Two-phase flow modelling is strongly dependent on flow patterns. For the purpose of objective flow pattern identification, a capacitance sensor was developed for horizontal two-phase flow in small diameter tubes. Finite element simulations were made during design to study the effect of vapour distribution, wall thickness and electrode angle. A test rig was constructed and a series of experiments was done with horizontal air–water flow in a 9 mm tube. The sensor test results are presented in time, amplitude and frequency domain. Flow regime characterization with the capacitance measurements is clearly possible.

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a b s t r a c tThis paper presents a signal analysis method used for condensing refrigerants that results in a modification in the prediction method for heat transfer based on probabilistic time-fractional results. Development of an objective visual method for discrimination of flow patterns and determining probabilistic time-fractions in intermittent flow is presented. The frequency domain was identified as the main candidate for discrimination of sub-regimes present in intermittent flow. Experimental work was conducted using refrigerants R-22 and R-134a, at an average saturation temperature of 40 C, with mass fluxes ranging from 200 to 700 kg=m 2 s, and with test section inlet vapour qualities ranging from 0.65 down to 0.10.These test conditions mostly represent intermittent flow. The new time fraction-corrected flow regimebased heat transfer correlation is heavily based on the [36] correlation. The modified correlation predicted the experimental data with a mean absolute deviation of 10%.

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