NUCLEATE POOL BOILING FROM SELECTIVE LASER MELTED MICROGROOVES/ MICROCAVITIES SURFACES WITH HFE-7000
Microscale surface modification techniques for enhancing nucleate pool boiling performance have shown significant progress in the last three decades. Selective laser melting (SLM), with the ability to fabricate highly complex and ordered structures, offers an alternative surface modification technique for promoting boiling. This technique utilizes a laser source which selectively melts and fuses the base metal powder in accordance to pre-programmed models in successive layers. With adequate control of the laser intensity and scanning positions, structured microscale surfaces can be produced.
In the present study, two 10 mm × 10 mm microstructured surfaces were fabricated using the SLM technique with AlSi10Mg metallic powder of 20 to 63 µm distribution size range. Surfaces 1 and 2 contain 500 µm and 700 µm sized microcavities, respectively. In addition, the microcavities were separated by microgrooves with average distances of 120 and 150 µm. Saturated pool boiling experiments were performed on these surfaces with HFE-7000 in a thermosyphon. The results show that the microstructured surfaces enhanced heat transfer by up to 30% as compared to a plain surface and critical heat flux as high as 50.5 W/cm2 was achieved. In addition, the microgrooves were observed to be active nucleation sites whereas the microcavities were found to be inactive sites. These observations agree well with the theoretical analysis performed, where the active cavities sizes were calculated to be between 0.05 and 164 µm. Finally, correlations are proposed to characterize the pool boiling curves of these surfaces taking into consideration the effects of their microfeatures.