Abstract: Apparatus and method for producing at high efficiency vaporization a precisely controllable, continuously adjustable gas-phase flow of a vaporizable liquid (e.g., hydrogen peroxide) in a carrier gas (e.g., air) are disclosed. The gas-phase product flow can be substantially continuous, low-temperature, unsaturated with respect to the vaporized vaporizable liquid, and of substantially constant vaporized vaporizable liquid concentration as a function of time. Fine particles of the vaporizable liquid are produced and introduced into the flow of carrier gas/vapor in a vaporization plenum with a sufficient flow of carrier gas/vapor to provide a curtain of carrier gas/vapor between substantially all of the fine particles of vaporizable liquid and the inner surface of the vaporization plenum.