Competing effects of impinging jets and crossflow on the vapor transport and drying performance

Impinging jet flow and crossflow play different roles in drying. Jets enhance heat and mass transfer by disrupting the boundary layer at the material interface, while crossflow removes moisture accumulated in the drying volume. Excessive crossflow, however, can adversely affect the impinging jets, reducing their effectiveness. This study investigates how the relative strength of crossflow and impinging jets affects vapor transport and mass transfer. To understand the competing effects of impinging jets and crossflow on the drying performance, the local relative humidity, surface temperature, and drying rate were measured under different crossflow-to-jet velocity ratios ( R ). Experiments were conducted during the constant-rate drying period using a multiple-jet impingement system with superimposed crossflow. The results show that increasing R from 0 to 0.5 enhanced the local Nusselt and Sherwood numbers. Further increasing R from 0.5 to 1.0 reduced local relative humidity but progressively decreased the local heat transfer and drying rate due to deterioration of jet impingement regions. When crossflow became dominant ( R > 1), the mass transfer efficiency of the jet impingement declined substantially. These findings demonstrate that mass transfer is governed by the balance between boundary-layer disruption, vapor transport, and heat transfer, rather than by vapor removal alone. Real-time measurements of local temperature and humidity fields provided insights into the mass transfer boundary conditions, enabling optimization of jet impingement drying systems.