B215 Experimental Discussion of Mechanism of Boiling Heat Transfer by using Simultaneous Measurements of Two-Dimensional Temperature Field under Heated Surface and Behavior of Boiling Vapor Bubble

Bubbles have been observed moving along heated wires during subcooled nucleate boiling as they are driven by Marangoni convection around the bubbles. This paper presents more detailed observations of the vapor bubble interactions and moving bubble behavior during subcooled nucleate boiling on a heated microwire. The experimental results show that moving bubbles coalesce or rebound from other bubbles and that bubbles hop on the wire. These observations show how bubble interactions significantly affect nucleate boiling heat transfer rates and how Marangoni flow plays an important role in microscale nucleate boiling heat transfer mechanisms.

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Thermal Bubble Dynamics Under the Effect of Acoustic Vibration

ASME 2009 7th International Conference on Nanochannels, Microchannels and Minichannels ◽

10.1115/icnmm2009-82085 ◽

2009 ◽

Author(s):

Xiaopeng Qu ◽

Huihe Qiu

Keyword(s):

Heat Transfer ◽

Acoustic Field ◽

Vapor Bubble ◽

Boiling Heat Transfer ◽

High Speed ◽

Bubble Dynamics ◽

Acoustic Vibration ◽

Micro Electro Mechanical System ◽

Mems Technology ◽

Enhanced Boiling

The effect of acoustic field on the dynamics of micro thermal bubble is investigated in this paper. The micro thermal bubbles were generated by a micro heater which was fabricated by standard Micro-Electro-Mechanical-System (MEMS) technology and integrated into a mini chamber. The acoustic field formed in the mini chamber was generated by a piezoelectric plate which was adhered on the top side of the chamber’s wall. The dynamics and related heat transfer induced by the micro heater generated vapor bubble with and without the existing of acoustic field were characterized by a high speed photograph system and a micro temperature sensor. Through the experiments, it was found that in two different conditions, the temperature changing induced by the micro heater generated vapor bubble was significantly different. From the analysis of the high speed photograph results, the acoustic force induced micro thermal bubble movements, such as forcibly removing, collapsing and sweeping, were the main effects of acoustic enhanced boiling heat transfer. The experimental results and theoretical analysis were helpful for understanding of the mechanisms of acoustic enhanced boiling heat transfer and development of novel micro cooling devices.

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Incipient Flow Boiling in a Vertical Channel With a Wavy Wall

2010 14th International Heat Transfer Conference, Volume 1 ◽

10.1115/ihtc14-22809 ◽

2010 ◽

Cited By ~ 1

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.

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