An unheated, essential oil diffuser relies on a pressurized air stream to educt oil from a reservoir, followed by separators including separation chambers and an annular channel. The latter is a long channel having an aspect ratio (L/d) of from about 10 to about 120, for length L and thickness d. Thickness d is effective diameter, also known as hydraulic diameter (4 times c.s. area, divided by “wetted” or exposed perimeter), and may be from about 25 to about 100 thousandths of an inch (0.6 to 2.5 mm) across the thin passage, with a target range of from about 55 to 75 mils (0.7 to 1 mm). This geometry provides laminar flow at Reynolds number values less than a few hundred for virtually its complete distance of from under one inch (25 mm) to over three inches (76 mm).
