Following an introduction to the macro-level heat recirculation pioneered by Echigo, we introduce phonon recycling, especially in nonequilibrium conditions. We review the sources of nonequilibrium (i.e., hot) phonons and their assisted and unassisted absorptions leading to electronic excitations. We then review an example of phonon recycling in high-power current circuits using heterobarriers with potentials matching with the optical phonon energy. This integrated hot-phonon absorbing barrier (HPAB) can reduce the operating temperature, the net heat generation, and the power consumption of these devices.
Numerical simulations of two-phase Rayleigh-Bénard convection in a cylindrical cell with particles or vapor bubbles suspended in the fluid are described. The particles or bubbles are modeled as points, the Rayleigh number is 2×106 and the fluids considered are air, for the particle case, and saturated water for bubbles. It is shown that the presence of a second phase has a profound effect on the flow and heat transfer in the cell. The heat capacity of the particles and the latent heat of the liquid are used, in dimensionless form, as control parameters to modulate these effects. It is shown that, as these parameters are varied, the nature of the flow in the cell changes substantially, in some cases with adverse and in others beneficial effects on the Nusselt number. By the analysis of several aspects of the numerical results, a physical discussion of several mechanisms is provided.
This paper presents a review of the state of the art in the area of cable-driven parallel mechanisms. The basic kinematic architecture of cable-driven parallel mechanisms is first recalled and the associated kinematic and static model is briefly exposed. Fundamental problems are formulated, including the definition of the wrench matrix, the wrench-closure workspace and the wrench-feasible workspace. Advances that have been made in the determination of such workspaces are reported. The dynamics and control of cable-driven parallel mechanisms are then considered, first for fully constrained cable-driven parallel mechanisms and secondly for cable-suspended parallel mechanisms. Calibration and identification issues are also addressed and various alternative architectures of cable-driven parallel mechanisms are reported. Finally, applications are considered and open issues are mentioned.
Flow problems with moving boundaries and interfaces include fluid–structure interaction (FSI) and a number of other classes of problems, have an important place in engineering analysis and design, and offer some formidable computational challenges. Bringing solution and analysis to such flow problems motivated the development of the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) method. Since its inception, the DSD/SST method and its improved versions have been applied to a diverse set of challenging problems with a common core computational technology need. The classes of problems solved include free-surface and two-fluid flows, fluid–object and fluid–particle interaction, FSI, and flows with solid surfaces in fast, linear or rotational relative motion. Some of the most challenging FSI problems, including parachute FSI and arterial FSI, are being solved and analyzed with the DSD/SST method as a core technology. Better accuracy and improved turbulence modeling were brought with the recently-introduced variational multiscale (VMS) version of the DSD/SST method, which is called DSD/SST-VMST (also ST-VMS). In specific classes of problems, such as parachute FSI, arterial FSI, aerodynamics of flapping wings, and wind-turbine aerodynamics, the scope and accuracy of the FSI modeling were increased with the special ST FSI techniques targeting each of those classes of problems. This article provides an overview of the core ST FSI technique, its recent versions, and the special ST FSI techniques. It also provides examples of challenging problems solved and analyzed in parachute FSI, arterial FSI, aerodynamics of flapping wings, and wind-turbine aerodynamics.
Since there were large waves on the film, the minimum wetting rate (MWR) was greatly affected by the waves. The contact angle of the film at the top edge of the stable dry-patch varied periodically synchronizing with the arrival of the waves. When the contact angle exceeded the maximum advancing contact angle, the top edge of the dry-patch began to move downward, i.e. the rewetting of the dry-patch was initiated. The MWR was properly given by considering the force balance at the top edge of the dry-patch that when the maximum of the dynamic pressure of the film fluctuating according to the waves exceeds the film holding force by surface tension corresponding to the maximum advancing contact angle. Many tiny bubbles were observed in the film in the falling film boiling and the upward flow boiling. The bubble generation in the film might create a dry-patch locally in the film. If the film flow coming to the dry-patch could not rewet it, the CHF condition occurred. In the falling film boiling, since the long film flow might have a larger disturbance of the film flow than the short film flow, the CHF of the long falling film boiling was higher than the CHF of the short falling film boiling. The disturbance of the film flow of upward flow boiling was larger than that of the falling film boiling. Thus, the CHF of the upward flow boiling was larger than the CHF of the falling film boiling. The CHF of those were predicted with a unique correlation except for the constant that expressed the difference of the degree of the disturbance of the film flow. The CHF of the flat mini-channels were also predicted well with the CHF correlation except for the constant. The constant, i.e. the CHF, was lower than of course the CHF of the upward flow boiling and also than the CHF of the falling film boiling. Since a wall effect due to the viscosity that suppressed the growth of the film flow disturbance was enhanced in the flat mini-channels, the disturbance of the film flow on the heat transfer surface was reduced and the CHF might become smaller. Correlations for the wavelength, the maximum film thickness and the wave velocity were introduced. The proposed correlations required only a film flow rate, physical parameters and geometrical dimensions. These values of the wave characteristics were required in the correlations of the MWR and the CHF. What is left toward the next step is to incorporate these characteristics of the waves with the MWR and CHF correlations.
Nanometer-scale components (nano-components) often exhibit characteristic mechanical behavior different from those of bulk counterparts. In this paper, we review a series of experimental studies on the mechanics of their fracture focusing especially on the interfacial strength in the nano-components, which consist of dissimilar nano-layers. Since the stress concentrated region is proportionally scaled down for shrinkage of component size, it becomes a few nanometers or at most a few tens of nanometers in the nano-components. We particularly pay attention to the availability of "stress" as the governing quantity of cracking, which is on the basis of the concept of continuum mechanics. We also investigate the effect of nano-scale stress concentration on the fatigue behavior of metals in nano-components. Finally, we discuss future directions on the further experimental exploration on the fracture mechanics in nano-components; the tensile testing of nano-rod and the fracture due to the stress concentration in the single nanometer scale.
In the past 250 years, natural resources have been consumed with very high speed and the earth is seriously damaged and polluted. Tribology supported powerful and high speed machinery run by the energy from coal and oil in the period with technologies of saving energy and materials. Many kinds of resources reserves including those of energy and metals are being depleted within one hundred years. Revolutional technologies of sustainability and zero-emission are being strongly required in the world industries to establish new lifestyles of real health and sustainability for the eternal living of human beings and other lives in a symbiotic way. Tribology is expected to develop its science and technology for the needs in industries and support a new industrial revolution.