Experimental study of evaporation of palm biodiesel with multi-walled carbon nanotubes additives at elevated temperatures

Abstract

Evaporation characteristics of palm biodiesel blended with multi-walled carbon nanotubes (MWCNTs) with different concentrations and outer diameters at ambient temperatures between 473 and 673 K have been investigated. Nano-additives were dispersed in concentration doses of 100 ppm and 200 ppm and outer diameters of 10–20 nm and 30–50 nm. Results showed that droplets underwent an initial heating period and a steady evaporation period without the occurrence of micro-explosions or puffing. In the steady evaporation period, the D²-law could be applied for all mixtures. Then droplets completely vaporised at the end of their lifetime. MWCNTs with smaller outer diameters (10–20 nm) exhibited a significantly greater enhancement of the evaporation constant across all temperatures, while larger outer diameters (30–50 mm) only provided improvement at higher ambient temperatures (> 600 K). A high degree of temperature dependence with the concentration of larger MWCNTs (30–50 nm) was observed with retardation of evaporation at lower ambient temperatures (< 523 K) and significant enhancement at higher ambient temperatures (> 600 K). The results suggested an internal aggregation mechanism of MWCNTs contributing to heat transfer to be responsible for this behaviour. Smaller MWCNTs (10–20 nm) with lower concentration (100 ppm) were found to provide the maximum enhancement of evaporation in the temperature domain of interest.