Accuracy Analysis of Direct Infrared Temperature Measurements of Two-Phase Confined Flows

The characterization and modeling of confined two-phase flows is still one of the most challenging and interesting objectives of the scientific community since it both helps the understanding of the thermo-fluid dynamic phenomena and the development of reliable design tools for the industries. The visualization techniques exploited so far in the literature, allowed to accurately describe the two phase hydrodynamic principles but very little information about evolution of the fluid temperature distribution can be found. The present work is devoted to the accuracy analysis of direct infrared temperature measurements of two-phase confined flows by means of a high resolution and fast infrared camera. A test rig is built to calibrate the camera by varying the fluid (n-perfluorhexane) and the ambient temperatures. A lumped parameter radiation model is developed to quantify the effect of the involved parameters (ambient temperature, back screen temperature and its emissivity, tube transmissivity, fluid transmissivity etc.), in case the experimental conditions differ from the calibration. The IR measurements are performed on a real two-phase passive heat transfer device. Considering the uncertainty related to the calibration procedure and the difference between the calibration and the actual experimental conditions, the maximum error of the IR temperature measurements is ±2°C. The IR technique also allowed to detect temperature gradients within the fluid and temporal temperature distributions of relatively fast thermo-fluid dynamic events.