Dynamic Measurements Using FDM 3D-Printed Embedded Strain Sensors.

3D-printing technology is opening up new possibilities for the co-printing of sensory elements. While quasi-static research has shown promise, the dynamic performance has yet to be researched. This study researched smart 3D structures with embedded and printed sensory elements. The embedded strain sensor was based on the conductive PLA (Polylactic Acid) material. The research was focused on dynamic measurements of the strain and considered the theoretical background of the piezoresistivity of conductive PLA materials, the temperature effects, the nonlinearities, the dynamic range, the electromagnetic sensitivity and the frequency range. A quasi-static calibration used in the dynamic measurements was proposed. It was shown that the temperature effects were negligible, the sensory element was linear as long as the structure had a linear response, the dynamic range started at ∼ 30 µ ϵ and broadband performance was in the range of few kHz (depending on the size of the printed sensor). The promising results support future applications of smart 3D-printed systems with embedded sensory elements being used for dynamic measurements in areas where currently piezo-crystal-based sensors are used.

Oscillations During Flow Boiling in Single Microchannels.

Flow boiling of degassed double-distilled water in a single 50 × 50 µm and 100 × 50 µm microchannel was investigated on the basis of experimental measurements and high-speed visualization. The visualized events during boiling were analyzed in terms of the bubble frequencies and boiling front oscillations in microchannels. A digital image sequence analysis algorithm was composed to determine the time dependence of bubble and meniscus locations. The results show (i) the dynamic characteristics of boiling in microchannels, (ii) the increase of fundamental oscillation frequencies with increasing heat flux and temperature of the microchannel bottom, (iii) the amplitudes of the flow boiling oscillations are inversely proportional to the fundamental frequencies. The outcomes of the study are important as the oscillations during boiling in single microchannels are experimentally confirmed to be predictable in terms of oscillation frequencies and amplitudes trends and dependencies. This knowledge is especially significant at constructing efficient two-phase micro heat exchangers, micro mixers or micro reactors, as the cross section and the length of the channel become exceedingly important design parameters in micro devices with boiling.