This paper reports an experimental investigation of the heat transfer features of new and recycled Alumina (Al2O3) nanofluids (NFs) in the pool boiling (PB) system. The mixture of ethylene glycol (EG) and distilled water (DW) is selected as the base fluid (BF), and NFs samples of two low concentrations (0.01 and 0.05 vol.%) of Al2O3 nanoparticles were prepared. Furthermore, the characteristics of the prepared NFs are evaluated to investigate the heat transfer performance as well as the reusability of the NFs for long-term applications and recycling consideration. Although there have been a large number of boiling studies with NFs, the current study is the first of its kind that addresses the mentioned operation conditions of recycling NF samples. The results are compared with the relevant BF in terms of properties, critical heat flux (CHF), burnout heat flux (BHF), and the convection coefficient of the Al2O3 NFs in the PB system. The results showed good enhancements in both CHF and BHF of these NFs yielding up to 60% and 54% for BHF at 0.05 vol.%, respectively. The reusage of the previously used (recycled) Al2O3 NF showed a considerable increase in heat transfer performance compared to base fluids but slightly lower than the newly prepared one. The results of the reused nanofluids demonstrate the great prospects of their recyclability in heat transfer systems and processes such as in pool boiling.
Keywords: burnout heat flux; critical heat flux; nanofluids; pool boiling; recycling.