Abstract
The enhancement of thermal conductivity and local convective heat transfer coefficient by nanofluid of Fe2O3/water has been studied experimentally for the improvement of the thermal desalination processes using a newly developed sophisticated noninvasive heat transfer coefficient probe that is flush mounted on the inner wall surface of the test section. Fe2O3 nanoparticles have been selected due to their magnetic characteristic for improving the thermal efficiency of desalination since they can be collected by magnet and reused. The volume fraction of 0.01-0.09% using different nanoparticle sizes of 3 nm, 10 nm, and 20 nm has been used at varying experimental temperatures of 25, 45, and 65 degrees C in laminar and turbulent flow regimes. The thermal conductivity and local heat transfer coefficient increased with the increase of the Fe2O3/water nanofluids volume fraction and temperature. Also, decreasing the nanoparticle size enhanced the thermal conductivity as well as the local heat transfer coefficient. In the laminar flow regime, the change in the thermal boundary layer film thickness is small compared with that of the turbulent flow regime. Therefore, the enhancement of the local heat transfer coefficient in the turbulent flow regime is larger than that of the laminar flow regime for all the experimental conditions.The maximum enhancement in the thermal conductivity was 32%, whereas the enhancement in the local heat transfer coefficient was 70% for 3 nm at 0.09 volume fraction and 65 degrees C. The improvement in the local heat transfer coefficient was larger than that in the thermal conductivity due to a decrease in the thermal boundary layer film thickness. The correlation of Y. M. Xuan and Q. Li, ASME J. Heat Transfer 125, 151 (2003) which accounts for the nanoparticles, presence in terms of volume fraction, predicts our results well and their trends for the conditions studied at 65 degrees C with the variation in nanoparticles volume fraction and size. The improvement we obtained in the thermal conductivity and local heat transfer coefficient will enable thermal improvement of desalination processes.