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.

Characteristics of Pool Boiling Bubble Dynamics in Bead Packed Porous Structures

2009 ◽  
Author(s):  
Calvin H. Li ◽  
Ting Li ◽  
Paul Hodgins ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Heating Surface ◽  
Theoretical Models ◽  
Porous Structures ◽  
Pool Boiling Heat Transfer ◽  
Simulation Results

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. At low heat flux of 18.9 kW/m2, a single spherical bubble formed at nucleation sites of a heating surface and departed to the interstitial spaces of porous structure. When heat flux increased to 47 kW/m2, a single bubble grew into a Y shape between beads layers and connected with others to generate a horizontal vapor column. As heat flux reached 76.3 kW/m2, vertical vapor columns obtained strong momentum to form several major vapor escaping arteries, and glass beads were pushed upward by the vapor in the escaping arteries. According to Zuber’s hydrodynamics theory, choking will take place when the size of vapor columns reaches a certain value that is comparable to the critical hydrodynamic wavelength of the vapor column in plain surface pool boiling. The experimental and simulation results of this investigation illustrated that, under the geometric constrains of bead packed porous structures, similar characteristics had been induced to trigger the earlier occurrence of vapor column chocking inside porous structures. 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 to that in a plain surface situation at low heat flux situations, and could trigger the earlier occurrence of critical heat flux (CHF) by trapping the vapor into interstitial space and forming a vapor column net. 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 Characteristics of Inclined pHEMA-Coated Surfaces

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Abdolali Khalili Sadaghiani ◽  
Ahmad Reza Motezakker ◽  
Alsan Volkan Özpınar ◽  
Gözde Özaydın İnce ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Surface Orientation ◽  
Maximum Enhancement ◽  
Pool Boiling Heat Transfer ◽  
Coated Surfaces

New requirements for heat exchangers offered pool boiling heat transfer on structured and coated surfaces as one of the promising methods for effective heat removal. In this study, pool boiling experiments were conducted on polyhydroxyethylmethacrylate (pHEMA)-coated surfaces to investigate the effect of surface orientation on bubble dynamics and nucleate boiling heat transfer. pHEMA coatings with thicknesses of 50, 100, and 200 nm were deposited using the initiated chemical deposition (iCVD) method. De-ionized water was used as the working fluid. Experiments were performed on horizontal and inclined surfaces (inclination angles of 10 deg, 30 deg, 50 deg, and 70 deg) under the constant heat flux (ranging from 10 to 80 kW/m2) boundary condition. Obtained results were compared to their plain surface counterparts, and heat transfer enhancements were observed. Accordingly, it was observed that the bubble departure phenomenon was affected by heat flux and wall superheat on bare silicon surfaces, while the supply path of vapor altered the bubble departure process on pHEMA-coated surfaces. Furthermore, the surface orientation played a major role on bubble dynamics and could be considered as a mechanism for fast vapor removal from surfaces. Bubble coalescence and liquid replenishment on coated surfaces had a promising effect on heat transfer coefficient enhancement on coated surfaces. For horizontal surfaces, a maximum enhancement of 25% relative to the bare surface was achieved, while the maximum enhancement was 105% for the inclined coated surface under the optimum condition. iCVD was proven to be a practical method for coating surfaces for boiling heat transfer applications due to the obtained promising results.

Pool Boiling Heat Transfer of Water on Copper Surfaces With Nanoparticles Coating

2017 ◽  
Author(s):  
Zhen Cao ◽  
Calle Preger ◽  
Zan Wu ◽  
Sahar Abbood ◽  
Maria E. Messing ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Deposition Time ◽  
Pool Boiling ◽  
Working Fluid ◽  
High Heat Flux ◽  
Pool Boiling Heat Transfer

Saturated pool boiling heat transfer is investigated experimentally on a copper substrate with copper nanoparticle coatings at atmospheric pressure, in terms of critical heat flux (CHF) and heat transfer coefficient (HTC). Experiments are carried out on the substrate surface with a diameter of 12 mm using DI water as the working fluid. The coating is formed by stacking copper nanoparticles generated by an aerosol method. The aerosol nanoparticles are generated by a spark discharge generator with nitrogen gas as carrier gas and size-selected prior to electrostatic deposition. The thickness of the coating is quantified by the deposition time. In the present study, copper particles with diameter 35± 5 nm are selected, considering better coverage on the surface, while the deposition time is controlled as 4h and 8h, respectively. The boiling curves and heat transfer coefficient of MS-1 (4h deposition) and MS-2 (8h deposition) were compared with the BS (bare surface). The results show that CHFs of MS-1 and MS-2 are increased by 24% and 36%, respectively compared with the BS, while heat transfer is enhanced as well. High speed visualization tells that the coating provides more active nucleate sites and the hydrophobicity of the coating helps bubbles departure from the surface at low and moderate heat flux. At high heat flux, a hollow well occurs on MSs to supply liquid effectively to avoid dryout. Therefore, CHF and heat transfer are both improved.

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.

Nucleate Pool Boiling Heat Transfer of R134a and R134a-PVE Lubricant Mixtures on Smooth and Five Enhanced Tubes

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Wen-Tao Ji ◽  
Ding-Cai Zhang ◽  
Nan Feng ◽  
Jian-Fei Guo ◽  
Mitsuharu Numata ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Enhanced Tubes ◽  
Mass Fractions

Pool boiling heat transfer coefficients of R134a with different lubricant mass fractions for one smooth tube and five enhanced tubes were tested at a saturation temperature of 6°C. The lubricant used was polyvinyl ether. The lubrication mass fractions were 0.25%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 7.0%, and 10.0%, respectively. Within the tested heat flux range, from 9000 W/m2 to 90,000 W/m2, the lubricant generally has a different influence on pool boiling heat transfer of these six tubes.

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