Experimental study on subcooled flow boiling on heating surfaces with different thermal conductivities

Zou, Ling

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https://hdl.handle.net/2142/18442 Copy

Description

Title

Experimental study on subcooled flow boiling on heating surfaces with different thermal conductivities

Author(s)

Zou, Ling

Issue Date

2011-01-14T22:51:03Z

Director of Research (if dissertation) or Advisor (if thesis)

Jones, Barclay G.

Doctoral Committee Chair(s)

Jones, Barclay G.

Committee Member(s)

• Axford, Roy A.
• Uddin, Rizwan
• Newell, Ty A.

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• subcooled flow boiling
• high-speed digital video camera
• thermal conductivity

Abstract

Subcooled flow boiling is generally characterized by high heat transfer capacity and low wall superheat, which is essential for cooling applications requiring high heat transfer rate, such as nuclear reactors and fossil boilers. In this study, subcooled flow boiling on copper and stainless steel heating surfaces was experimentally investigated from both macroscopic and microscopic points of view. Flow boiling heat flux and heat transfer coefficient were experimentally measured on both surfaces under different conditions, such as pressure, flow rate and inlet subcooling. Significant boiling heat transfer coefficient differences were found between the copper and the stainless steel heating surfaces. To explain the different flow boiling behaviors on these two heating surfaces, nucleation site density and bubble dynamics were visually observed and measured at different experimental conditions utilizing a high-speed digital video camera. These two parameters are believed to be keys in determining flow boiling heat flux. Wall superheat, critical cavity size and wall heat flux were used to correlate with nucleation site density data. Among them, wall heat flux shows the best correlation for eliminating both pressure and surface property effects. The observed nucleation site distribution shows a random distribution. When compared to the spatial Poisson distribution, similarity between them was found, while the measured nucleation site distribution is more uniform. From experimental observations, for the two surface materials investigated, which have similar surface wettability but sharply different thermal properties, bubble dynamics displayed fairly similar behavior. The obtained experimental results indicate that thermal conductivity of heating surface material plays an important role in boiling heat transfer. This is due to thermal conductivity having a significant impact on the lateral heat conduction at the heating surface and consequently temperature uniformity of the heating surface. A model was then developed and solved numerically for heat conduction at the heating surface when bubbles are present. Several key parameters which impact lateral heat conduction and surface temperature profile were studied. These parameters include material thermal conductivity, bubble size, heating surface thickness, etc. Numerical results show that, temperature profile on the heating surface tends to be more uniform and have a lower average value on a heating surface with higher thermal conductivity, which agrees well with the experimental observation.

Graduation Semester

2010-12

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http://hdl.handle.net/2142/18442

Copyright and License Information

Copyright 2010 Ling Zou

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