An experimental investigation of microstructure surface roughness on pool boiling characteristics of TiO2 nanofluid

An experimental setup for pool boiling of dilute dispersions of titanium dioxide (TiO2) nanoparticle in water-ethylene glycol 50 (WEG50) as the base fluid was developed. The nanofluid was stabilized by using sodium lauryl sulfate as a surfactant. The heater surface roughness was affected by the deposition of nanoparticles during boiling which consequently changes the heat transfer characteristics. Three copper heater surface roughnesses: smooth, semi-rough and rough, were used. The effect of surface roughness and nanofluid on boiling heat transfer coefficient (BHTC), surface wettability and nucleation site density were examined. The results showed that BHTC and nucleation site density were increased by increasing the heater surface roughness in the base fluid of WEG50. The findings of this study revealed that the effect of volume concentration of nanofluid on the BHTC significantly depends on the heater surface roughness. At heater surface roughness of 0.062 mu m, BHTC increases compared to WEG50 base fluid for all volume concentrations of TiO2-WEG50 nanofluid. With increasing the volume concentration of nanofluid up to 0.005%, an increasing tendency in BHTC was observed but beyond that a decreasing trend was observed for heater surface roughness of 1.213 mu m. However, as heater surface roughness reaches 3.146 mu m, BHTC decreased by increasing nanofluid volume concentration, compared to WEG50 base fluid. Also, increment of heater surface roughness causes the nucleation site density to increase when either base fluid or nanofluid is used. By measuring static contact angle of sessile water droplet on heater surface before and after experiment, it was found that using TiO2-WEG50 nanofluid causes to surface wettability increased.