Viscoelasticity and elastocapillarity effects in the impact of drops on a repellent surface

We investigate freely expanding viscoelastic sheets. The sheets are produced by the impact of drops on a quartz plate covered with a thin layer of liquid nitrogen that suppresses shear...

Measuring Heat Transfer From Firebrands to Surfaces

Firebrands are an important mechanism of fire spread and one of the primary ways in which wildland fires ignite structures. Inverse heat transfer using thin steel plates has been shown to be an effective method for measuring heat transfer distributions from firebrands. To fully understand the dynamic process of heat transfer from firebrands to surfaces; however, it is necessary to view the underside of the firebrands, which is not possible through a steel plate. This work develops a method of inverse heat transfer using a visually transparent quartz plate and a long-wave (7.5–14.0 μm) infrared camera to facilitate visual access to the firebrands from all angles. The heat flux measurements using a quartz plate were compared with heat flux measurements using a steel plate and finite element heat transfer simulations for radiation-dominant tests using heater panels. Additionally, heat transfer measurements using cuboidal oak firebrands were conducted using both the quartz and steel plates. A corrective factor was developed based on the ratio of the effective emissivity of the quartz and stainless-steel plates at typical firebrand temperatures. The measured heat fluxes were within 1–6% after correcting for radiant energy transmitted through the quartz which was absorbed by the stainless-steel plate.

Plasma Channel Extension by Femtosecond Laser Filamentation with a Circular Aperture Quartz Plate

We propose a new approach of extending the laser filament plasma channel. By adding a circular aperture quartz plate before the focusing lens, the extension of the plasma channel is doubled. The effects of different diameters, thicknesses of the circular aperture quartz plate and different pulse energies on the length of the plasma channel were investigated. The experimental results show that the thickness of the quartz plate and the depth of the hole have little effects on the plasma channel of the filament, and the diameter of the hole in the center of the quartz plate has a significant effect on the length of the optical filament. The moving-focus model is used to explain the extension of the optical filament.

Gold-implanted plasmonic quartz plate as a launch pad for laser-driven photoacoustic microfluidic pumps

Enabled initially by the development of microelectromechanical systems, current microfluidic pumps still require advanced microfabrication techniques to create a variety of fluid-driving mechanisms. Here we report a generation of micropumps that involve no moving parts and microstructures. This micropump is based on a principle of photoacoustic laser streaming and is simply made of an Au-implanted plasmonic quartz plate. Under a pulsed laser excitation, any point on the plate can generate a directional long-lasting ultrasound wave which drives the fluid via acoustic streaming. Manipulating and programming laser beams can easily create a single pump, a moving pump, and multiple pumps. The underlying pumping mechanism of photoacoustic streaming is verified by high-speed imaging of the fluid motion after a single laser pulse. As many light-absorbing materials have been identified for efficient photoacoustic generation, photoacoustic micropumps can have diversity in their implementation. These laser-driven fabrication-free micropumps open up a generation of pumping technology and opportunities for easy integration and versatile microfluidic applications.