Experimental Study of Microscale Bubble Growth and Departure Dynamic Over a Surface With Constant Heat Flux Boundary Condition

2003 ◽  
Author(s):  
Saeed Moghaddam ◽  
Kenneth T. Kiger
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Constant Heat Flux ◽  
Transport Processes ◽  
Flux Boundary Condition ◽  
Boiling Heat Transfer Coefficient ◽  
Competing Models ◽  
Microscale Transport

Boiling heat transfer has been the subject of research for many years, with a substantial amount of effort devoted to understanding the microscale transport processes of nucleate boiling. This information is essential to determine appropriate expressions for the boiling heat transfer coefficient. As a result, several different competing models based on the bubbling dynamics and its associated heat transfer mechanisms have been hypothesized to account for the sensible and latent heat transport and liquid motion adjacent to the heat transfer surface. Many of the early models were based on the assumptions that growth, departure and the associated pumping action of the bubbles are responsible for heat transfer during nucleate boiling. Jakob [1] and Rohsenow [2] were apparently the first to postulate that the process of growth and departure of the bubble is responsible for the induced motion of the liquid adjacent to the heat transfer, as in any single-phase convection process. Rohsenow [2] modeled the heat transfer by using bubble diameter as a characteristic length to determine a Nusselt number based on a defined Reynolds and Prandtl number. Even with the same line of reasoning, Rohsenow’s analysis resulted in a different formulation compared to Froster and Zober [3], who implemented an alternate hypothesis for the velocity of the bubble interface used in defining the Reynolds number. Other models of this nature were also proposed by Forster and Greif [4] and Zuber [5].

Pool Boiling Heat Transfer with Nanotube Arrays Surface on Titanium

2012 ◽  
Vol 550-553 ◽  
pp. 2913-2916 ◽  
Author(s):  
Jin Liang Tao ◽  
Xin Liang Wang ◽  
Pei Hua Shi ◽  
Xiao Ping Shi
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Test Fluid ◽  
Porous Coating ◽  
Pool Boiling Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

In this paper, a new porous coating was formed directly on the surface of titanium metal via anodic oxidation. And by the SEM, the morphology of the coating, which is composed of well-ordered perpendicular nanotubes, was characterized. Moreover, taking deionized water as the test fluid, a visualization study of the coating on its pool boiling heat transfer performance was made. The results demonstrated that compared with the smooth surface, the nucleate boiling heat transfer coefficient can increase 3 times while the nucleate boiling super heat was reduced 30%.

Experimental Study of Flow Boiling Heat Transfer Coefficient of FC-72 Over Micro-Pin-Finned Surfaces

2010 ◽  
Author(s):  
Y. F. Xue ◽  
M. Z. Yuan ◽  
J. J. Wei
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Nucleate Boiling ◽  
Flow Boiling Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

Experiments of flow boiling heat transfer coefficient of FC-72 were carried out over simulated silicon chip of 10×10×0.5 mm3 for electronic cooling. Four kinds of micro-pin-fins with the dimensions of 30×60, 30×120, 50×60, 50×120 μm2 (thickness, t × height, h) respectively, were fabricated on the chip surfaces by the dry etching technique to enhance boiling heat transfer. A smooth chip was also tested for comparison. The experiments were conducted at three different fluid velocities (0.5, 1 and 2m/s) and three different liquid subcoolings (15, 25 and 35K). All micro-pin-finned surfaces show a considerable heat transfer enhancement compared to the smooth surface. Both the forced convection and nucleate boiling heat transfer contribute to the total heat transfer performance. The contribution of each factor to the total heat transfer has been clearly presented in the flow boiling heat transfer coefficient curves. In a lower heat flux region, the heat transfer coefficient increases greatly with increasing fluid velocity, but increases slightly with increasing heat flux, indicating that the single-phase forced convection dominates the heat transfer process. With further increasing heat flux to the onset of nucleate boiling, the heat transfer coefficient increases remarkably. For a given liquid subcooling, the curves of flow boiling heat transfer coefficient at fluid velocities of 0.5 and 1 m/s almost follow one line for each surface, showing insensitivity of nucleate boiling heat transfer to fluid velocity. However, at the largest fluid velocity of 2 m/s, the slope of the flow boiling heat transfer coefficient curves for micro-pin-finned surfaces becomes smaller, indicating that the forced convection also plays an important role besides the nucleate boiling heat transfer. The curves of the flow boiling heat transfer coefficient can be used to determine the boiling incipience at different fluid velocities, which provides a basis for the suitable fluid velocity selection in designing highly efficient cooling scheme for electronic devices.

Latent and Sensible Heat-Transfer Rates in the Boiling of Binary Mixtures

1982 ◽  
Vol 104 (3) ◽  
pp. 474-478 ◽  
Author(s):  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Heat Transport ◽  
Binary Mixtures ◽  
Boiling Heat Transfer ◽  
Constant Heat Flux ◽  
Absolute Pressure ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Heat Transfer Coefficient

Nucleate pool boiling bubble departure data were obtained for the liquid nitrogen-argon cryogenic binary mixture system at 1.3 atmospheres absolute pressure. The latent and sensible heat transport rates at individual boiling sites were calculated from the data to deduce their effect on the degradation in the boiling heat-transfer coefficient in binary mixtures. The latent heat-transfer rate is a result of the bubble evaporation mechanism and the sensible heat-transport rate is due to cyclic thermal boundary layer stripping by departing bubbles. The latent and sensible heat-transport rates at individual boiling sites were found to decrease to a minimum at the maximum vapor-liquid mole fraction difference for both constant heat flux and wall superheating conditions. The large decrease in binary boiling heat-transfer coefficients was thus partially explained by the retardation of these two mechanisms and should be included in any model for predicting boiling heat-transfer coefficients in binary and multicomponent mixtures.

scholarly journals Pool Boiling Amelioration by Aqueous Dispersion of Silica Nanoparticles

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2138
Author(s):  
Sayantan Mukherjee ◽  
Naser Ali ◽  
Nawaf F. Aljuwayhel ◽  
Purna C. Mishra ◽  
Swarnendu Sen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Boiling Heat Transfer ◽  
Base Fluid ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Surface Wettability ◽  
Bulk Fluid ◽  
Pool Boiling Heat Transfer

Non-metallic oxide nanofluids have recently attracted interest in pool boiling heat transfer (PBHT) studies. Research work on carbon and silica-based nanofluids is now being reported frequently by scholars. The majority of these research studies showed improvement in PBHT performance. The present study reports an investigation on the PBHT characteristics and performance of water-based silica nanofluids in the nucleate boiling region. Sonication-aided stable silica nanofluids with 0.0001, 0.001, 0.01, and 0.1 particle concentrations were prepared. The stability of nanofluids was detected and confirmed via visible light absorbance and zeta potential analyses. The PBHT performance of nanofluids was examined in a customized boiling pool with a flat heating surface. The boiling characteristics, pool boiling heat transfer coefficient (PBHTC), and critical heat flux (CHF) were analyzed. The effects of surface wettability, contact angle, and surface roughness on heat transfer performance were investigated. Bubble diameter and bubble departure frequency were estimated using experimental results. PBHTC and CHF of water have shown an increase due to the nanoparticle inclusion, where they have reached a maximum improvement of ≈1.33 times over that of the base fluid. The surface wettability of nanofluids was also enhanced due to a decrease in boiling surface contact angle from 74.1° to 48.5°. The roughness of the boiling surface was reduced up to 1.5 times compared to the base fluid, which was due to the nanoparticle deposition on the boiling surface. Such deposition reduces the active nucleation sites and increases the thermal resistance between the boiling surface and bulk fluid layer. The presence of the dispersed nanoparticles caused a lower bubble departure frequency by 2.17% and an increase in bubble diameter by 4.48%, which vigorously affects the pool boiling performance.

Wall Thermal Conductivity Effects on Nucleation Site Interaction During Boiling: An Experimental Study

2010 ◽  
Author(s):  
Yu Yan Jiang ◽  
Hiroshi Osada ◽  
Masahide Inagaki ◽  
Nariaki Horinouchi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Stainless Steel ◽  
Boiling Heat Transfer ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Uniform Heat Flux ◽  
Stainless Steel Surface

The past decades have witnessed the diverse applications of boiling heat transfer enhancement in the removal of high density heat flux released by electronic components or power devices. People have developed many enhanced surfaces to obtain the highest heat transfer coefficient in nucleate boiling or to raise the CHF. In the boiling arena bubbling and nucleation site density play core parts, and hence it is crucial to correlate them quantitatively with surface structure and heat transfer conditions. For example one can determine by that correlation the best arrangement of boiling cavities for a given heat flux. However, the bubbling is highly influenced by inter-bubble actions. It has been found that the interactions can considerably change the bubble’s size, frequency and spatial distribution. The interactions are needed to be taken accounts of for a good correlation. Researchers tried to formulate the interactions as a single function of the inter-site spacing but have obtained contradictory conclusions, as suggests that they depend also on other parameters. In the present study we conducted a saturated boiling heat transfer experiment to investigate the interactions with respects to both the inter-site spacing and the wall thermal conductivity. The test section was fabricated by both copper and stainless steel, whose surface has two cylindrical artificial cavities of 50μm in diameter. It was heated with a uniform heat flux. The results show that both the bubble diameter Db and frequency f are functions of the inter-cavity distance s, but they vary in different manners in the copper and the stainless steel surfaces. In the copper surface, we observed evident enhancement of the boiling heat transfer at 1> S >0.4 and a slight inhibitive effect at 1.6> S >1, where S = s/Db. On the contrary the two nucleate sites in the stainless steel surface interfere with each other giving rise to evident suppression of boiling heat transfer at 1.6> S >0.65 and only slight enhancement at 0.65> S >0.3. Note that the copper’s thermal conductivity is 22 times larger than the stainless steel. Numerical simulation has revealed that the temperature variation beneath the copper cavities is much less than the stainless steel, which partly explains the differences in our experimental results. It is suggested that modeling the bubble interactions should take accounts of not only the distance-to-diameter ratio but also the fluid and wall properties.

Effect of Inclination on Pool Boiling of FC-72 Dielectric Liquid on Porous Graphite

2005 ◽  
Author(s):  
Jack L. Parker ◽  
Mohamed S. El-Genk
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Inclination Angle ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Porous Graphite ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

Saturation pool boiling experiments of FC-72 liquid on a flat, porous graphite and smooth copper surfaces measuring 10 × 10 mm investigated the effect of surface orientation on nucleate boiling and Critical Heat Flux (CHF). The inclination angle of the surface increased from 0° (upward-facing) to 60°, 90°, 120°, 150°, and 180° (downward facing). Results demonstrated significant increases in the nucleate boiling heat transfer coefficient and CHF on porous graphite, compared to those on copper. At low surface superheats, increasing the inclination angle increases the nucleate boiling heat transfer coefficient, which decreases with increased inclination angle at high surface superheats. These results and the measured decreases of CHF with increased inclination angle are consistent with those reported earlier by other investigators for dielectric and non-dielectric liquids. On smooth surfaces and micro-porous coatings, the reported fractional decreases in CHF with increased inclination angle are almost identical, but markedly larger than those measured in this work on porous graphite. On these surfaces the reported CHF in the downward-facing position (180° inclination) is ∼10–20% of that in the upward-facing position (0° inclination), compared to ∼53.3% on porous graphite. The CHF values of FC-72 liquid on porous graphite, which also decreased with increased inclination angle, are correlated using the general form suggested by Kutatelatze (1961) to within ± 5% of the experimental data.

Enhancement of Saturation Boiling of PF-5060 on Microporous Copper Dendrite Surfaces

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Central Processor ◽  
Surface Layers ◽  
Reliable Operation ◽  
Electrochemically Deposited ◽  
Nucleate Boiling Heat Transfer ◽  
Cu Substrates ◽  
Boiling Heat Transfer Coefficient

Experiments are performed to investigate saturation boiling of degassed PF-5060 dielectric liquid on microporous copper dendrite surface layers deposited on 10×10 mm2 Cu substrates. The electrochemically deposited surface layers are of different thicknesses (145.6 μm, 46.3 μm, and 33.1 μm). The thickest layer gives the best results: the saturation CHF of 25.27 W/cm2 occurs at a surface superheat of only 2.9 K and the maximum nucleate boiling heat transfer coefficient, hMNB, near the end of the fully developed nucleate boiling region, is 8.76 W/cm2 K. In addition, nucleate boiling ensues at a surface temperature slightly above saturation (<0.5 K), with no temperature excursion. The temperature excursions before initiating boiling on the 46.3 μm and 33.1 μm thick Cu nanodendrite surface layers are small (3.7 K and 6 K), corresponding to surface temperatures of ∼55.1°C and 57.4°C, respectively. These temperatures are much lower than recommended (85°C) for reliable operation of most silicon electronics and central processor units.

Nucleate Pool Boiling of Nitrogen With Different Surface Conditions

1968 ◽  
Vol 90 (4) ◽  
pp. 437-444 ◽  
Author(s):  
P. J. Marto ◽  
J. A. Moulson ◽  
M. D. Maynard
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Past History ◽  
Pool Boiling ◽  
Testing Procedure ◽  
Nucleate Boiling ◽  
Test Surface ◽  
Surface Conditions ◽  
Boiling Heat Transfer Coefficient ◽  
Teflon Coating

Pool-boiling heat transfer of liquid nitrogen from circular, 1-in.-dia horizontal disks was studied. Surface conditions included copper and nickel mirror finishes, and copper surfaces which were roughened, grease-coated, and Teflon-coated. Artificial cavities were manufactured, including mechanically drilled cylindrical holes of diameter 0.0043 and 0.015 in., and also a 0.022-in.-dia spark cut conical hole. Results indicate that a systematic testing procedure is necessary to obtain reproducible nucleate-boiling data. Surface roughness and surface material alter the nucleate-boiling curve. A grease coating significantly decreases the nucleate-boiling heat-transfer coefficient. A Teflon coating has very little effect. Past history of the test surface, including the length of time spent while boiling, can change boiling results. The effect of artificial cavities on both natural convection and nucleate-boiling was determined.

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