• Title, Summary, Keyword: evaporator

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Effects of Fin Conduction and Superheat Unbalance on the Performance of an Evaporator (핀의 전도 열전달 및 과열도 변화에 따른 증발기 성능 특성에 관한 연구)

  • Choi Jong Min;Kim Yongchan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.3
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    • pp.216-222
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    • 2005
  • An experimental investigation was executed to determine the capacity degradation due to fin conduction and non-uniform refrigerant distribution in a multi-path evaporator with cross-counter flow. The finned-tube evaporator, which had a three-path and three-depth-row, was tested by controlling inlet quality, exit pressure, and exit superheat for each refrigerant path. The capacity reduction due to superheat unbalance between each path was as much as $25\%$ for non-cutting evaporator, even when the overall evaporator superheat was kept at a target value of $5.6^{\circ}C$. It indicates that the internal heat transfer within the evaporator assembly causes the partial capacity drop. The capacity of cutting-evaporator with respect to non-cutting evaporator was enhanced according to the increment of air flow rate when superheat or superheat unbalance increased.

Analysis of Characteristics on Small Air-Conditioning Type Evaporator (소형 공조용 증발기의 특성 해석)

  • 김재돌;윤정인;김영수;문춘근
    • Journal of the Korean Society of Marine Engineering
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    • v.25 no.3
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    • pp.573-580
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    • 2001
  • When investigating optimum design of the evaporator in the refrigeration and heat pump systems, there is still lack of data for the dynamic characteristics of the evaporator, This is due to the fact that the static characteristics in the evaporator are absolutely difficult to measure and are burdened with uncertainties. In this study, the simulation works for static characteristics in the evaporator of small air conditioner are carried out to obtain the data of dynamic characteristics. In the simulation, the test evaporator is divided by two-phase evaporating region and single-phase heating region. The major parameters are refrigerant flow rate, heat transfer coefficient of air, air velocity and air temperature. The results show that the calculation method for tube length is an easy-to-use to model analysis of static characteristics and to determine state of refrigerant in the evaporator. The effects of the four parameters on the length of evaporating completed point and heat flow rate to the evaporator are clarified.

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이젝터가 부착된 냉동시스템의 성능실험

  • 이원희;김윤조;김민수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.10
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    • pp.993-1001
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    • 2001
  • Experimental investigation on the performance of dual-evaporator refrigeration system with an ejector has been carried out. In this study, a hydrofluorocarbon (HFC) refrigerant R134a is chosen as a working fluid. The condenser and two-evaporators are made as concentric double pipes with counter-flow type heat exchangers. Experiments were performed by changing the inlet and outlet temperatures of secondary fluids entering condenser, high-pressure evaporator and low-pressure evaporator at test conditions keeping a constant compressor speed. When the external conditions (inlet temperatures of secondary fluid entering condenser and one evaporator) are fixed, results show that coefficient of performance (COP) increases as the inlet temperature of the other evaporator rises. It is also shown that the COP decreases as the mass flaw rate ratio of suction fluid to motive fluid increases. The COP of dual-evaporator refrigeration system with an ejector is superior to that of a single-evaporator vapor compression system by 3 to 6%.

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Evaporator Thermal Performance Prediction on Automotive Air Conditioning System (자동차 공조장치용 증발기의 전열 성능 예측)

  • Kim, J.S.;Kang, J.K.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.3 no.4
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    • pp.297-305
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    • 1991
  • Recently, automotive air conditioning system manufacturers have been made a great efforts on the system compactness and high efficiency. This growing interest comes improvements in evaporator thermal performance, one of the most important factors affecting the performance of air conditioning system. In order to improve design of compact type evaporator, this study executes performs to develop a computer program for evaporator thermal performance prediction of automotive air conditioning system. The brief summaries of this study are as follows: 1) To predict the overall thermal performance of serpentine type evaporator, the new simulating method is developed. 2) The calculations are performed as functions of oil mass concentration and refrigerant two-phase distribution at inlet manifold of evaporator. 3) The validity of this simulating program is confirmed by comparing the predicted thermal performance results to experimental results of practical available evaporator. 4) Based on these results, suggestions are made to improve the thermal performance of evaporator.

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Analysis of Performance Characteristics in the Counter and Parallel Type Plate Evaporator with Operating Methods (대향류와 평행류형 판형 증발기에서 운전방식에 따른 성능특성 분석)

  • Bae, Kyung-Jin;Cha, Dong-An;Kwon, Oh-Kyung
    • Journal of the Korea Society For Power System Engineering
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    • v.17 no.3
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    • pp.50-56
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    • 2013
  • The analysis of performance characteristics was carried out in the plate type evaporator with counter and parallel flow. To investigate performance of evaporator with water inlet temperature and refrigerant mass flow rate were changed. As a result, when the inlet temperature of water is $8^{\circ}C$, capacity of parallel flow evaporator higher than counter flow is 0.35%. But as the inlet temperature of water rises from $8^{\circ}C$ to $16^{\circ}C$, capacity of counter flow type evaporator higher than parallel flow type is 0.12%, 0.27%, 1.1%, 1.6%, respectively. The findings showed that counter flow type evaporator has a larger capacity than those that were parallel flow type evaporator. As the refrigerant mass flow rate rises, capacity and pressure drop increases in the counter and parallel flow type evaporator.

The Effect of Non-uniform Superheat on the Performance of a Multi-path Evaporator (다중 유로에서 과열도의 불균형에 따른 증발기의 성능 특성에 관한 연구)

  • 최종민;김용찬
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.12
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    • pp.1043-1048
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    • 2003
  • An experimental investigation was executed to determine the capacity degradation due to non-uniform refrigerant distribution in a multi-path evaporator. In addition, the possibility of recovering the capacity reduction by controlling the refrigerant distribution among refrigerant paths was assessed. The finned-tube evaporator, which had a three-path and three-depth-row, was tested by controlling inlet quality, exit pressure, and exit superheat for each refrigerant path. The capacity reduction due to superheat unbalance between each path was as much as 30%, even when the overall evaporator superheat was kept at a target value of 5.6$^{\circ}C$. It may indicate that the internal heat transfer within the evaporator assembly caused the partial capacity drop. For the evaporator having air mal-distributions, the maximum capacity reduction was found to be 8.7%. A 4.5% capacity recovery was obtained by controlling refrigerant distribution to obtain the target superheat at the outlet of each path.

Dynamic Analysis of Evaporator for Optimum Control in Refrigeration System (냉동사이클의 최적 제어를 위한 증발기 동특성 해석)

  • Jeong, S.K.;Hua, Li;Choi, K.H.;Yoon, J.I.;Kim, E.P.
    • Journal of the Korea Society For Power System Engineering
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    • v.9 no.1
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    • pp.82-88
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    • 2005
  • This paper presents numerical study on dynamic characteristics of evaporator to control evaporator superheat and compressor capacity with optimum condition in refrigeration system. It is very important to reduce energy consumption and to keep room temperature within a very restricted range with minimum oscillation in some special applications of the refrigeration system. Heat exchange is mainly happened in the evaporator. So, making mathematical model of evaporator and analyzing evaporator characteristics are necessary in order to control the superheat and the capacity of the system. A mathematical model based on the one dimensional partial differential equations representing mass and energy conservation and a tube-wall energy is described. A set of ordinary differential equation is formulated by integrating separately over the two regions(two-phase and vapor) generally presented in a heat exchanger.

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Effects of Mesh Size in a Flat Evaporator and Condenser Cooling Capacity on the Thermal Performance of a Capillary Pumped Loop

  • Boo, Joon-Hong
    • Journal of Mechanical Science and Technology
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    • v.14 no.1
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    • pp.121-129
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    • 2000
  • The thermal performance of a flat evaporator for capillary pumped loop (CPL) applications was investigated. Two to four layers of coarse wire screen wicks were placed onto the heated surface to provide irregular passages for vapor flow. The evaporator and condenser were separated by a distance of 1.2 m and connected by individual liquid and vapor lines. The wall material was copper and the working fluid was ethanol. The experimental facility utilized a combination of capillary and gravitational forces for liquid return, and distribution over the evaporator surface. The tubing used for vapor and liquid lines was 9.35 mm or less in diameter and heat was removed from the condenser by convection of air. A heat flux of up to $4.9{\times}10^4$ $W/m^2$ was applied to a flat evaporator having dimensions of 100 mm by 200 mm, 20 mm thick. The thermal resistance of the system as well as the temperature characteristics of the system was investigated as the evaporator heat flux and the condenser cooling capacity varied. The performance of the evaporator and effect of condenser cooling capacity were analyzed and discussed.

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A Study on the Boiling Heat Transfer Characteristics Using Loop Type Thermosyphon

  • HAN, Kyu-il;CHO, Dong-Hyun
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.52 no.3
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    • pp.257-262
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    • 2016
  • Flexible two-phase thermosyphons are devices that can transfer large amounts of heat flux with boiling and condensation of working fluid resulting from small temperature differences. A flexible two-phase thermosyphon consists of a evaporator, an insulation unit, and a condenser. The working fluid inside the evaporator is evaporated by heating the evaporator in the lower part of the flexible two-phase thermosyphon and the evaporated steam rises to the condenser in the upper part to transfer heat in response to the cooling fluid outside the tube. The resultant condensed working fluid flows downward along the inside surface of the tube due to gravity. These processes form a cycle. Using R134a refrigerant as the working fluid of a loop type flexible two-phase thermosyphon heat exchanger, an experiment was conducted to analyse changes in boiling heat transfer performances according to differences in the temperature of the oil for heating of the evaporator, the temperature variations of the refrigerant, and the mass flows. According to the results of the present study, the circulation rate of the refrigerant increased and the pressure in the evaporator also increased proportionally as the temperature of the oil in the evaporator increased. In addition, the heat transfer rate of the boiler increased as the temperature of the oil in the evaporator increased.

Effects of Air Flow Nonuniformity on the Thermal Performance of a Compact Evaporator for Natural Working Fluids (밀집형 자연냉매 증발기의 열성능에 미치는 불균일 공기유동분포의 영향)

  • 박병규;김근오;김무근
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.11
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    • pp.1114-1124
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    • 2001
  • The application of carbon dioxide as an attractive natural working fluid in air cooling and heating system is increasingly important in view of the CFC substitution problem. The thermal performance of compact evaporator was analyzed using section-by-section method. The effects of the two-dimensional nonuniformity of air flow through the evaporator is presented. The detrimental effect of the aid flaw nonuniformity on the thermal performance of the evaporator is found to be significant for many typical applications. It is shown that total heat transfer rate of evaporator using $CO_2$ is higher than that using R134a at the simulation conditions.

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