An experimental study was carried out to investigate the CHF condition for flow boiling of R134a in single circular micro-tubes with inner diameters of 0.50 mm and 0.96 mm. The effects of mass flux, saturation pressure, inlet subcooling, tube diameter, and vapor quality on CHF were studied. The flow parameters investigated were as follows: exit pressures of 670, 890, and 1160 kPa; mass fluxes of 300–1500 kg/m2s; and inlet subcooling of 5, 20, and 40 °C. CHF occurred under saturated conditions. CHF was found to increase with an increase in mass flux, tube diameter, and inlet subcooling. CHF decreased with increasing saturation pressures and increasing vapor qualities. The experimental data were compared to three CHF correlations — the Bowring correlation, the Katto-Ohno correlation, and the Thome correlation. The correlations predicted the correct experimental trend.

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