title: Infrared thermography for monitoring of freeze-drying processes: instrumental developments and preliminary results.
abstract: Coupling an infrared (IR) camera to a freeze dryer for on-line monitoring of freeze-drying cycles is described for the first time. Normally, product temperature is measured using a few invasive Pt-100 probes, resulting in poor spatial resolution. To overcome this, an IR camera was placed on a process-scale freeze dryer. Imaging took place every 120 s through a Germanium window comprising 30,000 measurement points obtained contact-free from -40 °C to 25 °C. Results are presented for an empty system, bulk drying of cheese slurry, and drying of 1 mL human serum in 150 vials. During freezing of the empty system, differences of more than 5 °C were measured on the shelf. Adding a tray to the empty system, a difference of more than 8 °C was observed. These temperature differences probably cause different ice structures affecting the drying speed during sublimation. A temperature difference of maximum 13 °C was observed in bulk mode during sublimation. When drying in vials, differences of more than 10 °C were observed. Gradually, the large temperature differences disappeared during secondary drying and products were transformed into uniformly dry cakes. The experimental data show that the IR camera is a highly versatile on-line monitoring tool for different kinds of freeze-drying processes.
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, (IRMM) Retieseweg 111, B-2440 Geel, Belgium. Electronic address: hakan.emteborg@ec.europa.eu.
authors.forename: Håkan
authors.initials: H
authors.lastname: Emteborg
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, (IRMM) Retieseweg 111, B-2440 Geel, Belgium.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Zeleny
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, (IRMM) Retieseweg 111, B-2440 Geel, Belgium.
authors.forename: Jean
authors.initials: J
authors.lastname: Charoud-Got
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, (IRMM) Retieseweg 111, B-2440 Geel, Belgium.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Martos
authors.affiliation: Martin Christ Gefriertrocknungsanlagen GmbH, An der Unteren Söse 50, D-37520 Osterode, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Lüddeke
authors.affiliation: InfraTec GmbH Infrarotsensorik und Messtechnik, Gostritzer Str. 61-63, D-01217 Dresden, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Schellin
authors.affiliation: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, (IRMM) Retieseweg 111, B-2440 Geel, Belgium.
authors.forename: Katharina
authors.initials: K
authors.lastname: Teipel
mesh_terms: D002611:Cheese / Q000032:analysis; D019963:Clinical Chemistry Tests / Q000295:instrumentation / Q000379:methods; D004867:Equipment Design; D019649:Food Industry / Q000295:instrumentation / Q000379:methods; D005612:Freeze Drying / Q000295:instrumentation / Q000379:methods; D006801:Humans; D007259:Infrared Rays; D044967:Serum / Q000737:chemistry; D013817:Thermography / Q000295:instrumentation / Q000379:methods
keywords: freeze-drying; human serum; infrared camera; infrared spetcroscopy; lyophilization; processing; spatial resolution; thermography; water in solids