Combination of different nozzle concepts for simultaneous optimization of heat transfer and its uniform distribution in convection drying applications

AbstractPrecise coating processes demand sensitive drying processes. The present work investigates the operation of hybrid convective drying nozzles for combining impingement nozzles with impingement-free nozzles. Impingement-free nozzles show good uniformity, whereas impingement nozzles are characterized by higher heat transfer but greater non-uniformity across the pitch. Volumetric flow ratio between the nozzle types, lateral distance, substrate distance and angle of impingement are the parameters of this study. Compared with purely impingement-free nozzles, the combination can achieve increased heat transfer with moderate losses in distribution uniformity. A divergent impingement jet with a small lateral distance and a small substrate distance proves to be advantageous. In addition, a consideration of energy requirements shows that impingement-free nozzles, due to their lower resistance, can deliver the same volume flow rates with lower blower power. As a result, the reduction of the impingement component in the hybrid nozzle is advantageous in terms of energy.Keywords: CoatingRoll2Rolldrying nozzleheat transfer Disclosure statementNo potential competing interest was reported by the authors.Table 1. Outlet velocity and Reynolds numbers for different volumetric flow ratios and nozzle types.Display TableTable 2. Coefficient of variation for different impingement angles.Download CSVDisplay Table