Modelling of wave velocity, wave frequency and interfacial friction factor in vertical upward and downward annular flow

Abstract

Accurate closure laws for roll wave velocity, roll wave frequency and interfacial friction factor are crucial for eddy diffusivity modelling of heat transfer coefficient and liquid film thickness in annular flow boiling. The focus of this work is to develop suitable models for these parameters from flow boiling data by the authors and adiabatic two-phase flow data in open literature. The flow boiling data were obtained from a test loop consisting of a vertical 6mmID transparent heated test section and the test fluid was HFE-7000 refrigerant. The flow boiling data for mean roll wave velocity, mean roll wave frequency and interfacial friction factor were functions of the mass flux, vapor quality, wall heat flux and flow orientation relative to gravity. Models for predicting the roll wave parameters and interfacial friction factor in annular two-phase flow were developed and these models were validated using flow boiling data from this work and adiabatic data from open literature with the mean absolute percentage error (MAPE) serving as the figure of merit. The proposed model for the roll wave velocity of upward and downward flow boiling predicted the measured data within ±15 % with MAPE of 5.0 % and 2.2 % respectively. In the case of roll wave frequency, the proposed model for upward and downward flow boiling predicted the measured data within ±20 % with MAPE of 7.02 % and 5.87 % respectively. These correlations also reproduced the mass flux, vapor quality and wall heat flux dependence of these wave parameters in both flow orientations relative to gravity. The proposed models for the wave velocity and wave frequency predicted literature data for adiabatic gas-liquid flows within ±30 % with maximum MAPE of 16.4 % and 35.2 % respectively. The predicted roll wave velocity and roll wave frequency were also used to predict the measured flow boiling interfacial friction factor. The predicted interfacial friction factor was within ±30 % of the measured data with MAPE of 10.8 % and 20.3 % for upward and downward flow respectively.