INTERACTIONS BETWEEN HEAT TRANSFER AND BUBBLE FORMATION IN NUCLEATE BOILING

1998 ◽  
Author(s):  
Dieter Gorenflo ◽  
Andrea Luke ◽  
Elisabeth Danger
Keyword(s):  
Heat Transfer ◽  
Bubble Formation ◽  
Nucleate Boiling

Numerical Study of Bubble Growth on a Micro-Finned Surface

2011 ◽  
Author(s):  
Woorim Lee ◽  
Gihun Son
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Removal Rate ◽  
Bubble Formation ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
Finned Surface ◽  
Fin Spacing

Bubble growth on a micro-finned surface, which can be used in enhancing boiling heat transfer, is numerically investigated by solving the conservation equations of mass, momentum, and energy. The bubble deformation or the liquid-vapor interface is determined by the sharp-interface level-set method, which is modified to include the effect of phase change and to treat the contact angle and the evaporative heat flux from the liquid microlayer on an immersed solid surface of a microfin. The numerical method is applied to clarify bubble growth and heat transfer characteristics on a surface including fin and cavity during nucleate boiling which have not been provided from the previous experimental studies. The effects of single fin, fin-cavity distance, and fin-fin spacing on the bubble dynamics are investigated. The micro-fin is found to affect the activation of cavity. The fin-cavity configuration is found to determine the bubble formation in a cavity. The vapor removal rate is also observed to significantly depend on the fin-fin spacing.

A Compact Nanostructure Integrated Pool Boiler for Microscale Cooling Applications

2009 ◽  
Author(s):  
Muhsincan S¸es¸en ◽  
Cem Baha Akkartal ◽  
Wisam Khudhayer ◽  
Tansel Karabacak ◽  
Ali Kos¸ar
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
High Efficiency ◽  
Cooling System ◽  
Bubble Formation ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
External Energy ◽  
Excessive Heat ◽  
Aluminum Base

An efficient cooling system consisting of a plate, on which copper nanorods (nanorods of size ∼100nm) are integrated to copper thin film (which is deposited on Silicon substrate), a heater, an Aluminum base, and a pool was developed. Heat is transferred with high efficiency to the liquid within the pool above the base through the plate by boiling heat transfer. Near the boiling temperature of the fluid, vapor bubbles started to form with the existence of wall superheat. Phase change took place near the nanostructured plate, where the bubbles emerged from. Bubble formation and bubble motion inside the pool created an effective heat transfer from the plate surface to the pool. Nucleate boiling took place on the surface of the nanostructured plate helping the heat removal from the system to the liquid above. The heat transfer from nanostructured plate was studied using the experimental setup. The temperatures were recorded from the readings of thermocouples, which were successfully integrated to the system. The surface temperature at boiling inception was 102.1°C without the nanostructured plate while the surface temperature was successfully decreased to near 100°C with the existence of the nanostructured plate. In this study, it was proved that this device could have the potential to be an extremely useful device for small and excessive heat generating devices such as MEMS or Micro-processors. This device does not require any external energy to assist heat removal which is a great advantage compared to its counterparts.

Macro- to Microscale Boiling Heat Transfer From Metal-Graphite Composite Surfaces

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Wen-Jei Yang ◽  
Nengli Zhang ◽  
Daniel L. Vrable
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Boiling Heat Transfer ◽  
Thermal Hysteresis ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Transfer Enhancement ◽  
Bubble Generation ◽  
Composite Surface ◽  
Graphite Composite

This paper introduces a novel heat transfer enhancement surface, referred to as metal-graphite composite surface. It is comprised of high thermal conductivity graphite microfibers interspersed within a metal matrix (copper or aluminum) to enhance the bubble formation at the nucleation sites, and significantly improve the nucleate boiling heat transfer. Experiments revealed that its boiling heat transfer enhancement is comparable or in some respect even superior to the commercially available boiling heat transfer enhancement surfaces such as porous boiling surface and integral roughness surface. In addition, it does not result in any extra pressure loss and it minimizes surface fouling. Macro- to microscale heat transfer phenomena of the composite surfaces is treated. Discussions include characteristics of the surface, enhancement mechanisms, critical heat flux, boiling thermal hysteresis, bubble generation, growth and departure, and applications in electronic cooling, and under reduced gravity conditions.

Effects of Pore Diameters and System Pressure on Saturated Pool Nucleate Boiling Heat Transfer From Porous Surfaces

1982 ◽  
Vol 104 (2) ◽  
pp. 286-291 ◽  
Author(s):  
W. Nakayama ◽  
T. Daikoku ◽  
T. Nakajima
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
High Heat ◽  
Porous Surface ◽  
Operational Parameters ◽  
High Heat Transfer ◽  
System Pressure ◽  
Nucleate Boiling Heat Transfer

The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11. Boiling curves and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150 μm, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1, 0.23 MPa. The boiling curves exhibit certain trends effected by the diameter and population density of pores. A combination of high system pressure and pore sizes of 100 or 150 μm dia enables boiling to persist even when the wall superheat is reduced to an extremely low level of 0.1 K. A noteworthy feature of porous surface boiling is that intense bubble formation does not necessarily yield a high heat-transfer performance. Examination of the data indicates that liquid suction and evaporation inside the cavities are a proable mechanism of boiling with small temperature differences.

Heat Transfer Mechanisms of Propane Boiling on Horizontal Steel Tubes With Smooth and Enhanced Surfaces

2010 ◽  
Author(s):  
A. Luke ◽  
Bjo¨rn C. F. Mu¨ller
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mild Steel ◽  
Transfer Coefficient ◽  
Steel Surface ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Mild Steel Surface ◽  
The Heat Transfer Coefficient

The trend towards a better understanding of the fundamentals of nucleate boiling in re-entrant cavities is supported by the variation of the heating surface’s characteristics and the identification of parameters influencing the heat transfer at enhanced tubes. The optimized surface of enhanced evaporator tubes supports the bubble formation by providing stable nucleation sites, which are cavities that trapped the necessary amount of vapor to generate the next bubble. The optimal size of the cavities for bubble formation depends on various thermodynamic properties of the fluid and the wall material. The knowledge of these physical mechanisms is important for the further optimization. The influence of micro- and macrostructures on the overall heat transfer coefficient is investigated with the refrigerant R134a and the hydrocarbon propane (R290) boiling in a wide range of reduced pressures (p* = ps/pc = 0.03 to 0.5) and heat fluxes (0.05 to 100 kW/m2). The measurements are carried out using a standard apparatus and a horizontally positioned, electrically heated surface with various wall materials. Two different materials — copper and mild steel — with the same surface preparation by polishing are investigated. Furthermore, heat transfer measurements are carried out on a plain mild steel tube and on an industrially manufactured surface of the GEWA-PB type. The polished surfaces demonstrate a deterministic microstructure, the roughness parameters depends strongly on the measurement direction. The heat transfer coefficient as function of the heat flux of the polished copper tube can be described by the correlation of the VDI Heat Atlas, while the mild steel surface differ from former investigations due to the deep re-entrant cavities remaining from the drawn surface. The onset of boiling is nearly the same of both materials because of these cavities on the mild steel surface. As presented in the recent years, the heat transfer of nucleate boiling at tubes with subsurface channels can be divided into different domains, each influenced by different parameters like wettability, the product of vapor density and evaporation enthalpy. The identification of parameters influencing the bubble formation is done by heat transfer measurements, high-speed-video recording and photographic documentation. The experimental results of this work are compared to results of the polished surfaces. The heat transfer coefficient increases drastically for the enhanced tube, especially for beginning nucleation. The same α-q-relationship as on plain tubes is observed for higher pressures and heat fluxes but for three times higher values of the heat transfer coefficient α.

Dynamic Model of Enhanced Boiling Heat Transfer on Porous Surfaces—Part I: Experimental Investigation

1980 ◽  
Vol 102 (3) ◽  
pp. 445-450 ◽  
Author(s):  
W. Nakayama ◽  
T. Daikoku ◽  
H. Kuwahara ◽  
T. Nakajima
Keyword(s):  
Heat Transfer ◽  
Dynamic Model ◽  
Boiling Heat Transfer ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Vital Role ◽  
Structured Surfaces ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer ◽  
Enhanced Boiling

Enhancement of nucleate boiling heat transfer has been studied with the structured surfaces composed of interconnected internal cavities in the form of tunnels and small pores connecting the pool liquid and the tunnels. The boiling curves of R-11, water and nitrogen show 80 to 90 percent reduction of wall superheat required to transfer the same heat flux as that on plain surfaces, when the pore diameter is set around 0.1 mm. The experimental data on bubble formation showed a significant contribution of latent heat transport to the enhancement. A visualization study made with a transparent structured model suggested that the liquid suction into the tunnel is triggered by the bubble growth at active pores and subsequent evaporation inside the tunnel plays a vital role in driving the bubble formation cycle. This observation led to a conception of the dynamic model expounded in Part II.

The Influence of Subcooling on the Frequency of Bubble Emission in Nucleate Boiling

1989 ◽  
Vol 111 (3) ◽  
pp. 747-751 ◽  
Author(s):  
R. L. Judd
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Surface Area ◽  
Boiling Heat Transfer ◽  
Heat Load ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Transfer Model ◽  
Emission Frequency

The experimental results reported in Ibrahim and Judd (1985) in which bubble period first increased and then decreased as subcooling varied over the range 0 ≤ θsat ≤ 15° C is interpreted by means of a comprehensive boiling heat transfer model incorporating the contributions of nucleate boiling, natural convection, and micro-layer evaporation components. It is shown that bubble emission frequency varies to accommodate the impressed heat load in the manner described above because changes in subcooling cause the heat flux within the area influenced by the formation and departure of bubbles to change in the opposite sense to the fraction of the surface area within which bubble formation and departure occurs. The mechanism responsible for the nucleation of bubbles at exactly the frequency required at each level of subcooling is the object of continuing research.

The Effect of Dissolving Gases or Solids in Water Droplets Boiling on a Hot Surface

2001 ◽  
Vol 123 (4) ◽  
pp. 719-728 ◽  
Author(s):  
Qiang Cui ◽  
Sanjeev Chandra ◽  
Susan McCahan
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Sodium Bicarbonate ◽  
Sodium Carbonate ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Water Droplets ◽  
Dissolved Carbon ◽  
Dissolved Carbon Dioxide ◽  
Dissolved Salts

We conducted experiments on the effect of dissolving either a gas (carbon dioxide) or a solid salt (sodium carbonate or sodium bicarbonate) in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 100°C to 300°C. We recorded the boiling of droplets with a video system, and photographed droplet impact using short-duration flash photography. At surface temperatures that were too low to initiate nucleate boiling, dissolved salts were found to reduce the evaporation rate since they lower the vapor pressure of water. Dissolved gas had the opposite effect: it came out of solution and formed bubbles in the liquid, enhancing evaporation. In the nucleate boiling regime dissolved carbon dioxide enhanced heat transfer by a small amount. However, sodium carbonate prevented coalescence of vapor bubbles and produced foaming in the droplet, greatly enhancing heat transfer and reducing the droplet lifetime to approximately half that of a pure water drop. Sodium bicarbonate, which decomposes to give carbon dioxide and sodium carbonate when heated, produced an even larger enhancement of heat transfer. When the surface temperature was raised above the Leidenfrost temperature of water, droplets went into film boiling and bounced off the surface following impact. Dissolved carbon dioxide was found to suppress heterogeneous bubble formation in the droplet during impact. However, dissolved salts promoted bubble formation and led to droplet break-up during impact.

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