Experimental study on thermal performance of copper nanofluids in a miniature heat pipe fabricated by wire electrical discharge machining

A cylindrical miniature heat pipe (MHP) with a diameter of 1.9 mm and a length of 130 mm was designed and fabricated via wire electrical discharge machining in this study. A special elastic fixture was designed for the micro grooves machining process. Water based copper nanofluids with mass concentrations ranged from 0.5 wt% to 1.5 wt% were prepared and tested in the MHP. Both the transient response and heat transfer capability of the MHP with copper nanofluids and DI water were studied experimentally. The MHP with nanofluids had a slightly slower startup response compared to the one with DI water. However, the heat transfer capability of the MHP with nanofluids was greatly improved to 250 mW (q = 8.82 W/cm2), while that of the MHP with the basefluid (DI water) was only 100 mW (q = 3.53 W/cm2). At the heat load of 150 mW, the MHP with 0.5 wt% nanofluid showed a minimum thermal resistance of 0.33 °C/W. The effects of mass concentration, filling ratio and heat load were investigated as well.