Flow Source

– Defines the method used to emit smoke and fire.

Mesh: Create smoke/fire directly from the object’s mesh. With this option selected there are two additional settings: Surface and Volume.

Particle System: Create smoke/fire from a particle system (type Emitter) on the flow object. With this option selected, there is a box to select a particle system and one additional Tab: Particle Size.

Blender Smoke Source Mesh Particle System