [GGT]). Finally, we visualized our results with Manhattan plot. Results: In GLM analysis, perfluorooctanesulfonate were positively associated with ALT (odds ratio [OR]: 2.2; 95% confidence interval [CI]: 1.39-3.46; padjusted = 0.0147) and perfluorodecanoic acid showed positive association with GGT (OR: 2.73; 95% CI: 1.36-5.5; padjusted = 0.0256). Plasma mercury showed positive association with GGT (OR: 1.45; 95% CI: 1.14-1.84; padjusted = 0.0315). Using a plastic container while keeping food in the refrigerator was associated with elevated GGT compared to using a glass container (OR: 1.51; 95% CI: 1.16-1.95; padjusted = 0.0153). 2-ethyl-5-oxohexyl phthalate, showed a negative trend with all 3 indices, with AST (OR: 0.54; 95% CI: 0.39-0.73; padjusted = 0.00357), ALT (OR: 0.5; 95% CI: 0.34-0.75; padjusted = 0.036), GGT (OR: 0.55; 95% CI: 0.4-0.76; padjusted = 0.00697). Bisphenol S and frequent use of sunblock cream showed negative association with ALT (OR: 0.77; 95% CI: 0.66-0.89), and GGT (OR: 0.25; 95% CI: 0.11-0.55), respectively. Conclusions: We conducted an exploratory study on environmental exposure and human liver function. By using EWAS methodology, we identified 7 factors that could have potential association with liver function.