Quantitative measurement of vapor concentration distribution for two-phase water flow in microchannels

Cavitation in the microchannel can affect the flow characteristics and cause corrosion damage to the microchannel. Quantitative vapor concentration characteristics inside the microchannel are a prerequisite for understanding the cavitation characteristics in microfluidics and cavitation simulation prediction. In this paper, high-speed visible-light imaging at the nanosecond timescale and micrometer spatial scale was used to study the vapor concentration in microchannels. The steady-state image was discretized from sub-millisecond scale (200 μs) to nanosecond scale images (20 ns) based on the equivalent same exposure time. The occurrence probabilities of the vapor and liquid phases at each pixel position can be calculated by means of proper segmentation of the vapor and liquid phases in the nanosecond cavitation images. The quantitative measurement of vapor-phase concentration in steady-state flow in a microfluidic channel was successfully realized with the accumulation of vapor-phase probability of nanosecond images. Vapor-phase concentrations of 0–100% can be effectively distinguished by this method, and the mixed flow characteristics of two cavitations can be quantified. In addition, the cavitation concentration mapped from the steady-state grayscale image was compared with the results of quantitative concentration measurements.