A miniature optical extinction heated probe for fog droplet measurements in steam turbines

¹ ETH, Department of Mechanical and Process Engineering, Laboratory for Energy Conservation, 8092 Zurich, Switzerland
² AUTh, Department of Mechanical Engineering, Laboratory of Fluid Mechanics and Turbomachinery, 54124 Thessaloniki, Greece

^* Ilias Bosdas: ibosdas@ethz.ch
^† Michel Mansour: mansour@lec.mavt.ethz.ch
^‡ Anestis I. Kalfas: akalfas@auth.gr
^§ Reza S. Abhari: abhari@lec.mavt.ethz.ch

Abstract

The knowledge of droplet size distribution and concentration allows us to calculate the wetness fraction and the isentropic turbine efficiency as well as to provide significant data for erosion modeling. For that purpose, a miniature optical extinction probe with a diameter of 9.4mm was designed, manufactured and tested. The probe is equipped with a heater, which maintains all optical components of the probe clean from any water contamination. In this paper the matrix inversion algorithm is presented in order to calculate the droplet diameter and concentration out of the spectral turbidity measurements. An ultrasonic atomizer was characterized in terms of droplet size and concentration with an established Phase Doppler Anemometry (PDA) system in order to have a reference spray environment for the proof of concept of the newly developed probe. Measurements were performed and results have shown a good agreement between the PDA technique and the optical extinction probe at various axial locations from the nozzle exit of the droplet generator.