• Title/Summary/Keyword: Boiling Heat Transfer

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Experimental study on nucleate boiling heat transfer enhancement using an electric field (전기장을 이용한 핵비등 열전달 촉진에 관한 실험적 연구)

  • Gwon, Yeong-Cheol;Kim, Mu-Hwan;Gang, In-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.12
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    • pp.1563-1575
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    • 1997
  • To understand EHD nucleate boiling heat transfer enhancement, EHD effects on R-113 nucleate boiling heat transfer in a non-uniform electric field were investigated. The pool boiling heat transfer and the dynamic behavior of bubbles in d.c./a.c. electric fields under a saturated or subcooled boiling were studied by using a plate-wire electrode and a high speed camera. From the pool boiling heat transfer study, the shift of the pool boiling curve, the increase of the heat transfer and the delay of ONB and CHF points to higher heat fluxes were observed. From the dynamic behavior of bubbles, it was observed that bubbles departed away from the whole surface of the heated wire in radial direction due to EHD effects by a nonuniform electric field. With increasing applied voltages, the bubble size decreased and the active nucleation site and the departure number of bubbles showed the different trend. The present study indicates that the EHD nucleate boiling heat transfer is closely connection with the dynamic behavior of bubbles and the secondary flow induced near the heated surface. Therefore, the basic studies on the bubble behavior such as bubble frequency, bubble diameter, bubble velocity and flow characteristics are necessary for complete understanding of the enhancement mechanism of the boiling heat transfer using an electric field.

MECHANISM OF NUCLEATE BOILING HEAT TRANSFER FROM WIRES IMMERSED IN SATURATED FC-72 AND WATER (전열면적 및 유체의 종류가 핵비등 열전달에 미치는 영향과 그 원인)

  • Kim, J.H.;You, S.M.;Park, J.Y.
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.232-239
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    • 2001
  • The present study is an experimental investigation of nucleate boiling heat transfer mechanism in pool boiling from wire heaters immersed in saturated FC-72 coolant and water. The vapor volume flow rate departing from a wire during nucleate boiling was determined by measuring the volume of bubbles, varying $25{\mu}m,\;75{\mu}m,\;and\;390{\mu}m$, from a wire utilizing the consecutive-photo method. The effects of the wire size on heat transfer mechanism during a nucleate boiling were investigated by measuring vapor volume flow rate and the frequency of bubbles departing from a wire immersed in saturated FC-72. One wire diameter of $390{\mu}m$ was selected and tested in saturated water to investigate the fluid effect on the nucleate boiling heat transfer mechanism. Results of the study showed that an increase in nucleate boiling heat transfer coefficients with reductions in wire diameter was related to the decreased latent heat contribution. The latent heat contribution of boiling heat transfer for the water test was found to be higher than that of FC-72. The frequency of departing bubbles was correlated as a function of bubble diameters.

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A Experimental Study on the Boiling Heat Transfer Characteristics of Nanofluids by the Size and Mixing Ratio of Graphene Particle (그래핀 입자의 크기와 혼합비율이 나노유체의 비등열전달에 미치는 영향에 대한 실험적 연구)

  • Park, Sung-Seek;Kim, Young Hun;Kim, Nam-Jin
    • Journal of the Korean Solar Energy Society
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    • v.35 no.2
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    • pp.53-62
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    • 2015
  • Boiling heat transfer characteristic is very important in the various industries such as solar thermal system, power generation, heat exchangers, cooling of high-power electronics components and cooling of nuclear reactors. Therefore, in this study, boiling heat transfer characteristics such as critical heat flux (CHF) and heat transfer coefficient under the pool boiling state were tested using graphene nanofluids. Graphene used in this study, which have the same thermal conductivity but with different sizes. The experimental results showed that the highest the CHF and boiling heat transfer coefficient increase ratio for graphene nanofluids was at the 0.01 vol.%. At the present juncture, the CHF and boiling heat transfer coefficient increase ratio of the small-sized graphene nanofluids was higher than the large-sized graphene nanofluids.

A New Correlation on Heat Transfer Coefficient in Horizontal Multi Channels (수평 다채널에서의 열전달 계수에 관한 새로운 상관식)

  • CHOI, Yong-Seok;LIM, Tae-Woo
    • Journal of Fisheries and Marine Sciences Education
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    • v.28 no.5
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    • pp.1388-1394
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    • 2016
  • This paper presents a experimental study of two-phase flow boiling of FC-72 in multi channels. Flow boiling heat transfer coefficients are obtained with mass flux ranging from 152.9 to $353.9kg/m^2s$ and heat flux from 5.6 to $46.1kW/m^2$. The experimental results show that the heat transfer is governed by nucleate boiling mechanism in the low heat flux region. However, it is found that the effects of nucleate boiling and forced convection boiling are combined as the heat flux increases. A new correlation to predict the heat transfer coefficient is developed by using the dimensionless number such as Reynolds number, Weber number, boiling number. This correlation shows good predictive accuracy against the measured data.

Experimental Study on Effect of Boiling Heat Transfer by Ultrasonic Vibration (초음파 진동이 비등열전달 과정에 미치는 영향에 관한 실험적 연구)

  • Na Gee-Dae;Oh Yool-Kwon;Yang Ho-Dong
    • Journal of Energy Engineering
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    • v.15 no.1 s.45
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    • pp.35-44
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    • 2006
  • This study experimentally investigates effect of boiling heat transfer when ultrasonic vibration was applied. Under the wall temperature condition, temperature distribution in a cavity was measured during the boiling process and heat transfer coefficient of convection, sub-tooled boiling and saturated boiling states were measured with and without ultrasonic vibration, respectively. Also, the profiles of the pressure distribution in acoustic field measured by a hydrophone were compared with the augmentation ratios of heat transfer calculated by local heat transfer coefficient. Result of this study, heat transfer coefficient and augmentation ratio of heat transfer is higher with ultrasonic waves than without one. Especially, augmentation ratio of heat transfer is more increased the convection state than sub-cooled boiling and saturated boiling states. Acoustic pressure is relatively higher near ultrasonic transducer than other points where is no installed it and affects the augmentation ratio of heat transfer.

Flow Boiling Heat Transfer in a Horizontal Rectangular Microchannel (수평 사각 마이크로채널 내에서의 유동 비등 열전달)

  • Huh, Cheol;Kim, Moo-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.11 s.254
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    • pp.1043-1050
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    • 2006
  • An experimental investigation was performed to study flow boiling heat transfer of deionized water in a microchannel. Measurement and evaluation of boiling heat transfer coefficients were carried out using a single horizontal rectangular microchannel having a hydraulic diameter of $100{\mu}m$. Tests were performed for mass fluxes of 90, 169 and 267 $kg/m^2$s and heat fluxes of 200-700 $kW/m^2$. Test results showed that the measured boiling heat transfer coefficients had no dependence on mass flux and vapor quality. Most macro-channel correlations of boiling heat transfer coefficient did not provide reliable predictions.

Investigation of Boiling Heat Transfer Characteristics of Two-Phase Closed Thermosyphons with Various Internal Grooves

  • Han, Ku-Il;Cho, Dong-Hyun;Park, Jong-Un
    • Journal of Mechanical Science and Technology
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    • v.17 no.11
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    • pp.1739-1745
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    • 2003
  • The boiling heat transfer characteristics of two-phase closed thermosyphons with internal grooves are studied experimentally and a simple mathematical model is developed to predict the performance of such thermosyphons. The study focuses on the boiling heat transfer characteristics of a two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tube is also tested for comparison. Methanol is used as working fluid. The effects of the number of grooves, the operating temperature, the heat flux are investigated experimentally. From these experimental results, a simple mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphon. And also the effects of the number of grooves, the operating temperature, the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the predictions from the present mathematical model is obtained. The experimental results show that the number of grooves and the amount of the working fluid are very important factors for the operation of thermosyphons. The two-phase closed thermosyphon with copper tubes having 60 internal grooves shows the best boiling heat transfer performance.

Convective Boiling Two-phase Flow in Trapezoidal Microchannels : Part 2-Heat Transfer Characteristics (사다리꼴 미세유로의 대류비등 2상유동 : 2부-열전달 특성)

  • Kim, Byong-Joo;Kim, Geon-Il
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.11
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    • pp.718-725
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    • 2011
  • Characteristics of flow boiling heat transfer in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having 205 ${\mu}m$ of bottom width, 800 ${\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Tests were performed with R113 over a mass velocity range of 150~920 $kg/m^2s$, heat flux of 10~100 $kW/m^2$ and inlet pressures of 105~195 kPa. Flow boiling heat transfer coefficient in microchannels was found to be dominated by heat-flux. However the effect of mass velocity was not significant. Contrary to macrochannel trends, the heat transfer coefficient was shown to decrease with increasing thermodynamic equilibrium quality. A new correlation suitable for predicting flow boiling heat transfer coefficient was developed based on the laminar single-phase heat transfer coefficient and the nucleate boiling dominant equation. Comparison with the experimental data showed good agreement.

Mechanisms of Convective and Boiling Heat Transfer Enhancement via Ultrasonic Vibration (초음파 진동에 의한 대류 및 비등 열전달 촉진 원리에 관한 연구)

  • Kim, Yi-Gu;Kim, Ho-Young;Kang, Seoung-Min;Kang, Byung-ha;Lee, Jin-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.5
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    • pp.612-619
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    • 2003
  • This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when tile local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism.

Experimental study on the influence of heating surface inclination angle on heat transfer and CHF performance for pool boiling

  • Wang, Chenglong;Li, Panxiao;Zhang, Dalin;Tian, Wenxi;Qiu, Suizheng;Su, G.H.;Deng, Jian
    • Nuclear Engineering and Technology
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    • v.54 no.1
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    • pp.61-71
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    • 2022
  • Pool boiling heat transfer is widely applied in nuclear engineering fields. The influence of heating surface orientation on the pool boiling heat transfer has received extensive attention. In this study, the heating surface with different roughness was adopted to conduct pool boiling experiments at different inclination angles. Based on the boiling curves and bubble images, the effects of inclination angle on the pool boiling heat transfer and critical heat flux were analyzed. When the inclination angle was bigger than 90°, the bubble size increased with the increase of inclination angle. Both the bubble departure frequency and critical heat flux decreased as the inclination angle increased. The existing theoretical models about pool boiling heat transfer and critical heat flux were compared. From the perspective of bubble agitation model and Hot/Dry spot model, the experimental phenomena could be explained reasonably. The enlargement of bubble not only could enhance the agitation of nearby liquid but also would cause the bubble to stay longer on the heating surface. Consequently, the effect of inclination angle on the pool boiling heat transfer was not conspicuous. With the increase of inclination angle, the rewetting of heating surface became much more difficult. It has negative effect on the critical heat flux. This work provides experimental data basis for heat transfer and CHF performance of pool boiling.