Experimental Study on Fundamental Phenomena of Boiling Using Heat Transfer Surfaces With Well-Defined Cavities Created by MEMS (Effect of Spacing Between Cavities)

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Takato Sato ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Microelectromechanical Systems ◽  
Nucleate Boiling ◽  
Radiation Thermometer ◽  
Heat Transfer Surface ◽  
Bubble Coalescence ◽  
Back Side ◽  
Nucleation Sites ◽  
Nucleate Boiling Heat Transfer ◽  
Cylindrical Holes

Pool nucleate boiling heat transfer experiments were performed for water using heat transfer surfaces having unified cavities. Cylindrical holes of 10μm in diameter and 40μm in depth were formed on a mirror-finished silicon wafer of 0.525mm in thickness using Microelectromechanical systems technology. The test heat transfer surface was heated by a semiconductor laser beam. Experiments were conducted in the range of up to 4.54×104W∕m2. The temperature of the back side of the heat transfer surface was measured by a radiation thermometer. When the spacing between cavities was S∕Lc<0.8, the horizontal and declining coalescence of bubbles on the neighboring cavities were dominant. Strong thermal and bubble coalescence interactions between nucleation sites were observed in this situation. This vigorous bubble coalescence created strong convection. The heat carried by this convection accounted for a large part of the heat transfer. As the cavity interval became wide, S∕Lc≥1.2, the horizontal and the declining coalescence of the bubbles ceased. The coalescence was limited to the vertical or no coalescence. The thermal and bubble coalescence interactions between the nucleation sites became quite low, to the extent of being negligible. The bubbles themselves were key in carrying heat away from the heat transfer surface.

Experimental Study on Fundamental Phenomena of Boiling by Using Heat Transfer Surface With Well-Defined Cavities Created by MEMS: The Effect of Spacing Between Cavities

2006 ◽  
Author(s):  
Takato Sato ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Micro Electro Mechanical System ◽  
Heat Transfer Surface ◽  
Cylindrical Shape ◽  
Main Role ◽  
Nucleate Boiling Heat Transfer ◽  
Mems Technology ◽  
Strong Convection ◽  
Artificial Cavity

Pool nucleate boiling heat transfer experiments were performed for water by using the well-controlled and -defined heat transfer surfaces. Artificial cavity(ies) was (were) created on the mirror-finished silicon plate of 0.525 mm thickness by utilizing the Micro-Electro Mechanical System (MEMS) technology. Each cavity had cylindrical shape. The diameter and the depth of the cavity were 10μm and 40μm, respectively. Experiments were performed in a range of a heat flux ∼6.0 × 104 W/m2 for distilled water. When the cavity interval was close, the horizontal and declining coalescence of bubble on the cavities were dominant. This vigorous bubble coalescence created strong convection. The heat carried by this convection took a main part in the heat transfer when cavities were close. As the cavity interval became wide, the horizontal and declining coalescence did not take place anymore. The coalescence was limited only to the vertical lift or no coalescence. In this situation, bubbles grew large on the cavities and absorbed latent heat sufficiently. Bubbles themselves took the main role of carrying heat away from the heat transfer surface when cavities were further apart.

Experimental Study on Behavior of Bubbles and Temperature Fluctuation of Heat Transfer Surface by Using Heat Transfer Surface With Artificial Cavities Created by MEMS Technology

2009 ◽  
Author(s):  
Takato Sato ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Correlation Coefficients ◽  
Side Surface ◽  
Nucleate Boiling ◽  
Heat Transfer Surface ◽  
Back Side ◽  
Mems Technology ◽  
Standard Deviations ◽  
Thermal Influence

Pool nucleate boiling heat transfer experiments were performed for water using heat transfer surfaces having a unified cavity. A single cylindrical hole of 10 μm in diameter and 40 μm in depth was formed on a mirror-finished silicon wafer of 0.2 mm in thickness using the Micro-Electro Mechanical Systems (MEMS) technology. This silicon plate was used as the heat transfer surface. The back side of the heat transfer surface was heated by a semi-conductor laser beam. The back-side surface temperature was measured by a radiation thermograph with a temperature resolution of 0.08 K and a time resolution of 3 ms/line. Experiments were conducted in the range up to 1.35 × 105 W/m2. The standard deviations of the local fluctuating heat transfer surface temperature were calculated. So the cross-correlation coefficients between the cavity center and a certain point were calculated by using the standard deviations and the time-series surface temperature data. Then, the intensity of the thermal influence exerted by the boiling bubbles on the local position was derived. The thermal influence extents determined from the intensity were 2.1 – 3.3 times larger than the mean diameter of all departure bubbles in the present experimental range.

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.

Study on Nucleate Boiling Heat Transfer by Measuring Spatially Instantaneous Local Surface Temperature and Observing Instantaneous Bubble/Liquid Fluid Behavior

2013 ◽  
Author(s):  
Yasuo Koizumi ◽  
Kenta Hayashi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Heat Transfer Surface ◽  
Bubble Generation ◽  
Three Phase ◽  
Nucleate Boiling Heat Transfer

Pool nucleate boiling heat transfer experiments were performed for water at 0.101 MPa to examine the elementary process of the nucleate boiling. Heat transfer surface was made from a copper printed circuit board. Direct current was supplied to heat it up. The Bakelite plate of the backside of a copper layer was taken off at the center portion of the heat transfer surface. The instantaneous variation of the backside temperature of the heat transfer surface was measured with an infrared radiation camera. Bubble behavior was recorded with a high speed video camera. In the isolated bubble region, surface temperature was uniform during waiting time. When boiling bubble generation started, a large dip in the surface temperature was formed under the bubble. After the bubble left from the heat transfer surface, the surface temperature returned to former uniform temperature distribution. Surface temperature was not affected by the bubble generation beyond 1.6 mm from the center of the bubble. In the isolated bubble region, a convection term was approximately 80 % in total heat transfer rate. The importance of the three-phase interface line in the heat transfer should be checked carefully. In the intermediate and high heat flux region, the variation of surface temperature and heat flux were small. Rather those were close to their average values even at critical heat flux condition. It seemed that the large part of the heat transfer surface was covered with water even at the critical heat flux condition. The heat flux at the area that appeared to be the three-phase contact line was not so high and close to the average heat flux.

Experimental Study on Nucleation Site Interaction During Pool Nucleate Boiling by Using Three Artificial Cavities

2008 ◽  
Author(s):  
Takato Sato ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Latent Heat ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Heat Transfer Surface ◽  
Main Role ◽  
Micro Electro Mechanical Systems ◽  
Nucleate Boiling Heat Transfer ◽  
Mems Technology

Pool nucleate boiling heat transfer experiments were performed for water using heat transfer surfaces having unified cavities. Cylindrical holes of 10 μm in diameter and 40 μm in depth were formed on a mirror-finished silicon wafer of 0.2 mm in thickness using Micro-Electro Mechanical Systems (MEMS) technology. This silicon plate was used as the heat transfer surface. The test heat transfer surface was heated by a semiconductor laser beam. Experiments were conducted in the range of up to 1.35 × 105 W/m2. When the cavity spacing was narrow such as S = 1 or 2 mm, the convection created by the departure of coalesced bubbles played a main role in heat transfer when the heat flux was low. As the heat flux was increased, the coalesced bubbles absorbed enough heat to become large while the frequent bubble departure was maintained. As a result of it, the latent heat term in heat transfer became large to approximately 40%. When the cavity spacing was wide such as S = 4 mm, a bubble absorbed heat enough to become large before departure and the coalescence of bubbles were not prominent. Thus, the latent heat term took approximately 50% in heat transfer. With an increase in the heat flux, the vertical coalescence became to happen quite frequently. This coalescence made convection vigorous to increase the heat transfer. As a result of it, the convection term increased to 60% and the latent term decreased to 40%.

Mechanistic Prediction of Nucleate Boiling Heat Transfer–Achievable or a Hopeless Task?

2005 ◽  
Vol 128 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Active Sites ◽  
Bubble Dynamics ◽  
Functional Dependence ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Complex Nature ◽  
The Past ◽  
Nucleation Sites ◽  
Nucleate Boiling Heat Transfer

Over the last half of the twentieth century, a number of purely empirical and mechanism-based correlations have been developed for pool nucleate boiling. Empirical correlations differ from each other substantially with respect to the functional dependence of heat flux on fluid and surface properties, including gravity. The mechanism-based correlations require knowledge of the number density of active sites, bubble diameter at departure, and bubble-release frequency. However, because of the complex nature of the subprocesses involved, it has not been possible to develop comprehensive models or correlations for these parameters. This, in turn, has led to the pessimistic view that mechanistic prediction of nucleate boiling is a hopeless task. However, there is an alternative to the past approaches—complete numerical simulation of the boiling process. Value of this approach for bubble dynamics and associated heat transfer is shown through excellent agreement of predictions with data obtained on microfabricated surfaces on which active nucleation sites can be controlled.

Pool Nucleate Boiling on Heat Transfer Surface With Deposited Sea Salts

2016 ◽  
Author(s):  
Shinichiro Uesawa ◽  
Yasuo Koizumi ◽  
Mitsuhiko Shibata ◽  
Hiroyuki Yoshida
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Heat Transfer Surface ◽  
Artificial Seawater ◽  
Distilled Water ◽  
Nacl Solution ◽  
Nucleate Boiling Heat Transfer

Pool nucleate boiling heat transfer experiments of the 3.5 - 10wt% NaCl solution, the real seawater and the 3.5 - 10wt% artificial seawater solution as well as distilled water for the basis of comparison were performed to examine the effect of salts on boiling heat transfer. Seawater was injected into the reactor cores in the accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company. This study intended to provide base data to consider reactor core cooling by seawater. Boiling curves of the 3.5 - 10wt% NaCl solution, the real seawater and the 3.5 - 10wt% artificial seawater solutions as well as distilled water were well predicted with the Rohsenow pool nucleate boiling heat transfer correlation although the curves were a little shifted to the higher wall superheat region. The formation of secondary coalescent large bubble was suppressed in the experiments of the NaCl solutions, real seawater and the artificial seawater solutions, and small primary bubbles detached directly from the heat transfer surface. Sea salt deposition was observed only in the experiments of the 7.0wt% and 10wt% artificial seawater solutions. The deposited salt was calcium sulfate. Slow heat transfer surface temperature excursion occurred in the experiments of the 7.0wt% and 10wt% artificial seawater solutions after the heat flux was raised to 600 kW/m2 and 120 kW/m2, respectively. The critical heat flux of the 7.0wt% and 10wt% artificial seawater solutions were 600 kW/m2 and 120 kW/m2, respectively if the occurrence of the slow heat transfer surface temperature excursion was defined as the critical heat flux condition. The heat transfer surface temperature excursion might be caused by the growth of the deposited salt layer.

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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