Análise experimental do desempenho térmico de nanofluidos em radiadores automotivos

Nanofluids is a new class of fluids composed by solid nanoparticles dispersed in a fluid. This work concerns an experimental investigation about thermal performance of nanofluids in automotive radiators. A mixture of 70% water and 30% ethylene glycol (EG30%), used in some cooling systems, was replaced by 8 distinct nanofluids. The nanofluids composed by graphene and multi-walled carbon nanotubes (MWCNT) were produced by a two step method called high pressure homogenization, in mass concentrations between 0,05 and 0,3%, In addition, was produced water based MWCNT nanofluids, in concentrations between 0,05 and 0,16%. As a first step, the properties (thermal conductivity, viscosity and density) were experimentally measured. After that, the nanofluids were tested as coolants in automotive radiators, located in a wind tunnel strongly equipped to measure the heat transfer. The performance of nanofluids was evaluated in terms of heat transfer rate and pumping power. The liquid inlet temperature was fixed at 50, 60, 70 and 80oC, while the mass flow rate was between 30 and 130g/s. On the other hand, the air mass flow rate and air inlet temperature were fixed at 0,175kg/s and 25oC, respectively. The first step results indicated a slightly enhancement on the thermal conductivity related to the base fluid, up to 5%. With respect to viscosity, in the case of MWCNT/WATER nanofluids, was observed a significant enhancement (up to 54%). Similar behavior was not found for EG30% based nanofluids, for which was obtained viscosity close to the base fluid, except for tests at 80oC, which was observed enhancements up to 30% on this property. In the second step results, referent to the tests in radiators, the results shown a slightly drop in the thermal performance with nanofluids. The worses performances were found to MWCNT/WATER nanofluids, for which the maximum drop verified was 22%. For EG30% based nanofluids, were found results slightly higher to base fluid in some test conditions, however, for most cases the performance were closed or lower the EG30%. In general, the analyzed nanofluids didn’t show potential to replace the conventional coolant. The obtained results are discrepant from literature, in which the heat transfer is analized, in the most os cases, in function of Reynolds number, but in an additional analysis, it was concluded that the Reynolds number is not an appropriate reference parameter to evaluate the thermal performance of nanofluids in internal flow.