The biomaterial coatings for bone tissue regeneration described in this study promote bioactivity. The ceramic-polymer composite coatings deposited on polylactide (PLA) plates contain polymers, namely polyvinylpyrrolidone (PVP)/polyethylene glycol (PEG), while the ceramic phase is hydroxyapatite (HA). Additionally, collagen (COL) and glutathione (GSH) are components of high biological value. Bone tissue materials requires additionally demanding tribological properties, which are thoroughly described in this research. These findings, presented herein for the first time, characterize this type of highly specific composite coating material and their indicate possible application in bone regeneration implants. Implementation of the collagen in the PVP/PEG/HA composite matrix can tailor demanding tribological performance, e.g., anti-wear and friction reduction. The addition of the ceramic phase in too high a content (15%) leads to the decreased swelling ability of materials and slower liquid medium absorption by composite coatings, as well as strong surface roughening and loosening tribological properties. In consequence, small particles of HA from the very rough composite crumble, having a strong abrasive effect on the sample surface. In conclusion, sample C composed of PVP/PEG/GSH/COL/HA (5%) exhibits high bioactivity, strong mechanical and tribological properties, the highest free surface energy, porosity, and accepted roughness to be implemented as a material for bone regeneration.
Bubble Sauter Mean Diameter (SMD) in gas-liquid multiphase system is of particular interest and the quantification of gas characteristics is still a challenge today. In this contribution, multiphase Computational Fluid Dynamic (CFD) simulations are combined with Population Balance Model (PBM) to investigate the bubble SMD in baffled stirred tank reactor (STR). Hereby, special attention is given to the phenomenon known as the fluid macro-instability (MI), which is a large-scale low-frequency fluid velocity variation in baffled STRs, since the fluid MIs have a dominating influence on the bubble breakage and coalescence processes. The simulations, regarding the fluid velocity, are validated with Laser Doppler Anemometry (LDA) experiments, in which the instant radial velocity is analyzed through Fast Fourier Transform (FFT) spectrum. The frequency peaks of the fluid MIs are found both in the simulation and in the experiment with a high degree of accuracy. After the validation, quantitative predictions of overall bubble SMD with and without MIs are carried out. Due to the accurate prediction of the fluid field, the influence of the fluid MI to bubble SMD is presented. This result provides more adequate information for engineers working in the field of estimating bubble SMDs in baffled STRs.
Zusammenfassung In der vorliegenden Arbeit werden aus dem Vergleich experimenteller Daten ffir den Sauterdurchmesser d32 und den Hold-up rp mit Gleichungen aus der Literatur fiir den verwendeten konischen Turbinenr/ihrer fiir gas-flfissig Systeme Modellgleichungen ffir d32 und ~o angegeben.Die notwendigen Anpassungen der Proportionalit~its-konstante in den Literaturgleichungen werden auf der Basis fluiddynamischer PMnomene erl~iutert. Sie lassen sich durch fluiddynamische Ergebnisse einer frfiheren Untersuchung mit Laser-Doppler-Anemometrie begrfinden.Koaleszenzph/inomene werden im Modell beriicksichtigt, wobei eine Analogie zu Blasens~iulen zugrundegelegt wird und sich als tragf~ihig erwiesen hat. Argumente ffir die Notwendigkeit der Berficksichtigung der lokalen Fluiddynamik bei der Modellierung van Dispergiervorgfingen werden vorgelegt. Modelling of Sauter mean diameter and hold-up for a conical turbine in a gas-liquid dispersionAbstract By comparing the experimental data of the Sauter-mean-diameter d32 and the hold up q~ with models from literature, there are presented equations for d32 and (p for the used conical turbine in gas-liquid systems. The necessary adjustment of the proportionality constants of the literature equations will be explained on the basis of fluiddynamical phenomena. It can be established by fluiddynamical results of a former study carried out with laserdoppler-anemometry.Coalescence phenomena are taken into account in the model using an analogy to bubble columns. The analogy to bubble columns turns out to be suitable. Arguments for the necessity of considering the local fluiddynamics in the modelling of dispersions are presented. FormelzeichenA [m 2 ] Phasengrenzfl~iche a [-] Exponent Korrespondenz an: Alfons Mersmann ar [ m 2 / m 3 ] phasenbezogene Grenzfl~iche b [-] Exponent C [-] Konstante C1 [-] Konstante C2 [-] Konstante d [m] Rfihrerdurchmesser (d = 0.1 m) dl [m] Partikeldurchmesser d32 [m] Sauterdurchmesser d~ [m] Sauterdurchmesser ohne Koaleszenzeinflufl Er [J] Oberfl/ichenenergie FI [-] Fluidkennzahl H [m] Einfiillh6he ni [-] Anzahl der Partikel p [-1 Exponent q [-] Exponent At [s] charakteristische Zeitdifferenz w~ [m/s] Blasengeschwindigkeit wE [m/s] Gasleerrohrgeschwindigkeit fl [l/s] Koaleszenzrate c [W/kg] spezifische Leistung 0c [kg/m 3] Dichte der kontinuierlichen Phase 0d [kg/m 3] Dichte der dispersen Phase cr [N/m] Grenzfl~ichenspannung ~) [-] Hold-up 1 Einleitung In der Literatur werden ffir bestimmte Grundrfihraufgaben unterschiedliche Rfihrertypen empfohlen [1, 2]. Die Auswahl der Rfihrer geschieht dabei nach bestimmten Eigenschaften, die zur Erfiillung der Rfihraufgabe unabdingbar sind.So wird beispielsweise der 6-Blatt-Scheibenrfihrer ffir das Dispergieren in gas-fliissig oder fliissig-flfissig Systemen als besonders geeignet angesehen. Ffir das Suspendieren wiederum gilt der 6-Blatt-Scheibenrfihrer als ungeeignet und der Propellerrfihrer als empfehlenswert [3]. Die Empfehlungen basieren einerseits auf praktischen Erfahrungen und andererseits auf rein theoretisch b...
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