Laser Interferometric Investigation of the Microlayer Evaporation Phenomenon

1975 ◽  
Vol 97 (1) ◽  
pp. 88-92 ◽  
Author(s):  
C. M. Voutsinos ◽  
R. L. Judd
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
Heater Surface ◽  
Nucleate Boiling Heat Transfer ◽  
Interferometric Investigation ◽  
Microlayer Evaporation ◽  
Laser Interferometric

An experimental investigation is presented in which the growth and evaporation of the microlayer underlying a bubble forming on a glass heater surface has been studied using laser interferometry and high speed photography. The results presented for a single bubble indicate that the microlayer thickness is of the order of 5 μm. Subsequent analysis of these results confirms that the microlayer evaporation phenomenon is a significant heat transfer mechanism, representing approximately 25 percent of the total nucleate boiling heat transfer rate for the conditions investigated.

A Comprehensive Model for Nucleate Pool Boiling Heat Transfer Including Microlayer Evaporation

1976 ◽  
Vol 98 (4) ◽  
pp. 623-629 ◽  
Author(s):  
R. L. Judd ◽  
K. S. Hwang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Methylene Chloride ◽  
Significant Proportion ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
Evaporation Heat ◽  
Microlayer Evaporation

The results of an experimental investigation are presented in which dichloromethane (methylene chloride) boiling on a glass surface was studied using laser interferometry and high-speed photography. New data for active site density, frequency of bubble emission, and bubble departure radius were obtained in conjunction with measurements of the volume of microlayer evaporated from the film underlying the base of each bubble for various combinations of heat flux and subcooling. These results were used to support a model for predicting boiling heat flux incorporating microlayer evaporation, natural convection, and nucleate boiling mechanisms. Microlayer evaporation heat transfer is shown to represent a significant proportion of the total heat transfer for the range of heat flux and sub-cooling investigated.

Influence of System Pressure on Microlayer Evaporation Heat Transfer

1978 ◽  
Vol 100 (1) ◽  
pp. 49-55 ◽  
Author(s):  
H. S. Fath ◽  
R. L. Judd
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Methylene Chloride ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
High Speed Photography ◽  
System Pressure ◽  
Evaporation Heat ◽  
Microlayer Evaporation

Evaporation of the microlayer underlying a bubble during nucleate boiling heat transfer is experimentally investigated by boiling dichloromethane (methylene chloride) on an oxide coated glass surface using laser interferometry and high speed photography. The influence of system pressure (51.5 kN/m2—101.3 kN/m2) and heat flux (17 k W/m2—65 kW/m2) upon the active site density, frequency of bubble emission, bubble departure radius and the volume of the microlayer evaporated have been studied. The results of the present investigation indicate that the microlayer evaporation phenomenon is a significant heat transfer mechanism, especially at low pressure, since up to 40 percent of the total heat transport is accounted for by microlayer evaporation. This contribution to the overall heat transfer decreases with increasing system pressure and decreasing heat flux. The results obtained were used to support the model propounded by Hwang and Judd for predicting boiling heat flux incorporating microlayer evaporation, natural convection and transient thermal conduction mechanisms.

Variation of Superheat With Subcooling in Nucleate Pool Boiling

1991 ◽  
Vol 113 (1) ◽  
pp. 201-208 ◽  
Author(s):  
R. L. Judd ◽  
H. Merte ◽  
M. E. Ulucakli
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Constant Heat Flux ◽  
Heat Transfer Process ◽  
Heater Surface ◽  
Nucleate Boiling Heat Transfer ◽  
Microlayer Evaporation

An analysis is presented that explains the variation of superheat with subcooling that has been observed by a number of researchers investigating nucleate boiling heat transfer at constant heat flux. It is shown that superheat initially increases with increasing subcooling near saturated conditions because of the way in which changes in active site density and average bubble frequency with increasing subcooling affect the rate of heat removal from the heater surface by enthalpy transport and microlayer evaporation. As subcooling increases further, natural convection begins to play an increasingly important role in the heat transfer process. Ultimately, natural convection is able to accommodate the entire imposed heat flux, after which superheat decreases as subcooling increases. The success of the analysis in explaining the variation of superheat with subcooling suggests that the rate of the heat removal from the heater surface is completely determined by the mechanisms of enthalpy transport, natural convection, and microlayer evaporation.

Contribution of Microlayer Evaporation During Flow Boiling Inside Microchannels

2008 ◽  
Author(s):  
A. Mukherjee
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Cross Sectional ◽  
Thin Film Evaporation ◽  
Nucleate Boiling Heat Transfer ◽  
Microlayer Evaporation

Flow boiling through microchannels is characterized by nucleation and growth of vapor bubbles that fills the entire channel cross-sectional area. As the bubble nucleates and grows inside the microchannel, a thin film of liquid or a microlayer gets trapped between the bubble and the channel walls. The heat transfer mechanism present at the channel walls during flow boiling is studied numerically. These mechanisms are compared to the heat transfer mechanisms present during nucleate boiling and in a moving evaporating meniscus. It is shown that the thermal and the flow fields present inside the microchannels around the bubbles are fundamentally different compared to nucleate boiling or in a moving evaporating meniscus. It is explained that how thin film evaporation is responsible for creating an apparent nucleate boiling heat transfer mechanism inside the microchannels.

Experimental Study of Nucleate Boiling Heat Transfer Using Enhanced Space-Confined Structures

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Xuehu Ma ◽  
Chunjian Yu ◽  
Zhong Lan ◽  
Donghui Wang ◽  
Tao Bai
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
High Speed ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Large Area ◽  
Nucleation Sites ◽  
Nucleate Boiling Heat Transfer ◽  
Narrow Space ◽  
High Superheat

For narrow space boiling, it is difficult to release bubbles from the narrow space, especially on a large-area surface. To solve this problem, a new structure is designed in the present paper. An experimental study of pool boiling on the novel copper enhanced structure, with the separate ordinary confined spaces and the open channels between them, was conducted with water and ethanol. High-speed visualizations are performed to elucidate the bubble flow. The results show that the boiling performance of both water and ethanol can be enhanced effectively. The visualizations indicated that most active nucleation sites emerged in the confined channels and rarely appeared at the bare surfaces not covered by enhanced structures even at high superheat. The bubble diameter, the bubble departure frequency, and the numbers of nucleation sites are obtained using statistical methods. The results suggest that the magnitudes of bubble diameter of water are almost the same on the smooth and enhanced surfaces. The amount of nucleation sites on the enhanced surfaces is remarkably increased, indicating its key role in the boiling enhancement of water. The bubble departure frequency is increased on one of the enhanced surfaces while not increased on another, showing that it is also a significant factor for heat transfer enhancement under certain conditions. While for ethanol, all the three parameters are increased on the enhanced surfaces.

Bubble Ebullition on a Hydrophilic Surface

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Aritra Sur ◽  
Yi Lu ◽  
Carmen Pascente ◽  
Paul Ruchhoeft
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Working Fluid ◽  
Hydrophilic Surface ◽  
Nucleate Boiling Heat Transfer ◽  
Nucleate Bubble

Nucleate boiling heat transfer depends on various aspects of the bubble ebullition, such as the bubble nucleation, growth and departure. In this work, a synchronized high-speed optical imaging and infrared (IR) thermography approach was employed to study the ebullition process of a single bubble on a hydrophilic surface. The boiling experiments were conducted at saturated temperature and atmospheric pressure conditions. De-ionized (DI) water was used as the working fluid. The boiling device was made of a 385-um thick silicon wafer. A thin film heater was deposited on one side, and the other side was used as the boiling surface. The onset of nucleate boiling (ONB) occurs at a wall superheat of ΔTsup= 12 °C and an applied heat flux of q" = 35.9 kW/m2. The evolution of the wall heat flux distribution was obtained from the IR temperature measurements, which clearly depicts the existence of the microlayer near the three-phase contact line of the nucleate bubble. The results suggest that, during the bubble growth stage, the evaporation in the microlayer region contributes dominantly to the nucleate boiling heat transfer; however, once the bubble starts to depart from the boiling surface, the microlayer quickly vanishes, and the transient conduction and the microconvection become the prevailing heat transfer mechanisms.

Experimental Observations of the Microlayer in Vapor Bubble Growth on a Heated Solid

1983 ◽  
Vol 105 (3) ◽  
pp. 625-632 ◽  
Author(s):  
L. D. Koffman ◽  
M. S. Plesset
Keyword(s):  
High Speed ◽  
Time History ◽  
Laser Interferometry ◽  
Nucleate Boiling ◽  
Thickness Change ◽  
Transfer Rates ◽  
High Speed Cinematography ◽  
History Of ◽  
Microlayer Evaporation ◽  
Fringe Patterns

Experimental measurements of microlayer formation and of the time history of microlayer thickness change have been obtained for nucleate boiling of water and ethanol. These detailed measurements were obtained using laser interferometry combined with high-speed cinematography. The measurement technique is discussed in detail with emphasis on the difficulties encountered in interpretation of the fringe patterns. The measurements for water can be reasonably applied to the data of Gunther and Kreith, in which case it is concluded that microlayer evaporation alone cannot account for the increased heat transfer rates observed in highly subcooled nucleate boiling. It appears that microconvection must play at least an equal role.

Saturation Boiling of HFE-7000 Liquid on Inclined Rough Copper Surfaces

2020 ◽  
Author(s):  
Mohamed S. El-Genk ◽  
Mahyar Pourghasemi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Nucleate Boiling ◽  
Average Roughness ◽  
Copper Surfaces ◽  
Nucleate Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

Abstract Pool boiling experiments are performed to investigate the effects of inclination angle, θ, and average roughness, Ra, of uniformly heated 10 × 10 mm copper surfaces on saturation boiling of HFE-7000 dielectric liquid. Ra varied from 0.039 to 0.1.44 μm and θ from 0° (upward facing) to 180° (downward facing). In addition, high speed images and still photographs of nucleate boiling in the various regions and near CHF are captured to assist the interpretation of experimental results. The values of CHF and the maximum nucleate boiling heat transfer coefficient, hMNB, which occurs near the fully developed nucleate boiling region, increase with increasing Ra and/or decreasing θ. The corresponding surface superheats, however, decrease with increasing θ and/or Ra. In the upward facing orientation, CHF increases from ∼20.7 to ∼30.9 W/cm2 with increasing Ra from 0.039 to 0.144 μm, and the corresponding CHF values in the downward facing orientation are 7.1 and 8.9 W/cm2, respectively. Nucleate boiling heat transfer coefficient, hNB, in the discrete bubbles region at low surface superheats increases, while in the fully developed nucleate boiling region at high superheats it increases with increasing Ra and/or decreasing θ. The developed correlations for CHF and hMNB and corresponding superheats, as functions of Ra and θ, are in good agreement with the experimental data.

Study on Pool-Nucleate Boiling Heat Transfer Characteristics by Using Artificial Cavities

2006 ◽  
Author(s):  
Ryo Hateruma ◽  
Takato Sato ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Natural Circulation ◽  
Nucleate Boiling ◽  
Heat Transfer Surface ◽  
Finished Surface ◽  
Nucleate Boiling Heat Transfer ◽  
Mems Technology ◽  
Artificial Cavity

Pool boiling heat transfer experiments were performed by using the well-controlled/defined heat transfer surface for water. Uni-size and -shape artificial cavities were created on the mirror-finished silicon plate by utilizing the MEMS technology. Experimental results agreed well with what were predicted by the traditional boiling theory. The mirror-finished surface showed only the tendency of natural circulation heat transfer. The artificial-cavity heat transfer surface followed the pool-nucleate boiling trend. The onset of the pool-nucleate boiling was well predicted by the traditional pool-nucleate boiling theory. These results indicated that the artificial cavities behave just like natural cavities. The results indicated the artificial cavities are quite useful and promising to examine the true features of complicated boiling that have been overshadowed by complicatedness. From recorded high speed video pictures, the coalescence of bubbles that were growing on the cavities were classified into four categories; the normal lift (no coalescence), the vertical coalescence, the declining coalescence and the horizontal coalescence. As the cavity interval was increased, the horizontal coalescence decreases to zero, the vertical coalescence also decreases, and on the contrary to these, vertical coalescence and normal lift increase. The cavity interval 3 mm (S/Lc ≈ 1.2) seemed to be the border whether the horizontal coalescence occurs or not.

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