Seaweeds (marine macroalgae) are autotrophic organisms capable of producing many compounds of interest. For a long time, seaweeds have been seen as a great nutritional resource, primarily in Asian countries to later gain importance in Europe and South America, as well as in North America and Australia. It has been reported that edible seaweeds are rich in proteins, lipids and dietary fibers. Moreover, they have plenty of bioactive molecules that can be applied in nutraceutical, pharmaceutical and cosmetic areas. There are historical registers of harvest and cultivation of seaweeds but with the increment of the studies of seaweeds and their valuable compounds, their aquaculture has increased. The methodology of cultivation varies from onshore to offshore. Seaweeds can also be part of integrated multi-trophic aquaculture (IMTA), which has great opportunities but is also very challenging to the farmers. This multidisciplinary field applied to the seaweed aquaculture is very promising to improve the methods and techniques; this area is developed under the denominated industry 4.0.

The hydraulic conveying of solid-liquid concentrated suspensions in pipelines corresponds to complex flows where particles with different sizes, concentrations and flow velocities exhibit different flow regimens. Predicting their behavior is fundamental for the adequate design of pumping equipment and flow rigs. In traditional numerical approaches the turbulence production is assumed to be directly dependent on the increase of the particle size; this contradicts data from the literature where small particles cause an augmentation of turbulence and medium size particles attenuate turbulence. Also, in the traditional approach the same drag correlation is assumed to account for particle-fluid interaction in different flow regimes, which, in the case of turbulence augmentation and attenuation can differ considerably. In the present work numerical studies were conducted to simulate highly concentrated flows of settling medium sized particles using a Mixture Model, incorporating a Low Reynolds turbulence closure and a Schiller-Naumann drag correlation to depict the flow of concentrated solid-liquid suspensions. Since not all particle distributions were accurately portrayed, different drag correlations were implemented to provide a more adequate representation of the relative velocity between phases and particle distributions. Amongst the drag correlations implemented the Schiller & Naumann showed the best agreement for the highest particle concentrations at intermediate velocities, whilst the Haider & Levenspiel displayed the best fit with the experimental data for the highest flow velocities and particle concentrations. The Gidaspow-Schiller-Naumann drag correlation was more adequate for low flow velocities and with intermediate particle concentrations. With this work it is shown that using the same drag correlation for the numerical description of experimental data for highly concentrated settling solid-liquid flows does not adequately reproduce the different flow regimes

In the pulp and paper industry, the design of industrial equipment based on empirical correlations can be avoided using Computational Fluid Dynamics (CFD) tools. The present study aims at investigation of the turbulent pipe flow of concentrated Eucalyptus pulp suspension using the ANSYS FLUENT® CFD software package. The modelling strategy was a pseudo-homogeneous approach. The non-Newtonian behavior of the pulp suspension was introduced into the CFD code considering its viscosity as a function of a shear rate. Additionally, the existence of a water annulus at the pipe wall surrounding the core flow was taken into account. Four low-Reynolds k-ɛ turbulence models were selected in the present study aiming at describing the presence of a drag reduction effect. All the models used were able to reproduce the drag reduction effect. Additionally the Lam-Bremhorst model was modified taking into account alterations applied successfully by other authors for the turbulent flow of polymer solutions. A good correspondence between the peculiar S-shaped profile near the wall, for the dimensionless velocity, reported in literature for these systems and those obtained numerically was achieved. The approach followed was validated by comparing the numerical results of pressure drop with those from literature

Computational tools such as Computational Fluid Dynamics can be useful to predict the flow of pulp suspensions. The present study aims to simulate numerically the flow of concentrated pulp suspensions using CFD tools. A commercial CFD software was used, Ansys Fluent, to simulate the turbulent flow of Eucalyptus and Pine suspensions. A pseudo-homogenous approach was followed by considering the pulp viscosity as a function of shear rate and pulp consistency. The model takes into account the existence of a very thin layer surrounding the core region, near the pipe wall. It is studied the influence of the presence of fibers in the lubrication layer, by considering that the pulp consistency depends on the distance to the pipe wall. Two low-Reynolds number (LRN) k-ϵ turbulence models, Abe-Kondoh-Nagano and Chang-Hsieh-Chen, implemented in Ansys Fluent by using User-Defined-Functions, were studied. The drag reduction effect observed experimentally could be reproduced by both models. The LRN models were modified taking into account the modifications proposed in literature for the turbulent flow of polymers and solid particles when a drag reduction effect is present. The models were validated by comparing the calculated pressure drop with the experimental values.

Eucalyptus and Pine suspensions flow in a pipe was studied experimentally and numerically. Pressure drop was measured for different mean inlet flow velocities. Electrical impedance tomography (EIT), was used to evaluate the prevailing flow regime. Fibers concentration distribution in the pipe cross section and plug evolution were inferred from EIT tomographic images. A modified low-Reynolds-number k–ε turbulence model was applied to simulate the flow of pulp suspensions. The accuracy of the computational fluid dynamics (CFD) predictions was significantly reduced when data in plug regime was simulated. The CFD model applied was initially developed to simulate the flow of Eucalyptus and Pine suspensions in fully turbulent flow regime. Using this model to simulate data in the plug regime leads to an excessive attenuation of turbulence which leads to lower values of pressure drop than the experimental ones. For transition flow regime, the CFD model could be applied successfully to simulate the flow data, similar to what happens for the turbulent regime.