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

Abstract

In this work, we present a method that allows for the detection of the local flow regime in a metallic microchannel using on-channel electrical sensing elements. The development of the flow regime is analyzed along a straight channel (length: 63.5 mm, width: 1.5 mm, height: 0.5 mm) using 4 transparent electrodes fabricated on a glass lid. A constant heat flux boundary condition at the channel walls is applied to deionized water flow. Measurements are validated by recorded videos at the same locations as the sensing elements. The topology of the probability densities of impedimetric measurements shows a clear connection with visually observed flow regimes, including bubbly, slug, wavy/churn and annular flow. The method and test facilities show promising potential for further investigations into how variable channel geometries and local process parameters influence microchannel boiling.

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

“…Figure 1 presents the schematic diagram of the experimental apparatus used in this study and previously described in [35]. The experimental setup consists of a Pyrex reservoir to store deionized water.…”

“…Swagelok Stainless Steel fittings and Festo push in connectors were used to construct the flow loop. Figure 2 represents the exploded structure of the test device which was used [35,36]. As it is shown in the exploded view of the test section in Figure 2, the test section consists of a housing(1), a glass cover lid(5), a heater block(2) equipped with 6 DC electrical heater cartridges (8), and a stainless steel microchannel plate(4).…”

“…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).…”

“…In this work the test loop concept is similar but the LCR-meter is replaced with an impedance analyzer produced by Zurich Instruments (MFIA). The advantage of this newly developed system compared to our previous publication [35] is the time synchronization between the highspeed videos and impedance signals. The stainless steel channel is the counter electrode to the ITO electrode on the glass lid.…”

“…In the current work, we report the analysis of experimental data on the local heat transfer of water evaporation in a single stainless steel rectangular microchannel. In our previously published work, the proof of principle for determining the local flow regime by using impedance sensing has been shown [35] besides the application of analyzing slug flow [36]. As discussed above, the flow regime is vitally important for the heat transfer mechanism and thus for the estimation of the heat transfer coefficient.…”