Direct Numerical Simulation of Turbulent Heat Transfer Modulation in Micro-Dispersed Channel Flow

The object of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano- particles. We run Direct Numerical Simulation (DNS) for hydrodynamically fully-developed, thermally-developing turbulent channel flow at shear Reynolds number Re=150 and Prandtl number Pr=3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined.Comment: Pages: 305-32

Quantification of heavy particle segregation in turbulent flows: a Lagrangian approach

The way particles suspended in a turbulent flow are transported and segregated by turbulent structures is crucial in many atmospheric and industrial applications such as powder production and formation and growth of PM10 particulate. In recent years, this phenomenon has been studied from different viewpoints; lately, Osiptsov [1] proposed an alternative approach to quantify particle segregation, later followed by [2] and [3]. This method, referred to as ‘Full Lagrangian approach (FLA)’, evaluates the size of an infinitesimally small volume of particles and its changes in the course of time along each particle trajectory. The rate of deformation of this volume is related to the compressibility of the particle velocity field (e.g. [4]) which is an indicator of particle concentration. This method presents high computational efficiency in comparison with traditional Eulerian methods such as “box-counting”, for which a large number of particles is required to obtain accurate statistics. We decided to exploit FLA in a simple two-dimension synthetic turbulent flow field Direct Numerical Simulations of homogeneous isotropic turbulence, and to compare it with the MEPFV, a method proposed by [5] et al. essentially based on box counting. Preliminary results of the spatially averaged statistics of the rate of deformation are also presented, showing that the presence of singularities increases for large St numbers. In this work, we study the dispersion of identical, rigid and spherical particles in a carrier flow of mass density ρ and kinematic viscosity ν. Particles are assumed to be heavy (i.e. ρp/ρ » 1 where ρp is the particle density) with radii aρ much smaller than the smallest length scale of the flow. Upon neglecting gravity and Brownian effects, the equations of motion are [6]: 1 where xp and v are the position and velocity of the particle respectively, and u = u(xp, t) denotes the velocity of the carrier flow at the position of the particle. All variables have been made dimensionless by a typical time scale ד and a typical velocity scale U. The parameter is the Stokes number, which represents the ratio between the inertia driving the particle and the viscous damping action of the fluid

On the Motion of Particles in a Laminar Flow Bend

The interaction between the secondary and the axial flows in a bend and the effect they have upon the transport and deposition of suspended solid particles is investigated. The centrifugal forces acting on the particle, arising from the global curvature of the axial flow and the secondary Dean vortices set up by the pressure gradients and viscosity, cause the particles to cluster and segregate, and to deposit by impaction.JRC.H.4-Transport and air qualit

Short- and long-term effects of risperidone on catalepsy sensitisation and acquisition of conditioned avoidance response: adolescent vs adult rats

The effects of antipsychotic drugs (APDs) on the adolescent brain are poorly understood despite a dramatic increase in prescription of these drugs in adolescents over the past twenty years. Neuronal systems continue to be remodeled during adolescence. Therefore, when given in adolescence, antipsychotic drugs (APDs) have the potential to affect this remodeling. In this study we investigated the effects of chronic 22-day risperidone treatment (1.3 mg/kg/day) in both adolescent and adult rats. We examined short- and long-term changes in behaviour (catalepsy, locomotion and conditioned avoidance response (CAR)), and dopaminergic and serotonergic neurochemistry in the striatum and the nucleus accumbens. Here, we report that, both during chronic treatment and after a lengthy drug-free interval, risperidone induced a sensitised cataleptic response regardless of the age of exposure. Selectively in adolescents, risperidone-induced catalepsy was inversely correlated with striatal dopamine turnover immediately after chronic treatment. After a drug-free interval, a significant proportion of rats with prior adolescent risperidone treatment also failed to acquire CAR to a defined criterion. Our data provide evidence that the same chronic risperidone treatment regimen can induce contrasting short- and long-term neural outcomes in the adolescent and adult brains

Effect of the glucocorticoid receptor antagonist RU486 on MK-801 induced behavioural sensitization

Stress is known to modulate sensitisation to repeated psychostimulant exposure. However, there is no direct evidence linking glucocorticoids and sensitisation achieved by repeated administration of the NMDA receptor antagonist MK-801. We tested the hypothesis that co-administration of RU486, a glucocorticoid receptor (GR) antagonist, prior to repeated daily MK-801 injections would block the expression of locomotor sensitisation due to its dual effects on corticosterone and dopamine. We employed a repeated MK-801 administration locomotor sensitisation paradigm in male Sprague Dawley rats. RU486 or a dimethyl sulfoxide (DMSO) vehicle was co-administered with MK-801 or saline during the induction phase. Subsequent to withdrawal, rats were challenged with MK-801 alone to test for the expression of sensitisation. In a separate cohort of rats, plasma corticosterone levels were quantified from blood samples taken on the 1(st), 4(th) and 7(th) day of induction and at expression. One day after challenge, nucleus accumbens tissue levels of dopamine and its metabolites DOPAC and HVA were measured. During the induction phase, RU486 progressively enhanced locomotor sensitisation to MK-801. RU486 and MK-801 both showed stimulatory effects on corticosterone levels and this was further augmented when given in combination. Contrary to our hypothesis, RU486 did not block the expression of locomotor sensitisation to MK-801 and actually increased levels of dopamine, DOPAC and HVA in nucleus accumbens tissue. Our results showed that RU486 has augmentative rather than inhibitory effects on MK-801-induced sensitisation. This study indicates a divergent role for glucocorticoids in sensitisation to MK-801 compared to sensitisation with other psychostimulants