Modeling the Stiction Effect in Automatic Compressor Valves
The so-called stiction effect (or stiction force) is one of the sources of thermodynamic losses in compressor suction and discharge systems. The losses associated with the stiction effect are caused by a deformation of the lubricating oil film between the valve and the seat. This generates a delay in the valve opening, since larger pressure differencesbetween the cylinder and the discharge and/or suction chambers are needed to compensate for those effects. This paper advances a theoretical model for solving the dynamic behavior of a ring-shaped lubricant oil film between a discharge valve and the seat. The valve is allowed to move under the action of an external force due to the timedependent pressure difference between the cylinder and the discharge chamber. The main contributions of the model are the consideration of a finite amount of oil between the valve and the seat and mathematical relationships for calculating the initial condition for the oil film thickness. The model results are compared with those obtained with the Khalifa and Liu (1998) method. At conditions typical of discharge systems of domestic refrigeration compressors, viscous effects are the dominant component in the oil stiction force under dynamic conditions.