The influence of gravity on pressure drop and heat transfer in flow boiling
Klausner, James Frederick
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https://hdl.handle.net/2142/19126
Description
Title
The influence of gravity on pressure drop and heat transfer in flow boiling
Author(s)
Klausner, James Frederick
Issue Date
1989
Director of Research (if dissertation) or Advisor (if thesis)
Soo, Shaolee
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
There is considerable interest at the present time in developing efficient heat rejection systems for use in manned spacecraft. An experimental facility has been fabricated in which heat transfer, pressure drop, and vapor volume fraction in flow boiling of R11 can be studied in vertical upflow, vertical downflow, and horizontal flow configurations.
For the determination of frictional pressure drop and volume-averaged vapor volume fraction for vertical two-phase flows, both up and down, an improved measurement technique has been developed which provides significantly better accuracy than has previously been reported in the literature. Data have been obtained for both boiling and adiabatic flows, mainly in the annular flow regime. All vapor volume fraction data can be well correlated by a scheme based on Zuber-Findlay's drift flux model. The variation of frictional pressure drop with vapor volume fraction, mass flux and heat flux displays different characteristics for upflow, downflow, and horizontal flow. This observed behavior is believed to be linked to the instability of the liquid film, and gravity plays a role in the origin of the instability. A dimensionless film thickness is used to correlate the frictional pressure drop data.
It is through the behavior of the liquid film that gravity exerts its influence on flow boiling heat transfer. A mechanistic flow boiling heat transfer correlation is proposed in which the contribution to the total heat transfer from the bulk turbulent convection and from the ebullition process are assumed to be additive. The heat transfer due to the ebullition process is formulated by considering the latent heat transport associated with nucleation density, bubble growth, and bubble departure. Both components of heat transfer are dependent on liquid film thickness. The present correlation is compared against existing data over a wide range of flow boiling conditions. It is also compared against two existing flow boiling correlations. The present correlation generally correlates the data better, especially when the contribution to the total heat transfer due to the ebullition process is large. It is tentatively recommended for use for zero-g only after an empirical surface-fluid nucleation parameter is determined from zero-g flow boiling data. (Abstract shortened with permission of author.)
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