Dynamic Interfacial Tension Method for Measuring Gas Diffusion Coefficient and Interface Mass Transfer Coefficient in a Liquid

Abstract

This paper presents a new dynamic interfacial tension method for measuring the gas diffusion coefficient and the interface mass transfer coefficient in a liquid at a high pressure and a constant temperature. In the experiment, a see-through windowed high-pressure cell is filled with a test gas at a prespecified pressure and a constant temperature. Then a liquid sample is introduced by using a syringe delivery system to form a pendant liquid drop inside the pressure cell. With the dissolution of the gas into the pendant liquid drop, the dynamic interfacial tension between the test gas and the liquid keeps reducing and eventually reaches its equilibrium value when the saturation state is achieved. The sequential digital images of the pendant liquid drop are acquired and analyzed by applying computer-aided digital image acquisition and processing techniques to measure the dynamic interfacial tensions. Theoretically, a mass transfer model is developed to study the diffusion process of the gas inside the pendant liquid drop. This model is solved numerically by applying the semidiscrete Galerkin finite element method to obtain the transient gas concentration distribution inside the pendant liquid drop at any time. With a predetermined calibration curve of the equilibrium interfacial tension versus the equilibrium gas concentration for the gas−liquid system, the corresponding dynamic interfacial tension is calculated. The gas diffusion coefficient and the interface mass transfer coefficient are, thus, determined by finding the best fit of the theoretically calculated dynamic interfacial tensions to the experimentally measured data. This newly developed dynamic interfacial tension method is applied to measure the diffusion coefficient and the interface mass transfer coefficient of CO2 in a reservoir brine sample at P = 0.1−6.0 MPa and T = 27 °C.