The heat transfer characteristics of a mesoscale continuous oscillatory flow crystalliser with smooth periodic constrictions

The heat transfer performance of a 5 mm internal diameter (I.D.) mesoscale continuous oscillatory flow crystalliser with smooth periodic constrictions (herein called SPC meso-tube) is herein reported for the first time for both steady flow and unsteady oscillatory flow conditions. Experimental values of the tube-side Nusselt number,
Nut
, accompanied by an estimability analysis, emphasized the key role played by smooth constrictions and bulk flow velocity in controlling tube-side heat transfer, while revealing a weaker influence of oscillatory flow on heat transfer enhancement in the SPC meso-tube. Although the presence of smooth constrictions provided an increased surface area to volume (SAV) ratio, and recirculation zones which promoted heat transfer rates, a maximum 1.7-fold heat transfer augmentation was obtained when fluid oscillations were combined with smooth constrictions. The behaviour of the SPC meso-tube was such that increasing the net flow Reynolds number,
Ren
, from 11 up to 54 with the combination of smooth constrictions and oscillatory flow resulted in the attainment of higher rates of heat transfer up to a maximum
Nut
of 3.09. The Strouhal number,
St
, was also found to have a more significant effect on the heat transfer performance than oscillatory frequency,
f
. An empirical correlation was for the first time developed to describe the heat transfer characteristics of the SPC meso-tube, and predict
Nut
based on experimental data for the range of net flow and oscillatory flow conditions investigated. A parameter estimability approach was also implemented to enhance the prediction capability of the correlation. The approach was based on a sequential orthogonalisation, thanks to which the most influential factors affecting the tube-side heat transfer were identified given the available experimental data. Overall, the results accentuate the efficient heat transfer capabilities of the SPC meso-tube in the laminar flow regime, and its suitability for performing cooling crystallisations where tight temperature control of supersaturation is essential.