Simulation of salt diffusion in a pork (bacon) side using 3D imaging Schüller, R.B., Aastveit, A., and Egelandsdal, B. Norwegian University of Life Sciences, Ås, Norway.

Simulation of salt diffusion in a pork (bacon) side is a relatively complex task since such a piece often consists of different regions of skin, meat, fat and bone; each with diffusion coefficients that vary with orders of magnitude. Adding to this complexity is the arbitrary shape and topology of each region separately and combined.

This study presents a comprehensive solution for constructing high quality and accurate volumetric meshes based on 3D images obtained by a typical spiral CT scan.

Sample and CT Scan

Piece of pork belly

A typical piece of pork belly side was CT-scanned at the Norwegian University of Life Sciences using a Simens Somatom CT scanner. Resolution on the 2D slices is 0.5x0.5mm, and spacing in the Z direction is 5mm. Total number of slices is 37.

Segmentation in ScanIP

Scan and segmentation

In ScanIP three different domains were identified: fat (red), meat (blue), and bone (green) using threshold segmentation; (Hounsfield number values used: -253 to 13 for fat, 14 to 136 for meat and 137 to 201 for bone). Other segmentations tolls such as flood-fill were then used, followed by the morphology filter and more smoothing operations.

Mesh generation in ⁺ScanFE

Smoothed all tets mesh (more detailed image)

The 3 objects were meshed simultaneously in +ScanFE resulting in either a mixed tetrahedral/ hexahedral mesh or a pure tetrahedral mesh. In this case the all tets mesh consists of 844,163 elements, 169,765 nodes and 98,223 boundary faces. The mesh also incorporates an adaptive meshing scheme. A cross section of the final mesh on the left shows the inter-domain boundary faces.

3D transient diffusion in COMSOL Multiphysics®

A 3D transient diffusion simulation was carried out in COMSOL Multiphysics assuming that the exterior of the piece of meat is exposed to a saturated Sodium Chloride solution for 72 hours (i.e. Salting Period). A second simulation was then performed for a time period of 7 days (i.e. Equilibration Period) where the initial condition considered was the status of salt concentration distribution after the 72 hours Salting Period.

Salt concentration on cross section after 72 hours of Salting Period

Salt concentration on boundary during various stages of the Equilibration Period

Salt concentration on cross section after 7 days of Equilibration Period

Preliminary results indicate that the salt distribution after 7 days Equilibration Period is not uniform. Such a long period may indicate that the diffusion coefficients used were on the low side. The study has illustrated that Simpleware and COMSOL provide a very efficient tool to handle mass transfer simulation for real-life problems which can be very useful for the food processing industry. Future work will focus on using such an efficient methodology to predict salting time and final mean salt concentration in various pork belly sides.

Publication

Said, R., Schüller, R., Young, P., Aastveit, A., Egelandsdal, B., 2007. Simulation of salt diffusion in a pork (bacon) side using 3D imaging. In: Petit, J.-M., Squalli, O. eds. Proceedings of the European COMSOL Conference 2007, 23 - 24 October 2007 Grenoble. Grenoble: COMSOL France, Vol 2, 876-881.