Correlation Between Behaviors of the Vapor Bubbles and the Characteristics of the Heat Transfer Over the Heated Surface on MEB

2013 ◽  
Author(s):  
Takahito Saiki ◽  
Tomohiko Osawa ◽  
Ichiro Ueno ◽  
Chungpyo Hong
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Heated Surface ◽  
High Heat ◽  
Frame Rate ◽  
High Heat Flux ◽  
Heated Plate ◽  
Thin Wire ◽  
Vapor Bubbles

A series of experiments on subcooled pool boiling on a plate and on a thin wire are carried out. We focus on the condensation and collapse processes of vapor bubbles generated on the heated surface. We find the different patterns of the vapor bubble behaviors resulting in the emission of the microbubbles around the heated plate and the thin wire by employing high-speed observation with frame rate up to 150,000 frame per second (fps). From the experimental results, we provide a physical explanation on the correlation between the behavior of the vapor bubble at a high heat flux and the heat transfer characteristics. We propose this simple core-periphery model as a qualitative model for understanding the generation of the MEB.

Phenomenon and Mechanism of Spray Cooling on Nanowire Arrayed and Hybrid Micro/Nanostructured Surfaces

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Jian-nan Chen ◽  
Rui-na Xu ◽  
Zhen Zhang ◽  
Xue Chen ◽  
Xiao-long Ouyang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
High Speed ◽  
Spray Cooling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Enhancement ◽  
Nanostructured Surfaces ◽  
New Energy ◽  
Dry Out

Enhancing spray cooling with surface structures is a common, effective approach for high heat flux thermal management to guarantee the reliability of many high-power, high-speed electronics and to improve the efficiency of new energy systems. However, the fundamental heat transfer enhancement mechanisms are not well understood especially for nanostructures. Here, we fabricated six groups of nanowire arrayed surfaces with various structures and sizes that show for the first time how these nanostructures enhance the spray cooling by improving the surface wettability and the liquid transport to quickly rewet the surface and avoid dry out. These insights into the nanostructure spray cooling heat transfer enhancement mechanisms are combined with microstructure heat transfer mechanism in integrated microstructure and nanostructure hybrid surface that further enhances the spray cooling heat transfer.

Microbubble Formation in Collapsing Process of a Single Vapor Bubble Injected in Subcooled Pool

2009 ◽  
Author(s):  
Ichiro Ueno ◽  
Yasusuke Hattori
Keyword(s):  
Heat Flux ◽  
Vapor Bubble ◽  
High Speed ◽  
Narrow Range ◽  
Heated Surface ◽  
Lighting System ◽  
Vapor Bubbles ◽  
Bubble Behavior ◽  
Subcooled Liquid ◽  
Boiling Process

‘Microbubble emission boiling,’ known as MEB, is a phenomenon that emerges in a narrow range of subcooled condition with a higher heat flux than critical heat flux (CHF) accompanying with microbubble emission from the heated surface. The authors focus on the condensing process of vapor bubbles in order to comprehend the mechanism of the microbubble formation and emitting processes. In order to simplify a surely complex boiling process, the authors try to extract an interaction between the vapor bubble and the subcooled bulk in a boiling phenomenon, that is, growing and collapsing processes of a vapor bubble ejected to subcooled liquid bath. Vapor bubble is produced by vapor generate system, and ejected to a bulk of saturated distilled water at a designated degree of subcooling. The degree of subcooling is varied from 0 to 50 K. The growing/collapsing of vapor bubble behavior is detected by employing a high-speed camera at frame rates up to 50,000 fps with a back-lighting system. In the present study, the process of microbubble emission as well as the process of the irrupting vapor bubbles to the subcooled bulk is compared to that in a MEB on a thin wire.

Heat Transfer Controlled Collapse of a Cylindrical Vapor Bubble in a Vertical Isothermal Tube

1977 ◽  
Vol 99 (3) ◽  
pp. 392-397 ◽  
Author(s):  
D. R. Pitts ◽  
H. C. Hewitt ◽  
B. R. McCullough
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
High Speed ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Experimental Program ◽  
Bubble Collapse ◽  
Electric Heater ◽  
Vapor Bubbles ◽  
Experimental Apparatus

An experimental program was conducted to determine the collapse rate of slug-type vapor bubbles rising due to buoyancy through subcooled parent liquid in a vertical isothermal tube. The experimental apparatus included a vertical glass tube with an outer glass container providing a constant temperature water bath for the inner tube. The inner tube contained distilled, deaerated water, and water vapor bubbles were generated at the bottom of this tube with a pulsed electric heater. The parent liquid was uniformly subcooled with respect to the vapor bubble resulting in heat transfer controlled bubble collapse. Collapse rates and rise velocities were recorded by high-speed motion picture photography. Over a limited range of subcooling, the bubble collapse was well behaved, and a simple, quasi-steady boundary layer heat transfer analysis adapted from slug flow over a flat plate correlated the experimental results with a high degree of accuracy. Experimental results were obtained with tubes having inside diameters of 0.0127, 0.0218, and 0.0381 m and for a range of subcooling from 0.5 to 9.0 K.

Numerical Simulation of the Flow Field of a Confined, Submerged Slot Jet Impinging on an Oscillating Surface: A Parametric Study

2016 ◽  
Author(s):  
Srivathsan Ragunathan
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Heated Surface ◽  
Jet Impingement ◽  
High Heat ◽  
High Heat Flux ◽  
Lower Wall ◽  
Local Skin ◽  
Submerged Jet ◽  
High Heat Transfer

Impinging jets are an attractive option for spot-cooling of high heat flux devices because of the stagnation region surrounding the point of impingement and the resulting high heat transfer. In small devices with a small jet (microjet) , however, the cooled region due to just a single jet is small. One way to potentially increase this area exposed to the impinging jet is by oscillating the heated surface. In the current paper, the flow structure and transport in a confined and submerged jet impingement arrangement impinging on a wall oscillating horizontally is numerically studied with respect to both parameters governing jet impingement :Jet Reynolds Number (from 40 to 200), distance from the jet inlet to the impinging wall (z/d ratios of 2 and 5) and an oscillation parameter (oscillatory peak Reynolds Numbers of 55 and 110). OpenFOAM v 2.2.2, an open-source CFD code based on the finite volume method is used to solve the problem. The Grid Convergence Index (GCI) is used to estimate discretization uncertainty and error bars on all of the parameters calculated. The flow structure in a confined submerged jet is made up of a double recirculation zone (mostly attributed to the confining top wall) the reattachment regions are associated with a secondary peak in the Nusselt Number. Heat transfer is not studied in this paper. The effect of the oscillating lower wall on the locations of the primary and the secondary recirculation zones are studied with respect to all the parameters mentioned above over a complete oscillation cycle. The local skin friction coefficients along different sections on the lower wall are computed along sections of the oscillating wall and compared to the case where there is no oscillation.The results are anticipated to have significant impact on the heat transfer enhancement possible in such an arrangement.

Effect of Gravitational Orientation on Flow Boiling of Water in 1054 × 197 µm Parallel Minichannels

2004 ◽  
Author(s):  
Satish G. Kandlikar ◽  
Prabhu Balasubramanian
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
High Heat ◽  
Operating Conditions ◽  
Microgravity Environment ◽  
High Heat Flux ◽  
Two Phase ◽  
Mass Fluxes ◽  
Heat Transfer Degradation

Microchannels and minichannels are being considered for high heat flux applications under microgravity environment in space missions. An experimental study is undertaken to determine the effect of gravitational orientation on flow boiling characteristics of water in a set of six parallel minichannels, each 1054 μm wide by 197 μm deep and 63.5 mm long with a hydraulic diameter of 333 μm. Three orientations — horizontal, vertical downflow and vertical upflow — are investigated under identical operating conditions of heat and mass fluxes. High-speed images are obtained to reveal the detailed two-phase flow structure and liquid-vapor interactions. The experimental data and high speed flow visualization indicate that compared to the horizontal case, the flow becomes less chaotic for vertical upflow, while the reversed flow becomes more pronounced in vertical downflow case. The resulting in increase in the back-flow is responsible for channel-to-channel flow maldistribution and heat transfer degradation. From the heat transfer data it is concluded that the performance of the tested channels under microgravity environment will be similar to the horizontal flow case.

Cooling of a Heated Surface by Mist Flow

1994 ◽  
Vol 116 (1) ◽  
pp. 167-172 ◽  
Author(s):  
S. L. Lee ◽  
Z. H. Yang ◽  
Y. Hsyua
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Film ◽  
Heated Surface ◽  
High Heat ◽  
Dynamic Interaction ◽  
High Heat Flux ◽  
Steady Temperature ◽  
Mist Flow ◽  
High Level

Cooling requirements in modern industrial applications, such as the removal of heat from electronic equipments, often demand the simultaneous attainment of a high heat flux and a low and relatively uniform and steady temperature of the heated surface to be cooled. The conventional single-phase convection cooling obviously cannot be expected to function adequately, since the heat flux there is directly proportional to the temperature difference between the heated surface and the surrounding medium. To maintain a high heat flux, the temperature of the heated surface usually must be kept at a high level. An attractive alternative is cooling by a spray, which takes advantage of the significant latent heat of evaporation of the liquid. However, in conventional industrial spray coolings, such as in the case of the cooling tower of a power plant, the temperature of the heated surface usually remains relatively high and is nonuniform and unsteady containing numerous flashy hot spots. In order to optimize the performance of the spray cooling of a heated surface by a mist flow, a clear understanding is required of (1) the dynamic interaction between the droplets and the carrier fluid and (2) the thermal reception of the droplets at the heated surface. It is the dynamic interaction between the phases that is causing the droplets to deposit onto the heated surface. The thermal reception at the heated wall develops mass and heat transfer leading to the mode of cooling of the heated surface. In the present study, an experimental investigation was made of the combination of the dynamic depositional behavior of droplets in a water droplet-air mist flow with the use of a specially designed particle-sizing two-dimensional laser-Doppler anemometer. Also, the heat transfer characteristics at the heated surface were investigated in relation to droplet deposition on the heated surface for wide ranges of droplet size, droplet concentration, mist flow velocity, and heat flux. It was discovered that over a certain suitable range of combination of these parameters, a superbly effective cooling scheme could be established by the evaporation on the outside surface of an ultrathin liquid film. Such a film was formed on the heated surface by the continuous deposition of fine droplets from the mist flow. Under these conditions, the heat flux is primarily related to the evaporation of the ultrathin liquid film on the heated surface and thus depends less on the temperature difference between the heated surf ace and the ambient mist flow. The heated surface is quenched to a low, relatively uniform and steady temperature at a very high level of heat flux. Heat transfer enhancement as high as seven times has been found so far. This effective heat transfer scheme is here termed mist cooling.

Ultra-Cooling Heat Transfer Characteristics Using Cryogenic Micro-Solid Nitrogen Spray

2012 ◽  
Author(s):  
U. Oh ◽  
Jun Ishimoto ◽  
Naoki Harada ◽  
Daisuke Tan
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Spray Cooling ◽  
High Heat ◽  
Heat Transfer Process ◽  
Solid Particles ◽  
High Heat Flux ◽  
Heat Transfer Characteristics ◽  
Solid Nitrogen ◽  
New Type

The fundamental characteristics of heat transfer and cooling performance of micro-solid nitrogen particulate spray impinging on a heated substrate were numerically investigated and experimentally measured by a new type of integrated computational-experimental technique. The employed CFD based on the Euler-Lagrange model is focused on the cryogenic spray behavior of atomized particulate micro-solid nitrogen and also on its ultra-high heat flux cooling characteristics. Based on the numerically predicted performance, a new type of cryogenic spray cooling technique for application to a ultra-high heat power density device was developed. In the present integrated computation, it is clarified that the cryogenic micro-solid spray cooling characteristics are affected by several factors of the heat transfer process of micro-solid spray which impinges on heated surface as well as by atomization behavior of micro-solid particles.

An Experimental Investigation of Sub-Cooled Flow Boiling in Hypervapotron Cooling Configuration

2004 ◽  
Author(s):  
Peipei Chen ◽  
Barclay G. Jones ◽  
Ty A. Newell
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Subcooled Boiling ◽  
Reduced Pressure

This work reports on experimental studies to visualize nucleate boiling on the enhanced heat transfer surface of the hypervapotron for with application in the International Thermonuclear Experiment Reactor [ITER]. This research uses the simulant fluid Freon (R134A) instead of prototypic water to model the system performance. This results in much lower thermophysical conditions to represent the prototypic phenomena. By using reduced pressure, temperatures, etc, based on the critical physical properties of both working fluids, Freon and water, the dramatic drop in the level of these quantities with Freon allows the use of modest test conditions. The experiment was conducted for both saturated and subcooled boiling with different heat fluxes (from 50 to 300 kW/m2). A comparison of the heat transfer performance of finned structures and flat surfaces were examined under particular fluid conditions. The uniqueness of this work is the visualization method that allows direct observation of the subcooled boiling process of the Hypervapotron surfaces. Working with a high speed (12,000 frames per second), high fidelity digital camera with variable magnifications (from 1×–25×), the sub-cooled boiling phenomena was observed in detail. A major conclusion of this work is the existence of two separate zones linked to different energy removal efficiency in hypervapotron. Under high heat flux condition, enhanced boiling heat transfer (about 20–30% higher than flat surface) was observed for hypervapotron effect, while saturated boiling happened in the cavity, and a large portion of the region was vapor filled. The process of vapor bubble rotation in the slot appeared to be helpful to enhance energy transfer, as evidenced by an improved wetting condition on the heating surfaces.

Effect of Channel Width on Pool Boiling Enhancement of Open Microchannels With Selective Sintered Porous Coatings

2015 ◽  
Author(s):  
Arvind Jaikumar ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Underlying Mechanism ◽  
High Heat ◽  
Channel Width ◽  
High Heat Flux ◽  
Porous Coatings ◽  
Open Microchannel

Thermal management in microelectronic devices involves development of high heat flux removal systems to meet the cooling requirements. Pool boiling addresses these demands by using latent heat transfer. In this study, heat transfer surfaces are fabricated by depositing porous coatings on an open microchannel surface. Screen printing and sintering are identified as techniques to deposit porous coatings and ensure substrate bonding respectively. Firstly, the effect of selective enhancement was studied by depositing porous coatings on (i) fin tops only (sintered-fin-tops), (ii) channels only (sintered-channels), and (iii) completely covering the boiling surface (sintered-throughout). The pool boiling performance with saturated distilled water at atmospheric pressure was obtained and a maximum critical heat flux (CHF) of 313 W/cm2 at a wall superheat of 7.5 °C was reported here for a sintered-throughout surface. Furthermore, the effect of channel width on sintered-throughout surfaces was studied. The results indicated that channel width plays an important in improving the performance. High speed videos are taken to understand the underlying mechanism. Additional nucleation sites and separate liquid-vapor pathways are identified as contributing mechanisms for the enhancement in CHF and heat transfer coefficient (HTC).

Contribution of Microlayer Evaporation to Bubble Growth in Pool Saturated Boiling of Water

2013 ◽  
Author(s):  
Tomohide Yabuki ◽  
Takuya Saitoh ◽  
Osamu Nakabeppu
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Heated Surface ◽  
High Heat ◽  
High Heat Flux ◽  
Wall Heat Transfer ◽  
Heat Transfer Phenomenon ◽  
Microlayer Evaporation ◽  
Dry Out ◽  
Saturated Boiling

Heat transfer and formation characteristics of the microlayer are investigated by the surface temperature measurement with a MEMS thermal sensor and the wall heat transfer evaluation using an experimental data. The temperature data clearly indicated transition of heat transfer phenomenon on the heated surface from microlayer formation via dry-out of the microlayer to rewetting of the dry-out region. Microlayer evaporation transferred extremely high heat flux over 1 MW/m2 and was found to be the dominant heat transfer mechanism in the wall heat transfer during isolated bubble boiling of water. The contribution of microlayer evaporation to bubble growth was found to be 50% and not vary with wall superheat. Finally the spatial distribution of initial thickness of microlayer was calculated from the wall heat transfer.

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