Claudia Carotenuto

Shear flow over a porous layer: Velocity in the real proximity of the interface via rheological tests

In this paper, we have experimentally investigated the velocity profile of a fluid undergoing simple shear above a porous medium. To this end, we used for the first time rheological tests performed with a constant stress rheometer equipped with parallel plate geometry with a real porous medium glued on the lower plate. The velocity at the interface between the porous layer and the free fluid was inferred by extrapolating the linear velocity profile in the free fluid to the interface. These data were nicely compared with predictions obtained integrating the Brinkman extension of Darcy law in the porous medium together with Stokes equations in the free fluid coupled at the interface by the continuity of velocity and by the momentum balance suggested by Ochoa-Tapia and Whitaker [Int. J. Heat Mass Transfer 38(14), 2635 (1995)]. In the literature, the physical origin of the stress jump imposed by Ochoa-Tapia and Whitaker at the interface has been attributed to a perturbation of the velocity profile in the vici...

A new experimental technique to study the flow in a porous layer via rheological tests

This paper reports an experimental investigation of shear-driven flow above and below a porous medium. A new technique based on rheological measurements is proposed and illustrated. Two configurations are investigated: One where there is a shear driven flow above the porous layer. In this case, the velocity profile in the free fluid is directly measured together with the velocity at the interface. The other where a shear flow is induced in the free fluid below a moving porous layer. In this case, the stress transferred through the porous layer is directly measured. Our results show that the stress transferred to the free fluid is essentially the same in both configurations. We have verified this with two sandpapers with different roughness, used to mimic two slender porous layers. This result might be used to validate the different boundary conditions proposed in the literature and imposed at the interface between the two domains.

Compressive and Thermal Properties of Recycled EPS Foams

Optimization of moulding process in order to maximize the recycled fraction in EPS products is a key industrial goal. To this end effects of quality and quantity of recycled EPS upon physical properties of products are studied. Results show, on the one hand, that the introduction of a recycled fraction brings to products with a reduced density. On the other hand, small modifications of the process parameters allow for a reduction in this density decrease. Furthermore, results show that mechanical and thermal behaviour of EPS depend only on the materials density apart from the possible presence of a recycled fraction.

Effect of gas temperature on the capture of charged particles by oppositely charged water droplets

ABSTRACT This work reports experimental results on the effects of temperature (25, 45, and 65°C at different relative humidity) on the scrubbing of charged submicron particles by means of cold (25°C) droplets charged with opposite polarity. The aim of the study is to experiment how the capture of particles is influenced by the simultaneous presence of electrostatic and phoretic forces related to the occurrence of thermal and water vapor gradients close to the droplet surface. This information plays an important role in the development of wet electrostatic scrubbing (WES), an emerging technology for submicron and ultrafine particle capture. Tests were performed in a lab-scale system in which the particle laden-gas was scrubbed by a train of identic droplets. Particles were charged by a corona source while droplets are generated by electrospraying. Experiments revealed that for particles larger than about 250–300 nm, there were higher removal efficiencies in nonisothermal conditions, with limited differences between 45 and 65°C tests. For particles finer than about 150 nm, we sometimes observed lower removal efficiencies for higher gas temperatures, probably due to the difficulties in controlling particle charging for these particles. The experiments were interpreted with a consolidated stochastic model that predicted successfully the data at isothermal conditions, but was less effective for tests at higher gas temperatures. In our opinion, this discrepancy relies on synergies among the fluid dynamic field induced by droplet evaporation/condensation, the phoretic and the electrostatic forces, which are not considered in the model. Copyright

DGGE analysis of buffalo manure eubacteria for hydrogen production: effect of pH, temperature and pretreatments.

Buffalo dung is a low-cost substrate with plenty of carbohydrates, an optimal carbon/nitrogen ratio, and a rich microbial flora, and could become a valuable source of biogas. Therefore, in the present study we compared the type and amount of specific eubacteria to the different configurations of pH, temperature and thermal pretreatment after fermentation in batch reactors in order to understand the suitability of buffalo manure for hydrogen production. The phylogenetic structure of the microbial community in fermentation samples was studied using denaturing gradient gel electrophoresis to generate fingerprints of 16S rRNA genes. The sequences analysis revealed abundance of the phyla Bacteroidetes and Firmicutes, and in particular of the order Clostridiales. Very active hydrogen producing bacteria belonging to Clostridium cellulosi species were identified demonstrating the suitability of this substrate to produce hydrogen. Moreover, a large fraction of 16S-rDNA amplicons could not be assigned to lower taxonomic ranks, demonstrating that numerous microorganisms involved in anaerobic fermentation in digesters or bioreactors are still unclassified or unknown.

Effect of frequency on the complex viscosity of a concentrated non-Brownian suspension

The rheological behavior of a non-Brownian Newtonian concentrated suspension is investigated under oscillatory shear at different strain amplitudes and at two frequencies. The data are in agreement with the literature showing that the complex viscosity varies both with the number of oscillations imposed to the material and with the strain amplitude. We here also show that the response to the oscillatory shear depends on the applied frequency. This result is unexpected for a Newtonian suspension and implies the existence of some mechanism able to introduce a characteristic time into the system. Can it be cage elasticity?

Impact Forces of a Supercritical Flow of a Shear Thinning Slurry Against an Obstacle

In mountainous areas after long or intense rains, landslides may evolve into debris- or mud-flows. Their impact against obstacles may produce huge damages, sometimes with loss of lives. Prediction of the impact forces is required for a proper design of the flow barriers protecting risk prone areas. To this aim, both the effective characterization of the mud rheology and a suitable mathematical model of the flow propagation are needed. The present paper proposes a modeling framework in which the mudflow is idealized as the flow of a power-law fluid over an incline with a rigid impervious wall at the downhill end. The flow model employs the von Karman depth-integration of the one-dimensional mass and momentum conservation equations, in the long-wave approximation. The governing equations have been solved through a space/time second-order accurate numerical method. This modeling framework is applied to a test-case, based on the soil collected from Cervinara site (Avellino, South Italy), affected by a catastrophic landslide in 1999. The investigated soil is both the raw one and a washed one, the latter introduced to mimic the effect of an intense rain in terms of removal of the dissolved soil organic carbon. The rheology of both the shear-thinning mixtures has been deeply characterized in the form of a power-law function, and the dynamics of a dam-break wave ad its impact on an obstacle, has been numerically analyzed. It is shown that the removal of the soil organic carbon affects the propagation of the mudflow and at a minor extent the maximum forces and torques acting on the downstream wall. Remarkably, in the investigated conditions, the mudflow action consists of a strong impact occurring few seconds after the landslide triggering, and a subsequent cyclic loading of about three minutes.

Rheology and mechanics of polyether(ether)ketone – Polyetherimide blends for composites in aeronautics

In the present work rheological and mechanical properties of PEEK-PEI blends were investigated. Besides the pure components, blends with PEI concentration ranging from 10% to 90% in mass were considered. Oscillatory experiments in controlled atmosphere were conducted at different frequencies and temperatures. The frequency responses at different temperatures allowed using the TTS principle to reconstruct the master curves. All systems showed a shear thinning behavior and a flux index increasing with the percentage of PEI. The zero-shear viscosity was computed with the implementation of the Cross model and showed a decreasing behavior with the percentage of PEI. The relaxation time estimated from the crossover value of storage and loss moduli didn’t change significantly with blend composition, suggesting the non-sensibility of the elasticity of the system. Lastly, tensile tests were executed to investigate the dependence of Young modulus in the different blends.

Enhanced So2 Removal by Using Charged Water Droplets

This paper reports preliminary results on the absorption of SO2 from water charged droplets, produced by an electrospray operated in dripping mode. Our results show that the water charging allows a ≈50% increase of the SO2 absorption rate. Since the SO2 mass transfer coefficient depends mainly on the liquid-side mass transfer coefficient, we envisage that the increase of SO2 absorption rate is ascribable to the occurrence of droplet deformation and oscillation, driven by the reduction of surface tension caused by the presence of excess charge on the droplet surface. Experiments were successfully interpreted in light of an absorption model that specifically address the droplet formation and fall and considered the model of Matteson and Giardina (1974) to account the droplet charge effect.

Does the C/N ratio really affect the bio-methane yield? a three years investigation of buffalo manure digestion

Does the C/N ratio really affect the Bio-methane Yield? A three years investigation of Buffalo Manure Digestion Giovanna Guarino*, Claudia Carotenuto, Filomena di Cristofaro, Stefania Papa, Biagio Morrone, Mario Minale Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Università degli Studi di Napoli, via Roma 29, 81031 Aversa – CE, Italia. b Dipartimento di Scienze e Tecnologie Ambientali Biologiche e Farmaceutiche, Seconda Università degli Studi di Napoli, Via Vivaldi 43, 81100 Caserta, Italia. giovanna.guarino@unina2.it