Published on May 5, 2014
Two-Phase Flow Patterns and Flow-Pattern Maps Mostafa Ghadamyari M.SC Student, Mechanical Engineering, Tarbiat Modares University Spring 2014 1
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 2
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 : 3 Increasing Vg
Two-phase Flow-Patterns Horizontal Tube Flow-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 :
Two-phase Flow-Patterns Horizontal tube videos 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
Diabatic Two-Phase Flows Upward Flow 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
Diabatic Two-Phase Flows Condensation in 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,”
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
Flow Pattern Maps The Baker 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.
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 : 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
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 11
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