Pool boiling experiments on multiwalled carbon nanotube (MWCNT) forests

In this study, two silicon wafer substrates were coated with vertically aligned multiwalled carbon nanotubes (MWCNT) "forests" and were used for pool boiling studies. The MWCNT forests (9 and 25 mu m in height) were synthesized on the silicon wafer substrates using chemical vapor deposition (CVD) process. The substrates were clamped on a cylindrical copper block with embedded cartridge heaters. The heat flux was measured using sheathed K-type thermocouples, which were placed inside the cylindrical copper block. Pool boiling experiments using refrigerant PF-5060 as the working liquid were conducted to obtain the pool "boiling curve." The experiments were conducted in nucleate and film boiling regimes to investigate the effect of MWCNT height on pool boiling performance. Reference (control) experiments were also performed with an atomically smooth bare silicon wafer (without MWCNT coating). The results show that the MWCNT forests enhanced critical heat flux (CHF) by 25-28 % compared to control experiments. For the film boiling regime, Type-B MWCNT (25 mu m in height) yields 57% higher heat flux at Leidenfrost point (film boiling regime) compared to control experiments. However, for the Type-A MWCNT (9 mu m in height) the film boiling heat flux values are nearly identical to the values obtained for the control experiments performed on bare silicon.