Determining a pressure response function of the hose and sensor arrangement for measurements of dynamic pressure in a dry gas seal film

Abstract

This work shows the estimation of the pressure response function between the pressure developed at the working film of a dry gas seal and the dynamic pressure measurement at the end of a flexible hose (attenuated pressure) used to monitor the film pressure of the seal. The arrangement of the flexible hose and connector translates the recording point of the dynamic pressure produced in the fluid film formed between the seal rings to a pressure sensor mounted outside of the seal. This arrangement is used in the experimental tests of a dry gas seal because the little space that exists inside the seal housing does not allow the installation of the pressure sensor directly behind the stationary sealing face. The response function thus estimated helps to correct the dynamic pressure signal recorded by the pressure sensor due to the attenuation that is induced along the hose path. The pressure response function for the combination of the 115 mm-long flexible hose, connector and sensor is predicted with CFD numerical simulations following experimental tests. The numerical results show a natural frequency of the fluid contained in the flexible hose within the expected range of frequencies in the film (pulsations). This natural frequency affects the dynamic pressure measured by the sensor during the experimental test because the pulses of the grooves in the rotating ring excite the fluid mass contained in the hose. The complex polynomial function resulting from the study is employed to correct the dynamic pressure in the experimental tests of a dry gas seal with spiral grooves of 15° and 11° inlet angle.