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Heat Exchanger Fouling and Cleaning VII
July 1-6, 2007 - Tomar, Portugal
| Editors: |
Hans Müller-Steinhagen, Institute of Technical Thermodynamics, German Aerospace Centre (DLR)
and Institute for Thermodynamics and Thermal Engineering, University of Stuttgart, Germany
M. Reza Malayeri, University of Stuttgart, Germany
A. Paul Watkinson, The University of British Columbia, Canada |
The articles for these proceedings are peer-reviewed.
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INCORPORATION OF A CONSIDERATION OF FOULING INTO THE DESIGN OF VERTICAL THERMO-SIPHON RE-BOILERS
G.T. Polley, Universidad de Guanajuato, Mexico
S.J. Pugh, IHS ESDU International plc, London, U.K.
ABSTRACT:
Two causes of under-performance within the tubes of
vertical thermo-siphon re-boilers (VTR’s) are considered:
premature dry-out within the unit and chemical reaction
fouling at the tube wall. In many cases dryout is itself a
cause of fouling.
Both of these causes depend on re-boiler geometry. Some
geometry performs satisfactorily. Other geometry performs
poorly.
There are two basic forms of flow boiling: nucleate flow
boiling and convective flow boiling. In nucleate flow
boiling part of the vaporisation results from the formation of
bubbles of vapour on the heated surface. Unfortunately, a
thin liquid film (the micro-layer) formed beneath these
bubbles can fully evaporate and dissolved solids can deposit
on the heated surface.
Under convective flow boiling conditions the vapour shear
generated by the two-phase flow results in the formation of
a thin liquid film on the tube wall. This film moves at high
velocity and provides very effective heat transfer. The result
is a marked reduction in wall temperature and suppression
of the nucleate boiling process. It is clearly desirable to
move from a nucleate boiling mechanism to a convective
boiling situation over as short a tube length as possible. The
length of tube that is subject to nucleate boiling is again a
function of re-boiler geometry.
Wall shear is important in suppression of chemical reaction
type fouling. Shear is function of recirculation rate and
vapour mass quality. Again these factors depend on
reboiler geometry.
In this paper the authors describe how the better geometry
can be identified.
G.T. Polley and S.J. Pugh, "INCORPORATION OF A CONSIDERATION OF FOULING INTO THE DESIGN OF VERTICAL THERMO-SIPHON RE-BOILERS" in "Heat Exchanger Fouling and Cleaning VII", Hans Müller-Steinhagen, Institute of Technical Thermodynamics, German Aerospace Centre (DLR)
and Institute for Thermodynamics and Thermal Engineering, University of Stuttgart, Germany
M. Reza Malayeri, University of Stuttgart, Germany
A. Paul Watkinson, The University of British Columbia, Canada
Eds, ECI
Symposium Series, Volume RP5 (2007). http://services.bepress.com/eci/heatexchanger2007/45
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