AbstractStudies of the evaporation and drying rates in an experimental concurrent spray dryer, 8 in. in diameter and 14 ft. high, are reported for various operating air temperatures. It was found that the total evaporation and drying time could be accurately predicted by employing a step‐by‐step method of calculation. Owing to the probable absence of internal diffusional resistance in the small particles, less than 30 μ, produced in the dryer, no significant falling‐rate period was observed. This was in marked contrast with tray‐drying experiments carried out on the same substance, under similar drying conditions. The results also confirmed that a Nusselt number of 2 can safely be used in spray‐drying heat transfer ca