Effects of laser microtextured surfaces in condensation heat transfer

Some major application areas of microtextured surfaces are found in the energy, biomedical, transportation and aerospace sectors. In relation to the energy sector, microtextured surfaces provide an energy efficient and cost-effective passive mechanism for increased heat transfer during matter's phase change in energy recovery systems. This study explores the viability of laser microprocessing as an attractive manufacturing route for generating textured surfaces and compares with the results from a previous study involving microgeometries created by micro-wire electro discharge machining (µWEDM). Two types of stainless steel SS316L insert, produced via casting followed by machining, as well as by selective laser melting (SLM), were used as the workpieces. A number of microtextured geometries were produced on the workpieces' planar top faces using a nanosecond fibre laser (1064 nm wavelength) operating with 0.066 and 0.25 mJ laser energy, 10 and 80 kHz frequencies, 400, 600 and 700 mm/s beam scanning speeds, and 25 and 60 µm set distances between the unidirectional textured grooves/laser tracks. The textured surfaces were subsequently scanned using a 3D optical scanner for evaluating the depth and width of the geometries. The scanning electron micrographs showed comparable groove geometries produced via both laser and µWEDM. During condensation experiments, the laser textured surfaces typically exhibited higher differential temperature, ΔT (~11.9-28.9%) with respect to the unstructured specimens. Additionally, the textured SLM samples generally showed greater heat transfer quality (~3.7-5.7% higher ΔT) than their cast and machined counterparts.