Two-Phase Flow Patterns and Flow-Pattern Maps

Two-Phase Flow Patterns and Flow-Pattern Maps

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  Two-Phase Flow Patterns andFlow-Pattern Maps Mostafa Ghadamyari M.SC Student, Mechanical Engineering, Tarbiat Modares University Spring 2014 1
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  Why study two-phaseflows? 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 2
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  Two-phase Flow-Patterns Flow patterndefinition:  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 : 3 Increasing Vg
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  Two-phase Flow-Patterns Horizontal TubeFlow-patterns : 4  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 :
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  Two-phase Flow-Patterns Horizontal tubevideos Vertical tube videos 5  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
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  Diabatic Two-Phase Flows UpwardFlow Boiling In A Vertical & Horizontal Tube : 6  Pressure drop & Heat transfer coefficient are related to two-phase Flow Patterns  Collier, J. G., and Thome, J. R., 1994,Convective Boiling and Condensation
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  Diabatic Two-Phase Flows Condensationin Horizontal Tube : 7  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,”
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  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, … 8
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  Flow Pattern Maps TheBaker flow-pattern map for horizontal gas-liquid cocurrent flow. 9 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.
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  Flow Pattern Maps TheTheoretical Taitel and Dukler flow- pattern map for horizontal gas-liquid cocurrent flow : The Kattan–Thome–Favrat flow- pattern map compared to the Steiner map : 10 Evaluated for R410A at Tsat=5°C in a 13.84 mm internal diameter tube at different heat fluxes X : Martinelli parameter X= [(dP/dZ)L / (dP/dZ)G]^0.5
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  Summary  We discussedabout:  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 11
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