1,721,216 research outputs found
Termographic testing on buildings using a simplified heat transfer model
No full textThermographic testing is widely used to analyze inner wall structures. Many variables, including nonhomogeneous optical and thermal characteristics, still make these applications difficult. The materials inside the investigated walls are unknown and the nonhomogeneous optical and thermal characteristics change in every small surface. Plaster delaminations can also stop heating propagation through the wall. These typical difficulties in thermographic applications can be overcome by selecting the appropriate heating method. One requirement is that the mathematical heating model, even if approximated, must take into account thermal and optical characteristics of the materials that determine the surface temperature and the actual environmental conditions. The heat transfer equations can be analytically solved by simplifying boundary conditions on superficial temperature and incoming heat flux. The approximate solutions allow the testing of the necessary heating in order to obtain thermal images from the inner parts of the wall. Special attention has to be paid to the heating system. It is not easy to obtain a uniform heating condition through masonry thickness. Heat propagation must reach the inner part of the wall without significant variation due to lateral diffusion. Different kinds of models are discussed in the present work. The models supply effective heating processes (by convection or radiation) in field conditions. The setup carried out in actual field conditions at an ancient church in northern Italy and the results of the mathematical model are presented
Kelvin : il secondo principio della termodinamica
No full textWilliam Thomson, primo barone di Kelvin svolse una vastissima e apparentemente eclettica attività sperimentale che spaziò dall’elettromagnetismo alla termodinamica, dai cavi per telecomunicazioni all’invenzione di nuove tecnologie per la navigazione marittima. Queste attività lo portarono alla realizzazione di innumerevoli brevetti industriali che furono sempre accompagnati da brillanti intuizioni teoriche, combinate ad un eccellente livello di formalismo matematico, dimostrando una capacità di sintesi fisico-matematica fuori dal comune. Amava definirsi un “filosofo naturale” e fu indiscutibilmente nel suo secolo uno dei più grandi scienziati capaci di unire pratica sperimentale e formulazione teorica. Retrospettivamente egli deve parte della sua fortuna al fatto di essere nato e aver vissuto per tanti anni all’apice dell’accademia del più potente impero industriale del diciannovesimo secolo: l’impero britannico
Heat losses and 3D diffusion phenomena for defect sizing procedures in video pulse thermography
No full textDynamical thermographic techniques like video pulse thermography are very useful for the non-destructive testing of structural components. In literature different models were proposed, which allow to describe the time evolution of the thermal contrast for materials with sub-superficial defects. In the case of circular defect the time evolution of the full width half maximum (FWHM) of the thermal contrast was studied both theoretically and experimentally. Nevertheless a mismatch in defect sizing between experimental results and theoretical simulations was found. Possible explanations of this disagreement was analysed. A factor widely neglected is the heat loss (radiation and convection). In this paper a theoretical analysis of the influence of these contributions is reported. Furthermore in order to explain the experimental evidence of FWHM time evolution we introduced a correction due to lateral heat diffusion around the defect. In this way a possible explanation for the experimental results was obtained. Brick samples with a circular flat bottom hole as defect was tested both for the interest in defect sizing in building material through NDT and for the low thermal diffusivity of this material which allows the study of the phenomenon in a slow motion
Indagini non distruttive a Palazzo Ducale a Urbino: l’ispezione termografica per il rilievo di strutture in profondità
No full textInvestigating STEM course choices through physics knowledge surveys
Full text linkThe choice of STEM courses is often influenced by previous educational career. In particular, in the scientific field, the learning of specific and at the same time paradigmatic topics plays a fundamental role. This research aims to assess nuclear physics knowledge in a sample of high school and university students through a multiple-choice survey. We analyzed and compared the results between the two samples and against a fixed threshold value. We also examined subgroups within the high school and university samples. The study considered influences from school background, learning continuity, and gender differences. We found a significant correlation between teaching hours and test results. The analysis provides insights into physics education and the quantitative relationship between teaching and knowledge acquisition. A specialistic knowledge that students can use as a tool for orientation towards STEM university choices
La scienza nel pallone : i segreti del calcio svelati con la fisica
No full textIl calcio non è fatto soltanto di emozioni, ma anche di numeri. A che velocità può viaggiare un pallone? Qual è la probabilità di segnare un rigore? E perché la palla a volte devia dalla sua traiettoria naturale, consentendo di realizzare gol «impossibili»?
Come ogni fenomeno, anche il calcio obbedisce a leggi naturali studiate dalla fisica e dalla matematica, che risultano essenziali per comprendere ciò che succede sul campo.
I processi che governano il gioco - dai diversi modi in cui si può colpire la palla alla biomeccanica dei tiri più acrobatici, fino alle illusioni ottiche che ingannano giocatori e arbitro - sono analizzati con rigore scientifico e leggerezza di scrittura, per svelare i segreti dello sport più popolare al mondo
Frying an egg to study heat transport: an engaging and didactic experiment
No full textUsing everyday life examples is proven didactically useful for teaching physics, as it presents effective applications of physical laws. Cooking and food, in particular, serve two useful purposes: on one side, they are able to engage students in the study of physics with familiar examples; on the other side, thanks to the wide range of physical phenomena involved, they can help teachers in introducing many new topics and in driving students in the understanding of physics laws. In this paper, we propose an experiment to investigate the cooking process of a fried egg. We show how an egg, a frying pan and a thermal camera can be valuable tools to drive students towards the physical science and how, with a single experiment, it is possible to introduce many different phenomena, from the laws of heat transmission to phase transitions. The experiment can be proposed to high school students as an engaging activity, but it is also a valuable exercise for undergraduate students, as it involves a large amount of non-trivial physics far from a typical textbook approach
Analysis of thermal properties of wheelchair cushions with thermography
No full textThermal properties of wheelchair cushions have been traditionally studied with thermistor probes, which provide temperature values of limited areas (spot analysis). In this paper, we describe a novel procedure based on thermography for assessing the distribution of temperature over the entire surface of wheelchair cushions. The thermal transient during contact with the body (heating phase) and after use (cooling phase) is considered. The procedure was tested in four different seat cushions (with a gel pad, air-filled cells, gel-filled bubbles and foam-filled bubbles) used by a normal subject. Observed results were compatible with the predicted outcomes based on an analysis of the materials and structures. Specifically: (i) air-filled cushions exhibited the fastest thermal transients, gel cushions the slowest transients, while cushions with a mixed structure exhibited intermediate behaviour; (ii) cushions made from flat surfaces of foam exhibited the highest peak temperatures (30.8°C) as compared to those with air-filled cells (30.35°C) or bubble-shaped surfaces (29.7°C); (iii) the average temperature under the thighs was significantly higher than that under the ischiatic area in all cushions (29.6°C compared with 28.7°C, p<0.05). It is shown that the present method can be used to differentiate between different cushions. Although the ‘macro-analysis’ inherent in thermography appears to be suited for improving cushion design, this approach should be further investigated to determine its reliability
Cuocere un uovo per insegnare la fisica - Cooking an egg to teach physics
No full textThe wide range of phenomena involved in food processing can provide
countless ideas for introducing new topics of physics, capturing the interest of
students with everyday examples. We show that studying the cooking of an egg
with a thermal camera can be surprising and instructive and provide non-trivial
examples of heat transmission, thermal properties of materials, and of concepts
such as latent heat and phase transitions. The experiment can be an engaging
activity for high school students, but can also be proposed as an inquiry-based
activity for university students who will have a chance to apply their knowledge
of physics to a real phenomenon
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