Effects of surface modification on the pool boiling heat transfer of MWNTs/water nanofluids

The influences of covalent and non-covalent functionalization on the pool boiling heat transfer performance of MWNTs nanofluids were experimentally investigated under different weight concentrations. Relevant pool boiling heat transfer coefficients (HTCs) of MWNTs nanofluids were measured on a cooper flat surface in a pool. The obtained results are further compared with that of the deionized water as a base fluid. The results show that the MWNTs nanofluid with CTAB as non-covalent modification presents poor HTCs, which decreases with increasing the MWNTs concentration due to the deposition of nanoparticles and lower contact angle between nanofluids and heating surface. However, the MWNTs-COOH and MWNTs-OH nanofluids using the COOH and OH groups as covalent modifications show higher pool boiling HTCs than the base fluid, and they increase as the MWNTs concentration increases. The maximum HTC enhancements can reach 34.2% and 53.4% for MWNTs-COOH and MWNTs-OH nanofluids, respectively. This implies the covalent modifications for the MWNTs nanofluid could avoid the deposition of nanoparticles and benefit to HTC enhancements.