Influence of flow regimes on temperature heterogeneities within a scraped surface heat exchanger

In industrial applications, fluids processed in scraped surface heat exchan gers often show large temperature heterogeneities at the exchanger outlet. Our study deals with the thermal evolution of model fluids, Newtonian and n on-Newtonian in heating or cooling conditions and allows us to link the phe nomena of appearance and disappearance of temperature heterogeneities with the changes in the flow pattern within the exchanger. Based on literature d ata dedicated to scraped surface heat exchangers as well as to annular spac es without blades, we have shown that thermally homogeneous products can be obtained when Taylor vortices appear in the exchanger. Studies done on the exchanger with and without blades show that the thermal behavior is basica lly the same for both geometries but with a difference in critical Taylor n umbers value for change in heat transfer regime. The presence of blades pro motes the appearance of instabilities at lower values of generalized Taylor number (Ta-g = 10 with blades; Ta-g = 39 without blades). It shows as well , that the value of critical Taylor number in scraped surface heat exchange r closely depends upon the flow-rate even for very low values for Re-axg (R e-axg < < 1).