• Title/Summary/Keyword: subcooling temperature

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Thermodynamic Modeling of Parallel Flow Condenser for Automotive Air Conditioning System (자동차용 평행류 응축기의 열성능 모델링)

  • 김일겸;고재윤;박상록;임장순
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.8
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    • pp.771-779
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    • 2001
  • In this study, a simulation program has been developed to predict the performance of a parallel flow condenser of an air conditioning system for an automobile. The well-known correlations for he heat transfer rates and the pressure drops are included in this model. It is fond that the numerical model can predict the heat transfer rate and the pressure drop accurately. As the condensing pressure increases of fixed air inlet temperature, the heat transfer rate increases and the pressure drop decreases. The effect of he degree of subcooling on the performance of the condenser is greater than that of the degree of super-heating because the ratio of the area occupied by he tow-phase refrigerant the total area is significantly affected by he degree of subcooling rather than the degree of superheating.

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액막류의 MHF점에 관한 실험적 연구

  • 김영찬;서태원
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.10
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    • pp.960-965
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    • 2001
  • The minimum heat flux conditions are experimentally investigated for the subcooled liquid film flow on the horizontal plate. The experimental results show that the minimum heat flux point temperature becomes higher with the increase of the velocity and the subcooling of the liquid film flow. However, the effect of distance from the leading edge of the heat transfer plate on the minimum heat flux is almost negligible. Also, the experimental results show that the propagation velocity of wetting front increases with increasing the velocity and the subcooling of the liquid film flow.

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Effect of Oxidation Multi-Walled Carbon Nanotubes for Methane Hydrate Formation (산화탄소나노튜브를 이용한 메탄 하이드레이트 형성)

  • Park, Sung-Seek;Kim, Nam-Jin
    • Journal of the Korean Solar Energy Society
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    • v.30 no.5
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    • pp.11-16
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    • 2010
  • Methane hydrate is crystalline ice-like compounds which formed methane gas enters within water molecules composed cavity and each other from physically-bond at specially temperature and pressure condition. $1m^3$ of methane hydrate can be decomposed into the maximum of $216m^3$ of methane gas under standard condition. If these characteristics of hydrate are utilized in the opposite sense, natural gas can be fixed into water in the form of a hydrate solid. Therefore the use of hydrate is considered to be a great way to transport and store natural gas in large quantity. However, when methane hydrate is formed artificially, the amount of gas that is consumed is relatively low, due to the slow reaction rate between water and methane gas. Therefore for practical purposes in the application, the present investigation focuses on increasing the amount of gas consumed by adding chemically oxidized OMWCNTs to pure water. The results show that when 0.003 wt% of oxidation multi-walled carbon nanotubes was added to pure water, the amount of gas consumed was almost four times more than that of pure water indicating its effect in hydrate formation and the hydrate formation time decreased at alow subcooling temperature.

Performance Analysis of a Seawater Ice Machine Applied Two-stage vapor compression refrigeration system for Various Refrigerants (2단 증기 압축식 냉동시스템을 적용한 해상용 제빙장치의 냉매에 따른 성능 분석)

  • Yoon, Jeong-In;Son, Chang-Hyo;Heo, Seong-Kwan;Jeon, Min-Joo;Jeon, Tae-Young
    • Journal of Power System Engineering
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    • v.20 no.2
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    • pp.85-90
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    • 2016
  • Coefficient of performance (COP) for two-stage compression system is investigated in this paper to develop seawater ice machine. The system performance is analyzed with respect to degrees of superheating and subcooling, condensing and evaporating temperatures, compression and mechanical efficiencies and mass flow ratio in an inter-cooler. The main results are summarized as follows : The COP of the system grows when the mass flow ratio, subcooling degree and evaporating temperature edge up. Contrariwise, the system performance descends in case that superheating degree and condensing temperature increase. The most effective factor for the COP is the mass flow rate ratio. Each refrigerant has different limitation for a value of the mass flow ratio in the inter-cooler because of difference in material property.

An Experimental Study on the Performance Characteristics of Cooling System for Aircraft External Reconnaissance Stores (항공기 외장형 정찰 장비용 냉각 시스템의 성능 특성에 관한 실험적 연구)

  • Jung, Daeyoon;Lee, Hang Bok
    • Journal of the Korea Institute of Military Science and Technology
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    • v.16 no.1
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    • pp.74-80
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    • 2013
  • In this paper, we have proposed a vapor cycle refrigeration system as a cooling system to provide cooling air to the aircraft external reconnaissance stores. In the proposed vapor cycle system, receiver which prevents refrigerant from subcooling was eliminated and thermal expansion valve was replaced with electronic expansion valve. The vapor cycle refrigeration system is aimed to provide cooling air to the reconnaissance stores which is added to the aircraft in the form of external store. The wide temperature range of ambient air from the flight conditions can decrease the cooling performance and can make the refrigeration system unstable in low ambient temperature. Performance characteristics of the vapor cycle refrigeration system has been experimented under air conditions which is derived from the flight envelope. From the experiments, the vapor cycle refrigeration system has been proved to provide enough cooling air to the reconnaissance equipment and to be stable under all the flight conditions.

A Comparative Study on the Effect of THF and Oxidized Carbon Nanotubes for Methane Hydrate Formation (메탄 하이드레이트 생성을 위한 THF와 산화 탄소나노튜브의 영향에 대한 비교 연구)

  • Park, Sung-Seek;An, Eoung-Jin;Kim, Nam-Jin
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.12
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    • pp.769-775
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    • 2011
  • Methane hydrate is formed by physical binding between water molecules and methane gas, which is captured in the cavities of water molecules under the specific temperature and pressure. $1m^3$ hydrate of pure methane can be decomposed to the methane gas of $172m^3$ and water of $0.8m^3$ at standard condition. Therefore, there are a lot of practical applications such as separation processes, natural gas storage transportation and carbon dioxide sequestration. For the industrial utilization of hydrate, it is very important to rapidly manufacture hydrate. So in this study, hydrate formation was experimented by adding THF and oxidized carbon nanotubes in distilled water, respectively. The results show that when the oxidized carbon nanofluids of 0.03 wt% was, the amount of gas consumed during the formation of methane hydrate was higher than that in the THF aqueous solution. Also, the oxidized carbon nanofluids decreased the hydrate formation time to a greater extent than the THF aqueous solution at the same subcooling temperature.

Performance Analysis of an Ammonia(R717) and Carbon Dioxide(R744) Two-Stage Cascade Refrigeration System ($NH_3-CO_2$를 사용하는 이원 냉동 시스템의 성능 분석)

  • Son, Chang-Hyo
    • Journal of the Korean Institute of Gas
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    • v.14 no.1
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    • pp.1-7
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    • 2010
  • In this paper, cycle performance analysis of $NH_3-CO_2$(R717-R744) two-stage cascade refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, compressor efficiency, and condensing and evaporating temperature in the ammonia(R717) high temperature cycle and the carbon dioxide low temperature cycle. The main results were summarized as follows : The COP of two-stage cascade refrigeration system increases with the increasing subcooling degree, but decreases with the increasing superheating degree. The COP of two-stage cascade refrigeration system decreases with the increasing condensing temperature, but increases with the increasing evaporating temperature. And the COP of two-stage cascade refrigeration system increases with increasing the compressor efficiency. Therefore, superheating and subcoolng degree, compressor efficiency, and evaporating and condensing temperature of $NH_3-CO_2$(R717-R744) two-stage cascade refrigeration system have an effect on the COP of this system.

Exergy Analysis of R744 OTEC Power Cycle with Operation Parameters (작동변수에 따른 R744용 해양온도차 발전 사이클의 엑서지 분석)

  • Yoon, Jung-In;Son, Chang-Hyo;Baek, Seung-Moon;Kim, Hyeon-Ju;Lee, Ho-Saeng
    • Journal of Advanced Marine Engineering and Technology
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    • v.36 no.8
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    • pp.1036-1042
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    • 2012
  • This paper describes an analysis on exergy efficiency of R744 OTEC power system to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, evaporation and condensation temperature, and turbine and pump efficiency, respectively. The main results are summarized as follows : As the evaporation temperature, superheating degree, and turbine and pump efficiency of R744 OTEC power system increases, the exergy efficiency of this system increases, respectively. But condensation temperature and subcooling degree of R744 OTEC power system increases, the exergy efficiency of this system decreases, respectively. The effect of evaporation temperature and pump efficiency on R744 OTEC power system is the largest and the lowest among operation parameters, respectively. Therefore, the refrigerant temperature in the evaporator must be closely to the surface seawater temperature to enhance the exergy efficiency of R744 OTEC power system.

A Study of Rewetting Temperature in Cooling of Hot Surfaces (高溫表面의 冷却時 再水着 溫度 에 관한 硏究)

  • 정문기;이영환;박종석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.4
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    • pp.463-470
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    • 1985
  • In this study a parametric analysis for the rewetting temperature was made with 572 data obtained from the single tube experiment. The rewetting temperature was also evaluated by measuring the vaporization time of a liquid drop on a hot surface at the elevated pressures. The results showed that the rewetting temperature increased with flooding rate, inlet subcooling pressure and initial wall temperature, and decreased with increasing axial elevation. Based on the results obtained, the rewetting temperature correlation was suggested. From the comparison of correlated rewetting temperatures with measured values, it showed that the correlated values fell within .+-.5% error from the measured values.

A Study on the Subcooled Boiling Heat Transfer in a Horizontal Tube (수평관내 냉매의 과냉비등열전달에 관한 연구)

  • 김종헌;김철환
    • Journal of Advanced Marine Engineering and Technology
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    • v.18 no.3
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    • pp.26-33
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    • 1994
  • A new reliable method to prediet the axial vapor fraction distribution from the measured probability density of the liquid bulk temperature is suggested in this paper. And also the actual quality of the subcooled boiling flow is easily calculated from the liquid bulk temperature. When the heat generating rate is reached to the CHF value, the sharp wall temperature increasing by the wall temperature fluctuation is occurred under the CHF condition. This paper presents the simple wall temperature fluctuation model of transition boiling by the repeating process of overheating and quenching, when the coalescent bubble passes slowly near the wall. Experiments for the subcooled R-113 flow are carride-out in the range of(0.9399~4.461)${\times}10^6$kg/$m^2$hr mass velocity and 10~3$0^{\circ}C$ intel subcooling condition.

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