Experimental study on visualized flow boiling in a narrow rectangular channel

An experimental visualization investigation is carried out to study the characteristics of flow boiling in a narrow channel represented by flow patterns, local void fraction variations and the net vapor generation (NVG) point. The experiment is conducted in a narrow rectangular channel with the size of 1 mm × 30 mm × 650 mm, which is heated by two sides using transparent ITO (Indium Tin Oxides) film for better visualization effect. In this study, it is found that the flow pattern transition boundary of heated vapor-water flow is consistent with several existing flow pattern transition lines for air-water flow experimental data and flow pattern transition criteria in narrow rectangular channel. Based on the experimental data of the void fraction and the thermodynamic equilibrium quality at the NVG point, assessments of the accuracy of existing models and correlations are performed. Finally, new empirical correlations for more accurate predictions for the void fraction and the NVG point are proposed based on the experimental results. The predictions using the present correlations agree well with the experimentally measured values with a mean absolute error (MAE) of 46.07% for the void fraction and 36.19% for the NVG point. • Double-side transparent ITO film heating method was used for better visualization. • Obtaining flow pattern, NVG point and local void faction through image processing. • Flow regime map for vapor-water flow in narrow channel is analyzed and compared. • Comprehensive assessments of existing correlations for NVG points and void faction. • New correlations for void fraction and NVG point with higher accuracy are proposed.