Application of two-color LIF thermometry to nucleate boiling

International audience; Fundamental comprehension of bubble growth on a heated surface is primordial to better understand the heat transfer during boiling phenomena. The behaviour of a bubble growing at a heated surface has been extensively studied by many authors using different numerical methods. To validate and complete these simulations, suitable experimental data are required. Due to the rapid evolution of the optical techniques and the digital image processing techniques, the non-intrusive methods becomes efficient in local velocity and temperature measurements around a growing bubble. In the present investigation, the two-colour LIF thermometry method is used to measure the temperature distribution at the bubble interface. The bubble is nucleated on a heated copper surface starting from an artificial cavity. Ethanol was used as test liquid. In fact during the growth of a vapour bubble, it is quite challenging to measure the temperature distribution by PLIF thermometry method because of the relatively high range temperature of the fluid (60°C - 70°C). The two dyes technique is adopted for avoiding the influence of the laser intensity inhomogeneity due to temperature gradient. Sulforhodamine101 and Rhodamine B are used as temperature insensitive and sensitive dyes, respectively. The calibration between the two cameras is carried out by a Camera Calibration Toolbox for Matlab to determine a mapping that makes both cameras' views coincide with each other. A temperature calibration is performed to calculate the relation between the temperatureT and an independent incident light function f . The evolution of the temperature field obtained through these experiments during a bubble growth will be reported and discussed. The successfully correction of the inhomogeneous lighting due to the reflection at the bubble surface shows the necessity of the two-color LIF thermometry in boiling experiments. Since the zone of interest is small compared with the entire CCD sensor size of the cameras. Further experimental works are in progress to improve our study by increasing the optical magnification and by applying a 3D particle tracking algorithm.