Bubble column reactors are widely used in many industrial applications due to their simplicity and safety of operation. Despite these advantages, the design and scale‐up of bubble column reactors is still challenging especially for industrial conditions at elevated pressure and temperature. One reason is the uncertainties concerning the specific interfacial area which is directly dependent on the bubble size distribution, bubble velocity, and gas hold‐up. All these parameters are difficult to measure under industrial conditions due to the opaqueness of the bubbly flow and the safety risks of using organic solvents at elevated pressures and temperatures. This article introduces endoscopic bubble image velocimetry, a new measuring method that enables the detection of bubble sizes and bubble velocities in organic solvents at elevated pressure and temperature (pmax = 1.85 MPa and Tmax = 70 °C) for maximal gas hold‐ups of 16 %. For this system it becomes evident that the bubble size distribution for low superficial gas velocities is almost unaffected by pressure and temperature, whereas the bubble velocity decreases slightly.
In den 1980er und 90er Jahren wurden intensive und erfolgreiche Forschungsprogramme durchgeführt, um die integrale Beschreibung und Auslegung von Blasensäulenreaktoren zu verbessern. Zur Jahrtausendwende wurden dann insbesondere lokale Mess-und Modellierungsmethoden verfeinert. Die Ergebnisse dieser lokalen Modelle sind bisher jedoch oft nur unzureichend in die integralen Auslegungsgleichungen eingeflossen, da eine große Lücke zwischen den betrachteten Zeitund Ortsskalen besteht. Geeignete Mittelungs-und Filterverfahren fehlen ebenso wie Übertragungsregeln, um von den meist akademischen Stoffsystemen und Bedingungen zu industriellen Anwendungen zu gelangen. Der Artikel gibt einen Einblick in den Status quo im Bereich der Modellierung von Blasenströmungen und zeigt Wege auf, die künftig zu einer umfassenderen Modellierung und besseren Übertragbarkeit führen könnten.In the 1980s and 1990s intensive and successful research has been conducted to improve the integral description and design of bubble column reactors. At the turn of the century, in particular local measurement and modeling methods were refined. The results of these local models have often been poorly incorporated into the design of integral equations, as there is a significant gap between the observed temporal and spatial scales. Appropriate averaging and filtering processes are missing as much as transfer rules, to proceed from the most academic material systems and conditions towards industrial applications. The article describes the status quo in the field of modeling of bubbly flows and outlines novel methods that may lead to a more comprehensive modeling and better transferability in the future. Abbildung 1. Instationäre Strömungsverhältnisse in einer Blasensäule nach Fan [9]. Abbildung 2. Übersicht über die komplexen Abhängigkeiten zwischen einstellbaren und nicht-einstellbaren Parametern in Blasenströmungen.Abbildung 6. Abhängigkeit des Gasgehalts von der Gasleerrohrgeschwindigkeit unter Angabe des Strömungsregimes. Abbildung 7. Mit der PRIME-Methode berechnete Blasenkette in Flüssigmetall (links) [62] und mit der Front-tracking-Methode berechneter Blasenschwarm (rechts) [55]. Abbildung 8. Vergleich des integral gemessenen Gasgehalts mit den Korrelationen von Sotelo [76] und Behkish [75] bei Variation der Gasleerrohrgeschwindigkeit. Technikumsreaktor DN300 (Innendurchmesser 288 mm, Höhe 1,6 m), Begasung durch Tellerbegaser (poröse Membran, Lochdurchmesser 1 mm), Temperatur 19°C. Abbildung 9. Gasgehalt vs. Gasleerrohrgeschwindigkeit für Hamburger Leitungswasser sowie Leitungswasser von verschiedenen Standorten (Salzgehalt nachgestellt). www.cit-journal.com
Citronella candles are widely used as insect repellants, especially outdoors in the evening. Because these essential oils are unsaturated, they have a unique potential to form secondary organic aerosol (SOA) via reaction with ozone, which is also commonly elevated on summer evenings when the candles are often in use. We investigated this process, along with primary aerosol emissions, by briefly placing a citronella tealight candle in a smog chamber and then adding ozone to the chamber. In repeated experiments, we observed rapid and substantial SOA formation after ozone addition; this process must therefore be considered when assessing the risks and benefits of using citronella candle to repel insects.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.