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Dipartimento di Scienze e Metodi dell'Ingegneria
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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2023 - Experimental measurements and CFD modelling of hydroxyapatite scaffolds in perfusion bioreactors for bone regeneration [Articolo su rivista]
D’Adamo, Alessandro; Salerno, Elisabetta; Corda, Giuseppe; Ongaro, Claudio; Zardin, Barbara; Ruffini, Andrea; Orlandi, Giulia; Bertacchini, Jessika; Angeli, Diego

In the field of bone tissue engineering, particular interest is devoted to the development of 3D cultures to study bone cell proliferation under conditions similar to in vivo ones, e.g. by artificially producing mechanical stresses promoting a biological response (mechanotransduction). Of particular relevance in this context are the effects generated by the flow shear stress, which governs the nutrients delivery rate to the growing cells and which can be controlled in perfusion reactors. However, the introduction of 3D scaffolds complicates the direct measurement of the generated shear stress on the adhered cells inside the matrix, thus jeopardizing the potential of using multi-dimensional matrices. In this study, an anisotropic hydroxyapatite-based set of scaffolds is considered as a 3D biomimetic support for bone cells deposition and growth. Measurements of sample-specific flow resistance are carried out using a perfusion system, accompanied by a visual characterization of the material structure. From the obtained results, a subset of three samples is reproduced using 3D-Computational Fluid Dynamics (CFD) techniques and the models are validated by virtually replicating the flow resistance measurement. Once a good agreement is found, the analysis of flow-induced shear stress on the inner B-HA structure is carried out based on simulation results. Finally, a statistical analysis leads to a simplified expression to correlate the flow resistance with the entity and extensions of wall shear stress inside the scaffold. The study applies CFD to overcome the limitations of experiments, allowing for an advancement in multi-dimensional cell cultures by elucidating the flow conditions in 3D reactors.

2023 - Friction and wear of DLC films deposited on additive manufactured AlSi10Mg: the role of surface finishing [Articolo su rivista]
Salerno, E.; Casotti, D.; Paolicelli, G.; Gualtieri, E.; Ballestrazzi, A.; Gazzadi, G. C.; Bolelli, G.; Lusvarghi, L.; Valeri, S.; Rota, A.

2022 - Liquid flow in scaffold derived from natural source: experimental observations and biological outcome [Articolo su rivista]
Salerno, Elisabetta; Orlandi, Giulia; Ongaro, Claudio; D'Adamo, Alessandro; Ruffini, Andrea; Carnevale, Gianluca; Zardin, Barbara; Bertacchini, Jessika; Angeli, Diego

This study investigates the biological effects on a 3D scaffold based on hydroxyapatite cultured with MC3T3 osteoblasts in response to flow-induced shear stress (FSS). The scaffold adopted here (B-HA) derives from the biomorphic transformation of natural wood and its peculiar channel geometry mimics the porous structure of the bone. From the point of view of fluid dynamics, B-HA can be considered a network of micro-channels, intrinsically offering the advantages of a microfluidic system. This work, for the first time, offers a description of the fluid dynamic properties of the B-HA scaffold, which are strongly connected to its morphology. These features are necessary to determine the FSS ranges to be applied during in vitro studies to get physiologically relevant conditions. The selected ranges of FSS promoted the elongation of the attached cells along the flow direction and early osteogenic cell differentiation. These data confirmed the ability of B-HA to promote the differentiation process along osteogenic lineage. Hence, such a bioactive and naturally derived scaffold can be considered as a promising tool for bone regeneration applications.

2021 - Influence of the Thermophysical Model on the CFD Analysis of Oil-Cooled Transformer Windings [Relazione in Atti di Convegno]
Salerno, E.; Leonforte, A.; Angeli, D.

A disc-type winding of an oil-immersed power transformer is modeled with Computational Fluid Dynamics. Different approaches are implemented to evaluate the feasibility of the Boussinesq approximation: (i) constant fluid properties, (ii) variable viscosity and thermal diffusivity and (iii) temperature-dependent fluid properties. Temperature and flow distributions are reconstructed and put into relation with physical phenomena and model assumptions. Their comparison suggests that numerical results are fairly sensitive to the thermophysical model as long as the buoyancy force is a relevant component of the flow. Nonetheless, all the cases converge to very close predictions of the hot-spot value and location, with possibly positive implications for the use of reference parameters when deriving flow and heat transfer correlations for this topic.

2017 - Foam evolution in a processed liquid solution [Relazione in Atti di Convegno]
Salerno, Elisabetta; Levoni, Paolo; Barozzi, Giovanni Sebastiano; Malfatto, Annalisa

Foam formation in a carbonated solution undergoing pouring and decompression is investigated with the use of high-speed imaging. Operational conditions similar to those encountered in industrial bottling processes are applied to inspect the mechanisms that control the foaming behavior in practical filling applications. The evolution of the foam column during pressure release is analyzed in quantitative terms by extracting the foam thickness from the images. The bubble dynamics inside the solution and the destabilization processes on the foam column are seen to have a paramount effect on the observed foam evolution trend. The contributions to foam formation given by the nuclei entrained in the bulk liquid and by the bubble-generating sites on the container walls are finally distinguished and discussed.

2017 - Notes and experiments on the statics of capillary columns [Relazione in Atti di Convegno]
Barozzi, Giovanni Sebastiano; Corticelli, Mauro Alessandro; Angeli, Diego; Salerno, Elisabetta

Experimental results are summarized, concerned with the statics of liquid columns in capillary tubes under non-standard conditions. Three configurations are considered: 1. inclined capillary tubes; 2. capillary effect in the horizontal branch of an L-shaped tube; 3. capillary columns in a vertical tube. The effect of inclination on capillary rise (1.) had already been explored in [1] using water in glass-tubes, and it was found that the vertical rise progressively reduces for increasing the tube inclination. This behavior is now confirmed for n-Hexadecane (C16H34). For L-shaped capillaries (2.), the length of the horizontal branch of the tube occupied by the liquid is detected, as a function of the elevation of the branch itself over the feeding pool. The statics of suspended liquid columns (3.) is investigated for two configurations, namely: i. freely suspended columns, and, ii. edge-ending columns. In the latter case, the evaporation transient is also tracked. Even if the experimental basis is limited, the results are sufficient to highlight some of the peculiar features of the statics of capillary columns under the above conditions. In particular, it is shown that the contact angle hysteresis plays a fundamental role in all the cases considered.

2015 - Air entrainment in the primary impact of single drops on a free liquid surface [Relazione in Atti di Convegno]
Salerno, Elisabetta; Levoni, Paolo; Barozzi, Giovanni Sebastiano

Air-bubble entrainment produced by the impact of water drops on a liquid pool is investigated with the use of high-speed imaging. A wide range of drop volumes and impact velocities is considered to determine how the entrainment mechanisms change with varying the impact conditions. Five different entrainment regimes are distinguished on the basis of the observed flow phenomena. Their characteristic features are described in terms of bubble formation, crater evolution, jetting and secondary drop ejection. A regime map is reconstructed in the Froude-Weber space. Results obtained in the present study show good agreement with the phase diagrams reported in the literature and contribute to complete the scenario of the entrainment regimes. Quantitative data about the size and the residence times of the entrained nuclei are also presented.

2013 - PIV experiments on a valve for the handling of liquids [Relazione in Atti di Convegno]
Salerno, Elisabetta; Levoni, Paolo; Angeli, Diego; Barozzi, Giovanni Sebastiano

Particle Image Velocimetry (PIV) is employed to investigate the flow field inside the dummy of a prototype valve to be used for the industrial dosage of liquids. Velocity fields are reconstructed in three regions of the valve passages and for two values of the flow rate. Distilled water is used as the working fluid. Optical limitations were faced during the setup of the apparatus and a description of the expedients adopted is reported. Time-averaged velocity fields reveal the presence of critical fluid behaviours such as throttling, asymmetric flows and vortex generation. Those effects strongly affect the valve performance. The quality of PIV measurements is verified by comparing the experimental data with the results of RANS-based numerical simulations. Contour maps and velocity profiles obtained with the two methods show a very good agreement, thus demonstrating the reliability of PIV in this specific context. A first attempt was also made to characterize the jet flow at the valve outlet using PIV. It is found that in this case the accuracy of the measurements deteriorates, due to the presence of fluid-dynamic instabilities at the jet surface.