A series of experiments on flow boiling heat transfer coefficient of R134a in three horizontal circular smooth copper tubes with inner diameters of 1.002, 2.168, and 4.065 mm were conducted. A total of 397 experimental data points are obtained for a mass flux range of 185-935 kg/m(2) s, a heat flux range of 18.0-35.5 kW/m(2), a saturation pressure range of 0.578-0.82 MPa, and a vapor quality range of 0.03-1.0. The effects of heat flux, saturation pressure, vapor quality, mass flux, and diameter on the heat transfer coefficient are analyzed and the results indicate that the heat transfer coefficient is higher for smaller tubes and for higher saturation pressure while the effects of heat flux, mass flux, and vapor quality are different for different tubes. There are 28 existing correlations of flow boiling heat transfer compared with the experimental data, and the comparison results indicate that the best correlation has a mean absolute deviation of 12.1% and has strong ability to trace the tendency of the heat transfer coefficient with vapor quality. Besides, an experimental database of R134a flow boiling heat transfer is complied, which contains 3000 data points, including 397 from the current experiments and 2603 from 21 published papers. The 28 existing correlations are evaluated with the database, providing a guide for selecting a suitable correlation for specific applications of R134a flow boiling heat transfer. (C) 2015 Elsevier Ltd. All rights reserved.