cially its work process related to testing procedures applied to soft-ware components in order to assess their compliance with the pub-lished CAPE-OPEN interface specifications.

189*

Optimum Experimental Design for theDetermination of Enzyme OperatingStability

M a n f r e d E s t l e r *

A n d r e a s S . B o m m a r i u s * , * *

H e l g e W e r n e r * , H e i k o L u f t *

E k a t e r i n a K o s t i n a * * *

H a n s G e o r g B o c k * * *

J o h a n n e s P . S c h l o e d e r * * *

* Degussa AG, P.O. Box 1345, D-63403 Hanau, Germany

**School of Chemical Engineering, Georgia Institute of Technology,315 Ferst Drive, Atlanta, GA, 30332-0363, U.S.A.

*** Interdisciplinary Center for Scientific Computing (IWR),University of Heidelberg, Im Neuenheimer Feld 368,D-69120 Heidelberg, Germany

To evaluate enzymes in a process environment, quantities such astotal turnover number (TTN) [moles of product / mole of catalyst] orhalf-life [hours] are important to understand performance relativeto alternative catalysts. These long-term properties of biocatalystscan be calculated on the basis of an adequate kinetic model iden-tified from few short-time experiments.

The estimation of kinetic model parameters for enzy-matic processes is a challenging task. It will be shown that applica-tion of optimal experimental design techniques can significantlyimprove the design of experiments, such that the measurementscontain maximal information for the estimation of the model para-meters. As a result, it turns out that few short-time experiments aresufficient for model identification.

190*

Synthesis and ThermophysicalCharacterization of Silica-OrganicHybrid Aerogel

D r . S u n Y o u n g K i m 1

T a e - J i n Y i m 1

P r o f . K i - P u n g Y o o 1

2 D i p l . - C h e m . I . S m i r n o v a2 P r o f . D r . - I n g . W . A r l t

1Dep't. of Chem. Eng., Sogang University, C.P.O. Box 1142, Seoul121-742, South Korea

2Fachgebiet Thermodynamik und Thermische Verfahrenstechnik,TK 7, TU Berlin, Berlin, Germany

Low density silica-organic hybrid aerogels were fabricated by sol-gel processing and supercritical fluid drying techniqueswith silicateand polymeric MDI(diphenylmethane diisocyanate). By FTIR, it

was found that there exist siloxane group at frequency 1100, H inOH group at 3500, C=O group at 1700 and C-N group at 1400 inthe hybrid aerogels. Thermal conductivity of the hybrid aerogelswas measured by the transient hot-wire method. Among measuredaerogel samples, the lowest valueof thermal conductivity was0.0184W/mK. The sample with this conductivity also showed low density,0.0848 g/cm3 and the specific surface area, 292.504 m2/g. Also it wasconformed that the silica-organic hybrid aerogel was hydrophobicbehavior and it does not absorb water at all.

191*

Gas-Solid Heat Transfer withSolid Phase Change

S . P e t r e s c u

I . M a m a l i g a

C . P e t r e s c u

Technical University of Iasi, Department of ChemicalEngineering , Bd. D. Mangeron 71, 6600, Iasi, Romania,E-mail: spetresc@ch.tuiasi.ro

This paper presents an experimental study of heat transfer in gas-solid systems accompanied by phase change. Heat transfer duringthe melting of a single particle in direct contact with a gaseous ther-mal agent was studied. The experiments were performed withspherical ice particles, 0.045 m in diameter, having a temperatureof 264.6 K, and hot air with different temperatures and veloci-ties. The dependencies of the melting rate and of the coefficientags with the air velocity and the dependence of the Nusselt withthe Reynolds number are represented. The results obtained revealan increase of vm and ags with temperature and air velocity. Since airvelocity has the main influence on ags one may assert that the re-sistance at heat transfer is concentrated mainly in the gaseous film.

Figure.Experimental set-up; 1 ± melting chamber, 2 -electrical hea-ter,3 ± ventilator, 4 ± technical balance, 5 ± rod, 6 ± ice parti-cle, 7 ± clamp, 8 ± valve, 9 ± contact thermometer, 10 ± relay,11- control thermometer, R1, R2 ± pipes.

647C o m p u t a t i o n a l E n g i n e e r i n gChemie Ingenieur Technik (73) 6 I 2001