Serafim Bakalis

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.

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

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.

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 20 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

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

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.

... 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. ...

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

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.

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

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.

Mercury porosimetry is a widely used method for pore structural characterisation but, often, half of the data obtained in any given experiment, in the form of the retraction curve, is simply not used. This may be because mercury retraction is significantly less well understood than ...

Three-dimensional magnetic resonance imaging (MRI) and micro-computed X-ray tomography (micro-CXT) have been combined to study the entrapment of mercury within nanoporous silica materials following porosimetry. MR images have been used to construct structural ...

Mercury porosimetry is a widely used method for pore structural characterisation but, often, half of the data obtained in any given experiment, in the form of the retraction curve, is simply not used. This may be because mercury retraction is significantly less well understood than ...

Three-dimensional magnetic resonance imaging (MRI) and micro-computed X-ray tomography (micro-CXT) have been combined to study the entrapment of mercury within nanoporous silica materials following porosimetry. MR images have been used to construct structural ...