Development of suction pipe design criterion to secure oil return to compressor

In the present work, phenomena associated with counter current flow limitation (CCFL) were experimentally investigated using small diameter tubes in order to suggest criterion for which the oil return is secured. The test section is made of Pyrex glass tube to allow visual observation. The inner diameter of the test tube is 7mm and the height is 1m. The inclination of test tubes varied from vertical to crank type with various horizontal lengths. Waterair flow and lubricant oil-air flow were examined through a series of experiment at various liquid flow rates. In this experimental study, flow reversal and flooding phenomena were visually observed and two-phase flow rate were measured. Flow reversal point represents the air flow rate when the liquid film begins to flow downwards in the tube below the liquid inlet location. Whole supplied liquid flows upward when the gas flow rate is larger than this value. So the flow reversal point can be interpreted as oil return criterion and the flow reversal points were measured using various shape of test section in a wide range of liquid flow rate. The gas velocities for the flow reversal point appeared to be similar over a certain range of liquid flow rate. Flooding point was defined as the air flow rate when liquid starts to flow above the liquid inlet part. The air flow rate needed to cause flooding is inversely proportional to the liquid flow rate. Both flow reversal and flooding velocity also depend on the inclination angle, horizontal length and liquid property