The flow of water and steam in an electrically powered micro heat exchanger consisting of an array of 68 wavy microchannels in parallel, each 200 μm wide, 100 μm deep and approximately 40mm long, was investigated by high speed videography. Semi-quantitative, time and space resolved information about the void fraction was extracted by pixel intensity calculations. Fluctuations at sub-audio frequencies (pulsation) were always visible in the microchannel array. Pulsation on the outlet went into a minimum with increasing heating power, accompanied by a shift in the lateral distribution of channels filled with more steam or water, respectively. Almost complete evaporation could be achieved with this microstructure at a water mass flow rate of 86 kg m−2 s−1. Differences between the test device and typical devices for applications in thermal and process engineering are identified.

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