New experimental techniques were developed to measure the in-tube condensation heat transfer coefficient. In this study, very low heat dissipation rates such as several watts from the mini-channel could be estimated and low mass flow rates below the 0.2 kg/h could be measured with reasonable uncertainties. To the authors' knowledge, these techniques provide a unique experimental apparatus for measuring the condensation heat transfer coefficients inside the sub-millimeter hydraulic diameter single channels. By careful design and construction of the experimental apparatus, the characteristics of the local heat transfer and pressure drop were experimentally investigated using the condensing R134a two-phase flow, in a horizontal single round tube, with an inner diameter of 0.691 mm. Tests were performed for a mass flux of 100--600 kg/m(2)s, a heat flux of 5-20 kW/m(2), and a saturation temperature of 40 degreesC. The experimental data of the Nusselt number and two-phase frictional pressure gradient are presented and compared with the existing correlations. (C) 2004 Elsevier Ltd. All rights reserved.