We have developed and applied an Eulerian-Lagrangian model for the transport, formation, break-up, deposition and re-entrainment of particle agglomerates. In this paper, we focus on agglomeration and break-up. Simulations were carried out to investigate what changes in the turbulent flow are inflicted by the presence of the agglomerates. Also, the dependence of the properties of the agglomerates on the Reynolds number of the flow and on the strength of the bonds between the primary particles is studied. The presence of the agglomerates attenuates the turbulence and thereby lowers the Reynolds stresses. As a result, the flow rate increases at constant pressure drop when agglomerates are formed (up to a certain dimension). If the agglomerates surpass this dimension, long-distance viscosity effects become dominant and a flow rate decrease occurs. The characteristics of the agglomerates are largely insensitive to the Reynolds number, provided the flow is turbulent. The agglomerates have an open and porous structure, and a fractal dimension of 1.8-2.3. Their mean mass scales exponentially with the strength of the internal bonds. Contrary to assumptions that are typically made in engineering models in the literature, agglomerates do not preferentially break into two fragments of similar size.@en

We present a model for the formation, break-up, deposition and re-entrainment of solid particle agglomerates in turbulent flows. The turbulent flow of the liquid carrier is represented through Direct Numerical or Large Eddy Simulations. The structure of the agglomerates, which are formed by inter-linked spherical primary particles, is explicitly taken into account in this model. While firstly still ignoring deposition and re-entrainment, we present results on the properties of the agglomerates formed both in channel flow, and in flow in a cylindrical pipe. The collision rate of the agglomerates is found to be under-predicted by the Saffman & Turner collision kernel by up to a factor of 10. We also present results on the modification of the turbulence due to the presence of the agglomerates. Furthermore, results on the deposition and re-entrainment rate of the agglomerates, as well as on the additional streamwise pressure drop induced by the deposition are presented. Ultimately, the results obtained this way are used to construct improved engineering models for predicting asphaltene deposition during crude oil production.This research was carried out in the context of the Integrated Systems Approach to Petroleum Production (ISAPP) Knowledge Center. ISAPP is a joint project of the Netherlands Organization for Applied Scientific Research (TNO) and Delft University of Technology, sponsored by ENI, Petrobras, and Statoil.@en

In this work, we consider a combined momentum-mass source immersed boundary method that can be used to easily simulate flows in domains with arbitrary wall topographies, taking advantage of existing standard fast solvers for straight walls. This method is incorporated into a standard second-order finite-volume code with a Fast Fourier Transform solver, previously used for direct numerical simulations of flow in pipes with a straight wall, making it possible to study the influence of a large range of roughness topographies on the flow. The method is validated for both laminar and turbulent flow over walls with sinusoidal undulations. The implementation of the immersed boundary method preserves the second-order accuracy of the original code, and first-order methods are presented to calculate the shear-stress and the pressure-drag at the wall. Results for turbulent flow over walls represented by a single wave-number, as well as by a superposition of many wave-numbers, show that the flow in the outer layer is not affected by the nature of the wall topography, provided that the variation in the diameter is not too large. Furthermore, it is found that the relative contributions of the pressure and the shear to the total drag on the wall behave similarly to undulated channel flow, when considered as a function of an effective slope parameter. © 2014 Elsevier Ltd.@en

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