Comparatively experimental study on the boiling thermal performance of metal oxide and multi-walled carbon nanotube nanofluids

This work aims to focus on the flow boiling heat transfer characteristics of metal oxide and multi-walled carbon nanotube nanofluids inside an annulus heat exchanger. The flow boiling heat transfer coefficient and thermal fouling resistance parameter is experimentally quantified at different operating conditions including different heat and mass fluxes, mass concentration of nanofluid, and bulk temperature of nanofluid. In order to prepare the nanofluids, multi-walled carbon nanotubes (MWCNT), alumina and copper oxide nanoparticles were dispersed into deionized water. Based on the type of nanoparticle, different techniques were implemented for stabilizing the nanofluids such as functionalizing process for MWCNT, pH setting, ultra-sonic dispersion and adding the surfactant for metal oxide nanofluids. Results of time-Settlement experiments showed that functionalizing process can provide longer and reliable stability for MWCNT nanofluid. As a continuation, thermal conductivity of nanofluids was experimentally measured and compared to those of available in the literature. Then, experiments were carried out on the upward flow boiling heat transfer characteristics of nanofluids. According to the results, MWCNT/water nanofluid had higher thermal conductivity, higher boiling thermal performance and lower thermal fouling resistance value in comparison with other nanofluids. Likewise, boiling thermal performance of MWCNT nanofluids was found to be intensified, when heat and mass flux and concentration of nanofluids increased. The experimental heat transfer coefficients were also validated by comparing to the well-known correlations and available data in the literature. (C) 2015 Elsevier B.V. All rights reserved.