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Abstract
1- Introduction
2- Experimental
3- Model development
4- Results and discussion
5- Conclusion
References
Abstract
The effect of viscosity on heat transfer behaviour is analyzed for binary mixtures (ionic liquid + water and nanofluid + water) over the base fluid (water). Viscosities of 1-butyl-3-methylimidazolium bromide with water under ambient pressure are studied at different concentrations (0.1–0.6% w/w) and temperatures (296–336 K). Viscosities of nanofluid (γ-Al2O3/water) are estimated at the same concentration and temperature range and then compared with the ionic liquid solution. Viscosity of aqueous 1-butyl-3-methylimidazolium bromide solution increases with concentration and decreases with temperature. A similar trend is observed for γ-Al2O3/water. In addition, a model is developed with response surface methodology and artificial neural network to predict the viscosity of 1-butyl-3-methylimidazolium bromide with water.
Introduction
Viscosity is a property which describes the internal friction of a moving fluid. It is an important thermophysical property in fluid flow and heat transfer. In many fluid flow problems, viscosity is assumed to be a constant parameter. However, viscosity varies with temperature when the flow is associated with transfer of heat. To accurately model the flow behaviour and estimate heat transfer rates, it is essential to consider the variation of viscosity with temperature [1,2]. When compared with other thermophysical properties viscosity demonstrates a considerable variation. Hence it becomes necessary to incorporate the correction in the fluid flow model based on the behaviour of fluid with respect to temperature-dependent viscosity [3]. The variation in temperature-dependent viscosity plays a major role in laminar heat transfer and friction factor for non-circular conduits or ducts of different geometries [3–5]. It has been shown that the variation in temperaturedependent viscosity in a curved circular tube with water as a working fluid, plays a relatively major role on velocity and thermal profiles, compared to other thermophysical properties like specific heat, thermal conductivity and density [6]. In regards to viscosity variation, it results in a larger local Nusselt number when compared with that obtained from using constant viscosity [3,7]. The use of constant viscosity ignores the effect of decreased flow resistance leading to the generation of the secondary flow of fluid and its impact on convective heat transfer enhancement. Frictional losses in the fluid – the result of the microscopic interaction of molecules between layers – are governed by the viscosity of the fluid.