Sensor system with PDMS-embedded Fiber Bragg Gratings for measuring slug frequency in air–water flow

This paper introduces a novel method for measuring slug frequency in air–water flow within long horizontal pipes—a critical parameter for estimating pressure drop, liquid holdup, and heat transfer in the intermittent regime of two-phase flows. The proposed method is non-invasive, simple to manufacture, and seamlessly integrates into the monitored pipe. This method uses a sensor system consisting of two Fiber Bragg Grating (FBG) sensors embedded in polydimethylsiloxane (PDMS), integrated into a clamp that houses the sensors on opposite sides, with one positioned at the top and the other at the bottom. In addition, the method includes an algorithmic procedure that processes the wavelength data captured by these sensors to determine the slug frequency. Experiments were conducted in a laboratory flow loop to validate the effectiveness of the proposed method. The slug frequency estimations obtained using experimental data and the proposed method were compared against those derived from a conventional video-based technique. The results demonstrated good agreement, confirming the method’s reliability. • Novel instrument using fiber Bragg gratings in PDMS slabs to measure slug frequency. • Procedure for processing wavelength signals for accurate slug frequency estimation. • Validation of the sensor system against the conventional video-based approach.