Computational modelling of latent heat storage systems with integrated phase change materials in building applications

89 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Υπολογιστική Μηχανική”Ο σκοπός αυτής της διπλωματικής εργασίας είναι να εκτιμήσει την επίδραση θερμικών συστημάτων, τα οποία ενσωματώνουν υλικά αλλαγής φάσης, με την ανάπτυξη υπολογιστικών εργαλείων. Στην εισαγωγή, μια σύντομη θεώρηση καταλήγει στο ότι, ο σύγχρονος τρόπος ζωής απαιτεί μεγάλες ποσότητες ενέργειας στον κτιριακό τομέα, ούτως ώστε να καλυφθούν οι ανάγκες φωτι- σμού και θερμικής άνεσης. Τα συστήματα αερισμού, θέρμανσης και κλιματισμού καταναλώνουν, ίσως, την περισσότερη ενέργεια, και για τον λόγο αυτό η απόδοσή τους παίζει σημαντικό ρόλο στην εξοικονόμηση ενέργειας. Μία, σχετικά, νέα γενιά εφαρμογών μπορεί να καταστήσει τα συστήματα αυτά πιο αποδοτικά. Οι εφαρμογές αυτές υιοθετούν την χρήση υλικών αλλαγής φάσης. Τα υλικά αυτά μπορούν και συσσωρεύουν ενέργεια υπό την μορφή λανθάνουσας θερμότητας. Με τον τρόπο αυτό επιτυγχάνεται η θερμοκρασιακή ομοιομορφία. Επίσης, η αποθηκευμένη θερμότητα μπορεί να χρησιμοποιηθεί σε μελοντικό χρόνο. Τα υλικά αυτά, ο τρόπος λειτουργίας τους, καθώς και τα ιδιαίτερα χαρακτηριστικά τους μελετώνται στο δεύτερο κεφάλαιο. Στις περιπτώσεις που μελετώνται, οι κτιριακές εγκαταστάσεις θερμαίνονται λόγω της ηλιακής ακτινοβολίας. Επίσης, λόγω θερμοκρασιακών διαφορών, παρατηρούνται φαινόμενα φυσικής συναγωγής. Για τους λόγους αυτούς, ο ρόλος του τρίτου κεφαλαίου είναι να λειτουργήσει ως μια εισαγωγή σε φαινόμενα μεταφοράς και ρευστοδυναμικής. Επιπροσθέτως, θα αποδειχθεί, ότι η αναλυτική επίλυση του θερμοκρασιακού και του ροϊκού πεδίου είναι αδύνατη, συνεπώς η αριθμητική προσέγγιση κρίνεται απαραίτητη. Στοιχεία της υπολογιστικής μεθόδου των πεπερασμένων όγκων θα κλείσουν το κεφάλαιο αυτό. Στο τέταρτο κεφάλαιο, λαμβάνει χώρα η υπολογιστική μελέτη δύο περιπτώσεων. Αρχικά, περιγράφεται η πειραματική μελέτη συστήματος περσίδων, στο οποίο έχει εγκατασταθεί υλικό αλλαγής φάσης. Εν συνεχεία, αναλύονται τα χαρακτηριστικά του υπολογιστικού μοντέλου. Τελικά, παρουσιάζονται τα αποτελέσματα της προσομοίωσης, τα οποία παρέχουν ικανοποιητική συμφωνία με τις τιμές του πειράματος, παρέχοντας πιστοποίηση στο υπολογιστικό εργαλείο. Στο δεύτερο σκέλος, μελετήθηκε ένα νέο σύστημα, το οποίο αποτελείται από περιστρεφόμενες περσίδες. Οι περσίδες ενσωματώνουν ένα στρώμα μονωτικού καθώς και υλικό αλλαγής φάσης. Εκτιμήθηκε η επίδραση του συστήματος στην θερμική συμπεριφορά εξωτερικού τοιχώματος, υπό δύο διαφορετικές κλιματικές συνθήκες. Τα αποτελέσματα δείχνουν ευνοϊκή επίδραση έναντι σε περιπτώσεις χωρίς την εγκατάσταση του συστήματος. Ωστόσο, προτείνονται συμπληρωματικές προσομοιώσεις και βελτιώσεις στο υπολογιστικό μοντέλο, για την εξαγωγή περαιτέρω χρήσιμων συμπερασμάτων. Τέλος, γενικά συμπεράσματα και προτάσεις για μελλοντική δουλειά κλείνουν αυτή την διπλωματική. Τα υλικά αλλαγής φάσης παρουσιάζουν θετικό αντίκτυπο σε κτιριακές εφαρμογές, ενώ το υπολογιστικό εργαλείο, που αναπτύχθηκε, δείχνει να έχει δυνατότητες εξέλιξης.The purpose of this thesis is to assess the effect of thermal systems that incorporate phase change materials, with the development of a computational tool. In the introduction, a brief consideration concludes, that the modern way of life requires large amounts of energy in the building sector, in order to meet the needs of lighting and thermal comfort. The ventilation, heating and air conditioning systems consume more energy, and therefore their performance plays a significant role in saving energy. A, relatively, new generation of applications can make these systems more efficient. These applications adopt the use of phase change materials. These materials can store energy in the form of latent heat. Thereby, it is necessary to study their behaviour, their advantages and, also, their limitations. In addition, previous works were investigated. This contributed in gaining insight and, also, a valuable fashion to treat the heat capacity: the effective heat capacity method. These topics are discussed in the second part. The investigated cases in this work, present complicated features: the buildings are heated with thermal radiation, natural convection is observed and multi-layer objects are employed. Hence, the role of the third chapter is to serve as an introduction to heat transfer phenomena and fluid dynamics. It is discussed, that an analytical approach on the temperature and flow fields is impossible. Hence, the computational method of finite volume will close this chapter The fourth chapter presents the computational study of two cases. Initially, the experimental study of a blind, which integrated a phase change material, is described. Then, the characteristics of the numerical model are presented. Eventually, the results of the simulation show a very good agreement to the experiment, verifying the method. Furthermore, a new developed system is investigated under two different environment conditions. This system consists of slats, in which an insulation layer and a phase change material are embedded. It will be installed on walls of existing building to improve their thermal characteristics. The results show the beneficial role of the specific applications in the summer period. More tests should be performed to obtain more useful information for winter days as well. In addition, an overview reveals the positive and negative features of this method, and countermeasures are suggested. Finally, general remarks of this work with comments and overall observations conclude this work. Thermal energy storage systems have, in general, a positive impact and we can gain the most out of them with careful design. The presented numerical method is considered suitable to simulate heat transfer phenomena and future simulation work is outlined.Ιωάννου Νικόλαο

Fluorine-18 fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography scan contributes to the diagnosis and management of brucellar spondylodiskitis

BACKGROUND: Limited data suggest that fluorine-18 fluoro-2-deoxy-D-glucose (F-18 FDG) positron emission tomography combined with computed tomography (PET/CT) scan may be useful for diagnosing infections of the spine. Brucellar spondylodiskitis might be devastating and current imaging techniques lack sensitivity and specificity. The aim of this prospective study was to determine the role of F-18 FDG PET/CT scan in the diagnosis of brucellar spondylodiskitis and in monitoring the efficacy of its treatment. METHODS: Ten consecutive patients with brucellar spondylitis were prospectively evaluated with PET/CT. Baseline evaluation included also magnetic resonance imaging (MRI) of the affected spine, indices of inflammation, the slide agglutination test (SAT), and the standard hematology and biochemistry. All cases were treated with suitable antibiotics until resolution or significant improvement of clinical and radiological (MRI) findings. Upon completion of treatment, they were re-evaluated with follow-up PET/CT scan. The maximum standardized uptake values (SUV) were measured and compared with SAT. RESULTS: In all patients there was an increased F-18 FDG activity in the infected spine region detected by the initial MRI. F-18 FDG PET/CT provided additional information, compared to MRI, in 4 (40%) patients. More specifically it revealed additional spine lesions (in 3 patients), lymphadenitis, arthritis, organomegaly, as well as new paravertebral soft tissue involvement and epidural masses. This additional information had an impact on the duration of treatment in these patients. At the end of treatment all patients had a complete clinical response; 5 patients had positive serology, 6 patients had residual MRI findings, while 9 had a positive PET/CT but with significantly decreased FDG uptake compared to baseline (median 2.6, range 1.4 – 4.4 vs. median 5.5, range 2.8 – 9.4, p = 0.005). During the follow up period (median 12.5 months) no relapses have been observed. No significant association was observed between the SUV and SAT. CONCLUSIONS: Our study suggests that in patients with brucellar spondylodiskitis F-18 FDG PET/CT scan can provide additional information on the spread of the infection, compared to MRI. Successful treatment is associated with a significant decrease in SUVmax values; thus, PET/CT scan may be a complementary method for determining the efficacy of treatment

The European Renal Association - European Dialysis and Transplant Association Registry Annual Report 2014 : a summary

Background: This article summarizes the European Renal Association - European Dialysis and Transplant Association Registry's 2014 annual report. It describes the epidemiology of renal replacement therapy (RRT) for end-stage renal disease (ESRD) in 2014 within 35 countries. Methods: In 2016, the ERA-EDTA Registry received data on patients who in 2014 where undergoing RRT for ESRD, from 51 national or regional renal registries. Thirty-two registries provided individual patient level data and 19 provided aggregated patient level data. The incidence, prevalence and survival probabilities of these patients were determined. Results: In 2014, 70 953 individuals commenced RRT for ESRD, equating to an overall unadjusted incidence rate of 133 per million population (pmp). The incidence ranged by 10-fold; from 23 pmp in the Ukraine to 237 pmp in Portugal. Of the patients commencing RRT, almost two-thirds were men, over half were aged >= 65 years and a quarter had diabetes mellitus as their primary renal diagnosis. By day 91 of commencing RRT, 81% of patients were receiving haemodialysis. On 31 December 2014, 490 743 individuals were receiving RRT for ESRD, equating to an unadjusted prevalence of 924 pmp. This ranged throughout Europe by more than 10-fold, from 157 pmp in the Ukraine to 1794 pmp in Portugal. In 2014, 19 406 kidney transplantations were performed, equating to an overall unadjusted transplant rate of 36 pmp. Again this varied considerably throughout Europe. For patients commencing RRT during 2005-09, the 5-year-adjusted patient survival probabilities on all RRT modalities was 63.3% (95% confidence interval 63.0-63.6). The expected remaining lifetime of a 20-to 24-year-old patient with ESRD receiving dialysis or living with a kidney transplant was 21.9 and 44.0 years, respectively. This was substantially lower than the 61.8 years of expected remaining lifetime of a 20-year-old patient without ESRD.Peer reviewe

Measurement of prompt open-charm production cross sections in proton-proton collisions at root s=13 TeV

The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb(-1). The differential production cross sections of the D*(+/-), D-+/-, and D-0 ((D) over bar (0)) mesons are presented in ranges of transverse momentum and pseudorapidity 4 < p(T) < 100 GeV and vertical bar eta vertical bar < 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.Peer reviewe

Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp collisions at √s = 13 TeV

Abstract The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (d̂ t) and chromomagnetic (μ̂ t) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable AFB(1) is used to approximate the asymmetry. Candidate t t ¯ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for t t ¯ final states. The values found for the parameters are AFB(1)=0.048−0.087+0.095(stat)−0.029+0.020(syst),μ̂t=−0.024−0.009+0.013(stat)−0.011+0.016(syst), and a limit is placed on the magnitude of | d̂ t| &lt; 0.03 at 95% confidence level. [Figure not available: see fulltext.

Development and validation of HERWIG 7 tunes from CMS underlying-event measurements

This paper presents new sets of parameters (“tunes”) for the underlying-event model of the HERWIG7 event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in HERWIG7, and are obtained from a fit to minimum-bias data collected by the CMS experiment at s=0.9, 7, and 13Te. The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for event shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the dat

MUSiC : a model-unspecific search for new physics in proton-proton collisions at root s=13TeV

Results of the Model Unspecific Search in CMS (MUSiC), using proton-proton collision data recorded at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys the observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.Peer reviewe

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV

A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-1) collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 GeV