Surface tension of evaporating nanofluid droplets |
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| Authors: | Ruey-Hung Chen Tran X. Phuoc Donald Martello |
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| Affiliation: | 1. Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia;2. Centre of Research Excellence in Renewable Energy, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, 31261, Kingdom of Saudi Arabia;1. Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong;2. School of Energy and Environment, City University of Hong Kong, Hong Kong;3. Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong |
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| Abstract: | Measurements of nanofluid surface tension were made using the pendant droplet method. Three different types of nanoparticles were used – laponite, silver and Fe2O3 – with de-ionized water (DW) as the base fluid. The reported results focus on the following categories: (1) because some nanoparticles require surfactants to form stable colloids, the individual effects of the surfactant and the particles were investigated; (2) due to evaporation of the pendant droplet, the particle concentration increases, affecting the apparent surface tension; (3) because of the evaporation process, a hysteresis was found where the evaporating droplet can only achieve lower values of surface tension than that of nanofluids at the same prepared concentrations; and (4) the Stefan equation relating the apparent surface tension and heat of evaporation was found to be inapplicable for nanofluids investigated. Comparisons with findings for sessile droplets are also discussed, pointing to additional effects of nanoparticles other than the non-equilibrium evaporation process. |
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