• Title/Summary/Keyword: Boiling

Search Result 2,195, Processing Time 0.029 seconds

Effect of particle sizes on CHF enhancement and boiling characteristics of nano-fluids (나노유체의 임계열유속 및 비등특성에 미치는 나노입자 크기의 영향)

  • Jo, Byeong-Nam;Kang, Jun-One;Yoo, Jai-Suk;Kim, Hyun-Jung
    • 한국가시화정보학회:학술대회논문집
    • /
    • 2006.12a
    • /
    • pp.125-130
    • /
    • 2006
  • The characteristics of boiling heat transfer and critical heat flux (CHF) behavior of nano-fluids were studied by using various sized silver and alumina nanoparticles. The diameter of nanoparticles was from 2 nm to 250 nm for silver and from 20nm to 40nm for alumina. Pool boiling characteristics and CHF enhancement of nano-fluids with different sized nanoparticles were compared with those of pure water and each nano-fluids. The experiment was performed at atmospheric pressure and the temperature of the pool was maintained constantly by using a flat immersed heater. The concentration of nano-fluids was uniform in all experiments as 0.01g/liter. The results showed that the measured boiling curves were shifted to the right. It demonstrated that the occurrence of nucleate boiling regime in nano-fluids retarded, compared with that of pure water. Also, in nano-fluids, the boiling curves showed that CHF of nano-fluids is significantly enhanced and represented the effect of particle size on boiling characteristics.

  • PDF

A study on the pulse boiling occurring inside the liquid pool of a closed two-phase thermosyphon (밀폐형 2상 열사이폰의 Pool 내부 Pulse Boiling에 관한 연구)

  • Kim, Cheol-Ju;Mun, Seok-Hwan;Gang, Hwan-Guk
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.21 no.10
    • /
    • pp.1254-1261
    • /
    • 1997
  • Pulse boiling, the unsteady periodic boiling phenomenon appearing in the evaporator of thermosyphons was investigated by many researchers. In the present study investigations were conducted to examine the evolution of flow patterns at the evaporator, and changes in thermodynamic state that each of liquid pool and vapor experiences through 1 cycle of pulse boiling process. For wall and liquid pool the degree of superheat for the onset of nucleation was examined. It revealed that the degree of superheat increased with the increase of pulse period, reaching to 16.5 deg.C and 23 deg.C for liquid pool and evaporator wall respectively at .tau.=80 sec. The data on flow patterns obtained through series of operation tests were plotted in the coordinates of heat flux and vapor pressure to get a regime map. Further this map could be used to figure out the conditions of pulse boiling for a thermosyphon.

Experimental Observations of Boiling and Flow Evolution in a Coiled Tube

  • Ye, P.;Peng, X.F.;Wu, H.L.;Meng, M.;Gong, Y. Eric
    • International Journal of Air-Conditioning and Refrigeration
    • /
    • v.16 no.1
    • /
    • pp.22-29
    • /
    • 2008
  • A sequence of visually experimental observations was conducted to investigate the flow boiling and two-phase flow in a coiled tube. Different boiling modes and bubble dynamical evolutions were identified for better recognizing the phenomena and understanding the two-phase flow evolution and heat transfer mechanisms. The dissolved gases and remained vapor would serve as foreign nucleation sites, and together with the effect of buoyancy, centrifugal force and liquid flow, these also induce very different flow boiling nucleation, boiling modes, bubble dynamical behavior, and further the boiling heat transfer performance. Bubbly flow, plug flow, slug flow, stratified/wavy flow and annular flow were observed during the boiling process in the coiled tube. Particularly the effects of flow reconstructing and thermal non-equilibrium release in the bends were noted and discussed with the physical understanding. Coupled with the effects of the buoyancy, centrifugal force and inertia or momentum ratio of the two fluids, the flow reconstructing and thermal non-equilibrium release effects have critical importance for flow pattern in the bends and flow evolution in next straight sections.

Forced Convective Boiling of Refrigerant-Oil Mixtures in a Bundle of Enhanced Tubes Having Pores and Connecting Gaps

  • Park, Ji-Hoon;Kim, Nae-Hyun;Kim, Do-Young;Byun, Ho-Won;Choi, Yong-Min;Kim, Soo-Hwan
    • International Journal of Air-Conditioning and Refrigeration
    • /
    • v.17 no.3
    • /
    • pp.81-87
    • /
    • 2009
  • The effect of oil on convective boiling of R-123 in an enhanced tube bundle is experimentally investigated at $26.7^{\circ}C$ saturation temperature. The enhanced tube had pores (0.23 mm diameter) and connecting gaps (0.07 mm width), which had been optimized using pure R-123. The effects of oil concentration (0 to 5%), heat flux (10 to $40\;kW/m^2$), mass velocity (8 to $26\;kg/m2^s$) and vapor quality are investigated. The oil significantly reduces the bundle boiling heat transfer coefficient. With 1% oil, the reduction is approximately 35%. Further addition of oil further reduces the heat transfer coefficient. The data are also compared with the pool boiling counterpart. The reduction in the heat transfer coefficient is smaller in a bundle (convective boiling) than in a pool (single-tube pool boiling), with larger difference at a smaller heat flux. Similar to pure R-123 case, the effects of mass velocity and vapor quality are negligible for the convective boiling of R-123/oil mixture.

The Local Measurements of Single Phase and Boiling Heat Transfer by Confined Planar Impinging Jets (평면충돌제트에 의한 단상 및 비등 열전달의 국소적 측정)

  • Wu, Seong-Je;Shin, Chang-Hwan;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.28 no.8 s.227
    • /
    • pp.895-901
    • /
    • 2004
  • Single-phase convection and nucleate boiling heat transfer were locally investigated for confined planar water jets. The detailed distributions of the wall temperature and the convection coefficient as well as the typical boiling curves were discussed. The curve for the single-phase convection indicated the developing laminar boundary layer, accompanied by monotonic increase of the wall temperature in the stream direction. Boiling was initiated from the furthest downstream as heat flux increased. Heat transfer variation according to the streamwise location was reduced as heat flux increased enough to create the vigorous nucleate boiling. Velocity effects were considered for the confined free-surface jet. Higher velocity of the jet caused the boiling incipient to be delayed more. The transition to turbulence precipitated by the bubble-induced disturbance was obvious only for the highest velocity, which enabled the boiling incipient to start in the middle of the heated surface, rather than the furthest downstream as was the case of the moderate and low velocities. The temperature at offset line were somewhat tower than those at the centerline for single-phase convection and partial boiling, and these differences were reduced as the nucleate boiling developed. For the region prior to transition, the convection coefficient distributions were similar in both cases while the temperatures were somewhat lower in the submerged jet. For single-phase convection, transition was initiated at $x/W{\cong}2.5$ and completed soon for the submerged jet, but the onset of transition was retarded to the distance at $x/W{\cong}6$ for the fee-surface jet.

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
    • /
    • v.54 no.1
    • /
    • pp.61-71
    • /
    • 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.

Pre-service Chemistry Teachers’ Understanding of the Boiling Process of a Liquid Mixture (액체 혼합물의 끓음에 대한 예비 화학교사의 이해)

  • Park, Kira;Yoon, Heesook
    • Journal of the Korean Chemical Society
    • /
    • v.59 no.5
    • /
    • pp.454-465
    • /
    • 2015
  • The goal of this study is to investigate pre-service chemistry teachers’ understanding of the boiling process of a liquid mixture. We surveyed 65 students in the chemistry program of the College of Education about the boiling point of a 50%(by mole) ethanol aqueous solution and the temperature changes during heating. We then interviewed 9 of these students. According to the survey results, the percent of the pre-service teachers who thought that the boiling point of the ethanol solution would be ‘between the boiling points of ethanol and water (78-100 ℃)’ and ‘the same as that of ethanol’ were 52.3% and 35.4%, respectively. The majority of those who stated the former explained that the boiling point of the ethanol solution increased due to the effects of attraction or blocking by water molecules. Most of those who believed the latter explained that physical properties such as the boiling point would not be changed by the addition of water. With regard to the temperature change during heating, 69.2% of the teachers thought that the temperature would increase gradually while boiling, which some thought resulted from the increasing amount of water in the solution as the ethanol boiled off. Others thought that two temperature plateaus would be observed as each component of the liquid mixture underwent phase transition at its specific boiling point. When asked about the particle model of the gas phase during the boiling and evaporation process, some students drew both ethanol and water during evaporation but only ethanol when boiling. We discussed several alternative concepts of pre-service chemistry teachers about the boiling process of liquid mixtures and ways to improve their understanding.

Experimental investigation of Geyser boiling in Thermosyphon for Solar Collector (태양열 집열용 써모사이폰의 Geyser boiling에 대한 실험적 연구)

  • Hong, J.K.;Bae, C.H.;Chung, K.T.;Suh, J.S.
    • Proceedings of the KSME Conference
    • /
    • 2004.11a
    • /
    • pp.1040-1045
    • /
    • 2004
  • This study has been carried out to investigate thermosyphon's geyser boiling phenomenon used to solar collector. evaporator section of thermosyphon used to solar collector is very much longer than that of condenser section. From the results from this study, Geyser boiling's cycle depends on cooling water, tilt angle and the applied heat load at the evaporator. In this study, according to heat load, the geyser boiling frequency is lower, but the amplitude higher. For the high tilt angle of heat pipe, the frequency and amplitude are lower and higher in the evaporator region, respectively. Whereas, these phenomena is in contrast in the condenser region.

  • PDF

An Experimental Study on Direct Cooling Performance using Pool Boiling from Micro-Porous Coated Surface (마이크로다공성 코팅된 발열체에서의 풀비등 직접냉각 성능에 관한 실험적 연구)

  • Kim, Tae-Gyun;Lee, Kyu-Jung;Kim, Yong-Chan;Park, Chan-Sung
    • Proceedings of the KSME Conference
    • /
    • 2004.11a
    • /
    • pp.1353-1358
    • /
    • 2004
  • An experimental study of pool boiling behavior on micro-porous enhanced square heater surfaces immersed in PF5060 is performed. The effects of heater orientation, Subcooling and substrate distance on the pool boiling heat transfer performance for the double heaters were investigated under increasing heat-flux conditions. The boiling performance of micro-porous coated surface was better than that of plain surface. The double heaters with upper substrate of 0.2cm substrate interval have lower boiling performances compared with the results for the double heaters with that of 0.5cm and 1.0cm substrate interval and without the substrate. In comparison to upper heater and below heater with orientation, the upper heater has lower superheat temperature than the below heater due to the bubble sweeping.

  • PDF

Stydy of Pool Boiling under Steady State using Ultrasonic Measurement (초음파 측정법을 이용한 정상상태의 푸울비등 연구)

  • 장길홍
    • Journal of Ocean Engineering and Technology
    • /
    • v.6 no.2
    • /
    • pp.35-40
    • /
    • 1992
  • A recently developed new technique for measuring the fraction of wetted area has applied to pool boiling of water. The basis of the new applied technique of ultrasonic makes use of the reflection of ultrasonic from the vapour surface to measure the fraction of wetted area values. The results are the measured fraction of wetted area values in nucleate and transition boiling and the pool boiling curve for water under steady state conditions. The measurement of this paper shows a fraction of wetted areaf around 0.98 at the critical heat flux for water.

  • PDF