CHINESE JOURNAL OF MECHANICAL ENGINEERING ·645·

if the length of pipe is shorter and ωnl/a is smaller, the natural frequency of system is

volume in this critical line is equal to 1, namely, Al/V=1。 The dimensionless volume is an important parameter used for   discriminating   between   internal   condensation   and

external condensation。 Al/V≥1, only internal   condensation

could occur; Al/V<1, only external condensation could occur。

The natural frequency n  effects the motion performance

5 Conclusions

of system directly,

too。

is a comprehensive parameter

(1) The dimensionless volume of discharging pipe is proposed as the first parameter to discriminate   occurrence

4。3 Analysis of interior condensation and exterior

condensation using dimensionless volume

Using  the  dimensionless  volume  of  discharging   pipe

of internal condensation or external condensation in a pneumatic system。 If the value of dimensionless volume  is

larger than or equal to 1, the internal condensation occurs in

and  A/V  as  comprehensive  parameter   of

system  possibly,  and  no   external  condensation   occurs;

condensation, we could  analyze the distribution of all   the

experimental points at which internal condensation and external condensation creates, and the analyzing results revealed the distribution of experimental points at which condensation or no condensation occurs in a certain regular rule  as  shown  in  Fig。  4,  in  which  A/V  is  abscissa axis

oppositely, If the value of dimensionless volume is smaller than 1, the external condensation occurs in system possibly, and no internal condensation occurs。

(2) Condensation  is  defined  that  interior condensation

occurs in smaller volume cylinder and  exterior condensation   occurs   in   larger   volume   cylinder。    The

andis ordinate axis。

problem of piding line for cylinder volume exists in this definition。 Instead of the volume of cylinder, the dimensionless volume can be directly used to determine whether internal condensation or external condensation occurs in system, which provides an effective quantitative definition method for internal condensation or external condensation。 Meanwhile, the authors provide a possibility of evaluation and discrimination of condensation by using comprehensive parameter in experimental study。

(3) The study on condensation in pneumatic system involves many problems, such as the whole process of internal condensation including status of compressed air changes during charging and discharging, the  water droplets producing and growing, the water droplets keeping in the system and the internal condensation occurring, or heat transfer taking place between the air and surface of

Fig。 4。 Distribution of experimental points at which internal condensation or external condensation occurs

The following can be noted by observing Fig。 4:

(1) The structural parameters of system in which internal condensation or external condensation meet a certain distribution。 In the area of upper left, external condensation occurs, and that of the lower right, internal condensation occurs。