Papers by Serafim Bakalis
Polymer Engineering and Science, 1998
The velocity field in the screw channels of a co-rotating twin-screw extruder was measured using ... more The velocity field in the screw channels of a co-rotating twin-screw extruder was measured using laser Doppler anemometry. Velocity distributions were measured for two screw elements having pitches of 14 and 28 mm, respectively. The magnitude of radial velocity component for both elements was no more than 10% of the magnitude of total velocity. The radial and the axial velocity components were similar for both screw elements. Wider range of tangential velocity values and steeper gradients near the flights were observed for smaller pitch screw element.
Food and Bioproducts Processing, 1999
ABSTRACT
Trends in Food Science & Technology, 1997
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International Journal of Food Science and Technology, 1997
Velocity measurements inside the screw channels of a co-rotating, self-wiping, twin-screw extrude... more Velocity measurements inside the screw channels of a co-rotating, self-wiping, twin-screw extruder were carried out. A laser Doppler anemometer (LDA) system was used to measure tangential and axial velocity components in the translational region of one of the screws of a twin-screw extruder. The velocity measurements were carried out using heavy corn syrup at different screw speeds and for two forwards conveying elements differing in their pitch. It was found that velocity profiles in the translational region were substantially affected by the pitch of the screw element, however, screw speed (30-90 r.p.m.) did not have a significant effect on the shape of the velocity profiles. The range of velocity values in a 14 mm pitch screw element was wider than that in a 28 mm pitch screw element. Experimentally measured velocity profiles were compared with predictions of a one-dimensional model, which showed that the model underpredicted the velocity values, for the 14 mm pitch element.
Advances in Polymer Technology, 1997
ABSTRACT
Journal of Food Engineering, 2002
Velocity measurements were carried out in the nip and translational regions of a co-rotating, sel... more Velocity measurements were carried out in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder using laser Doppler anemometry. Signi®cantly higher values of axial and tangential velocity components were measured in the nip region, indicating that the¯uid accelerated as it moved through the nip. The local volume¯ow rates in the nip and translational regions were calculated from the measured velocity ®eld. The volume¯ow rate in the nip was about four times higher than that in the translational region, indicating the positive displacement character of the nip region. The total volume¯ow rate calculated over the entire cross-section of the extruder was in agreement with the experimentally measured volume¯ow rate. Ó
Food Hydrocolloids, 2011
In the present study, an in-vitro mouth model to quantify salt release from food structures has b... more In the present study, an in-vitro mouth model to quantify salt release from food structures has been developed. In this instance biopolymer gels were used as model food systems. The model aimed to reproduce key phenomena occurring during oral processing, such as diffusion through the sample and compression. Salt release profiles from different gels (gelatin, gellan and alginate), under quiescent
Innovative Food Science & Emerging Technologies, 2009
ABSTRACT The motion of Time Temperature Integrators (TTI) has been assessed within a scale model ... more ABSTRACT The motion of Time Temperature Integrators (TTI) has been assessed within a scale model vessel designed for thermal processing of viscous complex food fluids using Positron Emission Particle Tracking (PEPT). The vessel, based on the ‘Vesuvio’ vessel made by Giusti Ltd, was filled with water and starch solutions of varying rheology and the effect of rotational speed and fill height was assessed. PEPT was used to measure both the motion of the fluid and the TTI separately, since for the TTI to give a reliable measure of the thermal processing it should be isokinetic and follow the fluid streamlines. For low viscosity fluids, significant settling of the particle relative to the fluid was observed. This did not occur for the more viscous starch solutions where the TTI and fluid behaved similarly regardless of the mixing quality, which was significantly affected by changing fill height and rotational speed. Sub-circulatory regions observed close to the impeller could lead to overprocessing of the food fluids based on TTI measurements in these regions, since they would be expected to be in the coldest part of the vessel. This study shows that TTI can be applied to the processing of viscous fluids within agitated thermal processes, provided that requisite knowledge of the fluid motion and likelihood of settling of the TTI is assessed in tandem.Industrial relevanceTime Temperature Integrators (TTI) are potentially very valuable tools for the measurement and validation of thermal processes. In this paper, conditions under which TTI would be expected to give valid thermal measurements in agitated batch vessels are assessed by measurement of their relative flow to the fluid using a novel visualisation technique. As well as ensuring the correct implementation of TTI, this work could be used to improve vessel design.
Innovative Food Science & Emerging Technologies, 2008
Time Temperature Integrators (TTIs) were used to investigate the process uniformity of an industr... more Time Temperature Integrators (TTIs) were used to investigate the process uniformity of an industrial scale 250 l agitated vessel. Factors such as fluid viscosity, fill level and direct and indirect heating have been examined. Different numbers of TTIs were added throughout each experiment and temperature was recorded using 2 thermocouples: one fixed in the centre and one on the wall of the vessel. TTIs were added at the start of the experiment and also at the end of the heat up time. Novel designs of TTI fitted inside either porous plastic balls or a series of plastic tie clips to prevent over-processing due to contact with the hot vessel wall were also used. P values recorded by the TTIs illustrated significant heterogeneity of heating for viscous fluids which could be partly overcome by steam injection. Overfilling also affected the heating efficiency, possibly due to changes in the flow field. The use of the novel TTIs enabled more accurate determination of the thermal processing of the fluid away from the vessel wall. This paper demonstrates that TTIs can be used for thermal monitoring and validation of processes in the food industry (centre and wall) which is more representative.
Innovative Food Science & Emerging Technologies, 2008
The use of supercritical carbon dioxide (scCO2) for the removal of moisture from cylindrical piec... more The use of supercritical carbon dioxide (scCO2) for the removal of moisture from cylindrical pieces of carrot has been investigated. The experiments were carried out at 20Â MPa pressure and the effects of temperature and co-solvent (ethanol) addition were examined. At the investigated conditions, comparisons with air-drying indicated that drying kinetics and the associated drying mechanisms differed between the techniques. The
Chemical Engineering Science, 2011
In recent years, rapid cooling processes have been developed to manufacture complex, three-dimens... more In recent years, rapid cooling processes have been developed to manufacture complex, three-dimensional shapes for confectionery products (e.g. chocolate Easter eggs). These processes are similar to injection moulding and casting processes used in the metallurgic and polymer industries. Although these manufacturing routes are commonly used, they are still poorly understood and thus not optimised. In traditional chocolate processing, cocoa butter
Journal of Food Science, 2003
ABSTRACT Positron-emission particle tracking (PEPT) is a method of following particles in opaque ... more ABSTRACT Positron-emission particle tracking (PEPT) is a method of following particles in opaque fluids inside metal equipment. Comparison of experimental and theoretical velocity distributions obtained in aluminum pipes indicated that PEPT can be used to measure velocity distributions in viscous fluids for conditions of relevance to the food industry. Velocities were also measured for a fluid containing starch particles using 2 tracers having diameters of 600 and 240 μm. Velocity profiles were not significantly different, but the smaller tracer passed closer to the flow boundaries. PEPT was also used to quantify the effect of headspace on the velocity distributions of rotating cans containing soup. While in fully filled cans, fluid moved in circular motion, addition of air altered this, resulting in D-shape velocity contours.
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2006
... Permissions & Reprints. Multiple-particle tracking—an improvement for positron particle t... more ... Permissions & Reprints. Multiple-particle tracking—an improvement for positron particle tracking. Z. Yang a , Corresponding Author Contact Information , E-mail The Corresponding Author , DJ Parker b , PJ Fryer a , S. Bakalis a and X. Fan b. ...
Journal of Supercritical Fluids, 2010
... compared to fresh pulp (87.6%). Arslan and Musa Ozcan [14] also reported that moisture conten... more ... compared to fresh pulp (87.6%). Arslan and Musa Ozcan [14] also reported that moisture content (dry weight basis) of fresh rosemary leaves was 13.2% and for dried leaves after 9 h of oven drying was 0.04%. From these results, one ...
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007
Positron Emission Particle Tracking (PEPT) is a powerful technique and capable of following a sin... more Positron Emission Particle Tracking (PEPT) is a powerful technique and capable of following a single tracer accurately and non-invasively in flow and mixing processes. It has been recently extended to observe the rotation of a large particle via tracking three small positron-emitting tracers mounted, with fixed separation distances, on the surface. The Multiple-Positron Emission Particle Tracking technique has been successfully
Chemical Engineering Science, 2006
ABSTRACT Positron emitting particle tracking (PEPT) can be used to trace the path of a radioactiv... more ABSTRACT Positron emitting particle tracking (PEPT) can be used to trace the path of a radioactive particle within opaque fluids in pilot scale equipment. Isokinetic tracers can be used to characterize flow fields inside such equipment. A pilot scale heat exchanger was designed and used with PEPT to evaluate the accuracy and applicability of the technique; measurements were performed over a range of flows found in food processing plant, including extruder flows. Velocity distributions were estimated from the measured tracer locations for a range of barrel speeds, flow rates and rheological properties. The flow field is 3D; barrel speed and flow rate had a more pronounced effect on the velocity distributions than the rheological properties of the fluids. The flow field was simulated using a simple 2D approach and a full 3D simulation. The simulated velocity distributions compared favourably to the experimentally determined profiles: trends were correctly predicted by the 2D model whilst statistical agreement was found between data and the 3D simulation. The agreement between PEPT and CFD reinforces the validity of both methods.
Aiche Journal, 2007
Positron Emission Particle Tracking is a powerful and noninvasive technique and has been successf... more Positron Emission Particle Tracking is a powerful and noninvasive technique and has been successfully used in a wide range of fundamental research and industrial applications. However, it is only capable of following a single tracer. This article presents a Multiple-Positron Emission Particle Tracking technique for tracking two freely moving particles in opaque systems and its application. The developed technique has been validated through tracking two stationary particles and two moving particles, respectively. The results showed that it is a reliable technique and can be potentially used to acquire more comparative information, such as the interactions and relative motions of particles with different sizes, densities, and material textures in multiphase systems. Tracking two polyethylene particles, labeled using 18F, in a cylindrical fluidized bed has been given as an example. The information obtained provides significant insights into phenomena in flow and mixing processes. © 2007 American Institute of Chemical Engineers AIChE J, 2007
Journal of The American Oil Chemists Society, 2010
A range of methods, mainly X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC), h... more A range of methods, mainly X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC), have been used to characterise the polymorphism of fats in food products. As sugars present in chocolate have a significant XRD pattern, partially overlapping with the signal of cocoa butter, XRD cannot be applied directly to chocolate. In this paper, the XRD signal of a molten sample, similar to the one for pure sucrose, was subtracted from the signal of a solid sample of chocolate to remove the impact of the crystallised sugar. The XRD patterns obtained were compared with the pattern of cocoa butter cooled under the same conditions. Strong peaks were observed at similar inter lamellar d spacings showing that the polymorphic state of cocoa butter in processed chocolate could be obtained using this method. Numerical integration of the peaks also allowed quantification of the degree of crystallinity present in the system during a typical process. The accuracy of the method developed was found to be dependent on the (cocoa butter)/(sugar) ratio in the chocolate used.
Chemical Engineering Science, 2011
Despite widespread use of the technique for a long time, the proper interpretation of mercury por... more Despite widespread use of the technique for a long time, the proper interpretation of mercury porosimetry data, particularly retraction curves, remains uncertain. In this work, the usefulness of two complementary techniques, mean-field density functional theory (MF-DFT) and micro-computerized X-ray tomography (micro-CXT), for aiding interpretation of ambiguous mercury porosimetry data has been explored. MF-DFT has been used to show that a specific, idiosyncratic form for the top of the mercury intrusion and extrusion curves is probably associated with a particular network structure where the smallest pores only form through connections between larger pores. CXT has been used to study the pore potential theory of hysteresis and entrapment directly using a model porous material with spatially varying pore wetting properties. CXT has also been used to directly study the percolation properties, and entrapment of mercury, within a macroporous pellet. Particular percolation pathways across the heart of the pellet have been directly mapped. The forms of entrapped mercury ganglia have been directly observed and related to retraction mechanisms. A combination of CXT and mercury porosimetry can be used to map spatial variation in pore neck sizes below the spatial resolution of imaging.
International Journal of Multiphase Flow, 2008
Solid motion can be classified into translational motion and rotational motion; both play an impo... more Solid motion can be classified into translational motion and rotational motion; both play an important role in a wide range of engineering processes. While translational motion has been extensively studied in various systems, there is a lack of information on rotational motion, possibly due to a lack of appropriate experimental techniques. For a number of mixing processes involving heat transfer for solid-liquid mixtures, the heat transfer coefficient between solid and liquid is critical in determining process times and overall product characteristics, and is greatly dependent on both rotational and translational behaviours of the solids, which ideally need to be studied simultaneously. This paper presents a new technique, Multiple-Positron Emission Particle Tracking (Multiple-PEPT), which can follow multiple particles simultaneously through a considerable thickness of surrounding material. Both translational and rotational motions of the solid can be reconstructed. The accuracy of the method for the translational velocity was better than 10% while for the angular velocity 23% for speeds up to 0.25 m/s. Multiple-PEPT will therefore offer the possibility to study translational and rotational motions for a range of engineering systems. The potential applications of tracking solid translational and rotational motions are illustrated by an example of tracking a cubed potato in a rotating can.
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Papers by Serafim Bakalis