MODELLING DESIGN OF MULTIPHASE BUBBLE-BED REACTORS IN ADVANCED FOOD-INDUSTRY APPLICATIONS … 1/3 J Zahradnik, M Ruzicka 1

1. MODELLING DESIGN OF MULTIPHASE BUBBLE-BED REACTORS IN ADVANCED FOOD-INDUSTRY APPLICATIONS … 1/3 J Zahradnik, M Ruzicka1, J Markos2, J Teixeira3, S Generalis4, N Thomas* 1.Inst Chem Proc Fundamentals Prague 2. Univeristy of Technology, Bratislava 3.University of Minho, Braga 4.Aston University, Birmingham * FRED Ltd – Aston Park, Birmingham B7’4BJ UK Neale@Thomas.net

2. Background set up 2/3 and 3/3 whilst browsing 1/3 Copernicus/WCCEGLS01-2 Copernicus/WCCEGLS01-3

3. Bubble Column / Loop, Hydrodynamics, Bio-Reaction, CFD, Food-Industry ABSTRACT EC Copernicus project (IC15-CT98-0904 / PL979021) catalysed by Dr Jindrich Zahradnik, sadly since deceased In dedication to his memory an overview of main elements website hosted by Aston University (www.copernicus.aston.ac.uk) collaborations facilitated by study exchangesenvisaged exploitation by sector industries

4. FOREWORD prior liaison on equipment evaluation and interpretation in flow fundamentals and implementations simple air-water systemsviscous solutions Chem Eng Sci 50, 3175-3186 electrolytic solutions Chem Eng Res Des 73, 341-346 effects on operational performance from bubble size amplification / inhibition by suppression of fragmentation and coalescence collapse of quiescence in uniformly base-sparged bubble beds, classical framework of patternised transition Chem Eng Sci 52, 3811-3826 bubble formation and release Int J Multiphase Flow 23, 671-682

5. SCOPE hydrodynamic fundamentals for roles of gas entry conditions couplings in near field behaviour and modal interpretations synergistic bubble interactions via nonlinear paradigms functionally applicable scalings for regime transition in real bubble columns instability inception in bubble columns analogous to thermal convective transition better interpretations of experimental data and its application by scaling correlations to bioreactor performance evaluation efficacy validation of “CFD” codes for configurational and operational options

6. CONTENT physical performance evaluations / correlations for circulation (M1) and oxygen transfer (T2) in airlift loops and bend effects (M3) to pilot scale plus pulsed delivery options (M4) overcoming inhibition in viscous broths, also mass-loading impairment of transport dynamics in floc-stabilised cultures (T3) implementation in real fermentations of citric acid (M2, M5) and for ethanol (T1) CFD aspects as familiarisation / implementation training exercise (G1) using FLUENT as established product with sustained support services emphasis on teaching / training tools for improved insight by biochemical bioprocess engineers lacking familiarity with intricate complexities (G2) of multiphase turbulence in simple fluids, never mind the challenging constitutions of real broths

7. CONTEXT columns and airlift loops as bioreactors suffer from inadequate design and scale-up descriptions of complex multiphase hydrodynamics stationary circulation patterns inadequate for capturing transport and exchange intensification by unsteady heterogeneities experimental methodsdelivered routine mapping of local statisticsemergently also access to trajectory statistics mimicked by CFD but only with retrospective assurance limited to idealised patterns induced by interior voidage non-uniformity little progress on nonlinear feedback via pressure perturbations over the sparger and evaluation of global transition modes. bioreactor realities entail particle transport and nutrient transfersusually underestimated by simple correlations from bubbling beds aloneoften adverse impact from overstressing of suspended biomass

8. STATUS numerous isolated and idealised evaluations of various facetsbut very little progress on integrated cogent frameworks of practical value GLS-B (B=biological) operations are still implemented and operated on the basis of application-specific empirical correlations … individually and proprietarily verified without meaningful reference to key underlying principles beyond traditional scaling relations that are in any case known to be flawed as indicated above sorry state beyond proven rules of thumb needingincorporation of first principles into traditional scalings … supplemented with specific performance evaluations … all to be incorpated into bio-kinetic extension of computer modelling as training aid for … biochemical practitioners daunted by self-evidently unfathomable fluid dynamic complexities

9. PHYSICAL BASICS considering columns (zero sectional mean flow) for formation and maintenance of uniform bubbly layers above plate distributors … three supposedly separable scales of scrutiny: bubbles (micro),clusters (meso), bed (macro) on microscale have hydrodynamic coupling between adjacent orifices in perforated plate spargers as determinant for establishment of uniform bubbly layer plate orifices fed from a common plenum exhibit pairwise interference manifested by bubbling mode as signatured in local pressure records Chem Eng Sci 55, 421-429 synchronous bubbling at low and high flow rates,is separated by broad asynchronous regimes , with stability thresholds affected by orifice spacings and barriers (plenum and liquid), also by column size

10. going from pairwise to multiple bubbling in lower synchronous regime triggered families of modes from completely asynchronous to completely synchronous Chem Eng Sci 54, 5223-5229 orifice interactions via gas and liquid were assessed and charcaterised, also orifice distribution symmetry for influence on resonant bubbling conditions. for mesoscale effects, idealised linear chains of rising bubbles (Reynolds #50-200) were force-law modelled akin to mass-spring-damper approaches Int J Multiphase Flow 26, 1141-1181

11. Buoyancy-drag-inertia balance then determines chain response via local / non-local interactionsand assumed end conditions (free / fixed) Free-end chains evolve to fragmented long-time structure via merger, separation, pairing, re-pairing and oscillation. Fixed-end chains sustain uniform spacing and rise faster, also exhibit spacing waves at low Reand chaos at high Re. macroscale modelling for collapse conditions of homogeneous regime with increasing voidage was done using kinematic and dynamic closures kinematic closure provides simple transparent representation via classical Darwin drift and Zuber-Findlay drift-flux formulations plus intermittency resulting 5-parameter formulae describe voidage-gas flow rate dependence predicting critical conditions for homogeneous regime instability and maximum voidage.

12. Experiments show excellent match as well as being consistent with published linear stability analysis Chem Eng Sci – accepted dynamic closure analoguesclassical Rayleigh-Benard convective instability at supercritical buoyancy flux

13.  Nusselt #Nu, Prandtl #Pr, Rayleigh #Ra, aspect #A captures onset of large-scale motion at critical Rac(A) bubbly convection layer is subcritically passive sparged liquid that breaks at supercritical gas flux soassign equivalent Nu*, Ra*, Pr* for equivalent Rac*(A) experiments in cylindrical columns avoid “corner” anomalies distorting underlying criterion – scaling excellent match with experimental data critical voidage Rayleigh number ecgH3/ **, 105 for infinite layers (A=D/H >>1), aspect ratio dependence (1+100A-11/4) in line with thermal findings  J Fluid Mech – submitted governing equations for thermal and bubbly layers h omologous for all practical purposes and formally so for zero bubble inertia and slip – also sedimentation of dispersed particles.

14. Background set up 2/3 and 3/3 whilst browsing 1/3 Copernicus/WCCEGLS01-2 Copernicus/WCCEGLS01-3