Heat transfer modeling of non-boiling gas-liquid slug flow using a slug tracking approach

Abstract

This study proposes a new set of equations for the energy balance for predicting the temperature distribution of gas-liquid slug flows using a slug tracking approach. The model proves able to work around non-physical oscillations of the temperature distribution found with a previously published set of equations for the energy balance. The main difference here is that rather than being applied to each structure (namely the liquid slug, the liquid film and the elongated bubble) individually, the temperature is assigned to the whole unit cell. Central Differencing Schemes were avoided since the problem is convection-dominant, thus preference to Upwind Differencing Schemes was given. Comparison of the new model with an experimental dataset for air-water flow in a 52-mm ID pipeline showed deviations of ±25% for the temperature and pressure gradients. An extra head loss term caused by the recirculation of liquid in the elongated bubble wake was introduced into the momentum balance, correcting an existing –20% systematic deviation found in the pressure gradient as computed by the former model. Simulations for an extended, 200-m long pipeline comparing isothermal, cooling and heating flows are also presented. These simulations demonstrate the competition of gas expansion caused by pressure drop and of gas expansion/contraction caused by mixture heating/cooling, and their consequences on the elongated bubble length increase/decrease, on the mixture acceleration/deceleration, on the coalescence rate of elongated bubbles, and on their statistic distributions.