This paper presents the mixing model for illuminating the influence of density, viscosity and the topographical height difference on the interfacial product-mixing in pipeline, in which a new virtual axial dispersion coefficient related with contamination concentration and its gradient was utilized. With the simplification of the Reynolds number of the mixture unvaried with the concentration, contamination concentration distribution relevant to density difference and gravitation acceleration etc was developed. When the Reynolds number of the mixture was a function of concentration, the mixing model was solved numerically by Crank-Nicholson implicit difference scheme. Analysis indicated that the effect of inclination angle on contamination decreases gradually with the increase of the distance traveled by the interface and the contamination Reynolds number. Particularly, the degree of effect became invisible when pipeline is in completely turbulent flow, and the Reynolds number is greater than the critical Reynolds number defined by Austin and Palfrey while the pipeline was considerably long. In the undulate long-distance multi-products pipeline, contamination due to topographical height difference can be ignored in turbulent flow while the Reynolds number is greater than critical Reynolds number.
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