Characterizing the cavitation development and acoustic spectrum in various liquids

A bespoke cavitometer that measures acoustic spectrum and is capable of operating in a range of temperatures (up to 750 degC) was used to study the cavitation behaviour in three transparent liquids and in molten aluminium. To relate these acoustic measurements to cavitation development, the dynamics of the cavitation bubble structures was observed in three Newtonian, optically transparent liquids with significantly different physical properties: water, ethanol, and glycerine. Each liquid was treated at 20 kHz with a piezoelectric ultrasonic transducer coupled to a titanium sonotrode with a tip diameter of 40 mm. Two different transducer power levels were deployed: 50% and 100%, with the maximum power corresponding to a peak-to-peak amplitude of 17 lm. The cavitation structures and the flow patterns were filmed with a digital camera. To investigate the effect of distance from the ultrasound source on the cavitation intensity, acoustic emissions were measured with the cavitometer at two points: below the sonotrode and near the edge of the experimental vessel. The behaviour of the three tested liquids was very different, implying that their physical parameters played a decisive role in the establishment of the cavitation regime. Non dimensional analysis revealed that water shares the closest cavitation behaviour with liquid aluminium and can therefore be used as its physical analogue in cavitation studies; this similarity was also confirmed when comparing the measured acoustic spectra of water and liquid aluminium

Marble quarries and local communities. The local community of Dionyssos

137 σ.Η παρούσα διπλωματική εργασία έχει σκοπό τη μελέτη των αντιδράσεων της τοπικής κοινωνίας απέναντι στα λατομεία μαρμάρου. Πραγματοποιήθηκε πρωτογενής έρευνα με ερωτηματολόγια στην περιοχή του Διονύσου Αττικής, όπυ κατά κύριο λόγο δραστηριοποιούνται λατομεία μαρμάρου.The following thesis aims to study the reactions of the local community towards the marble quarries. The study area chosen was the Municipality of Dionyssos in the Prefecture of Attica, Greece, where marble quarries are mainly found.Τερψιχόρη Δ. Πελεκάσ

Glass reactive sintering

With “glass reactive sintering” we may denote several technologies, with the common trend of viscous flow sintering of glass combined with physical and chemical reactions. The present paper aims at specifying the distinctive characters of glass sintering with reactions having a significant impact on the chemical composition and on the phase assemblage of the resulting products. The more conventional technology of sinter-crystallization (sintering with concurrent devitrification of glass powders) is presented in its more recent developments (e.g., additive manufacturing); a survey of more recent technologies concerning extensive glass/oxide additive interaction is presented as well