Title : Effect of mono and hybrid nanofluids on contact angle and heat transfer rate
Abstract:
Nowadays, nanofluids are involved in thermal energy systems as heat transfer fluids. Wetting properties and contact angle measurements play a crucial role in evaporation processes and are closely related to pumping power and corrosion problems.In this paper, the effect of nanoparticle addition on the wetting properties is discussed. TiO2, ZnO, CuO and SiO2 water and bio ethylene glycol based nanofluids are mixed together with various concentrations. The suspensions are prepared by two-step methods and their stability is checked by zeta potential analysis.The contact angle, pH, viscosity, and z potential are measured throughout the liquid phase. The addition of a small percentage of nanoparticles notably changing the contact angle, pH, and viscosity of the examined nanofluid. The research is carried under atmospheric pressure and in a range of temperatures of 20-110°C. Moreover, the work proposes a new correlation that takes into account the influence of the contact angle of the nanofluid on the heat transfer coefficient. The presentation will also discuss various methods of imaging wetting, e.g. Young-Laplace, tangent, and ellipse methods, and available goniometric techniques.The selection of appropriate methods and models to determine the contact angle must mainly consider the following: the thermal conditions of the experimental execution, i.e. temperature ranges, fluid type, and process dynamics. It is very important to ensure that the geometry and shape of the droplet are correctly mapped (as close as possible to the actual one). The digital goniometer measurement allows the use of at least five approximations of droplet shapes.The results are also modelled and used for efficiency calculations of the plate heat exchange system in solar installation with nanofluids.
