two-phase flow patterns and flow-pattern maps

Two-Phase Flow Patterns

and Flow-Pattern MapsMostafa Ghadamyari

M.SC Student, Mechanical Engineering, Tarbiat Modares University

Spring 2014

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Why study two-phase flows?

Example: Dead water Phenomenon

1893 Fridtjof Nansen

Occurs when fresh water rests on

dense salt water

Much of the energy results in

waves and turbulence of

interface

Reduce in traveling speed by 80%

If V>Vcritical Then the phenomenon

disappears

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Two-phase Flow-Patterns

Flow pattern definition:

Various gas-liquid interfacial

geometric configurations in two-phase flow systems.

The physical mechanisms

controlling two-phase pressure

drops and heat transfer

coefficients are intrinsically related

to the local flow patterns

Vertical tubes Flow-patterns :

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Increasing Vg


Horizontal Tube Flow-patterns :

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Stratified : Small Vg & VL

Increasing both Vg & VL : Wavy

Increased VL but small Vg : Plug, If

bubbles are small : Dispersed

Bubble

Plug + Increase Vg : Slug

Slug + Increase Vg : Annular and

then Mist

Different Conditions,

Different Flows :


Horizontal tube videos Vertical tube videos

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Ammonia @ 5C

Horizontal Tube, d=14mm

Zürcher, Thome, Favrat

Swiss Federal Institute of

Technology Lausanne

(EPFL).

Air & Water @ 25C

Vertical Tube, d=30mm

Zun and Polutnik

University of Ljubljana,

Slovenia

Diabatic Two-Phase Flows

Upward Flow Boiling In A Vertical & Horizontal Tube :

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Pressure drop & Heat transfer coefficient are related to two-phase Flow Patterns

Collier, J. G., and Thome, J. R., 1994,Convective Boiling and Condensation

Diabatic Two-Phase Flows

Condensation in Horizontal Tube :

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Condensation film forms Annular

flow in the entrance

As condensation continues, the

vapor velocity falls

At high flow rates, slug and

bubble flows are eventually

reached

At low flow rates large magnitude

waves and then stratified flow are formed.

Palen, J. W., Breber, G., and Taborek, K., 1979, “Prediction of Flow Regimes

in Horizontal Tube-Side-Condensation,”

Flow Pattern Maps

To predict local flow patterns, two-phase

flow-pattern maps are used.

Mostly developed for adiabatic conditions

First paper published in 1950

Two categories :

1. Empirical Flow-Pattern Maps

The Baker, Hewitt & Roberts, …

2. Theoretical Flow-Pattern Maps

Taitel and Dukler, …

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Flow Pattern Maps

The Baker flow-pattern map for

horizontal gas-liquid cocurrent flow.

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The Hewitt and Roberts flow-pattern

map for vertical upward gas-liquid

cocurrent flow

Based on observations of cocurrent flow of gaseous and

condensate petroleum products in horizontal pipes.

Flow Pattern Maps

The Theoretical Taitel and Dukler flow-

pattern map for horizontal gas-liquid

cocurrent flow :

The Kattan–Thome–Favrat flow-pattern map compared to the

Steiner map :

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Evaluated for R410A at Tsat=5°C in a 13.84 mm

internal diameter tube at different heat fluxes

X : Martinelli parameterX= [(dP/dZ)L / (dP/dZ)G]^0.5

Summary

We discussed about:

Different types of two-phase flow patterns

Flow patterns in horizontal and vertical tubes

Flow Pattern maps:

1. Experimental maps

Baker, Hewitt & Robert, …

2. Theoretical maps

Taitel & Dukler

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