• Title/Summary/Keyword: Enhanced Heat Transfer

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An Experimental Study on Pool Boiling Heat Transfer Enhancement of Structured Tubes Having Three-Dimensional Roughness (삼차원 조도를 가진 성형가공관의 R-134a 풀비등 열전달 촉진에 관한 실험적 연구)

  • Kim, Nae-Hyun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.28 no.5
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    • pp.195-201
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    • 2016
  • Enhanced tubes are widely used in air-conditioning and process industries. Structural tubes having three-dimensional roughness are well known to be able to significantly enhance pool boiling heat transfer of refrigerants. In this study, five structural enhanced tubes having different fin density, fin height, and fin gap width were tested using R-134a. Results showed that the heat transfer coefficient was increased with increased fin density. Within test range, the effect of fin height on pool boiling heat transfer coefficient was insignificant. The heat transfer coefficients of the optimum configuration (2047 fpm, 0.21 mm gap width) tube were lower than those of other commercial enhanced tubes. This might be due to the larger fin gap width of the present enhanced tube.

Pool Boiling Heat Transfer Coefficients of Water Up to Critical Heat flux on Enhanced Surfaces (열전달 촉진 표면에서 임계 열유속까지의 물의 풀 비등 열전달계수)

  • Lee, Yo-Han;Gyu, Kang-Dong;Jung, Dong-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.3
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    • pp.194-200
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    • 2011
  • In this work, nucleate pool boiling heat transfer coefficients(HTCs) of pure water are measured on horizontal 26 fpi low fin, Turbo-B and Thermoexcel-E square surfaces of 9.53 mm length. HTCs are taken from 10 $kW/m^2$ to critical heat flux for all surfaces. Test results show that critical heat fluxes(CHFs) of all enhanced surfaces are greatly improved as compared to that of a plain surface. CHFs of water on the 26 fpi low fin surface, Thermoexcel-E surface, and Turbo-B are increased up to 320%, 275%, and 150% as compared to that of the plain surface, respectively. CHF of the Turbo-B enhanced surface is lower than that of the 26 fpi low fin surface due to the surface geometry. The heat transfer enhancement ratios of the Thermoexcel-E surface, low fin surface and Turbo-B enhanced surface are 1.6~2.9, 1.6~2.1, 1.4~1.7 respectively in the range of heat fluxes tested. Judging from these results, it can be said that these types of enhanced surfaces can be used in heat transfer applications at high heat fluxes.

Pool Boiling Heat Transfer Coefficients of New Refrigerants on Various Enhanced Tubes (열전달 촉진관에서 신냉매의 풀비등 열전달계수)

  • 박진석;김종곤;정동수;김영일
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.8
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    • pp.710-719
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    • 2001
  • Pool boiling heat transfer coefficients (HTCs) of HCFC123, HFC134a, HCFC22, HFC407C, HFC410A and HFC32 wre measured on a horizontal smooth tube, 26 fpi low fin tube, Turbo-B and Thermoexcel-E enhanced tubes. AN experimental apparatus was designed such that all tubes heated by cartridge heaters could be installed at the same time to save the refrigerant. Data were taken in the pool of $7^{\circ}C$ with the heat flux decreasing from 80 kW/$m^2\;to\;5kW/m^2$. Test results showed that HTCs of pure refrigerants and those of a azeotrope were greatly influenced by reduced pressure. HTCs of HFC407C were 21~25% lower than those of HCFC22 due to mass transfer resistance. For all refrigerants, enhanced tubes with sub-surface and sub-tunnels showed the largest heat transfer enhancement. Especially the largest heat enhancement was obtained for HCFC123 whose reduced pressure is the lowest among al the refrigerants tested. This indicates that either Turbo-B or Thermoexcel-E enhanced tube would be the best choice when used with a low vapor pressure refrigerant.

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Pool boiling performance of an enhanced tube used in flooded refrigerant evaporator for turbo-refrigerator (터보냉동기용 만액식 증발기에 사용되는 성형가공관의 풀비등 성능)

  • 김태형;김내현
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.6
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    • pp.808-814
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    • 1999
  • Pool boiling performance of a metal-formed enhanced tube for a flooded refrigerant evaporator was experimentally investigated. Tests were performed for three different refrigerants(R-11, R-123, R-l34a), at two different saturation temperatures $4.4^{\circ}C \;and \;26.7^{\circ}C$ .Heat flux was varied from 10㎾/$m^2\;to\ 50㎾/$m^2$. Compared with the heat transfer coefficients of the smooth tube, the heat transfer coefficients of the enhanced tube were 6.6 times higher for R-11, 6.0 tines higher for R-123 and 3.5 times higher for R-l34a. The enhancements are comparable with those of foreign products. The heat transfer coefficients of R-l34a were higher than those of R-11 and R-123, either for the enhanced tube or for the smooth tube. At $4.4^{\circ}Csaturation temperature, however, the heat transfer coefficients of R-l34a were approximately the same as those of R-11, The effect of the saturation pressure on the boiling performance was similar to that of the smooth tube - the heat transfer coefficient increases as the saturation pressure increases.

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Pool Boiling Heat Transfer Coefficients of Hydrocarbon Refrigerants on Various Enhanced Tubes (열전달 촉진관에서 탄화수소계 냉매의 풀비등 열전달계수)

  • Park, Ki-Jung;Jung, Dong-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.12
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    • pp.1017-1024
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    • 2006
  • In this work, pool boiling heat transfer coefficients (HTCs) of five hydrocarbon refrigerants of propylene, propane, isobutane, butane and dimethylether (DME) were measured at the liquid temperature of $7^{\circ}C$ on a 26 fpi low fin tube, Turbo-B, and Thermoexcel-E tubes. All data were taken from 80 to $10kW/m^2$ in the decreasing order of heat flux. The data of hydrocarbon refrigerants showed a typical trend that nucleate boiling HTCs obtained on enhanced tubes also increase with the vapor pressure. Fluids with lower reduced pressure such as DME, isobutane, and butane took more advantage of the heat transfer enhancement mechanism of enhanced tubes than those enhancement ratios of $2.3\sim9.4$ among the tubes tested due to its sub-channels and re-entrant cavities.

Measurement of Heat Transfer Coefficient in a Flooded Evaporator through Wilson Plot Method (Wilson Plot을 이용한 만액식 증발기의 열전달계수 측정)

  • 윤필현;강용태;정진희
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.8
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    • pp.698-706
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    • 2004
  • Heat transfer coefficients of enhanced tubes in a flooded evaporator are measured through Wilson Plot method. And the correlations are proposed to design a flooded evaporators. Overall heat transfer coefficients are composed of the heat transfer coefficients both inside and outside tubes. Usually the experiments have been conducted separately. But there have been many difficulties like setting up the equipments and measuring the wall temperature. Wilson Plot method makes it possible to measure the separated transfer coefficients at the same equipment through experimental skills. So the cost and time can be reduced. And the results are reliable enough to use for design. Heat transfer coefficients inside the tube were able to be correlated uniquely in spite of various outside conditions. Boiling heat transfer of R134a is more dependent on the saturation temperature and much higher than that of R123.

The Experimental Study on the Heat Transfer of HFC134a for Condensation Tubes with Various Enhanced Surfaces (응축전열관 외부형상 변화에 따른 HFC134a의 열전달 실험)

  • Park Chan-Hyoung;Lee Young-Su;Jeong Jin-Hee;Kang Yong-Tae
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.8
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    • pp.613-619
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    • 2006
  • The objectives of this paper are to study the characteristics of heat transfer for enhanced tubes (19.05 mm) used in the condenser with high saturation temperatures and to provide a guideline for optimum design of a condenser using HFC134a. Three different enhanced tubes are tested at a high saturation temperature of $59.8^{\circ}C$ (16 bar); a low-fin and three turbo-C tubes.. The refrigerant, HFC134a is condensed on the outside of the tube while the cooling water flows inside the tube. The film Reynolds number varies from 130 to 330. The wall subcooling temperature ranges from $2.7^{\circ}C$ to $9.7^{\circ}C$. This study provides experimental heat transfer coefficients for condensation on the enhanced tubes. It is found that the turbo-C(2) tube provides the highest heat transfer coefficient.

Nucleate Pool Boiling of a Structured Enhanced Tube Used in a Flooded Refrigerant Evaporator

  • Kim, Nae-Hyun;Cho, Jin-Pyo;Choi, Kuk-Kwang
    • International Journal of Air-Conditioning and Refrigeration
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    • v.8 no.2
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    • pp.23-28
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    • 2000
  • In this study, pool boiling performance of a structured enhanced tube for a flooded refrigerant evaporator was experimentally investigated. Tests were performed for three different refrigerants(R-11, R-123, R-l34a). Compared with the heat transfer coefficients of the smooth tube, the heat transfer coefficients of the enhanced tube were 6.6 times larger for R-11, 6.0 times larger for R-123 and 3.5 times larger for R-l34a, which are comparable with the performance of foreign products. The heat transfer coefficients of R-l34a was higher than those of R-11 or R-123, both for the enhanced tube and for the smooth tube. At 4.4$^\circ$C saturation temperature, however, the heat transfer coefficients of R-l34a was approximately the same as those of R-11. The effect of the saturation pressure on the boiling performance was similar to that of the smooth tube-the heat transfer coefficient increased as the saturation pressure increased.

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Experimental Study on Heat Transfer Characteristics of HFC134a for Enhanced Tubes Used in a Flooded Evaporator (HFC134a 만액식 증발전열관 외부형상 변화에 따른 열전달 특성실험)

  • Yang, Seung-Woo;Lee, Young-Su;Jeong, Jin-Hee;Kang, Yong-Tae
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.12
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    • pp.971-976
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    • 2006
  • The objectives of this paper are to study the characteristics of pool boiling heat transfer for enhanced tubes used in the evaporator of turbo chiller and to provide a guideline for optimum design of an evaporator using HFC134a. Three different enhanced tubes are tested at 4 different saturation temperatures. The wall super heated temperature difference ranges from $0.5^{\circ}C\;to\;3.5^{\circ}C$. The refrigerant, HFC134a evaporates on the outside of the tube while the chilled water flows inside the tube. This study provides experimental heat transfer coefficients for evaporation on the enhanced tubes. It is found that the turbo-II tube provides the highest heat transfer coefficient.

Effect of Oil on Pool Boiling of Refrigerant on Enhanced Tubes having Different Pore Sizes (다공도가 다른 전열촉진관의 냉매 풀비등에 미치는 오일의 영향)

  • Kim Nae-Huyn;Lee Eung-Ryul;Min Chang-Keun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.3
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    • pp.254-261
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    • 2006
  • The effect of enhanced geometry (pore diameter, gap width) is investigated on the pool boiling of R-123/oil mixture for the enhanced tubes having pores with connecting gaps. Tubes with different pore diameters (and corresponding gap widths) are specially made. Significant heat transfer degradation by oil is observed for the present enhanced tubes. At 5% oil concentration, the degradation is 26 to 49% for $T_{sat}=4.4^{\circ}C$. The degradation increases 50 to 67% for $T_{sat}=26.7^{\circ}C$. The heat transfer degradation is significant even with small amount of oil (20 to 38% degradation at 1% oil concentration for $T_{sat}=4.4^{\circ}C$), probably due to the accumulation of oil in sub-tunnels. The pore size (or gap width) has a significant effect on the heat transfer degradation. The maximum degradation is observed for $d_p$ = 0.20 mm tube at $T_{sat}=4.4^{\circ}C$, and for $d_p$=0.23 mm tube at $T_{sat}=26.7^{\circ}C$. The minimum degradation is observed for $d_p$=0.27 mm tube for both saturation temperatures. It appears that the oil removal is facilitated for the larger pore diameter (along with larger gap) tube. The highest heat transfer coefficient with oil is obtained for $d_p$ =0.23 mm tube, which yielded the highest heat transfer coefficient for pure R-123. The heat transfer degradation increases as the heat flux decreases.