Investigation of critical heat flux (CHF) enhancement in flow boiling using carbon nanotubes/ water nanofluid

Many studies have shown critical heat flux (CHF) enhancement by adding metals and nonmetals nanoparticles to water in flow boiling. In this study, we investigated critical heat flux enhancement mechanism by adding multi-walled carbon nanotubes (MWCNTs) to pure water in flow boiling in a 2 m horizontal tube under atmospheric pressure. Also, the feasibility of MWCNTs-GA/water nanofluid as an advanced and economic coolant was assessed for cooling the high power thermal systems. For preparing this nanofluid, gum Arabic as a surfactant and MWCNTs as nanoparticles were used in the ratio 1:1 with concentrations of 0.001, 0.005, 0.01 wt%. The measuring zeta potential showed nanofluid stability. Results indicated the relative stability of suspension in all concentrations. Also the results of the experiments showed that the critical heat flux of the nanofluid increases with increasing in concentration and mass flux at the inlet temperatures of 60 and 70 °C. The CHF enhancement was observed for nanofluids and it was greater than that for pure water. It is due to the deposition of MWCNTs nanoparticles and improvement of wettability in the heat transfer surface. The maximum CHF enhancement was observed at 0.01 wt% concentration, a mass flux of 620 kg/m2s and the inlet temperature of 60 oC. The local exit equality of the nanofluid in a fixed mass flux at the inlet temperatures was less than that for pure water and the lowest local exit equality of nanofluid was at inlet temperature of 60 °C and concentration of 0.001wt%.