Pool boiling performance of laser-textured surfaces with time-dependent wettability

In last years, the direct laser texturing proved as environmentally friendly, scalable, flexible and efficient approach for surface functionalisation by creating appropriate surface features for enhanced boiling performance. When metal surface is laser-processed in open (oxygen-containing) atmosphere, it oxidizes and becomes (super)hydrophilic. However, it is well known that the wettability transition towards (super)hydrophobic state occur, if such a surface is exposed to the presence of hydrophobic contaminants. When water is used as a working fluid, this wettability transition can have a significant effect on nucleate boiling performance, which is investigated in this work.

Manufacturing of a 3d Finned Tube for Enhanced Boiling and Condensation Using Rolling-cutting-extruding Composite Forming

3D finned tube is a high efficient enhanced heat transfer element and its manufacturing has always been the focus of research’s attention. It is a challenging job to manufacture a 3D finned tube that can enhance both boiling and condensation because the enhanced boiling structure is completely different from the enhanced condensation structure due to different heat transfer enhancement mechanisms. An innovative rolling-cutting-extruding composite forming method is developed to realize the manufacture of a staggered stepped lattice finned tube (SLFT) with helical fins, two layers of staggered stepped lattice fins and inner helical threads, which can enhance boiling as well as condensation heat transfer. The three skewed rolling-cutting tools specially designed are uniformly distributed around the base tube and the kinematics conditions of rolling-cutting-extruding process is analyzed. The relative plunge depth of a rolling blade can’t exceed a certain limit value and the feeding angle has to be equal to the helix angle of outer helical fin. According to the kinematic conditions, the parameters of the rolling-cutting tool are selected and processing experiments of the SLFT are conducted.