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We have designed and characterized a simple Rayleigh-surface acoustic wave-based micropump, integrated directly with a fully enclosed 3D microfluidic system, which improves significantly the pumping efficiency within a coupled fluid whilst maintaining planar integration of the micropump and microfluidics. We achieve this by exploiting the Rayleigh-scattering angle of surface acoustic waves into pressure waves on contact with overlaid fluids, by designing a microfluidic channel aligned almost co-linearly with the launched pressure waves and by minimizing energy losses by reflections from, or absorption within, the channel walls. This allows the microfluidic system to remain fully enclosed--a pre-requisite for point-of-care applications--removing sources of possible contamination, whilst achieving pump efficiencies up to several orders of magnitude higher than previously reported, at low operating powers of 0.5 W. [ABSTRACT FROM AUTHOR]

Conversion of waste heat into usable electricity is now one of the important strategies for saving natural resources and minimizing impact on the environment. In contrast to Seebeck devices, utilizing a temperature gradient, pyroelectric scavengers use temporal temperature oscillations. Here, optimal strategies for pyroelectric energy harvesting are theoretically investigated from the point of view of non-stationary heat exchange for the application-relevant case of harvesting with a pyroelectric lamella from a fluid heat source. It is shown that for a fixed lamella thickness by choosing appropriate phase shift between the temperature oscillations and the voltage on the pyroelectric lamella, one can effectively operate at high frequencies and achieve a two to three-fold increase in specific power with respect to the classical Olsen cycle. A further increase in specific power is achieved by thinning down the lamella. For devices with a thickness down to a few hundreds of nanometers, specific power linearly increases with the inverse thickness. Further scaling down of the device is hampered with the heat exchange in the boundary layer. Our simulations for a representative pyroelectric Pb(Zr0,5Ti0,5)O3 predict harvestable powers of the order of kW/kg for a device with a thickness in the range from 100 nm to 1 μm, operating at hundreds of Hz. [ABSTRACT FROM AUTHOR]

Experiments were conducted to study spreading of droplets of liquid healing agents on tilted nanofiber mats, which is relevant in the framework of self-healing engineered materials with vascular networks. In the present situation, the effect of gravity on drop spreading is important, as well as the inclination angle and the mat thickness. In the control case of gravity-driven spreading of droplets on an inclined polydimethylsiloxane surface, the results agreed fairly well with the theoretical predictions in the framework of the lubrication theory for the intact surfaces. However, spreading on the inclined nanofiber mats revealed significant deviations from the theory due to the imbibition of liquid into the inter-fiber pores. The imbibition effect, which stems from the wettability-driven suction, increased as the mat thickness increased. Notably, the imbibition effect also increased as the inclination angle increased. [ABSTRACT FROM AUTHOR]