Nano spray dryers refer to using spray drying to create particles in the nanometer range.  Spray drying is a gentle method for producing powders with a defined particle size out of solutions, dispersions, and emulsions which is widely used for pharmaceuticals, food, biotechnology, and other industrial materials synthesis.
In the past, the limitations of spray drying were the particle size (minimum 2 micrometres), the yield (maximum around 70%), and the sample volume (minimum 50 ml for devices in lab scale).  Recently, minimum particle sizes have been reduced to 300 nm, yields up to 90% are possible, and the sample amount can be as small as 1 ml. These expanded limits are possible due to new technological developments to the spray head, the heating system, and the electrostatic particle collector.
To emphasize the small particle sizes possible with this new technology, it has been described as "nano" spray drying.  However, the smallest particles produced are in the sub-micrometre range common to fine particles rather than the nanometer scale of ultrafine particles.