A mass flow controller (MFC) was used to control the injection gas amount into volatile organic compounds (VOCs), each having a different evaporation rate, within straight tubes. As the moving velocities of the air bubbles within the straight tube had changed, a specific transient response occurred. The transient shape was a mushroom bubbles. From the experiment results, as the evaporation rate of VOCs ≧ 1, mushroom bubbles occur as the Reynolds number (Re) of the moving air bubbles reach a certain region. Moreover, the shapes mushroom bubbles were more apparent when volatility of the solvent was higher. As VOCs evaporation rate < 1, the mushroom bubble phenomenon did not occur, regardless how the Re values of the moving air bubbles had changed. When the Re values for acetone, methyl alcohol and butyl acetate were between 4381~4430, 2460~2490 and 1940~1980, respectively, the transient response phenomenon occurred.

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