Comparison of Heat Transfer Rates Around Moving and Stationary Bubbles During Nucleate Boiling

2005 ◽  
Author(s):  
David M. Christopher ◽  
Hao Wang ◽  
Xiaofeng Peng
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Nucleate Boiling ◽  
High Heat ◽  
Marangoni Flow ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Bubble Movement ◽  
Transfer Mechanisms

Nucleate boiling is known to be a very efficient method for generating high heat transfer rates from solid surfaces into liquids; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. This paper describes a numerical analysis of the heat transfer mechanisms around stationary and moving bubbles on a very thin microwire. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model was then used to study the heat transfer mechanisms around the bubbles. The analysis shows that the primary heat transfer mechanism is not the direct heat transfer to the bubble, but rather the large amount of convection around the outside of the bubble induced by the Marangoni flow that transfers at least twice as much energy from the wire than the heat transfer directly under the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles.

Microscale Vapor Bubble Interactions During Subcooled Nucleate Boiling on a Heated Wire

2007 ◽  
Author(s):  
Lu Zhang ◽  
David M. Christopher
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Bubble Behavior ◽  
Transfer Rates ◽  
Bubble Interactions ◽  
Heated Wire ◽  
Nucleate Boiling Heat Transfer ◽  
Transfer Mechanisms

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.

Effects of Pore Diameters and System Pressure on Saturated Pool Nucleate Boiling Heat Transfer From Porous Surfaces

1982 ◽  
Vol 104 (2) ◽  
pp. 286-291 ◽  
Author(s):  
W. Nakayama ◽  
T. Daikoku ◽  
T. Nakajima
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
High Heat ◽  
Porous Surface ◽  
Operational Parameters ◽  
High Heat Transfer ◽  
System Pressure ◽  
Nucleate Boiling Heat Transfer

The porous surface structure was manufactured with precision for the experimental study of nucleate boiling heat transfer in R-11. Boiling curves and the data of bubble formation were obtained with a variety of geometrical and operational parameters; the pore diameters were of 50, 100, 150 μm, there was a combination of pores of different sizes; and the system pressures were of 0.04, 0.1, 0.23 MPa. The boiling curves exhibit certain trends effected by the diameter and population density of pores. A combination of high system pressure and pore sizes of 100 or 150 μm dia enables boiling to persist even when the wall superheat is reduced to an extremely low level of 0.1 K. A noteworthy feature of porous surface boiling is that intense bubble formation does not necessarily yield a high heat-transfer performance. Examination of the data indicates that liquid suction and evaporation inside the cavities are a proable mechanism of boiling with small temperature differences.

Identification of Pool Boiling Heat Transfer Mechanisms From a Wire Immersed in Saturated FC-72 Using a Single-Photo/LDA Method

1996 ◽  
Vol 118 (1) ◽  
pp. 117-123 ◽  
Author(s):  
C. N. Ammerman ◽  
S. M. You ◽  
Y. S. Hong
Keyword(s):  
Heat Transfer ◽  
Latent Heat ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Laser Doppler Anemometry ◽  
Volumetric Flow Rate ◽  
Nucleate Boiling ◽  
Nucleate Boiling Heat Transfer ◽  
Unique Method ◽  
Transfer Mechanisms

A unique method to determine the vapor volumetric flow rate above a heated wire utilizing a single photograph and laser-Doppler anemometry is developed and discussed. The volumetric flow rate is combined with additional analyses to determine the overall contributions to the total heat flux from four nucleate boiling heat transfer mechanisms (latent heat, natural convection, Marangoni flow, and microconvection). This method is applied to a 75-μm wire immersed in a saturated, highly wetting liquid (FC-72). Latent heat is identified as the dominant mechanism in the fully developed nucleate boiling regime.

Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins

2003 ◽  
Vol 125 (2) ◽  
pp. 282-288 ◽  
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
High Heat ◽  
Horizontal Cylinder ◽  
High Conductivity ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Wide Range

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 106, non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in today’s high power density electronic components.

A Transducer for Measuring High Heat Transfer Rates

1970 ◽  
Vol 41 (12) ◽  
pp. 1732-1740 ◽  
Author(s):  
E. H. Schulte ◽  
R. F. Kohl
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Transfer Rates ◽  
High Heat Transfer

scholarly journals Properties of Kerosene-Aluminium Nanofluid used to Estimate the Overall Heat Transfer Rates during Regenerative/Film Cooling of Thrust Chambers

2019 ◽  
Vol 9 (1S3) ◽  
pp. 165-169
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Space Station ◽  
High Heat ◽  
Nano Particles ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Rocket Propulsion ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Large heat transfer rates are always desired for rocket propulsion applications as high heat loads are associated at the nozzle exit. Different strategies have been employed in order to have high heat transfer coefficients including use of liquid nitrogen, spray cooling etc. ISRO has planned to use aluminium based nano-particles with kerosene in order to cool launching vehicles including GSLV Mk III as it is the heaviest rocket that can carry large payloads. Recently, ISRO has announced to install its own International Space Station (ISS) in future and in such applications larger payloads are to be carried by the rocket. In this work, an analytical study on the thermodynamic properties of the aluminium nano-particles based kerosene nanofluid has been done and an attempt has also been made to develop a temperature and pressure dependent correlation that can be used in computational analysis of thrust chambers while film/regenerative cooling.

Rapid Boiling of Droplets in an Ambient Liquid at Partial Superheat

2007 ◽  
Author(s):  
Herman D. Haustein ◽  
Alon Gany
Keyword(s):  
Heat Transfer ◽  
Initial Conditions ◽  
High Heat ◽  
Heat Fluxes ◽  
Liquid Environment ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
High Superheat ◽  
Film Collapse ◽  
Critical Times

This work deals with the dynamics of rapid-boiling of a droplet, at medium-high superheat, rising in a host liquid environment. It considers the heat transfer, the superheat consumption and the hydrodynamics of the droplet as it boils. In the course of the research water-column experiments were conducted, and results are shown. Superheating was implemented by the sudden depressurization of the ambient liquid. Boiling was very rapid, concluding within several milliseconds, and high heat fluxes across the interface were obtained. Additionally, certain critical times in the boiling process were predicted and defined, and a novel criterion for the end of rapid boiling (liquid film collapse), is proposed. These defined critical times agree well with measured points of change in the boiling dynamics. From these results and analysis a deeper understanding of the three-fluid rapid boiling at medium-high superheat has been established, for the first time. In addition, various initial conditions were tested and their effect established qualitatively. This form of boiling, though being very rapid and sustaining high heat transfer rates, is non-explosive in nature, and therefore more designable and widely applicable.

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