Luca Bergamasco

Mesoscopic Moment Equations for Heat Conduction: Characteristic Features and Slow–Fast Mode Decomposition

In this work, we derive different systems of mesoscopic moment equations for the heat-conduction problem and analyze the basic features that they must hold. We discuss two- and three-equation systems, showing that the resulting mesoscopic equation from two-equation systems is of the telegraphist’s type and complies with the Cattaneo equation in the Extended Irreversible Thermodynamics Framework. The solution of the proposed systems is analyzed, and it is shown that it accounts for two modes: a slow diffusive mode, and a fast advective mode. This latter additional mode makes them suitable for heat transfer phenomena on fast time-scales, such as high-frequency pulses and heat transfer in small-scale devices. We finally show that, if proper initial conditions are provided, the advective mode disappears, and the solution of the system tends asymptotically to the transient solution of the classical parabolic heat-conduction equation.

Thermally triggered nanorocket from double-walled carbon nanotube in water

ABSTRACT In this work, we propose and investigate the use of double-walled carbon nanotubes (DWCNTs) as nanosized rockets. The nanotubes are immersed in water, and the propulsion of inner nanotube is achieved by heating the water encapsulated within the DWCNT. Considering a setup made of (5,5)(8,8) DWCNT, molecular dynamics simulations for different water temperatures show that the trajectory can be divided into four phases: trigger, expulsion, damping and final equilibrium. After analysing the dynamics and the involved forces, we find out that the inner nanotube expulsion is mainly controlled by van der Waals interactions between the nanotubes; whereas, the damping role is predominantly played by the external aqueous environment. Based on these results, we propose an analytical model able to predict both the triggering time for a given water temperature and the whole dynamics of nanorocket. The validity of such dynamical model can be extended also to a broader variety of DWCNT configurations, once the different forces acting on the inner nanotube are provided. The proposed model may contribute to assist the design of nanorockets in several nanotechnology applications, such as triggered drug delivery, cell membrane piercing, or colloids with thermophoretic properties.

The non-linear response of bubble clouds to pressure excitations

In this article we numerically investigate the non-linear response of a bubble cloud against a periodic pressure excitation. By exciting a planar bubble curtain with an external acoustic pulse of given amplitude and frequency, we characterize the global dynamic response of the system using phase diagrams representing the void fraction against the excitation pressure. Even in the absence of mass transfer, the void fraction around which the system oscillates increases when increasing the excitation amplitude. We show how the maximum pressures reached during the collapse of bubbles are higher in polydisperse bubble clouds than in monodisperse clouds for strong pressure pulses.