• Title/Summary/Keyword: Heat/mass Transfer

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An Experimental Study on Heat Transfer and Pressure Drop Characteristics during Supercritical Process of Carbon Dioxide in a Horizontal Tube (수평관 내에서 이산화탄소 초임계 가스냉각 과정의 열전달 및 압력강하 특성에 관한 실험적 연구)

  • 최이철;강병하;김석현
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.5
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    • pp.414-420
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    • 2004
  • The heat transfer and pressure drop characteristics associated with the gas cooling of the supercritical carbon dioxide in a horizontal tube have been investigated experimentally. This problem is of particular interest in the design of a gas cooler of cooling systems using $CO_2$refrigerant. The test section is consisted of 6 series of 455 mm in length, 4.15 mm ID copper tube, respectively. The effects of the inlet temperature, pressure and mass flow rate on the heat transfer and pressure drop of $CO_2$in a horizontal tube is studied in detail. The heat transfer coefficient of $CO_2$is varied by temperature, inlet pressure, and mass flow rate of $CO_2$. This has maximum value at near the pseudocritical temperature. The pressure drop is changed by inlet pressure and mass flow rate of $CO_2$. The results have been compared with those of previous work. The heat transfer correlation at the supercritical gas cooling process is also suggested.

Heat Transfer Characteristics on a Single Rotating Disk with a Shrouded Cover (슈라우드로 차폐되어진 단일회전디스크 표면의 열전달 특성)

  • Ryu, Goo-Young;Won, Chung-Ho;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.8
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    • pp.1029-1037
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    • 2000
  • The present study investigates the local heat/mass transfer characteristics on a rotating disk which is the top disk covered with a shroud in HDD. The naphthalene sublimation technique is employed to determine the local heat/mass transfer coefficients on the rotating disk. Flow field measurements using Laser Doppler Anemometry (LDA) and numerical calculations are performed to analyze the flow patterns induced by the disk rotation. HDD has been developed for compactness and speedy data access, thus the rotating velocity of the disk is increased and the height of a hub is decreased. The experiments are conducted for the various hub heights of 5, 10 and 15 mm, for the rotating Reynolds numbers of $5.5{\times}10^4$ to $1.1{\times}10^5$ and for the effects of the presence of a read/write head arm. The results show that the heat transfer on the rotating disk is enhanced considerably for the decrease of the hub height and for the increase of the rotating Reynolds number. The head arm inserted in the cavity decreases the heat transfer despite the enhancement of tangential RMS velocity because of the deficit of the momentum in the flow field.

Experimental Study of Air-cooled Condensation in Slightly Inclined Circular Tube (경사진 원형관에서의 공냉응축에 관한 실험적 연구)

  • Kim, Dong Eok;Kwon, Tae-Soon;Park, Hyun-Sik
    • The KSFM Journal of Fluid Machinery
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    • v.19 no.4
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    • pp.29-34
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    • 2016
  • In this study, the experimental investigation of air-cooled condensation in slightly inclined circular tubes with and without fins has been conducted. In order to assess the effects of the essential parameters, variable air velocities and steam mass flow rates were given to the test section. The heat transfer performance of air-cooled condensation were dominantly affected by the air velocity, however, the increase of the steam mass flow rate gave relatively weaker effects to total heat transfer capability. And in the experimental cases with the finned tube, the total heat transfer rate of the finned tube was significantly larger than that of the flat tube. From those results, it can be confirmed that the most important parameter for air-cooled condensation heat transfer is the convective heat transfer characteristics of air. Therefore, for the well-designed long-term cooling passive safety system, the consideration of the optimal design of the fin geometry is needed, and the experimental and numerical validations of the heat transfer capability of the finned tube would be required.

Cooling Heat Transfer Characteristics of CO2 in a Brazing Type Small Diameter Copper Tube (브레이징식 동세관내 CO2의 냉각 열전달 특성)

  • Oh, Hoo-Kyu;Son, Chang-Hyo
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.6
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    • pp.827-834
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    • 2009
  • The cooling heat transfer coefficient of $CO_2$ in a brazing type small diameter tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a $CO_2$ compressor, a mass flow meter, an evaporator and a brazing type small diameter tube as a test section. The mass flux of $CO_2$ is $400{\sim}1600$ [kg/$m^2s$], the mass flowrate of coolant were varied from 0.15 to 0.3 [kg/s], and the cooling pressure of gas cooler were from 8 to 10 [MPa]. The cooling heat transfer coefficients of the brazing type small diameter copper tube is about $4{\sim}11.7%$ higher than that of the conventional type small diameter copper tube. In comparison with test results and existing correlations, correlations failed to predict the cooling heat transfer coefficient of $CO_2$ in a brazing type small diameter copper tube. therefore, it is necessary to develope reliable and accurate predictions determining the cooling heat transfer coefficient of $CO_2$ in a brazing type small diameter copper tube.

Effects of Bleed Flow and Angled Ribs on Heat Transfer Distributions in a Rotating Square Channel (유출유동 및 각도진 요철이 회전하는 사각덕트 내 열전달분포에 미치는 영향)

  • Park, Suk-Hwan;Jeon, Yun-Heung;Kim, Kyung-Min;Lee, Dong-Hyun;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.1 s.256
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    • pp.76-82
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    • 2007
  • The present study investigated the effects of channel rotation and bleed flow on heat/mass transfer in a square channel with $45^{\circ}$ rib turbulators. The bleed holes were located between the rib turbulators on the leading surface and those on the trailing surface case by case. The tests were conducted under the conditions of various bleed ratios (0.0, 0.2, 0.4) and rotation numbers (0.0, 0.2, 0.4) at Re=10,000. The results suggested that heat/mass transfer characteristics were influenced by the Coriolis force, decrement of main flow rate, secondary flow by angled ribs and bleed hole location. As the bleed ratio (BR) increased, the heat/mass transfer decreased on both surfaces due to the reduction of main flow rate. With increment of the rotation number, heat/mass transfer also decreased and almost the same because the reattachment of the secondary flow induced by angled ribs was weakened on the leading surface and the secondary flow was disturbed on the trailing surface by the Coriolis force.

Evaporation Heat Transfer and Pressure Drop of Mixture Refrigerant R-22 and R-407C in a Diameter of 4.3 mm (4.3 mm 세관내 R-22와 R-407C의 증발 열전달과 압력강하)

  • Roh, G.S.;Son, C.H.
    • Journal of Power System Engineering
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    • v.12 no.4
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    • pp.26-31
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    • 2008
  • The evaporation heat transfer coefficient and pressure drop of R-22 and R-407C in a small diameter copper tube were investigated experimentally. The main components of the refrigerant loop are a receiver, a compressor, a mass flow mete, a condense and a double pipe type evaporate (test section). The test section consists of a smooth copper tube of 4.3 mm inner diameter. The refrigerant mass fluxes were varied from 100 to $300[kg/m^{2}s]$ and the saturation temperature of evaporator were $5[^{\circ}C]$. The evaporation heat transfer coefficients of R-22 and R-407C increase with the Increase in mass flux and vapor quality. The evaporation heat transfer coefficient of R-22 is about $7.3\sim47.1%$ higher than that of R-407C. The evaporation pressure drop of R-22 and R-407C increase with the increase of mass flux. The pressure drop of R-22 is about $8\sim20%$ higher than that of R-407C.

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Experimental study on the performance of a brazed plate heat exchanger (용접식 판형 열교환기의 성능에 관한 실험적 연구)

  • Kim, Jong-Ha;Yun, Jae-Ho;Kwon, Oh-Kyung;Kim, Jong-Hun;Ryu, Hae-Sung;Lee, Chang-Sik
    • Proceedings of the KSME Conference
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    • 2001.06d
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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.

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An Experimental Study on the Performance of a Brazed Plate Heat Exchanger (용접식 판형 열교환기의 성능에 관한 실험적 연구)

  • 김종하;권오경;윤재호;이창식
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.1
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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.

Experimental Study on R-410A Evaporation Heat Transfer Characteristics in Shell and Plate Heat Exchanger (셀 앤 플레이트 열 교환기에서의 R-410A 증발열전달에 관한 실험적 연구)

  • Kim In-Kwan;Kim Young-Soo;Park Jae-Hong
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.1
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    • pp.49-59
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    • 2005
  • The evaporation heat transfer experiments are conducted with the shell and plate heat exchanger (S&PHE) without oil in the refrigerant loop using R-410A. An experimental refrigerant loop has been established to measure the evaporation heat transfer coefficient h. of R-410A in a vertical S&PHE. Two vertical counter flow channels were formed in the S&PHE by three plates haying a corrugated trapezoid shape of a $45^{\circ}C$ chevron angle. UP flow of the boiling R-410A in one channel receives heat from the hot down flow of water in the other channel The effects of the refrigerant mass flux. average heat flux. refrigerant saturation temperature and vapor qualify are explored in detail. Similar to the case of a plate heat exchanger. even at a very low Reynolds number, the flow in the S&PHE remains turbulent. The Present data shows that the evaporation heat transfer coefficients of R-410A increased with the vapor qualify. The results indicate a rise in the refrigerant mass flux caused an increase in the h.. Raising the imposed wall heat flux is found to slightly improve h., while h, is found to be lower at a higher refrigerant saturation temperature. Based on the present data. empirical correlation of the evaporation heat transfer coefficient is proposed.

R-22 Condensation in Flat Aluminum Multi-Channel Tubes (알루미늄 다채널 평판관내 R-22 응축에 관한 연구)

  • Kim, Jung-Oh;Cho, Jin-Pyo;Kim, Nae-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.2
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    • pp.241-250
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    • 2000
  • In this study, condensation heat transfer tests were conducted in flat aluminum multi-channel tubes using R-22. Two internal geometries were tested ; one with smooth inner surface and the other with micro-fins. Data are presented for the followin~ range of variables ; vapor quality($0.1{\sim}0.9$), mass flux($200{\sim}600kg/m^2s$) and heat flux($5{\sim}15kW/m^2$). The micro-fin tube showed higher heat transfer coefficients compared with those of the smooth tube. The difference increased as the vapor quality increased. Surface tension force acting on the micro-fin surface at the high vapor quality is believed to be responsible. Different from the trends of the smooth tube, where the heat transfer coefficient increased as the mass flux increased, the heat transfer coefficient of the micro-fin tube was independent of the mass flux at high vapor quality, which implies that the surface tension effect on the fin overwhelms the vapor shear effect at the high vapor quality. Present data(except those at low mass flux and high quality) were well correlated by equivalent Reynolds number, Existing correlations overpredicted the present data at high mass flux.