This study presents an evaluation method of leakage flow through small axial and radial clearances between the orbiting and fixed scrolls of scroll compressors, where empirical friction factors were addressed. Leakage flow experiments were conducted for two refrigerants, CO2 and R22, flowing through the small axial and radial clearance models with a thin rectangular cross-sectional opening. The pressure drop in a pressurized closed vessel, due to leakage, was measured at a variety of initial pressure up to 3 MPa for CO2 and 0.6 MPa for R22. Darcy-Weisbach equation for the incompressible viscous fluid flow through the circular pipe was successfully applied to calculate the pressure drop due to leakage through the thin rectangular cross-section, where the empirical friction factors were determined and plotted on a Moody diagram. It was concluded that the working fluids are compressible and the leakage flow through the small clearances can be treated as the incompressible viscous fluid, where both the axial and radial clearance leakage flows can be represented by the same friction factor for both CO2 and R22 refrigerants, despite the significantly different working pressures. In addition it was addressed that the empirical friction factors were strongly dependent on the relative roughness of leakage channel surface.
