Falling-film evaporation over horizontal rectangular tubes: Part I—Experimental results.

• Experimentally measured falling-film evaporation heat transfer coefficients. • Effects of temperature, flow rate, tube spacing, tube row, and heat flux discussed. • Newly observed heat transfer coefficient trend that is not seen in round tubes. • New trend due to film breakdown quantified and supported by force balance. An experimental study on falling-film evaporation on horizontal rectangular tubes, the external geometry of extruded flat, microchannel tubes, was conducted. Previous falling-film evaporation studies have focused on horizontal and vertical round tubes, and the usage of microchannel tubes provides a promising new heat exchanger design option. The test sections used in this study have external dimensions of 203 × 1.42 × 27.4 mm (length × width × height) and were tested with water as the refrigerant. Heat transfer coefficients were measured for saturation temperatures from 10 to 30°C, test section spacings from 5 to 15 mm, heat fluxes from 10 to 20 kW m−2, and film Reynolds numbers of 48 to 544. This paper, Part I, reports the experimental methodology and the results, while in the companion paper, Part II, models for predicting heat transfer are presented. [ABSTRACT FROM AUTHOR]