Characteristics of Twophase Flows in Vertical Pipe W

Characteristics of Two-phase Flows in Vertical Pipe W. G. Sim/Hannam University, N. W. Mureithi/ Ecole Polytechnique, Montreal, B. M. Bae/KAERI, M. J. Pettigrew/ Ecole Polytechnique, Montreal,

Characteristics of Two-phase Flows in Vertical Pipe W. G. Sim/Hannam University, B. M. Bae/KAERI, N. W. Mureithi/ Ecole Polytechnique, Montreal, M. J. Pettigrew/ Ecole Polytechnique, Montreal, ABSTRACT: The characteristics of two-phase flow in a vertical pipe are investigated to gain a better understanding of vibration excitation mechanisms. An analytical model for two-phase flow in a pipe was developed by Sim et al. (2005), based on a power law for the distributions of flow parameters across the pipe diameter, such as gas velocity, liquid velocity and void fraction. An experimental study was undertaken to verify the model. The unsteady momentum flux impinging on a ‘turning tee’ (or a ‘circular plate’) has been measured at the exit of the pipe, using a force sensor. From the measured data, especially for slug flow, the predominant frequency and the RMS value of the unsteady momentum flux have been evaluated. It is found that the analytical method, given by Sim et al. for slug flow, can be used to predict the momentum flux.

Contents o Introduction o Drift Flux Model for Two-phase Flow in a Pipe o Power Law for Distributions of Flow Parameters o Average Values with Integral Analysis o Reynolds Transport Theorem Steady Momentum Flux, Unsteady Momentum Flux for Slug Flow o Experimental Investigations o Test Loops o Comparisons with Theory o Conclusions Hannam University , Ecole Polytechnique Montreal

Introduction o Initial Motivation o Slender Structural Elements - Fretting Wear Damage o Flow Mechanism of Two-phase Flow Homogeneous Model - Only for Bubbly Flow o Hydrodynamic Force – Momentum Flux o Analytical Approach for Dynamic Response Experimental Study, Reliable Prediction of Dynamic Response o Main Purpose o To investigate characteristics of two-phase flow in vertical pipe an analytical model proposed based on a power law, experimental study undertaken o To verify the analytical model, with experimental results o To obtain information on the reaction force Hannam University , Ecole Polytechnique Montreal

Drift Flux Model for Two-phase Flow in a Pipe Power Law for Distributions of Flow Parameters o Assumptions; - o neglecting adherence or reflection of bubble at the surface of the wall Distributions of Flow Parameters Void Fraction for bubbly flow for slug flow * Subscript “L” stands for local time average value Hannam University , Ecole Polytechnique Montreal Velocity distribution for gas and liquid

Average Values with Integral Analysis § Void Fraction § Velocity § Volumetric Quality § Flow Quality § Slip Ratio Hannam University , Ecole Polytechnique Montreal

Reynolds Transport Theorem o Momentum Equation where Hannam University , Ecole Polytechnique Montreal

o Steady Momentum Flux o Momentum Flux by Liquid o Momentum Flux by Gas o Momentum Multiplier where mass flux Hannam University , Ecole Polytechnique Montreal

Unsteady Momentum Flux for Slug Flow o Void Fraction; o Formulation; - Frequency for Slug Flow by Heywood and Richardson(1979) - Sequence of Momentum by liquid and Gas; Fourier series C=0. 0543 for vertical flow o Reduced Frequency; Hannam University , Ecole Polytechnique Montreal C =0. 0434 for horizontal flow

Unsteady Momentum Flux for Slug Flow o By Liquid o By Gas Hannam University , Ecole Polytechnique Montreal

o RMS Value of Reaction Force by Slug Flow Hannam University , Ecole Polytechnique Montreal

Experimental Investigations o Test Loops EPM HNU EPM HNU Length (m) 1. 52 1. 01 Inner Diameter (mm) 20. 8 30 Mixture Fine screen Multiple inlet holes (equally distributed ) High contraction ratio Control volume for the reaction force Turning Tee Circular Plate (Diameter=280 mm) Test Cylinder Hannam University , Ecole Polytechnique Montreal

Flow patterns (Taitel et al. , 1980) selected for bubbly and slug flow and dynamic time traces of the dynamic reaction force(HNU) Hannam University , Ecole Polytechnique Montreal

Typical force spectra given by EPM for Hannam University , Ecole Polytechnique Montreal

Typical force spectra given by HNU Hannam University , Ecole Polytechnique Montreal

Steady parameters given by HNU ( Blue; Green; Hannam University , Ecole Polytechnique Montreal ) Red;

Comparison of test results to analytical results ( __, o ; for sec EPM HNU Hannam University , Ecole Polytechnique Montreal )

Comparison of test results to analytical results ( _ _ , ___ ; ) for (Blue) and (Red) HNU Hannam University , Ecole Polytechnique Montreal EPM

Reduced Frequency (Azzopardi and Baker, 2003) EPM HNU Hannam University , Ecole Polytechnique Montreal

Conclusions o An analytical model for two-phase flow in a pipe, based on a power law The integral forms easily incorporated into models for momentum flux o Reaction force exerted by the momentum flux at the exit of the pipe. – – Two air-water loops were constructed. Momentum Flux (for bubbly flow; Force spectra (for bubbly flow, slug flow) Reduced frequency (for slug flow) , slug flow; o Good agreement shown between the results Hannam University , Ecole Polytechnique Montreal )