Flow Regime Detection of Boiling Flow in Microchannels Using Electrical Sensing Elements Validated by Videography

Abstract

In this work we present a method that provides the possibility to analyze directly the electrical properties of two-phase flow in microchannel boiling systems. It is shown that the use of impedimetric sensing techniques can be used to track two-phase boiling flow. In order to perform such measurements, the electrical impedance of the composite medium in the channel is measured using planar capacitive elements that are implemented over the channel on a glass lid. Working electrodes are fabricated using indium tin oxide on glass and are compressed against a precision machined metal microchannel. Therefore, it is possible to visually analyze two-phase flow inside the microchannel while simultaneously performing electrical impedance measurements. In order to prevent electrochemical reactions between the fluid inside the microchannel and electrodes on the glass lid, a thin layer of SU8 photoresist was deposited as a protective layer. The electrical impedance measurements were characterized over two-phase flow regimes including bubbly flow, slug flow and annular flow via comparison with simultaneous video recordings.