Modified Conductivity Probe Design for Two-Phase Flow Measurement in Very Narrow Channels

For designing basic and advanced safety features of nuclear, chemical, or other kinds of plants, boiling flow is one of the most crucial concepts. Several initial and boundary parameters, such as pressure, inlet subcooling temperature, mass flux, heat flux, and flow geometry, control the bubble dynamics and behavior. While a previous flow boiling experiment by the authors’ laboratory has revealed valuable parametric effects in four-sensor conductivity probes, these conventional probes feature near-wall blind zones that limit their coverage of radial profiles in narrower channels. An innovative five-sensor design has been therefore proposed and validated in the current study for reducing such blind zones. The new design has two leading sensors sharing three trailing sensors, and it uses the same principle as conventional four-sensor probes to calculate different properties of bubbles. New datasets of upward flow boiling have been collected using five-sensor probes of different sensor patterns in a narrow annular test section. The results are compared with each other’s to identify the design that gives better consistency. The boiling annular channel has an inner diameter of 25.4 mm and an outer diameter of 38.10 mm, with a heated inner rod length of 3 m. The conductivity probes are adopted to measure void fraction, gas velocity, and interfacial area concentration following a two-group description.