Experimental investigation of local processes in pool boiling along the entire boiling curve

摘要

Understanding of fundamental local processes in boiling is a key to improved understanding of the boiling process in general and is therefore also a key for better insights using modeling and simulation studies. Unfortunately, only little experimental data is available with respect to local processes. Furthermore, data for boiling on technically thick heaters and for all boiling regimes is even more limited. Towards improved understanding of the boiling process, miniaturized sensors for measurements of the local boiling dynamics and spatial dimensions have been developed. For studies of the two-phase flow characteristics above the heater surface a 4-tip optical probe with tip diameters below 1.5 urn has been developed. Steady-state measurements along the entire boiling curve have been carried out for distances between heater and probe ranging from 20 mm down to positions as close as 8 urn. Microth-ermocouples have been developed for measurements of local temperature fluctuations inside the heater very close to the surface. Thirty-six of these thermocouples have been arranged on an 1 x 1 mm sized quadratic grid at the center of the heater. The junctions of the microthermocouples are located 3.6 μm below the heater surface. These thermocouples are very useful to study local temperature fluctuations and also spatial wetting dynamics. Selected measurements along the entire boiling curve are presented.