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Laboratory of Rheology and Food Engineering

Applicazioni della reologia a processi industriali. Domenico Gabriele. LaRIA Laboratory of Rheology and Food Engineering. Laboratory of Rheology and Food Engineering. CONTRIBUTO DELLA REOLOGIA ALLE PROBLEMATICHE INDUSTRIALI. MATERIALI

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Laboratory of Rheology and Food Engineering

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  1. Applicazioni della reologia a processi industriali Domenico Gabriele LaRIA Laboratory of Rheology and Food Engineering Laboratory of Rheology and Food Engineering

  2. CONTRIBUTO DELLA REOLOGIA ALLE PROBLEMATICHE INDUSTRIALI MATERIALI • Caratterizzazione delle materie prime in funzione del loro utilizzo; • Caratterizzazione dei prodotti in funzione delle proprietà attese. PROCESSI • Progettazione di nuovi impianti in relazione delle proprietà delle materie prime e dei prodotti; • Controllo e miglioramento degli impianti esistenti in relazione alle proprietà di materie prime e prodotti.

  3. A rheologicalapproachto soft icecream production LaRIA Laboratory of Rheology and Food Engineering Laboratory of Rheology and Food Engineering

  4. Foams Multiphase system A viscoleastic medium entrapping gas bubble Shavingfoams Fire-fightingfoams Foodfoams(texturedeterminedby gas cells) Some applications in dairy industry Ice cream (frozen state) Instant Whipped cream (unfrozen state)

  5. Extrusion Gas Loss Under-pressure Emulsion Structure collapsing Soft Ice-Cream Aerated dairy emulsions The situation……. …. The new trend… “INSTANT” ICE CREAM • “Ready-to eat” ice cream • Seller point or home production • “Soft” structure • Reduction or absence of ice crystals • Low pressure aeration Ice Cream Frozen state Aerated emulsions Whipped cream Non Frozen state ……. Possible solution Aeration and storage at low-moderate pressure (4-8 atm), cooling, extrusion, bubble expansion High overrun, smooth texture, stabilisation through emulsion film properties Laboratory of Rheology and Food Engineering

  6. “Instant” Ice Creams • Productcharacteristics ….. • Stability • Icecreamtexture • Low icecontent • Flow through a nozzle at low temperature (T<0°C) • Low drivingforce (4-8 atm) • High overrun • Good gas retention • …. Emulsionrheologicalproperties…. • Low freezingpoint (no ice) • Low viscosity (flow at low temperature) • High elasticity (gas retention, propertexture) … Processconditions Operating conditions (T, P) Geometry (nozzle dimensions)

  7. New product development Optimal formulation…… • Fats • Water • Sugars • Emulsifiers • Proteins • Stabilizers RHEOLOGICAL CHARACTERISATION … and … ……Nozzle design BALANCE EQUATIONS Operating conditions Flow through the nozzle

  8. Material characterisation – 1 Sample characteristics Other emulsions (E2-E7) Base emulsion (E1) • Milk (whole and powder skim milk) • Vegetable fats • Glucose syrup • Dextrose • Emulsifiers1/stabilizers2 3:1 • Mixing, Homogenisation in ultrasound bath 1fatty acids mono and diglycerides 2carrageenan and guar gum

  9. Material characterisation – 2 ARES-RFS TA Instruments Parallel plates (50 mm) Freezing point Time cure (1 Hz; -1°C/min; T= 4 °C freezing point); Time sweep (1 Hz) Elastic component Frequency sweep test (0.1 – 10 Hz; T= -5°, 0°, 4°C); Low temperature viscosity Flow Curve (0.1 – 100 s-1; T= -5°, 0°, 4°C);

  10. Freezing point Sample E1 – Time cure….. …… Sample E1 – Time sweep FP  - 10°C FP - 9°C

  11. Flow curve Frequency sweep Sample E1

  12. Experimental results - 1 Dynamic tests Weak gel model (three-dimensional network)1 A, network strength z, network extension Flow curve Power law model k, consistency index n, flow index 1Gabriele et al., Rheol. Acta. 40 (2001)

  13. Experimental results - 2 Emulsion choice All data at -5°C

  14. t Foam fluidynamics Modelling of foam fluidynamics and expansion Simplifying the problem by considering different steps 1. Modelling of single gas bubble expansion in a viscoelastic medium (void fraction evaluation) 2. Modelling of foam extrusion through a can nozzle (flow of a compressible medium) Ice cream performance evaluation (overrun, residual mass)

  15. r R PG Pinf Single bubble model Bubble expansion - 1 time>0 Extruding foam through the nozzle P outside bubble<8 atm time=0 Foam inside the can Everywhere 8 atm 8 atm 1 atm P 8 atm • Pure bi-axial extension • Isothermal conditions • Equilibrium conditions for mass transfer Bubble expansion Main hypothesis Mechanical equilibrium at the bubble interface1 surface tension P pressure at infinite distance Lliquid density PGgas pressure inside the bubble 1Bird et al., (1977), Dynamics of Polymeric Liquids, Vol.1, Wiley,

  16. Bubble expansion - 2 Rheological constitutive equations Linear viscoelasticity Foods Weakly structured systems Weak gel model2 Ideal Gas constitutive equation Gas-liquid equilibrium constitutive equation Henry equation cN2O, concentration in liquid phase Final result 2Gabriele et al., Rheol. Acta. 40 (2001)

  17. Material properties evaluation Surface tension* Same value for all samples, s=49.3010-3 N/m Henry’s law parameter* Typical value for dairy emulsions *Codap S.p.A. Internal report

  18. Nozzle modelling - 1 A can having a constant volume connected to a nozzle where the emulsion flows Physical system Nozzle Actuator

  19. Nozzle modelling - 2

  20. Nozzle modelling - 3 Pseudo-homogeneous approach Uniform gas distribution “Equivalent transport properties” Main hypothesis Angular symmetry Isothermal system No slip Negligible normal stresses Power law fluid Balance equationsCylindrical coordinate system (r,z, ) Continuity Momentum Foam rheological constitutive equation3 Compressible medium From bubble expansion 3Gardiner et al., Fire Safety J. 31 (1998)

  21. Nozzle modelling - 4 Boundary conditions Initial conditions Pressure= 800 kPa Un-dissolved gas mass= 2.7 g Liquid mass= 250 g Geometry

  22. Nozzle modelling - 5 Solution Method Finite Elements FEMLAB Extra Fine Meshing generation 774 elements Typical velocity field Sample E5 T=-5°C

  23. Numerical Results - 1 Nozzle N1, Sample E5 P=8 atm; T=4°C

  24. Numerical Results - 2 Nozzle N2, Sample E7 P=8 atm; T=4°C

  25. Numerical Results - 3 Nozzle N1, different samples P=8 atm; T=4°C E7 E3 E5

  26. Numerical Results - 4 Sample F3 Nozzle N1, different P T=4°C E7, Nozzle N2, different P, T=4°C

  27. Numerical Results - 5 Nozzle N2, different samples P=8 atm; T=4°C E7 E3 E5

  28. Numerical Results - 6 Sample E7 (lowest freezing point) Nozzle N2, different T P=8 atm h and G=weak function of T

  29. Conclusions Formulation Rheological analysis related to “macroscopic” properties Relevant properties as function of ingredients “Suitable” emulsion selection • Process • Simplifiedfluiddynamicanalysis • - Single bubblegrowth(evaluationof “localproperties”: e) • - Foam flow (evaluationofmacroscopic data: P, flow rate)

  30. Conclusions • Simplemodel, sensitive to • - change in formulation(F1, F2, F3) • - operatingconditions(P=4, 6, 8 atm, T=0°, -10°C) • - Geometry(N1, N2) • Product performance • - emptying time, residual liquid, overrun Determination of the proper conditions for each emulsion Toolusefulfor industrial process/productoptimisation

  31. Thank for your attention…… LaRIA Laboratory of Rheology and Food Engineering

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