Saturation Boiling of PF-5060 Dielectric Liquids on Micro-Porous Copper Dendrites Surfaces

2009 ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Average Pore Size ◽  
Nucleate Boiling ◽  
Surface Layers ◽  
Average Pore ◽  
Porous Copper ◽  
Volume Porosity ◽  
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 micro-porous copper dendrites surface layers deposited on 10 × 10 mm Cu substrates. The electrochemically deposited surface layers are of different thickness (50, 70, and 220 μm), average pore size (15, 30 and 80 μm) and volume porosity (96, 94.3, and 93.6%). The thickest layer, deposited using 3.0 A/cm2 for 25s, 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 begins at surface temperature slightly above saturation (< 0.5 K) with no temperature excursion. The temperature excursions before initiating boiling on the 70 μm and 50 μm thick Cu nano-dendrites 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 CPUs.

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.

Subcooled Boiling of PF-5060 Dielectric Liquid on Microporous Surfaces

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Average Rate ◽  
Nucleate Boiling ◽  
Dielectric Liquid ◽  
Subcooled Boiling ◽  
Surface Layers ◽  
Electrochemically Deposited ◽  
Cu Substrates ◽  
Surface Saturation

Presented are the results of experiments that investigated nucleate boiling of PF-5060 on microporous Cu surface layers at saturation and 10 K, 20 K, and 30 K subcooling. The three microporous layers, electrochemically deposited on 10×10 mm2 Cu substrates and investigated herein, are ∼139 μm, 171 μm, and 220 μm thick. The critical heat flux increases linearly with increased subcooling, ΔTsub, at an average rate of 4.5%/K. For the 171 μm thick, Cu microporous surface, saturation boiling CHF of 27.8 W/cm2 increases to 63.25 W/cm2 at ΔTsub=30 K, while the saturation hMNB of 13.5 W/cm2 K decreases slightly to 12.7 W/cm2 K at ΔTsub=30 K. The values of the surface superheat, ΔTsat, at hMNB and CHF increase from 2.0 K and 2.16 K at saturation to 4.2 and 6.42 K at 30 K subcooling.

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.

Effects of Surface Roughness and Inclination Angle on Nucleate Boiling of PF-5060 Dielectric Liquid on Copper

2013 ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Arthur Suszko ◽  
Amir F. Ali
Keyword(s):  
Surface Roughness ◽  
Inclination Angle ◽  
Surface Heat Flux ◽  
Nucleate Boiling ◽  
Surface Heat ◽  
Dielectric Liquid ◽  
Average Roughness ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient ◽  
Experimental Values

Saturation pool boiling experiments of PF-5060 dielectric liquid are performed using eleven different Cu surfaces with average roughness, Ra = 0.21 to 1.79 μm, at inclination angle, θ, from 0° (upward facing) to 180° (downward facing). Nucleate boiling heat transfer coefficient, hNB, increases with increasing surface roughness and with decreasing inclination angle. The measured enhancements in hNB with increased surface roughness are in excess of 36%. In the upward facing orientation, the experimental values of hNB are correlated in terms of the surface heat flux in the experiments, q, as: hNB = A qB. The coefficient “A” increases from ∼0.14 to 0.23, while the exponent “B” decreases from 0.76 to 0.69 as Ra increases from 0.21 to 1.79 μm.

Saturation and Subcooled Boiling on Copper Nano-Dendrites Surfaces

2010 ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Amir F. Ali
Keyword(s):  
Nucleate Boiling ◽  
Subcooled Boiling ◽  
Structured Surfaces ◽  
Electrochemically Deposited ◽  
Cu Substrates

Nucleate boiling of PF-5060 liquid on nano-dendrites surfaces is investigated at saturation and ΔTsub = 10, 20 and 30 K. The electrochemically deposited surfaces layers on 10 × 10 mm Cu substrates are ∼ 139, 171 and 220 μm thick. CHF and hMNB are significantly higher and occur at lower ΔTsat than has been reported on plane, macro-, micro- and nano-structured surfaces. CHF increases linearly 4.5%/K, while hMNB, occurring at end of the fully developed nucleate boiling region, decreases and corresponding ΔTsat increases with increased subcooling. For the 171 μm-thick surface: CHFsat of 27.8 W/cm2 increases to 63.25 W/cm2 at ΔTsub = 30 K, while saturation hMNB of 13.5 W/cm2.K decreases to 12.7 W/cm2.K at 30 K subcooling. ΔTsat at hMNB and CHF increases from 2.0 K and 2.16 K at saturation to 4.2 and 6.42 K at 30 K subcooling.

The Inception of Nucleate Boiling With Liquid Nitrogen

1969 ◽  
Vol 91 (4) ◽  
pp. 1210-1216 ◽  
Author(s):  
D. W. Almgren ◽  
J. L. Smith
Keyword(s):  
Liquid Nitrogen ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Temperature Hysteresis ◽  
Total Heat Flux ◽  
Stable Temperature ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient ◽  
High Vapor ◽  
Theory And Experiment

The phenomena of patchwise boiling are discussed, and the significant parameters restricting the growth of a boiling patch are analytically determined to be: (a) a high nucleate-boiling heat-transfer coefficient, (b) a low total heat flux, (c) the absence of cavities with a trapped liquid vapor interface outside the boiling patch, (d) an appropriate value of wall thermal conductivity, and (e) a high vapor enthalpy per bubble. A qualitative agreement between theory and experiment was observed for items (a), (b), and (d). A surface finish was developed and tested in pool boiling of liquid nitrogen which eliminated the observed, stable temperature hysteresis at inception of nucleate boiling and maintained a low-temperature difference (Tw−Tsat) for the entire nucleate-boiling curve.

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.

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