Nucleate Pool Boiling From Coated and Spirally Wrapped Tubes in Saturated R-134a and R-600a at Low and Moderate Heat Flux

2000 ◽  
Vol 123 (2) ◽  
pp. 257-270 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Tsung-Ying Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Plasma Coating ◽  
Nucleate Boiling ◽  
Thermal Design ◽  
Transfer Coefficients ◽  
Porous Copper ◽  
Helical Angle ◽  
R 134A ◽  
Coated Surfaces

Pool nucleate boiling heat transfer experiments from coated surfaces with porous copper (Cu) and molybdenum (Mo) and spirally wrapped with helical wire on copper surfaces with micro-roughness immersed in saturated R-134a and R-600a were conducted. The influence of coating thickness, porosity, wrapped helical angle, and wire pitch on heat transfer and boiling characteristics including bubble parameters were studied. The enhanced surface heat transfer coefficients with R-600a as refrigerant found are 2.4 times higher than those of the smooth surfaces. Photographs indicate that the average number of bubbles and bubble departure diameters has been found to increase linearly with heat flux, while the bubble diameters exhibit opposite trend in both refrigerants. Furthermore, the heat transfer of the boiling process for the present enhanced geometry (coated and wrapped) was modeled and analyzed. The experimental data for plasma coating and spirally wrapped surfaces were correlated in terms of relevant parameters, respectively to provide a thermal design basis for engineering applications.

Subcooled Pool Boiling Experiments on Horizontal Heaters Coated With Carbon Nanotubes

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
V. Sathyamurthi ◽  
H-S. Ahn ◽  
D. Banerjee ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Heat Flux ◽  
Pool Boiling ◽  
Type A ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Test Fluid ◽  
Type B ◽  
Coated Surfaces

Pool boiling experiments were conducted with three horizontal, flat, silicon surfaces, two of which were coated with vertically aligned multiwalled carbon nanotubes (MWCNTs). The two wafers were coated with MWCNT of two different thicknesses: 9 μm (Type-A) and 25 μm (Type-B). Experiments were conducted for the nucleate boiling and film boiling regimes for saturated and subcooled conditions with liquid subcooling of 0–30°C using a dielectric fluorocarbon liquid (PF-5060) as test fluid. The pool boiling heat flux data obtained from the bare silicon test surface were used as a base line for all heat transfer comparisons. Type-B MWCNT coatings enhanced the critical heat flux (CHF) in saturated nucleate boiling by 58%. The heat flux at the Leidenfrost point was enhanced by a maximum of ∼150% (i.e., 2.5 times) at 10°C subcooling. Type-A MWCNT enhanced the CHF in nucleate boiling by as much as 62%. Both Type-A MWCNT and bare silicon test surfaces showed similar heat transfer rates (within the bounds of experimental uncertainty) in film boiling. The Leidenfrost points on the boiling curve for Type-A MWCNT occurred at higher wall superheats. The percentage enhancements in the value of heat flux at the CHF condition decreased with an increase in liquid subcooling. However the enhancement in heat flux at the Leidenfrost points for the nanotube coated surfaces increased with liquid subcooling. Significantly higher bubble nucleation rates were observed for both nanotube coated surfaces.

Bubble Dynamic Parameters and Pool Boiling Heat Transfer on Plasma Coated Tubes in Saturated R-134a and R-600a

2002 ◽  
Vol 124 (4) ◽  
pp. 704-716 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Chung-Guang Ke
Keyword(s):  
Heat Transfer ◽  
Saturation Temperature ◽  
Nucleation Site ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Bubble Dynamic ◽  
Porous Copper ◽  
R 134A ◽  
Coated Surfaces ◽  
Data Subject

An optical method for measuring the bubble dynamic data subject to an isolated bubble model is presented at low heat flux q⩽1kW/m2; while the operating heat fluxes are up to 30 kW/m2. By simultaneous measurements of departure diameters, velocities, frequencies and nucleation site densities, the heat transfer contribution of an individual active site is evaluated. A single phase heat transfer correlation was used to model the present heat transfer data. The test specimens consisted of tubes with porous copper (Cu) and molybdenum (Mo) plasma coated surfaces. The porosity (ε), the thickness of the porous layer (δ), and the mean pore diameter (η) of the tested tubes are the following: 0.055⩽ε⩽0.057,100⩽δ⩽300μm, and 3⩽η⩽4μm. The tests were carried out using R-134a and R-600a as working fluid at a saturation temperature of 18°C and with low and moderate heat fluxes (⩽1 kW/m2) for boiling visualization and related measurements (⩽30 kW/m2).

scholarly journals Pool Boiling Performance of Multilayer Micromeshes for Commercial High-Power Cooling

Micromachines ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 980
Author(s):  
Kairui Tang ◽  
Jingjing Bai ◽  
Siyu Chen ◽  
Shiwei Zhang ◽  
Jie Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Power ◽  
Rapid Development ◽  
Nucleate Boiling ◽  
Electronic Cooling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Commercial Applications

With the rapid development of electronics, thermal management has become one of the most crucial issues. Intense research has focused on surface modifications used to enhance heat transfer. In this study, multilayer copper micromeshes (MCMs) are developed for commercial compact electronic cooling. Boiling heat transfer performance, including critical heat flux (CHF), heat transfer coefficients (HTCs), and the onset of nucleate boiling (ONB), are investigated. The effect of micromesh layers on the boiling performance is studied, and the bubbling characteristics are analyzed. In the study, MCM-5 shows the highest critical heat flux (CHF) of 207.5 W/cm2 and an HTC of 16.5 W(cm2·K) because of its abundant micropores serving as nucleate sites, and outstanding capillary wicking capability. In addition, MCMs are compared with other surface structures in the literature and perform with high competitiveness and potential in commercial applications for high-power cooling.

Nucleate Boiling and Critical Heat Flux From Protruded Chip Arrays During Flow Boiling

1993 ◽  
Vol 115 (1) ◽  
pp. 78-88 ◽  
Author(s):  
C. O. Gersey ◽  
I. Mudawar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Single Phase ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Subcooled Flow

The effects of chip protrusion on the forced-convection boiling and critical heat flux (CHF) of a dielectric coolant (FC-72) were investigated. The multi-chip module used in the present study featured a linear array of nine, 10 mm x 10 mm, simulated microelectronic chips which protruded 1 mm into a 20-mm wide side of a rectangular flow channel. Experiments were performed in vertical up flow with 5-mm and 2-mm channel gap thicknesses. For each configuration, the velocity and subcooling of the liquid were varied from 13 to 400 cm/s and 3 to 36° C, respectively. The nucleate boiling regime was not affected by changes in velocity and subcooling, and critical heat flux generally increased with increases in either velocity or subcooling. Higher single-phase heat transfer coefficients and higher CHF values were measured for the protruded chips compared to similar flush-mounted chips. However, adjusting the data for the increased surface area and the increased liquid velocity above the chip caused by the protruding chips yielded a closer agreement between the protruded and flush-mounted results. Even with the velocity and area adjustments, the most upstream protruded chip had higher single-phase heat transfer coefficients and CHF values for high velocity and/or highly-subcooled flow as compared the downstream protruded chips. The results show that, except for the most upstream chip, the performances of protruded chips are very similar to those of flush-mounted chips.

Enhanced Flow Boiling Over Open Microchannels With Uniform and Tapered Gap Manifolds

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Satish G. Kandlikar ◽  
Theodore Widger ◽  
Ankit Kalani ◽  
Valentina Mejia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Flow boiling in microchannels has been extensively studied in the past decade. Instabilities, low critical heat flux (CHF) values, and low heat transfer coefficients have been identified as the major shortcomings preventing its implementation in practical high heat flux removal systems. A novel open microchannel design with uniform and tapered manifolds (OMM) is presented to provide stable and highly enhanced heat transfer performance. The effects of the gap height and flow rate on the heat transfer performance have been experimentally studied with water. The critical heat fluxes (CHFs) and heat transfer coefficients obtained with the OMM are significantly higher than the values reported by previous researchers for flow boiling with water in microchannels. A record heat flux of 506 W/cm2 with a wall superheat of 26.2 °C was obtained for a gap size of 0.127 mm. The CHF was not reached due to heater power limitation in the current design. A maximum effective heat transfer coefficient of 290,000 W/m2 °C was obtained at an intermediate heat flux of 319 W/cm2 with a gap of 0.254 mm at 225 mL/min. The flow boiling heat transfer was found to be insensitive to flow rates between 40–333 mL/min and gap sizes between 0.127–1.016 mm, indicating the dominance of nucleate boiling. The OMM geometry is promising to provide exceptional performance that is particularly attractive in meeting the challenges of high heat flux removal in electronics cooling applications.

Microporous Coatings to Maximize Pool Boiling Heat Transfer of Saturated R-123 and Water

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Joo Han Kim ◽  
Ajay Gurung ◽  
Miguel Amaya ◽  
Sang Muk Kwark ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Microporous Coating ◽  
Plain Surface ◽  
Improved Performance

The present research is an experimental study for the enhancement of boiling heat transfer using microporous coatings. Two types of coatings are investigated: one that is bonded using epoxy and the other by soldering. Effects on pool boiling performance were investigated, of different metal particle sizes of the epoxy-based coating, on R-123 refrigerants, and on water. All boiling tests were performed with 1 cm × 1 cm test heaters in the horizontal, upward-facing orientation in saturated conditions at atmospheric pressure and under increasing heat flux. The surface enhanced by the epoxy-based microporous coatings significantly augmented both nucleate boiling heat transfer coefficients and critical heat flux (CHF) of R-123 relative to those of a plain surface. However, for water, with the same microporous coating, boiling performance did not improve as much, and thermal resistance of the epoxy component limited the maximum heat flux that could be applied. Therefore, for water, to seek improved performance, the solder-based microporous coating was applied. This thermally conductive microporous coating, TCMC, greatly enhanced the boiling performance of water relative to the plain surface, increasing the heat transfer coefficient up to ∼5.6 times, and doubling the CHF.

Comprehensive Comparisons Between Evaporation and Pool Boiling on Thin Micro Porous Coated Surfaces

2006 ◽  
Author(s):  
Chen Li ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Media ◽  
Heated Surface ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Coated Surfaces ◽  
Dry Out

The evaporation and pool boiling on micro porous coated surfaces have been shown to provide among the highest heat transfer rates achievable from any type of surfaces. The heat transfer modes in these surfaces, present a number of interesting similarities and also, some fundamental differences, which are the result of the liquid supply methods to the heated surface. For the evaporation from porous coated surfaces, the liquid return to the heated surface is assisted by the capillary pressure at the liquid-vapor interface; while for pool boiling, gravity is the principal driving force that rewets the surface. In order to better understand the physical phenomena that governs the flow behavior of both the liquid and vapor phases, and the heat transfer process inside the porous media, comprehensive comparisons between these return mechanisms and their respective characteristics, and the performance and the critical heat flux (CHF) for each have been made, based on similar physical situations. These systematic comparisons illustrate that at a lower heat flux, the evaporation and pool boiling curves are almost identical due to the similar heat transfer modes, i.e., convection and nucleate boiling. While with further increases in heat flux, the heat transfer performance of the evaporation on micro porous media is generally superior to pool boiling on an identical surface. This shift is believed to be due to the fact that for evaporation on micro porous media, the heat transfer mode is dominated by the film evaporation, while in pool boiling, it is principally the result of fully developed nucleate boiling. It was also observed that the impact of the effective thermal conductivity of the porous coating on pool boiling performance is larger than for evaporation heat transfer on the identical micro porous coated surfaces. In general, the experimental data indicated that the CHF for evaporation heat transfer is much higher than for pool boiling on the same surfaces. The mechanism of CHF for evaporation on porous coated surfaces is believed to be the capillary limit; while for pool boiling the limit is the result of the hydrodynamic instabilities. This difference in mechanisms is clearly demonstrated by the experimental observations, where initially, the dry out process of the porous coated surfaces during evaporation is gradual, while for pool boiling; the entire surface reaches dry out in a very short time. In addition, the sensitivity of the CHF to the thickness of the porous coatings at a constant volumetric porosity and pore size, as well as the various optimal volumetric porosity of the CHF at a given thickness, are clearly the results of the differences induced by the various CHF mechanisms.

scholarly journals Pool Boiling Performance of Water and Self-Rewetting Fluids on Hybrid Functionalized Aluminum Surfaces

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1058
Author(s):  
Matic Može ◽  
Viktor Vajc ◽  
Matevž Zupančič ◽  
Radek Šulc ◽  
Iztok Golobič
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Energy ◽  
Nucleate Boiling ◽  
Etching Time ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Functionalized Surfaces ◽  
Microstructured Surfaces ◽  
Aluminum Surfaces

The boiling performance of functionalized hybrid aluminum surfaces was experimentally investigated for water and self-rewetting mixtures of water and 1-butanol. Firstly, microstructured surfaces were produced via chemical etching in hydrochloric acid and the effect of the etching time on the surface morphology was evaluated. An etching time of 5 min was found to result in pitting corrosion and produced weakly hydrophilic microstructured surfaces with many microcavities. Observed cavity-mouth diameters between 3.6 and 32 μm are optimal for efficient nucleation and provided a superior boiling performance. Longer etching times of 10 and 15 min resulted in uniform corrosion and produced superhydrophilic surfaces with a micropeak structure, which lacked microcavities for efficient nucleation. In the second stage, hybrid surfaces combining lower surface energy and a modified surface microstructure were created by hydrophobization of etched aluminum surfaces using a silane agent. Hydrophobized surfaces were found to improve boiling heat transfer and their boiling curves exhibited a significantly lower superheat. Significant heat transfer enhancement was observed for hybrid microcavity surfaces with a low surface energy. These surfaces provided an early transition into nucleate boiling and promoted bubble nucleation. For a hydrophobized microcavity surface, heat transfer coefficients of up to 305 kW m−2 K−1 were recorded and an enhancement of 488% relative to the untreated reference surface was observed. The boiling of self-rewetting fluids on functionalized surfaces was also investigated, but a synergistic effect of developed surfaces and a self-rewetting working fluid was not observed. An improved critical heat flux was only obtained for the untreated surface, while a lower critical heat flux and lower heat transfer coefficients were measured on functionalized surfaces, whose properties were already tailored to promote nucleate boiling.

scholarly journals Flow boiling heat transfer coefficient of R-134a/R-290/R-600a mixture in a smooth horizontal tube

2008 ◽  
Vol 12 (3) ◽  
pp. 33-44 ◽  
Author(s):  
Raja Balakrishnan ◽  
Lal Dhasan ◽  
Saravanan Rajagopal
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer ◽  
R 134A

An investigation on in-tube flow boiling heat transfer of R-134a/R-290/R-600a (91%/4.068%/4.932% by mass) refrigerant mixture has been carried out in a varied heat flux condition using a tube-in-tube counter-flow test section. The boiling heat transfer coefficients at temperatures between -5 and 5?C for mass flow rates varying from 3 to 5 g/s were experimentally arrived. Acetone is used as hot fluid, which flows in the outer tube of diameter 28.57 mm, while the test fluid flows in the inner tube of diameter 9.52 mm. By regulating the acetone flow rate and its entry temperature, different heat flux conditions between 2 and 8 kW/m2 were maintained. The pressure of the refrigerant was maintained at 3.5, 4, and 5 bar. Flow pattern maps constructed for the considered operating conditions indicated that the flow was predominantly stratified and stratified wavy. The heat transfer coefficient was found to vary between 500 and 2200 W/m2K. The effect of nucleate boiling prevailing even at high vapor quality in a low mass and heat flux application is high-lighted. The comparison of experimental results with the familiar correlations showed that the correlations over predict the heat transfer coefficients of this mixture.

Experimental Study of Heat Transfer Enhancement in Pool Boiling by Using 2-Ethyl 1-Hexanol an Additive

2014 ◽  
Vol 592-594 ◽  
pp. 1601-1606 ◽  
Author(s):  
Sameer Sheshrao Gajghate ◽  
Anil R. Aacharya ◽  
Anil T. Pise ◽  
Ganesh S. Jadhav
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Optimum Level ◽  
Transfer Coefficients ◽  
Nichrome Wire

The addition of additives to the water is known to enhance boiling heat transfer. In the present investigation, boiling heat transfer coefficients are measured for Nichrome wire, immersed in saturated water with & without additive. An additive used is 2-Ethyl 1-Hexanol with varying concentrations in the range of 10-10000 ppm. Extensive experimentation of pool boiling is carried out above the critical heat flux. Boiling behavior i.e. bubble dynamics are observed at higher heat flux for nucleate boiling of water over wide ranges of concentration of additive in water. Results are encouraging and show that a small amount of surface active additive makes the nucleate boiling heat transfer coefficient considerably higher, and that there is an optimum additive (500-1000ppm) concentration for higher heat fluxes. An optimum level of enhancement is observed up to a certain amount of additive 500-1000ppm in the tested range. Thereafter significant enhancement is not observed. This enhancement may be due to change in thermo-physical properties i.e. mainly due to a reduction in surface tension of water in the presence of additive.

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