Two-Phase Heat Transfer in 4.0 mm Tube under Different Gravity Conditions

Abstract

This study aimed to analyze the two-phase heat transfer in a vertical upward flow configuration under different gravity conditions. The facility is a new version of MicroBo (Microgravity Boiling), the working fluid used is perfluorohexane C6F14 and a 4.0 mm aluminum channel is arranged vertically to perform ebullition process. The platform used to get data in microgravity was the parabolic flight, which represents one of the most widely used platforms despite the period of time available to collect data is very short. The analysis of the results has been carried out following two main approaches: the first, ground-flight data comparison, for the study of variable gravity data collected during the 67th ESA campaign of parabolic flight held in November 2017, while the second, ground data analysis, to analyze the data collected on the ground in the ENEA laboratory with the same facility in December 2018. In particular ground - flight data have been analyzed comparing boiling curves at different flow rates, from a minimum of 5.3 l/h up to 17 l/h, in micro, hyper and normal gravity. The operating inlet pressure during experiments has been fixed at 1.6 bar with a heat flux range of 5.4 - 85.6 kW/m2. For what regard ground data boiling curves, with a flow rate of 10 l/h, are shown with a direct flow pattern visualization. The operating pressure has been fixed at 1.3 bar and 1.8 bar with a heat flux range of 2.5 - 94.6 kW/m2. For the latter analysis, it also has been carried out a qualitative study for the validation of the void fraction model, starting from the visualization of the images of flow patterns recorded during the acquisitions.