Experimental Investigations on the Pressure Fluctuations in the Sealing Gap of Dry Gas Seals With Embedded Pressure Sensors

Dry gas lubricated non-contacting mechanical seals (DGS) most commonly found in centrifugal compressors prevent the process gas flow into the atmosphere. Especially when high speed is combined with high pressure (high pv factors), DGS is the preferred choice over other sealing alternatives. Even the non-contacting seal is proved reliable; the ultra-thin gas film can still lead to a host of potential problems due to the possible contact.

In order to investigate the flow field in the sealing gap and to facilitate the numerical prediction of the seal performance, a dedicated test facility is developed to carry out the measurement of key parameters in the gas film. Gas in the sealing film fluctuated according to the seal inlet pressure, and the thickness of gas film depends on this fluctuated pressure. In this paper, the test facility, the measurement methods and the first results of static pressure in the sealing gap of DGS obtained in described test facility are presented. A DGS at 96mm balance diameter with three-dimensional grooves on the surface of the rotating ring, where the experimental investigations take place during dynamic running, is used. The static pressure in the gas film is measured, up to 20 bar and 8,100 rpm, by several high frequency ultraminiature pressure transducers embedded into the stationary ring. The frequency spectra of transient pressure waveforms measured by the pressure transducers demonstrate the two distinctive peaks corresponding to the rotational frequency of the shaft (135 Hz) and the groove passing frequency (2700 Hz which equals to the rotational frequency multiplied by the number of grooves). The experimental results are discussed and compared with the numerical model programmed in MATLAB [1]. The pressure fluctuations in the region of each sealing grooves are detected by the pressure probes with a measurement frequency of 48 kHz, the characteristic and magnitude of which have a good agreement with the numerical simulations. In additional to the pressure induced by the hydrodynamic behaviour of the sealing grooves, the pressure variations owing to the axial movement of seal shaft and stationary ring, also measured by proximity probes, are observed and discussed. It suggests the feasibility of measuring the pressure profiles of the standard industry DGS under pressurized dynamic operating conditions without altering the key components of the seal and thereby affecting the seal performance. Further work will be carried on with higher pressure including gap measurements to advance the measurement methodology.