Study on principle and experiment of external condensation of water vapor in pneumatic system

The external condensation is investigated by taking a typical pneumatic charging and discharging system as an example. The principle of external condensation is analyzed, and the judgment method is presented as follows: the external condensation occurs under the condition that the balance temperature of component surface is lower than environmental dew point; otherwise, it cannot happen. The experiment of charging and discharging with vertical load is conducted to measure the temperature of components surface, to observe and analyze the position and process of external condensation in the environment of constant temperature and humidity. Experimental results illustrate the external condensation appears with decreasing of the temperature of components surface in rod chamber side, and it cannot exist as increase of the temperature of components surface in no rod chamber side. The small dropwise condensation is produced in the beginning of external condensation, and it grows to be film condensation and then it turns into water drop falling along component surface under the action of gravity. Through analyzing the factors that affect condensation, the conclusion can be made that the condensation is more serious with more humid environment, heavier load and shorter period of charging and discharging. Furthermore, the protective measure should be employed to avoid external condensation, since the condensation may appear after several minutes.