Comparisons of thermal performances in a pulsating heat pipe by using a nanofluid and a self-rewetting nanofluid with carbon nanotubes

Abstract

Heat transfer performances of the ultrapure water, n-butanol self-rewetting fluid (SRF), multi-walled carbon nanotubes (MWCNTs) nanofluid (NF), and n-butanol self-rewetting MWCNTs nanofluid (SRNF) were investigated in a pulsating heat pipe (PHP). The highlight of this study was to analyze their thermal performances under different heating powers, inclination angles, and ambient temperatures. Experimental results indicated that all functional working fluids generally gave advantages in thermal transport performances relative to the ultrapure water in most cases. Furthermore, advantage of the SRF gradually emerged with increasing thermal input when compared with the ultrapure water and its enhancement ratio reached a maximum of 22%. In contrary, advantage of NF was demonstrated only when the thermal input exceeded 20W, and its enhancement percentage reached 16% at 35W. The SRNF exhibited an outstanding increase of the thermal transfer performance at a low heating power range. The augmented percentage of the SRNF was around 7–17% with the maximum value obtained at 35 W. The inclination angle also had a non-negligible impact on thermal performances of different working fluids, particularly, their thermal transfer limits in the PHP. In addition, a lower ambient temperature could generally raise the heat transmission performance of the PHP with operating fluids.