Experimental Investigation of Flow Condensation of Propylene in a horizontal Tube

openLa condensazione durante deflusso è un processo fisico molto diffuso, utilizzato nei condensatori adottati per diverse applicazioni come pompe di calore, impianti di condizionamento e nell’industria chimica. L'esigenza dell'industria della refrigerazione di trovare refrigeranti alternativi a HFC, caratterizzati da un ODP quasi nullo ma da un GWP troppo elevato, rende molto importante lo studio degli idrocarburi per le applicazioni a ciclo inverso. L'obiettivo del presente lavoro è studiare la condensazione del flusso di propilene all'interno di un tubo orizzontale liscio. La condensazione in flusso è un meccanismo di trasferimento del calore molto complesso che attualmente non può essere descritto da equazioni analitiche. Pertanto, l'analisi sperimentale diventa uno strumento importante per convalidare le correlazioni presentate in letteratura. Il lavoro sperimentale è stato condotto sfruttando un impianto di prova su scala industriale, il KIIR, che consente di impostare le condizioni termodinamiche all'ingresso della sezione di prova, dove avviene la condensazione parziale. La sezione di prova consiste in uno scambiatore di calore a fascio tubiero. Il propilene viene raffreddato da un olio in configurazione di flusso controcorrente. Il tubo sperimentale è stato dotato di sensori di temperatura e installato all’interno dell'apparato sperimentale. Ciascun test è stato eseguito in condizioni operative costanti in termini di pressione p, flusso di massa G e titolo di vapore x. L'analisi dei risultati a livello locale ha permesso di dimostrare la dipendenza del coefficiente di trasferimento di calore α dalla posizione radiale φ del tubo. In particolare, nelle condizioni di prova associate al verificarsi di un flusso stratificato, il coefficiente di trasferimento di calore α varia notevolmente in funzione della posizione radiale φ. Nelle condizioni di alta turbolenza e flusso anulare, il coefficiente di trasferimento di calore α è approssimativamente costante in funzione della posizione radiale φ. A causa delle incertezze del set-up sperimentale, queste osservazioni sono state più chiare nelle condizioni di prova in cui la differenza di temperatura media tra la sostanza in esame e l'olio di raffreddamento era più elevata. Inoltre, è stato possibile verificare sperimentalmente che il coefficiente di trasferimento del calore α aumenta all'aumentare del flusso di massa G. Allo stesso modo, è stato possibile verificare che il coefficiente di trasferimento di calore α diminuisce con l'aumento della pressione p. Confrontando i risultati relativi al trasferimento di calore complessivo e alle perdite di carico, si è dedotto che un elevato coefficiente di trasferimento di calore è sempre abbinato a un alto valore di perdite di carico.Flow condensation is a very widely spread physical process, used in condensers adopted for several applications like heat pumps, air conditioning systems, and the chemical industry. The urge of the refrigeration industry to find alternative refrigerants to HFC, characterized by null ODP but too high GWP, makes the study of hydrocarbons for inverse cycle applications very important. The goal of the present work is to study flow condensation of propylene inside a horizontal smooth tube. Flow condensation is a very complex heat transfer mechanism that currently, cannot be described by analytical equations. Therefore, experimental analysis becomes an important tool to validate the correlations presented in the literature. The present experimental work has been conducted exploiting an industrial scale test rig, KIIR, that allows to set the thermodynamics conditions at the inlet of the test section, where partial condensation occurs. The test section consists in a tube-shell-heat exchanger. Propylene is cooled down by an oil in counter-current flow configuration. The test tube has been equipped with temperature sensors and installed in the experimental apparatus and the measurement plan has been conducted. Each test has been executed under constant operating conditions in terms of pressure p, mass flux G and vapor quality x. The analysis of the local experimental results has allowed to observe the dependency of the heat transfer coefficient α on the radial position φ of the test tube. Specifically, under test conditions associated with the occurrence of stratified flow, the heat transfer coefficient α varies considerably as function of the radial position φ. Under the conditions associated with high turbulence and annular flow, the heat transfer coefficient α is approximately constant as function of the radial position φ. Because of the uncertainties of the experimental set up, these observations were clearer under the test conditions in which the average temperature difference between the test substance and the cooling oil was higher. Moreover, it was observed that the overall heat transfer coefficient α increases as the mass flux G increases. In the same way, it was possible to observe that the overall heat transfer coefficient α decreases as the pressure p increases. By comparing the results regarding overall heat transfer and pressure drops, it was verified that a high heat transfer coefficient is always coupled with a high value of pressure drops

A Proposal for a forest digital twin framework and its perspectives

3openInternationalItalian coauthor/editorThe increasing importance of forest ecosystems for human society and planetary health is widely recognized, and the advancement of data collection technologies enables new and integrated ways for forest ecosystems monitoring. Therefore, the target of this paper is to propose a framework to design a forest digital twin (FDT) that, by integrating different state variables at both tree and forest levels, creates a virtual copy of the forest. The integration of these data sets could be used for scientific purposes, for reporting the health status of forests, and ultimately for implementing sustainable forest management practices on the basis of the use cases that a specific implementation of the framework would underpin. Achieving such outcomes requires the twinning of single trees as a core element of the FDT by recording the physical and biotic state variables of the tree and of the near environment via real–virtual digital sockets. Following a nested approach, the twinned trees and the related physical and physiological processes are then part of a broader twinning of the entire forest realized by capturing data at forest scale from sources such as remote sensing technologies and flux towers. Ultimately, to unlock the economic value of forest ecosystem services, the FDT should implement a distributed ledger-based on blockchain and smart contracts to ensure the highest transparency, reliability, and thoroughness of the data and the related transactions and to sharpen forest risk management with the final goal to improve the capital flow towards sustainable practices of forest managementopenBuonocore, Luca; Yates, Jim; Valentini, RiccardoBuonocore, L.; Yates, J.; Valentini, R

Moddicom: a Complete and Easily Accessible Library for Prognostic Evaluations Relying on Image Features

Decision Support Systems (DSSs) are increasingly exploited in the area of prognostic evaluations. For predicting the effect of therapies on patients, the trend is now to use image features, i.e. information that can be automatically computed by considering images resulting by analysis. The DSSs application as predictive tools is particularly suitable for cancer treatment, given the peculiarities of the disease –which is highly localised and lead to significant social costs– and the large number of images that are available for each patient. At the state of the art, there exists tools that allow to handle image features for prognostic evaluations, but they are not designed for medical experts. They require either a strong engineering or computer science background since they do not integrate all the required functions, such as image retrieval and storage. In this paper we fill this gap by proposing Moddicom, a user-friendly complete library specifically designed to be exploited by physicians. A preliminary experimental analysis, performed by a medical expert that used the tool, demonstrates the efficiency and the effectiveness of Moddicom

Tough nanopaper structures based on cellulose nanofibers and carbon nanotubes

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The nature of dark energy

According to a variety of cosmological observations at small and large redshifts, the universe is composed by a large fraction of a weakly clustered component with negative pressure, called dark energy. The nature of the dark energy, i.e. its interaction and self-interaction properties, is still largely unknown. In this contribution we review the properties of dark energy as inferred from observations, with particular emphasis on the cosmic microwave background. We argue that the current dataset imposes strong constraints on the coupling of dark energy to dark matter, while it is still insufficient to constrain the equation of state or potential. Future data will dramatically improve the prospects