Onset of Boiling, Heat Transfer and Flow Patterns of Flow Boiling On the Superhydrophobic Porous Copper Surface in a Microchannel

2021 ◽  
Author(s):  
Yuhao Lin ◽  
Junye Li ◽  
Sun Jia ◽  
Wei Li ◽  
Yanlong Cao
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Copper Surface ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Porous Surface ◽  
Mass Fluxes ◽  
Porous Copper

Abstract To explore the effect of micro-structured porous surface on enhancing the heat transfer of flow boiling in a microchannel, the micro-porous copper surface was fabricated with microscale pores in ranges of 1-5 µm, which presented super-hydrophobicity. Subcooled flow boiling experiments were carried out to study the hydraulic and thermal transport performance in a single narrow rectangular microchannel. High-speed flow visualizations were conducted coupled with instrumental measurements to illustrate the effects of heat flux and mass flux on heat transfer performance and flow patterns for originally hydrophilic bare copper surface and superhydrophobic micro-porous structured surface. The onset of boiling (ONB) characteristics of both test surfaces were compared with predictive correlations with a good agreement and verified by the captured flow pattern images. Benefit from the superhydrophobic wettability provided by its micro-scale porous structures and a large number of potential nucleation sites, the required wall superheats, and imposed heat fluxes of onset of boiling both decreased for the modified surface. The flow patterns on the two surfaces varied, which resulted in the different trends of heat transfer coefficient with mass fluxes and heat fluxes. Because of the strengthened bubble departure process, the enhancement of the porous surface compared to the original bare surface gradually increased with mass fluxes. The average two-phase heat transfer coefficients of the superhydrophobic porous copper surface were enhanced for up to 74.84%, due to the earlier onset of boiling, higher frequency of bubble nucleation, and strengthened boiling intensity.

Subcooled Flow Boiling on Micro-Porous Structured Copper Surface in a Vertical Mini-Gap Channel

2019 ◽  
Author(s):  
Junye Li ◽  
Kan Zhou ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Copper Surface ◽  
Heat Fluxes ◽  
High Speed Flow ◽  
Subcooled Flow Boiling ◽  
Mass Fluxes ◽  
Speed Flow ◽  
Subcooled Flow

Abstract An experimental investigation of subcooled flow boiling in a large width-to-height-ratio, one-sided heating rectangular mini-gap channel was conducted with deionized water as the working fluid. The super-hydrophobicity micro-porous structured copper surface was utilized in the experiments. High speed flow visualization was conducted to illustrate the effects of heat flux and mass rate on the heat transfer coefficient and flow pattern on the surfaces. The mass fluxes were in the range of 200–500 kg/m2s, the wall heat fluxes were spanned from 40–400 kW/m2. With increments of imposed heat flux, the slopes of boiling curves for superhydrophobic micro-porous copper surfaces increased rapidly, indicating the Onset of Nucleate Boiling. Heat transfer characteristics were discussed with variation of heat fluxes and mass fluxes, the trends of which were analyzed with the aid of high speed flow visualization.

Investigation of Flow Boiling on Nanostructured Surfaces

2010 ◽  
Author(s):  
Saeil Jeon ◽  
Pratanu Roy ◽  
N. K. Anand ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Silicon Surface ◽  
High Speed ◽  
Flow Boiling ◽  
Copper Surface ◽  
Heat Fluxes ◽  
Test Fluid ◽  
Nanostructured Surfaces ◽  
Layer Effect

Flow boiling experiments were performed on copper, bare silicon and carbon nanotube (CNT) coated silicon wafer using water as the test fluid. Wall heat flux was measured by varying the wall superheat. The experiments were performed under pool boiling conditions (zero flow rate) as well as by varying the flow rates of water. The liquid sub-cooling was varied between 40 ∼ 60 °C. An infra–red camera was used to calibrate the surface temperature of the silicon wafers and the copper surface. Heat flux measurements were performed by using a calorimeter apparatus. High speed visualization experiments were performed to measure the bubble departure diameter, bubble departure frequency and bubble growth rate as a function of time. Heat flux values for all three surfaces were calculated from the temperature differences obtained by sheathed thermocouples inside the copper block in the calorimeter apparatus. Flow boiling curves were plotted to enumerate the enhancements in heat transfer. It was observed that MWCNT coated silicon surface enables higher heat fluxes compared to bare silicon surface. This enhancement can be ascribed to be due to the high thermal conductivity of the carbon nanotubes, micro-layer effect, enhancement of transient heat transfer due to periodic solid-liquid contact and increase in active nucleation sites on nanostructured surfaces.

Pressure Drop and Two Phase Flow During Boiling of FC-72 in a High Aspect Ratio Micro-Channel

2010 ◽  
Author(s):  
Yuan Wang ◽  
Khellil Sefiane ◽  
Rachid Bennacer
Keyword(s):  
Pressure Drop ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
High Speed ◽  
Flow Boiling ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Micro Channel ◽  
Growth Interface ◽  
Mass Fluxes

Liquid-vapour interface behaviours and the pressure drop fluctuation during flow boiling in a single rectangular micro-channel with high aspect ratio were experimentally investigated in the present study. A micro-channel with the hydraulic diameter of 727 μm was chosen, the aspect ratio of which was 10. FC-72 was used as the working liquid. Wide ranges of mass fluxes and heat fluxes were tested to study bubble dynamics and hydraulic instabilities during flow boiling. With the aid of high speed camera, various liquid-vapour interface behaviours during flow boiling were captured, such as bubble nucleation and growth, interface deformation, recoiling and rewetting. Based on the interface movement, the evaporation rate of the liquid was discussed. Evaporation rates of bubble nose and bubble tail at different mass fluxes and heat fluxes were compared. Besides, the effects of thermal and flow conditions on bubble geometry were discussed. Moreover, the pressure fluctuations resulting from boiling instabilities was remarkable. Fluctuation frequency was largely affected by the heat and mass fluxes.

A Photographic Study of Flow Boiling Stability on a Plain Surface With Tapered Manifold

2015 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Speed ◽  
Flow Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
High Heat Transfer ◽  
Plain Surface ◽  
High Heat Transfer Coefficient

Flow boiling in microchannels offers many advantages such as high heat transfer coefficient, higher surface area to volume ratio, low coolant inventory, uniform temperature control and compact design. The application of these flow boiling systems has been severely limited due to early critical heat flux (CHF) and flow instability. Recently, a number of studies have focused on variable flow cross-sectional area to augment the thermal performance of microchannels. In a previous work, the open microchannel with manifold (OMM) configuration was experimentally investigated to provide high heat transfer coefficient coupled with high CHF and low pressure drop. In the current work, high speed images of plain surface using tapered manifold are obtained to gain an insight into the nucleating bubble behavior. The mechanism of bubble nucleation, growth and departure are described through high speed images. Formation of dry spots for both tapered and uniform manifold geometry is also discussed.

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

An Experimental Study of Bubble Nucleation Frequency in Subcooled Flow Boiling

2010 ◽  
Author(s):  
Guodong Wang
Keyword(s):  
Flow Boiling ◽  
Rectangular Cross Section ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Dimensionless Frequency ◽  
Micro Channel ◽  
Subcooled Flow Boiling ◽  
Nucleation Frequency ◽  
Mass Fluxes ◽  
Subcooled Flow

In this paper, a simultaneous visualization and measurement study have been carried out to investigate bubble nucleation frequency of water in micro-channel at various heat fluxes and mass fluxes. A single micro-channel with an identical rectangular cross-section having a hydraulic of 137 μm and a heating length of 30 mm was used in this experiment. It is shown that the frequency of bubble nucleation increased drastically with the increase of heat flux and was also strongly dependent on the mass flux. A dimensionless frequency of bubble nucleation was correlated in terms of the Boiling number. The predictions of bubble nucleation frequency in the microchannel are found in good agreement with experimental data with a MAE of 10.4%.

Confined Bubble and Heat Transfer during Flow Boiling in a High Aspect Ratio Mini-Channel

2011 ◽  
Vol 312-315 ◽  
pp. 548-553 ◽  
Author(s):  
Yuan Wang ◽  
Khellil Sefiane
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Bubble Growth ◽  
Flow Boiling ◽  
Critical Time ◽  
Heat Fluxes ◽  
Equivalent Radius ◽  
Mass Fluxes ◽  
Transfer Mechanisms ◽  
Working Liquid

Single vapour bubble growth and heat transfer mechanism during flow boiling in a rectangular horizontal mini-channel were experimentally investigated. The hydraulic diameter of the channel was 1454 μm, with an aspect ratio (Win/din) of 10. Degassed FC-72 was used as the working liquid. In this paper, bubble equivalent radius was found to increase linearly till a critical time, beyond which the growth turned into exponential. Bubble growth rate increases with increasing heat flux. Heat transfer mechanisms of the bubble growth at different heat fluxes and mass fluxes were discussed. In addition, the relation between thermal and flow conditions with bubble temporal geometry was explored.

Heat Transfer and Pressure Drop for Flow Boiling of Water in Narrow Vertical Rectangular Channels

2003 ◽  
Author(s):  
Jianyun Shuai ◽  
Rudi Kulenovic ◽  
Manfred Groll
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
High Heat ◽  
Flow Patterns ◽  
Industrial Applications ◽  
Heat Fluxes ◽  
Experimental Conditions ◽  
Rectangular Channels

Flow boiling in small-sized channels attracted extensive investigations in the past two decades due to special requirements for transfer of high heat fluxes from narrow spaces in various industrial applications. Experiments on various aspects of flow boiling in narrow channels were carried out and theoretical attempts were undertaken. But these investigations showed large differences, e.g. up till now the knowledge on the development of flow patterns in small non-circular flow passages is very limited. This paper deals with investigations on flow boiling of water in two rectangular channels with dimensions (width×depth) 2.0×4.0 mm2 and 0.5×2.0 mm2 (corresponding hydraulic diameters are 2.67 mm and 0.8 mm). The pressure at the test section exit is atmospheric. For steady-state experimental conditions the effects of heat flux, mass flux and inlet subcooling on the boiling heat transfer coefficient and the pressure drop are investigated. Flow patterns and the transition of flow patterns along the channel axis are visualized and documented with a video-camera. Bubbly flow, slug flow and annular flow are distinguished in both channels. Preliminary flow pattern maps are generated.

Incipient Flow Boiling in a Vertical Channel With a Wavy Wall

2010 ◽  
Author(s):  
T. Netz ◽  
R. Shalem ◽  
J. Aharon ◽  
G. Ziskind ◽  
R. Letan
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
High Speed ◽  
Flow Boiling ◽  
Heated Surface ◽  
Vertical Channel ◽  
Infrared Camera ◽  
Heat Fluxes ◽  
Heated Wall ◽  
Boiling Incipience

In the present study, incipient flow boiling of water is studied experimentally in a square-cross-section vertical channel. Water, preheated to 60–80 degrees Celsius, flows upwards. The channel has an electrically heated wall, where the heat fluxes can be as high as above one megawatt per square meter. The experiment is repeated for different water flow rates, and the maximum Reynolds number reached in the present study is 27,300. Boiling is observed and recorded using a high-speed digital video camera. The temperature field on the heated surface is measured with an infrared camera and a software is used to obtain quantitative temperature data. Thus, the recorded boiling images are analyzed in conjunction with the detailed temperature field. The dependence of incipient boiling on the flow and heat transfer parameters is established. For a flat wall, the results for various velocities and subcooling conditions agree well with the existing literature. Furthermore, three different wavy heated surfaces are explored, having the same pitch of 4mm but different amplitudes of 0.25mm, 0.5mm and 0.75mm. The effect of surface waviness on single-phase heat transfer and boiling incipience is shown. The differences in boiling incipience on various surfaces are elucidated, and the effect of wave amplitude on the results is discussed.

Flow Boiling Heat Transfer on Micro Pin Fins Entrenched in a Microchannel

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Axial Distance ◽  
Mass Fluxes ◽  
Pin Fins

Flow boiling of 1-methoxyheptafluoropropane (HFE 7000) in 222 μm hydraulic diameter channels containing a single row of 24 inline 100 μm pin fins was studied for mass fluxes from 350 kg/m2 s to 827 kg/m2 s and wall heat fluxes from 10 W/cm2 to 110 W/cm2. Flow visualization revealed the existence of isolated bubbles, bubbles interacting, multiple flow, and annular flow. The observed flow patterns were mapped as a function of the boiling number and the normalized axial distance. The local heat transfer coefficient during subcooled boiling was measured and found to be considerably higher than the corresponding single-phase flow. Furthermore, a thermal performance evaluation comparison with a plain microchannel revealed that the presence of pin fins considerably enhanced the heat transfer coefficient.

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