Zusammenfassung Die Fortführung der bisherigen Arbeit kann in mehrere Richtungen ausgeführt werden.

Industrial drying is associated with significant energy consumption and greenhouse gas emissions. Given current climate and energy policy targets, improving drying processes through minimal modifi-cations and optimal operating points has become an important research topic. One such measure is air recirculation, which increases moisture. However, its effect on the efficiency and drying rate of an impingement flow dryer is not straightforward. In this study, we examine the optimal operating point of a dryer model while considering fan power and limited heat and mass transfer coefficients. We define the drying rate by solving a nonlinear system of coupled mass and energy balance equations for dry air, moist air, and superheated steam. To fairly compare these drying agents, we consider four normalization criteria: constant volumetric flow rate, constant mass flow rate, constant Reynolds number, and constant hydraulic power. The results show that increasing the moisture content of the drying agent reduces the drying rate but increases the efficiency for a given volumetric flow rate, hydraulic power, and Reynolds number. However, for a constant mass flow rate, the influence of humidity on the drying rate reverses beyond a specific inversion temperature.