CFD modeling of two-phase boiling flows in the slug flow regime with an interface capturing technique

The objective of this thesis was to improve the commercial CFD software Ansys Fluent to obtain a tool able to perform accurate simulations of flow boiling in the slug flow regime. The achievement of a reliable numerical framework allows a better understanding of the bubble and flow dynamics induced by the evaporation and makes possible the prediction of the wall heat transfer trends. In order to save computational time, the flow is modeled with an axisymmetrical formulation. Vapor and liquid phases are treated as incompressible and in laminar flow. By means of a single fluid approach, the flow equations are written as for a single phase flow, but discontinuities at the interface and interfacial effects need to be accounted for and discretized properly. Ansys Fluent provides a Volume Of Fluid technique to advect the interface and to map the discontinuous fluid properties throughout the flow domain. The interfacial effects are dominant in the boiling slug flow and the accuracy of their estimation is fundamental for the reliability of the solver. Self-implemented functions, developed ad-hoc, are introduced within the numerical code to compute the surface tension force and the rates of mass and energy exchange at the interface related to the evaporation. Several validation benchmarks assess the better performances of the improved software. Various adiabatic configurations are simulated in order to test the capability of the numerical framework in modeling actual flows and the comparison with experimental results is very positive. The simulation of a single evaporating bubble underlines the dominant effect on the global heat transfer rate of the local transient heat convection in the liquid after the bubble transit. The simulation of multiple evaporating bubbles flowing in sequence shows that their mutual influence can strongly enhance the heat transfer coefficient, up to twice the single phase flow value.

Audience attitudes towards simil sync: a pilot study

This thesis is based on a pilot investigation which explores the attitudes of a sample of Italian viewers towards the simil sync technique which in Italy is used for the dub of non-fictional television contents. The thesis seeks to analyse and define the characteristics of this dubbing modality which is often considered by scholars and professionals in the dubbing industry a hybrid modality of standard synchronised dubbing and voice-over. In order to investigate viewers’ attitudes, I organised 4 focus groups sessions which, due to the impact of Covid-19 pandemic, were carried out online. The online recruitment of participants, which was a difficult task, resulted in a small sample of eighteen participants (and two interviewees). The four online focus groups revealed that participants were aware of the simil sync technique. They recognised that the clips were dubbed in a different modality from standard synchronised dubbing. The characteristic that was mostly mentioned for detecting simil sync was the original soundtrack that was audible below the dub, followed by the identification of the genre of the programme in the clip and the absence of lip sync. Moreover, while simil sync with a barely audible original soundtrack received neutral or positive attitudes, simil sync with a more audible original soundtrack, instead, was tolerated or considered annoying. Simil sync passed unnoticed in the in-depth interviews in which the discussion about dubbing was not focused on the distinction between two dubbing modalities, for instance simil sync versus standard synchronised dubbing, but rather on the distinction between programmes that originated in Italian and those that were translated into Italian from another language and then dubbed.