• Title/Summary/Keyword: Condensing Flow

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Identification of Two-phase Flow Patterns in a Horizontal Tubular Condenser (수평 응축관내 2상유동양식의 판별에 관한 연구)

  • Lee, S.C.;Han, Y.O.;Shin, H.S.;Lee, H.D.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.5 no.1
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    • pp.65-72
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    • 1993
  • An experiment has been carried out to identify flow patterns in a horizontal condensing flow with R-113. Characteristics of flow patterns were determined based upon a statistical analysis of differential pressure fluctuations at an orifice. The probability density function and power spectral density function of instantaneous pressure drop curves for various flow conditions were obtained. In comparison to the results of air-water flows, the flow patterns in a condensing flow such as annular, wavy, slug and plug could be identified. The experimental data determined by this technique were compared with the flow pattern maps suggested by other investigators. The result indicates that the statistical characteristics of differential pressure fluctuations at an orifice may be a useful tool for identifying flow patterns both in condensing flows and in adiabatic two-phase flows.

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Numerical Study on FC-72 Condensing Flow in a Micro-Channel (마이크로채널 내의 FC-72 흐름응축에 관한 수치적 연구)

  • Kim, Sung-Min
    • Journal of the Korean Society of Visualization
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    • v.13 no.1
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    • pp.30-34
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    • 2015
  • This study concerns flow and heat transfer characteristics of FC-72 condensing flow in a micro-channel. A computational model of condensing flow with a hydraulic diameter of 1 mm is constructed using the FLUENT computational fluid dynamics code. The computed void fraction contour plots are presented for different mass velocities. The smooth-annular, wavy-annular, transition and slug flows are observed with the model, which are quite similar to those observed in a micro-channel experiment. The computed two-phase condensing heat transfer coefficient is compared with previous empirical correlation for two-phase condensation heat transfer in micro-channels.

A study on the development of the high efficiency condensing heat exchanger (고효율 응축형 열교환기 개발에 관한 연구)

  • Lee, Geum-Bae;Park, Sang-Il;Park, Jun-Tae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.5
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    • pp.589-601
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    • 1997
  • A computer simulation program of a high efficiency condensing heat exchanger is developed. The flue gas flows outside bare tube bundles both in strong cross flow and in weak counter flow and the cooling water inside the tubes. Condensing heat exchangers achieve high efficiency by reducing flue-gas temperatures to a level at which most of the water vapor in the flue gas is condensed and the latent heat associated with phase change of the water is recovered. The computer model has been verified by comparison with measured data. To verify the model, heat transfer coefficient was adjusted, along with the mass transfer diffusion coefficient and pressure drop coefficient, to achieve agreement between predicted and measured data. The efficiencies of heat exchanger increase 2.3 ~ 8.1% by condensations of 6.3 ~ 62.6% of the water vapor in the flue gas.

The Numerical Study on the Cobustion Characteristics and the Heat Transfer Characteristics of Heat Exchanger for Condensing Gas Boiler (응축형 가스보일러 연소기의 연소특성 및 열교환기의 열전달특성에 관한 수치적 연구)

  • Kim, S.C.;Kum, S.M.;Lee, C.E.
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.71-78
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    • 2001
  • It was numerically studied that characteristics of fluid flow and heat transfer in a tube with disk and annular baffle for heat exchanger of condensing boiler. Using a finite volume technique and CFD code, STAR-CD, the governing equations were solved and the temperature and flow fields were investigated. The interval between tube and annular baffle, height and diameter of baffle were selected as important design parameters, and the effects of these parameters on heat transfer and fluid flow were studied. As a result, in the case of with interval, the pressure was decreased but heat transfer was increased. Also heat transfer was slowly increased as the size of disk and annular baffle were increased and the distance between baffles were decreased.

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Experimentation and modeling on the flow of R407c and R290 through capillary tubes (R407C 및 R290 냉매에 대한 모세관내 유동특성 실험 및 모델링)

  • 김용찬;조일용;최종민
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.4
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    • pp.492-498
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    • 1999
  • Mass flow rates of R407C and R290 through capillary tubes were measured with various capillary tube geometries and flow conditions. For all refrigerants tested in the present study, mass flow rate through the capillary tube was strongly dependent on the condensing pressure, subcooling and capillary length and diameter. The flow rate of R407C was 5~10[%] higher than that of R22 at the same condensing temperature and degree of subcooling, while flow rate for R290 was 40[%] lower than that for R22. Based on experimental results, an empirical correlation was developed using Pi theorem to predict the mass flow rate through capillary tubes. The predicted flow rates using the model were consistent with the experimental data within ${\pm}$10[%].

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Flow and Pressure Drop Characteristics of R22 in Adiabatic Capillary Tubes

  • Kim, Min-Soo;Kim, Sung-Goo;Ro, Sung-Tack
    • Journal of Mechanical Science and Technology
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    • v.15 no.9
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    • pp.1328-1338
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    • 2001
  • The objective of this study is to present flow and pressure drop characteristics of R22 in adiabatic capillary tubes of inner diameters of 1.2 to 2.0mm, and tube lengths of 500 to 2000mm. Distributions of temperature and pressure along capillary tubes and the refrigerant flow rates through the tubes were measured for several condensing temperatures and various degrees of subcooling at the capillary tube inlet. Condensing temperatures of R22 were selected as 40, 45, and 50$^{\circ}C$ at the capillary tube inlet, and the degree of subcooling was adjusted to 1 to 18$^{\circ}C$. Experimental results including mass flow rates and pressure drops of R22 in capillary tubes were provided. A new correlation based on Buckingham II theorem to predict the mass flow rate through the capillary tube was presented considering major parameters which affect the flow and pressure drop characteristcis.

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Performance Analysis of Cascade Refrigeration System with Respect to Refrigerants Appling to High Temperature Cycle (고온측 냉매에 따른 이원 냉동시스템의 성능 분석)

  • Yoon, Jung-In;Jeon, Min-Ju;Son, Chang-Hyo
    • Journal of Power System Engineering
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    • v.21 no.3
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    • pp.45-50
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    • 2017
  • This paper presents the Coefficient of performance(COP) and mass flow ratio of cascade refrigeration system with respect to refrigerants appling to high temperature cycle. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporating temperature, condensing temperature and internal heat exchanger effectiveness in high temperature cycle. The result of this study is as follows : The COP of cascade system increases with increasing degree of superheating and subcooling, compressor efficiency and internal heat exchanger effectiveness except increasing condensing temperature. The mass flow ratio of low and high temperature cycle increases with increasing evaporating temperature and condensing temperature, but decreases with increasing internal heat exchanger effectiveness, degree of superheating and subcooling. Also, the mass flow ratio has no correlation with compressor efficiency at high temperature cycle.

The Numerical Study on the Heat Transfer Characteristics of Heat Exchanger for Condensing Gas Boiler (응축형 가스보일러 열교환기의 열전달특성에 관한 수치적 연구)

  • Kim, Seok-Cheol;Geum, Seong-Min;Lee, Chang-Eon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.12
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    • pp.1853-1860
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    • 2001
  • Characteristics of fluid flow and heat transfer in a tube with disk and annular baffle for heat exchanger of condensing boiler was numerically studied. The STAR-CD code was used to solve the governing equations and the temperature and flow fields were investigated. The interval between tube and annular baffle, height and diameter of baffle were selected as important design parameters, and the effects of these parameters on heat transfer and fluid flow were studied. As a result, in the case of with interval, the pressure was decreased, but heat transfer was increased. Heat transfer was slowly increased as the size of disk and annular baffle were increased and the distance between baffles were decreased. The pressure drop was rapidly changed fur diameter and size of disk and annular baffle. In addition, it was desirable that optimal conditions to design heat exchanger were about B$\_$a/R=0.5, L/R=1.

Condensing Heat Transfer Characteristics on a Heat Pump System Using Non-Azeotropic Refrigerant Mixtures (비공비혼합냉매를 사용하는 열펌프의 응축열전달 특성)

  • 박기원;오후규;김욱중
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.4
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    • pp.1125-1133
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    • 1995
  • Experiments were performed to investigate the condensing heat transfer characteristics of non-azeotropic mixtures of R-22 and R-114 in a heat pump system with a horizontal smooth tube as a condenser. The ranges of parameters, such as heating capacity, mass flow rate of refrigerant and quality were 780-3,480W, 24-71kg/h, and 0-1, respectively. The overall compositions of R-22 in a R-22/114 mixture were 25, 50, 75 and 100 per cent by wight. The results show that the overall condensing heat transfer coefficients for the mixtures were lower than the pure R-22 values. Local heat transfer coefficient of the pure R-22 was hghest at the top of the test tube. The local heat transfer coefficient of R-22/114 (50/50 wt%) at side and bottom of the test tube was higher than that at the top. From the obtained data, a prediction for the condensing heat transfer coefficients of the mixture was done based on the method of Fujii.

Heat Flow Analysis of Inner Groove Tube for Latent Heat Exchanger in Condensing Gas Boiler (콘덴싱 가스보일러 잠열교환기의 이너 그루브 튜브 열유동 해석)

  • Yong, Kyeong-Jung;Lim, Byung-Chul;Park, Sang-Heup
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.7
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    • pp.4052-4056
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    • 2014
  • These days, household condensing gas boilers are an obligatory trend. The use of environmentally-friendly boilers that emit less pollutant, such as CO and NOx, are strongly recommended. In this paper, heat flow analysis of the additional inner groove in the tube of the secondary latent heat exchanger was studied to increase the efficiency. A 20% difference in the heat transfer area was obtained with the addition of an inner grove, which showed an increase in the amount of heat transferred. This was confirmed using three-dimensional numerical analysis. With the addition of an inner groove, the exit temperature increased by $1^{\circ}C$. This increase in exit temperature was considered to be a substantial increase in the efficiency of the condensing gas boiler.