Helmut Wiggers

Preparation of spray dried submicron particles: Part B – Particle recovery by electrostatic precipitation

ABSTRACT The low bioavailability of poorly water‐soluble drugs is currently one of the major focuses of pharmaceutical research. One strategy currently being investigated to overcome this limitation is to decrease the particle size of the active pharmaceutical ingredients (API). An innovative process for this is spray drying with spray conditioning, which can produce submicron particles. One challenge resulting from this process is the recovery of these dispersed particles from a gas flow. Electrostatic precipitation is a common technique for air purification purposes, but an adapted electrostatic precipitator (ESP) design is necessary to achieve high collection efficiencies. The ESP design in this work uses the precipitation method of Penney filters which separates charging and collection into two stages. The ESP dimensions depend on various assumptions and simplifications. Several experiments were conducted to assess the performance of the ESP and characterize its behaviour in long‐term tests. The crucial parameters in the charging process are the residence time as well as the operating voltage. These constraints were examined to enhance the collection efficiency. Based on these tests it was possible to determine a suitable charging length as well as the dimensions of the collection stage. In conclusion, an ESP customized for collecting particles in the range of 0.1–1&mgr;m was designed, built and tested, and collection efficiencies higher than 99% were achieved for submicron particle size distributions. For a robust process continuous cleaning of the charging stage is necessary.

Messergebnisse und Simulationen der Lichtreflexion an Tropfen bei der Messung mit Fasersensoren (Results of Measurement and Simulation of the Light Reflection from Drops on Fibre Sensors)

Diese Arbeit stellt eine Messtechnik vor zur Charakterisierung von Mehrphasenströmungen mit einem optischen Fasersensor. Gemessen wird der Verlauf des Tropfenaufpralls auf dem Sensorende. Der komplexe Signalverlauf wird anhand zweier Simulationen erklärt. Die experimentellen Ergebnisse zeigen eine gute Übereinstimmung mit den Berechnungen. Ein Modell der Totalreflexion am Wasserrest, der auf dem Faserende verbleibt, erklärt eine bestimmte Signaleigenschaft. This paper presents a measuring technique that uses an optical fiber sensor for the characterization of a multi-phase flow. The measurement monitors the process of the drop impingement on the sensor tip. The complex signal is explained using two simulations. The experimental calculations agree well with the theoretical results. A model for the total reflection at the remaining water on the fiber tip explains a certain signal attribute.