Marcelo A. L. Gonçalves

Mechanistic Modeling of the Convective Heat Transfer Coefficient in Gas-Liquid Intermittent Flows

The development of a mechanistic procedure to estimate the convection heat transfer in horizontal gas-liquid intermittent—or slug—flow is presented. In broad terms, the mean convective heat transfer coefficient is calculated following an averaging procedure based on the unit cell model of the slug flow pattern. The flow parameters (i.e., unit cell frequency, liquid slug and elongated bubble length and velocity, and liquid hold-up) were obtained from empirical data for air/water flows in a 15 m-long, 25.4 mm ID copper pipe and for natural gas (mostly methane and ethane) and oil or water flows in an actual size, 200 m-long, 150 mm ID steel pipe. A time-averaging procedure based on the unit cell parameters was then used to calculate the mean convective heat transfer coefficient. The slug flow parameters taken on the small scale air/water loop and the actual size pipeline were used for comparisons. Heat transfer data from the small scale air/water loop were used to validate the results calculated using the averaging procedure. Finally, the approach herein proposed also showed good agreement with previously published data and well-known correlations.

Horizontal Slug Flow in a Large-Size Pipeline: Experimentation and Modeling

The knowledge of the slug flow characteristics is very important when designing pipelines and process equipment. When the intermittences typical in slug flow occurs, the fluctuations of the flow variables bring additional concern to the designer. Focusing on this subject the present work discloses the experimental data on slug flow characteristics occurring in a large-size, large-scale facility. The results were compared with data provided by mechanistic slug flow models in order to verify their reliability when modelling actual flow conditions. Experiments were done with natural gas and oil or water as the liquid phase. To compute the frequency and velocity of the slug cell and to calculate the length of the elongated bubble and liquid slug one used two pressure transducers measuring the pressure drop across the pipe diameter at different axial locations. A third pressure transducer measured the pressure drop between two axial location 200 m apart. The experimental data were compared with results of Camargos1 algorithm (1991, 1993), which uses the basics of Dukler & Hubbards (1975) slug flow model, and those calculated by the transient two-phase flow simulator OLGA.

Hydrate Plug Movement by One-Sided Depressurization

A new model that accurately predicts hydrate plug displacement during a one-sided depressurization is presented. This model is both simple to handle and rigorous in the physical representation of the phenomenon. It was implemented as a finite volume transient simulator capable of determining the flow field coupled with the plug displacement dynamics after its detachment. It takes into consideration velocity, pressure and temperature profiles across chambers upstream and downstream the plug at each instant of time, as well as pipe deformation due to pressure variations inside the chambers. Typical cases for deep offshore production are analyzed. The influence on the plug displacement of the gas composition, the temperature variation due to the heat loss to the environment and high pressure variation is addressed. Results show that, depending on the conditions, and after performing a careful risk evaluation, it may be safe to remediate hydrate plug by one-sided depressurization in a number of typical situations in offshore production scenario.© 2012 ASME