Applying nanomaterials and nanotechnology in lubrication has become increasingly popular and important to further reduce the friction and wear in engineering applications. To achieve green manufacturing and its sustainable development, water-based nanolubricants are emerging as promising alternatives to the traditional oil-containing lubricants that inevitably pose environmental issues when burnt and discharged. This review presents an overview of recent advances in water-based nanolubricants, starting from the preparation of the lubricants using different types of nanoadditives, followed by the techniques to evaluate and enhance their dispersion stability, and the commonly used tribo-testing methods. The lubrication mechanisms and models are discussed with special attention given to the roles of the nanoadditives. Finally, the applications of water-based nanolubricants in metal rolling are summarised, and the outlook for future research directions is proposed.
The paper analyzes laminar forced convection heat transfer for both single and mixture phase models utilizing Al 2 O 3 -water and CuO-water nanofluids as the working fluid and examines the effect of internal fins in the collector tubes in order to improve collector efficiency. A physical model with governing equations has been defined. Finite volume method has been utilized for discretizing governing equations and finite element method has been utilized for three-dimensional analysis of solar plate model with finned tubes. Convective heat transfer coefficient, Nusselt number and shear stress have been analyzed for Reynolds numbers from 200 to 700 with 0-5% volume fractions of nanofluid. Moreover, the efficiency of the collector has been investigated for constant flow rates from 0.02 to 0.04 mL/s and variable overall heat loss coefficient for the same range of volume fractions of nanofluid. It has been found that increment of shear stress and heat transfer coefficient occurred with the increment of concentration of nanoparticles and the Reynolds number. Investigation of particle size has not shown any notable variation with the mixture phase model. Mixture-phase model gives comparatively lower values due to the reduction of viscosity near the wall. Noticeable increment of efficiency has been observed by changing working fluid from Al 2 O 3 -water to CuO-water which has been further improved by utilizing variable overall heat loss coefficient. Efficiency increases up to 6.5% and 8.7% than the base fluid for utilizing Al 2 O 3 -water and CuO-water nanofluid respectively. Additionally, utilizing internal fins to the riser tubes, the efficiency increases up to 11%.
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