EXPERIMENTAL INVESTIGATION ON STEAM-WATER DIRECT CONTACT CONDENSATION USING LASER-INDUCED FLUORESCENCE (LIF)

Abstract

The objective of this study is to conduct the experiments in the steam-water direct contact condensation and to investigate on the heat transfer characteristic such as the heat transfer coefficient, the pool temperature distribution and the bubble equivalent diameter using the laser-induced fluorescence (LIF) and the image processing technique. As a working fluid, deionized (DI) water purified by the reverse osmosis method is utilized. The experiments are performed at pool temperatures of 70-95°C ± 1°C, with different steam mass fluxes of 5-65 kg/m^2 ·s on a 9.525 mm nozzle. The pool temperature is measured using the LIF and thermocouples, and the surface area of the bubble and the volume flow rate are calculated by the imaging processing technique. The averaged heat transfer coefficient is evaluated in a range of 24.57-179.78 kW/m^2 ·K. It is found that the heat transfer coefficient in unstable condensation region has high sensitivity on both the pool temperature and the steam mass flux. Using LIF method, the time-averaged temperature field of the entire pool is visualized, which could be utilized to evaluate not only the averaged heat transfer coefficient but also the local heat transfer coefficient since it is possible to measure the instantaneous local temperature change that could not be measured using thermocouples only. The bubble equivalent diameter is found in range of 0.033-0.114 m. The analysis on the change in the pattern of the bubble equivalent diameter due to increase of the steam mass flux and the pool temperature shows that the unstable isolated bubble occurred at the low mass flux region gradually tends to transform to the stable jet shape since the regime of the steam condensation is changed from the unstable condensation to the stable condensation as the steam mass flux increases.