(301g) Influence of MESH Refinement Near Walls in HEAT Transfer Predictions in Stirred Tanks

Heat transfer in stirred tank reactors (STR) is widely used in the chemical industry. Dimple jackets, halp-pipe jackets and internal coils are employed for both heat addition or removal.  The aim of this work is to obtain a CFD model for these systems in order to improve their design. To obtain a reliable CFD model, it is very important to understand the effect of the dimensionless parameter y⁺ in the prediction of the heat transfer at the heat exchanging surfaces. This work shows this analysis for a STR with internal helical coils. The validation of the model used the experimental results published by Oldshue and Gretton  (1954), which  were compared with the CFD results. The numerical CFD data was obtained by the ANSYS CFX 14.0 package. It has been noticed that the variable y⁺ did not show any significant effect on the prediction of the primary flows generated by the impeller. However, when it came to the prediction of the heat transfer coefficient, it showed a strong influence and results indicate it is necessary to use values of y⁺ <0,1 (using the SST turbulence model) to guarantee that the near wall treatment of the data predict correctly the flow.

• Oldshue, J. Y. and Gretton, A. T., “Helical Coil Heat Transfer in Mixing Vessels”, Chem. Engng. Progress, V. 50, n° 12, p. 615-621, 1954.