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.

Investigation of water microchannel boiling flow regimes using electrical sensing elements along a single microchannel

“…Impedance amplitudes and corresponding probability density curves were used as metrics to analyze boiling flow from a new perspective. This research was partially presented before [38] in constant temperature test conditions. To the best of authors knowledge, this investigation is the first time that electrical impedance sensors are implemented over boiling processes using de-ionized water as the application fluid in a metallic microchannel.…”

“…Working electrodes on the glass are fabricated using wet-etched indium tin oxide (ITO) and covered with a hard-baked SU8 layer. Details regarding cleanroom fabrication process are explained in our previous published works [25,37,38]. The design of the housing and assembled modules are explained in detail in the previous publications as well [37,38].…”

“…Details regarding cleanroom fabrication process are explained in our previous published works [25,37,38]. The design of the housing and assembled modules are explained in detail in the previous publications as well [37,38]. For every experiment condition shown in figure 4, video recording of the boiling flow was performed with a DSLR camera (Canon 500D) mounted to a objective with a magnification of 4X and a high speed camera (CHRONOS) in all electrical sensor locations.…”

Local Heat Transfer Analysis in a Single Microchannel with Boiling DI-Water and Correlations with Impedance Local Sensors

“…Therefore, simultaneous electrical sensing and visual inspection were possible in each sensor location. The details of the glass lid fabrication method were previously explained in [37]. The contacting of the probes was done using spring probes (11).…”

“…The sensors are 1.7 mm wide and 2 mm long located on the 1.5 mm wide and 0.5 mm deep channel. In previous publications, the sensor fabrication, channel details method, and data acquisition with LCR-meter Hioki-IM3536 were reported [35,50,51]. In this work the test loop concept is similar but the LCR-meter is replaced with an impedance analyzer produced by Zurich Instruments (MFIA).…”