This paper presents a transparent microfluidic chip designed for continuous-flow photochemistry applications with integrated electrical sensing. The transparent chip design allows for microscale photochemistry, and permits direct, real-time visual/electrical observation. The microchip uses optically transparent indium tin oxide (ITO) electrodes for reagent and phase tracking. High-speed videography was performed to validate the electrical measurement data.

Determination of local heat transfer coefficient at the interface of channel wall and fluid was the main goal of this experimental study in microchannel flow boiling domain. Flow boiling heat transfer to DI-water in a single microchannel with a rectangular cross section was experimentally investigated. The rectangular cross section dimensions of the experimented microchannel were 1050 $\mathsf{\mu }$m × 500 $\mathsf{\mu }$m and 1500 $\mathsf{\mu }$m × 500 $\mathsf{\mu }$m. Experiments under conditions of boiling were performed in a test setup, which allows the optical and local impedance measurements of the fluids by mass fluxes of 22.1 $\mathrm{kg}·{\mathrm{m}}^{-2}·{\mathrm{s}}^{-1}$ to 118.8 $\mathrm{kg}·{\mathrm{m}}^{-2}·{\mathrm{s}}^{-1}$ and heat fluxes in the range of 14.7 $\mathrm{kW}·{\mathrm{m}}^{-2}$ to 116.54 $\mathrm{kW}·{\mathrm{m}}^{-2}$. The effect of the mass flux, heat flux, and flow pattern on flow boiling local heat transfer coefficient and pressure drop were investigated. Experimental data compared to existing correlations indicated no single correlation of good predictive value. This was concluded to be the case due to the instability of flow conditions on one hand and the variation of the flow regimes over the experimental conditions on the other hand. The results from the local impedance measurements in correlation to the optical measurements shows the flow regime variation at the experimental conditions. From these measurements, useful parameters for use in models on boiling like the 3-zone model were shown. It was shown that the sensing method can shed a precise light on unknown features locally in slug flow such as residence time of each phases, bubble frequency, and duty cycle.

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 four 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.