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Prediction of onset of nucleate boiling, net vapour generation and subcooled CHF in coiled tubes

Berechnung des Einsetzens von Blasensieden, der Nettodampferzeugung und der kritischen Wärmestromdichte bei unterkühltem Sieden in gewendelten Rohren

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Abstract

The heat transfer characteristics of a coiled steam generating tube are very different from those of a straight tube. For example, the critical heat flux (CHF) in coiled tubes is less than that in straight tubes for subcooled boiling and significantly higher at higher qualities. In this paper, predictive methods are developed for the determination of the point of onset of nucleate boiling, the point of net vapour generation and the critical heat flux condition in curved ducts. The methods are based on the assumption that these phenomena are governed by the local hydro- and thermodynamic conditions which can be predicted using computational fluid dynamics techniques. Good agreement has been obtained with available experimental data.

Zusammenfassung

Die Wärmeübertragung in einem gewendelten Dampferzeugerrohr ist sehr verschieden von der in einem geraden Rohr. So ist zum Beispiel der kritische Wärmestrom in gewendelten Rohren geringer als im geraden Rohr für unterkühltes Sieden, aber beträchtlich höher bei höheren Dampfgehalten. In dieser Arbeit wurden Methoden entwickelt, um das Einsetzen des Blasensiedens und der Nettodampferzeugung sowie die Bedingung für den kritischen Wärmestrom in gekrümmten Kanälen vorauszuberechnen. Diese Methoden beruhen auf der Annahme, daß diese Vorgänge durch die örtlichen hydro- und thermodynamischen Bedingungen bestimmt werden, die sich aus Rechenverfahren der Fluiddynamik ermitteln lassen. Mit den verfügbaren experimentellen Daten herrschte gute Übereinstimmung.

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Abbreviations

C p :

specific heat at constant pressure

d :

tube diameter

D :

coil (bend) diameter

G :

mass flux

h :

heat transfer coefficient

i fg :

latent heat of vapourisation

Nu :

Nusselt number =hd/λ

Pe :

Peclet number =Re Pr

Pr :

Prandtl number = μC p/λ

q″:

heat flux

Re :

Reynolds number =u m d/ν

T :

temperature

u m :

mean flow velocity

x :

quality

α :

thermal diffusivity

λ :

thermal conductivity

μ :

dynamic viscosity

ϱ :

density

σ :

surface tension

a :

axial direction

b :

bulk

c :

coil

i :

inner

l :

liquid phase

m :

mean

NVG:

at the point of net vapour generation

ONB:

at the point of onset of nucleate boiling

ref:

at the reference point

s :

straight tube

sat:

saturated state

t :

tube

w :

wall

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Authors and Affiliations

  1. Department of Chemical Engineering and Chemical Technology, Imperial College of Science, Technology and Medicine, SW7, 2BY, London, UK

    S. Jayanti & G. F. Hewitt

Authors
  1. S. Jayanti
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  2. G. F. Hewitt
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Dedicated to Prof. Dr.-Ing. F. Mayinger's 60th birthday

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Jayanti, S., Hewitt, G.F. Prediction of onset of nucleate boiling, net vapour generation and subcooled CHF in coiled tubes. Wärme- und Stoffübertragung 26, 301–305 (1991). https://doi.org/10.1007/BF01591662

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  • DOI: https://doi.org/10.1007/BF01591662

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