Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Dwight Cooke ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Silicon Chips ◽  
Heat Of Evaporation

Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. It was determined that surface modifications to silicon chips can improve the heat transfer coefficient by a factor up to 3.4 times the performance of a plain chip. Surfaces with microchannels have shown to be efficient for boiling heat transfer by allowing liquid to flow through the open channels and wet the heat transfer surface while vapor is generated. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.

Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

2010 ◽  
Author(s):  
Dwight Cooke ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Electronic Cooling ◽  
High Heat Flux ◽  
Heat Of Evaporation ◽  
Cooling Ability

Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.

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.

Characteristics of Pool Boiling Bubble Dynamics in Bead Packed Porous Structures

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Calvin H. Li ◽  
Ting Li ◽  
Paul Hodgins ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Computer Simulation ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Theoretical Models ◽  
High Heat Flux ◽  
Porous Structures ◽  
Pool Boiling Heat Transfer

Spherical glass and copper beads have been used to create bead packed porous structures for an investigation of two-phase heat transfer bubble dynamics under geometric constraints. The results demonstrated a variety of bubble dynamics characteristics under a range of heating conditions. The bubble generation, growth, and detachment during the nucleate pool boiling heat transfer have been filmed, the heating surface temperatures and heat flux were recorded, and theoretical models have been employed to study bubble dynamic characteristics. Computer simulation results were combined with experimental observations to clarify the details of the vapor bubble growth process and the liquid water replenishing the inside of the porous structures. This investigation has clearly shown, with both experimental and computer simulation evidence, that the millimeter scale bead packed porous structures could greatly influence pool boiling heat transfer by forcing a single bubble to depart at a smaller size, as compared with that in a plain surface situation at low heat flux situations, and could trigger the earlier occurrence of critical heat flux by trapping the vapor into interstitial space and forming a vapor column net at high heat flux situations. The results also proved data for further development of theoretical models of pool boiling heat transfer in bead packed porous structures.

Pool Boiling Heat Transfer on Vertical Micro Porous Coated Surface in Confined Space

2008 ◽  
Author(s):  
Chien-Yuh Yang ◽  
Chien-Fu Liu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Confined Space ◽  
Pool Boiling Heat Transfer ◽  
Coated Surface

Attributed to its high heat transfer coefficient, evaporating cooling involving the use of micro heat exchangers is considered a possible thermal management solution for cooling of high heat flux electronic devices. The present work desires to develop high-performance micro heat exchangers operating in the evaporation regime. The pool boiling heat transfer performance on one plain plate and one micro porous coated plate were tested in a vertical open and a 1-mm confined spaces. The test results show that the heat transfer was enhanced by the confined space at low and moderate heat fluxes but degraded at high flux condition on plain surface. The micro porous coating may significantly enhance the pool boiling performance. However, the heat transfer characteristic in confined space is not exactly the same as that on open surfaces. Owing to the interaction of forced removal of the superheated liquid due to the bubble departure and retard the departure of bubbles by the confined plate, there is no much difference for pool boiling heat transfer on micro porous coated surface in confined and unconfined spaces at low and moderate heat fluxes. At high heat flux, large amount of bubbles were confined by the cover plate. This caused the partial dry out and significant degrade on heat transfer performance.

Nanofluid Boiling Heat Transfer and Critical Heat Flux Enhancement: Mechanism to Be Revealed

2013 ◽  
Author(s):  
Junmei Wu ◽  
Jiyun Zhao ◽  
Yun Wang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Bubble Dynamics ◽  
High Heat ◽  
Solid Particles ◽  
High Heat Flux ◽  
Transfer Performance

As a novel strategy to improve heat transfer characteristics of fluids by the addition of solid particles with diameters below 100 nm, nanofluids exhibits unprecedented heat transfer properties and are being considered as potential working fluids to be used in high heat flux systems such as nuclear reactors, electronic cooling systems and solar collectors. The present paper reviews the state-of-the-art studies on nanofluid boiling heat transfer performance and critical heat flux (CHF) enhancement. It is found that some results on nanofluids boiling heat transfer performance are inconsistent or contradictory in data published. The knowledge on the mechanism of nanofluids boiling CHF enhancement is insufficient. Bubble dynamics of nanofluids boiling is suggested to be investigated to identify the exact contributions of solid surface modifications and suspended nanoparticles to CHF enhancement in nanofluids boiling heat transfer.

Pool Boiling Heat Transfer Augmentation in a Novel Aqueous Binary Mixture of Surfactants

2020 ◽  
Author(s):  
Prashant Pawar ◽  
Abdul Najim ◽  
Anil Acharya ◽  
Ashok Pise
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Flux ◽  
Binary System ◽  
Binary Mixture ◽  
Bubble Growth ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
High Heat Flux

Abstract This paper investigates the augmentation of heat transfer during pool boiling in a novel aqueous binary mixture of surfactants. The surfactants used were Sodium Dodecyl Sulphate (anionic), Centrimonium Bromide (cationic), and Nicotine (non-ionic). The aqueous binary mixtures SDS-CTAB, CTAB- Nicotine, and SDS-Nicotine were prepared on the volume percentage basis. The augmentation was investigated by studying a single bubble growth in an aqueous binary mixture of surfactants. The investigation was conducted at two values of heat fluxes to probe the effect of heat flux on bubble growth. A reduction in surface tension was attained by SDS-CTAB, CTAB-Nicotine, and SDS-Nicotine aqueous binary systems compared to its individual aqueous surfactant solutions at their optimum concentrations. The most significant surface tension result was obtained by the novel SDS-Nicotine aqueous binary system at 25:75 volume percentages. A decrement in the bubble departure diameter and an increment in the release frequency were observed for SDS-Nicotine aqueous binary system both heat fluxes. The boiling heat transfer coefficient of SDS-Nicotine aqueous binary system was found to be increased by 36.32% and 58.67% compared to saturated water at low and high heat flux, respectively.

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

Observations of the Critical Heat Flux Process During Pool Boiling of FC-72

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
J. Jung ◽  
S. J. Kim ◽  
J. Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
High Heat ◽  
Line Length ◽  
Boiling Curve ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Ir Camera

Experimental work was undertaken to investigate the process by which pool-boiling critical heat flux (CHF) occurs using an IR camera to measure the local temperature and heat transfer coefficients on a heated silicon surface. The wetted area fraction (WF), the contact line length density (CLD), the frequency between dryout events, the lifetime of the dry patches, the speed of the advancing and receding contact lines, the dry patch size distribution on the surface, and the heat transfer from the liquid-covered areas were measured throughout the boiling curve. Quantitative analysis of this data at high heat flux and transition through CHF revealed that the boiling curve can simply be obtained by weighting the heat flux from the liquid-covered areas by WF. CHF mechanisms proposed in the literature were evaluated against the observations.

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