Effects of Surface Roughness and Slip Flow on the Performance of a Spiral Groove Gas Face Seal

Considering the effects of surface roughness and slip flow, the extended Reynolds equation presented by Makino et al [1] is used to set up the finite element model for a non-contact spiral groove dry gas face seal (S-DGS). The analyses for a typical S-DGS at low speed (≤ 500 rpm) and low pressure (≤ 0.606 MPa) showed that the effect of slip flow on the sealing performance is significant for 0.05≤ K_n < 1.0, where K_n refers to the Knudsen number, but the effect of surface roughness on the sealing performance varies with the different areas of both the two faces. When the standard deviation of composite roughness is less than 1.0 micron and in the range of 0.5≤ K_n≤ 1.0, the effects of surface roughness and slip flow diminished on gas film stiffness and frictional work but are still significant on the leakage rate. The effect of surface roughness of the spiral groove bottom is significant and should be considered, but the effects of the other surface roughness, i.e. the soft ring surface roughness and the un-grooved hard ring surface roughness, are negligible only when the value of the standard deviation of composite roughness meets with API standards.