The Component Displacement Process of Two Miscible but Dissimilar Fluids Transported Sequentially in a Multiproduct Pipeline

Abstract

A single-phase incompressible bicomponent transient oil mixing model was established based on the mechanism of flow, heat, and mass transfer of refined oils to obtain the flow field and concentration distribution of the component at the mixed segment during the batch transportation process. A new model for the axial diffusion coefficient was proposed, which included the turbulent diffusion coefficient and the coefficients derived from the differences in fluid physical properties. The new diffusion coefficient calculation formula presented in this paper could make the error very small when the calculated concentration distribution value of the mixing section is compared with the experimental value. Based on the many factors that affect the flow features during the oil replacement process in the mixed-oil section, the main dimensionless parameters (Reynolds, Peclet, Prandtl, Richardson, Schmidt) are selected by using the dimensional analysis method. The mixed segment had a high Pr and Pe. With an increasing concentration of lighter oil, the Pr decreased while the Pe and Re increased. The Ri was always less than 1, which implied that the buoyancy is not important, and the gravity effect can be ignored during the generation process of oil mixing according to the definition of Ri that buoyancy is dominant when it is greater than 1. The change of Sc versus the concentration of gasoline was small, and Sc was always close to 100, which indicated that the momentum diffusion was greater than the mass diffusion in the process of oil mixing. Sensitivity analysis was carried out based on the tailing amount and tailing length of the mixed section. It was concluded that the influence of pipe diameter, flow rate, temperature, and diffusion coefficient on the tailing amount and tailing length had the same trend. A single-phase incompressible two-component transient oil-mixing model is established to obtain the flow field and component concentration distribution in the mixing section during batch transportation in this paper. The flow characteristics and tailing phenomena of the mixed-oil section are determined by studying the dimensionless numbers (Reynolds, Peclet, Prandtl, Richardson, Schmidt) in the oil change process of the mixed-oil section. The experimental results could predict the distribution of oil mixture concentration under specific working conditions. The influences of the difference of oil physical properties, turbulence effect as well as the adsorption effect of the pipe wall on the distribution of oil mixture concentration have also been discussed. The research results show that this technology provides the location and concentration distribution of the mixed oil segment when it is applied to practical cases, which gives technical support for detecting and cutting the mixed oil segment during the process of batch transportation and also guides the accurate cutting of the mixing segment.