CFD analysis of the flow pattern and local shear rate in a scraped surface heat exchanger

Abstract A numerical investigation of a scraped surface heat exchanger (SSHE) was undertaken using the commercial CFD code FLUENT to characterize the shear rates for Newtonian and Non-Newtonian fluids. Simulations are carried out in standard geometries of SSHE. The electrochemical method was first employed to achieve experimental measurements of the shear rates. A two-dimensional model was created to perform the simulation, keeping the dimensions and flow parameters of the experiment. Because of the symmetry of the geometry, a bidimensional resolution of the continuity and momentum equations was conducted. A hybrid mesh was retained with a grid refinement between the tip of the blades and stator where high shear rates occur. A single reference frame approach was then applied to obtain the laminar steady-state flow induced by the rotation of blades in the geometry. A grid refinement in the zone localized between the tip of the blades and the stator is used. A comparison of predictions with experimental measurements was carried out, showing relative agreement between shear rates ( S max ) predicted and measured for three fluids (HV45, CMC and guar gum). The little differences observed were principally explained by the 2D simulation which neglects Taylor vortices, when Taylor number ( Ta g ) exceeds a critical value. In the case of HV45, rotating velocity can influence the scraper angle position due to the floating blade. This can induce a change in the gap between the tip of the blade and stator assembly (from 90 to130 μm) that was investigated here.

[1]  Denis Flick,et al.  Heat transfer with freezing in a scraped surface heat exchanger , 2005 .

[2]  J. Legrand,et al.  Transfert de matiere global liquide-paroi pour des ecoulements associant tourbillons de taylor et circulation axiale forcee , 1982 .

[3]  R. D. Goede,et al.  Heat transfer properties of a scraped-surface heat exchanger in the turbulent flow regime , 1993 .

[4]  Eric Dumont,et al.  Flow regimes and wall shear rates determination within a scraped surface heat exchanger , 2000 .

[5]  S. Craig,et al.  Heat transfer to pseudoplastic fluids in laminar flow , 1962 .

[6]  W. J. Beek,et al.  A mechanism for heat transfer in a Votator-type scraped-surface heat exchanger , 1971 .

[7]  K. McCarthy,et al.  FLOW PROFILES OF POWER LAW FLUIDS IN SCRAPED SURFACE HEAT EXCHANGER GEOMETRY USING MRI , 1999 .

[8]  W. J. Beek,et al.  Flow phenomena in a scraped-surface heat exchanger (“Votator”-type) , 1971 .

[9]  M. Härröd.  METHODS to DISTINGUISH BETWEEN LAMINAR and VORTICAL FLOW IN SCRAPED SURFACE HEAT EXCHANGERS , 1990 .

[10]  Thomas J. Hanratty,et al.  An experimental study of the unsteady nature of the viscous sublayer , 1963 .

[11]  Thomas Ohlsson,et al.  A computer simulation program for evaluation of the continuous heat treatment of particulate food products. Part 2: Utilisation , 1993 .

[12]  O. Wein,et al.  SIMULTANEOUS MEASUREMENT OF FILM THICKNESS AND WALL SHEAR STRESS IN WAVY FLOW OF NON-NEWTONIAN LIQUIDS , 1987 .

[13]  Jack Legrand,et al.  Shear rates investigation in a scraped surface heat exchanger , 2003 .

[14]  D. L. Pyle,et al.  Numerical study of 2D heat transfer in a scraped surface heat exchanger , 2004 .

[15]  Velocity profiles and frictional pressure drop for shear thinning materials in lid-driven cavities with fully developed axial flow , 2006 .

[16]  M. Härröd.  SCRAPED SURFACE HEAT EXCHANGERS.: A literature survey of flow patterns, mixing effects, residence time distribution, heat transfer and power requirements. , 1986 .

[17]  Etude de la perte de charge dans un echangeur de chaleur à surface raclée traitant des produits newtoniens et non-newtoniens , 1986 .

[18]  E. Windhab,et al.  Non-Newtonian flow behaviour in narrow annular gap reactors , 2001 .

[19]  Jack Legrand,et al.  Determination of heterogeneities in a scraped surface heat exchanger using electrochemical sensors , 2005 .

[20]  S. Patankar.  Numerical Heat Transfer and Fluid Flow , 2018, Lecture Notes in Mechanical Engineering.

[21]  Eric Dumont,et al.  Electrodiffusional wall shear rate analysis in scraped surface heat exchanger , 2000 .

[22]  Da-Wen Sun,et al.  Applications of computational fluid dynamics (cfd) in the food industry: a review , 2002 .

[23]  J. Leuliet,et al.  Modélisation de la vitesse de cisaillement apparente dans un échangeur de chaleur à surface raclée. Application aux performances thermiques avec des produits non newtoniens , 1987 .