Small-scale oscillations

Kim, K. I., Ohtani, H. and Uehara, Y., Experimental study on oscillating behavior in a small-scale compartment fire, Fire Safety J., 1993, 20, 377-84. 

At such small scales, the experimenters cannot see the motor working by any means except an electron microscope. Although the motor is simple conceptually, its precision is incredible—it operates at the atomic level, controlling the motion of atoms as they shuffle back and forth between nanoparticles. B. C. Regan, Zettl, and their colleagues published the report Surface-Tension-Driven Nanoelectromechani-cal Relaxation Oscillator in Applied Physics Letters in 2005. As the researchers note in their report, [SJurface tension can be a dominant force for small systems, as illustrated in their motor. This is a prime example of the different forces and situations that must be taken into account in the nanoworld. 

Much of chemistry occurs at small scales. As Dalton and other scientists realized, atoms are the basic units of matter and combine chemically to form molecules. Although chemists usually work with substantially larger amounts of matter, researchers in the field of nanotechnology are beginning to develop the techniques to manipulate matter on the atomic and molecular scale. By finding the right conditions in which atoms and molecules will assemble into functional structures, or by constructing tiny machines that oscillate, researchers have entered the domain of the atom. 

On small scales, these sources of pressure determine the evolution of perturbations. Consider once again Eq. 10.10. When the wavenumber k > kj, or conversely when the wavelength is smaller than the Jeans length, pressure dominates over gravity and the fluid oscillates with angular frequency u csk. The detailed solution actually involves Bessel functions when expansion is correctly taken into account, and there are additional complications due to gravitational interactions with any pressureless component such as CDM which can continue to collapse. 

In a recent work [69], we were able to reveal that the sharkskin merely originates from a local interfacial instability of the boundary condition near the die exit wall. Specifically, the oscillation of adsorbed chains between their coil and stretch states produces a small scale periodic perturbation on the overall die swell and makes the extrudate surface appear rough or sharkskin like. 

What does matter, though, is the difference between laminar and turbulent flow. A common misconception is that if you see vortices (swirling motion), the flow is turbulent. That is not necessarily true. In turbulent flow, there are fine-scale oscillations on time scales of 0.1 ms, and spatial fluctuations on the scale of 30 pm (30 x 10 m, or 3% of 1 mm). To model turbulent flow, one option is direct numerical simulation (DNS). In DNS, the Navier-Stokes equations are integrated in time on a very small spatial scale. 

Subsequently, the interesting effect of wall thickness w on the waveguide is examined. While the staircase solutions are not sensitive to such small-scale details, Figure 7.3(b) shows that HO simulations follow the variation of w and react positively to its changes. Note the absence of any oscillations in the frequency spectrum, mainly attributed to the schemes of Chapter 2. 

Pipeline transportation of liquid hydrogen is realized on a small scale and short range. Stainless steel is usually taken for the inner line with low heat conduction spacers as a support in the vacuum jacket. The Kennedy Space Center in Florida uses an LH2 and LOX pipeline of 500 m length with an irmer pipe diameter of 0.15 m. Flow rates achieved are up to 250 LH2 per minute and 100 m LOX per minute, respectively [12]. Transfer is realized by applying pressure, no pumps. Major concerns besides heat leakage is the mechanical stress imposed on the irmer line due to contraction / expansion, pressure oscillations upon cooldown, or two-phase flow. 

On the other hand, researchers interested in mass transport in water waves have shown that a similar phenomenon occurs for incompressible flow (see [4] for an example). The salient feature is when an obstacle oscillates with high frequency in the quiescent viscous fluid. In this case the steady streaming emerges from both sides of the obstacle along the oscillating direction at small viscosity [5]. Increased importance of the acoustic streaming in small scales has been addressed in [6]. 

---