CHF enhancement of CNT-COOH nanofluids in the boiling experiment with a downward-facing heating surface

The effects of carboxylated carbon nanotube (CNT-COOH) nanofluids prepared with various surfactants were researched on the pool boiling heat transfer coefficients (HTC) and critical heat fluxes (CHF). Sodium dodecyl sulfate (SDS), and gum arabic (GA) were used to improve the dispersion and stability of CNT-COOH nanofluids. Then, preparing different weight concentrations of each nanofluid (CNT-COOH/GA-water and CNT-COOH/SDS-water nanofluid) and investigated for their thermal performance. The result shows that the CHF of both nano-fluids was significantly increased in a specific concentration range. Furthermore, the CNT-COOH/SDS-water nanofluids have lesser pool boiling HTC compared with reverse osmosis (R.O.) water, and CNT-COOH/GA-water nanofluids slightly increase at 0.005 g/L and 0.02 g/L. By conducting roughness and hydrophilia of the heating surface tests, it is speculated that the CNT-COOH deposition produced during the boiling process is the main reason for affecting HTC and CHF. The deposition has a complex hydrophilic microstructure, which makes the water droplets entering the interior can take away a large amount of heat on the heating surface and then enhance CHF.