Prediction of Contact Angle of Nanofluids by Single-Phase Approaches

Nur Çobanoğlu,Raul Martínez-Cuenca,Patrice Estellé,Ziya Haktan Karadeniz,Matthias H Buschmann

doi:10.3390/en12234558

Abstract

Wettability is the ability of the liquid to contact with the solid surface at the surrounding fluid and its degree is defined by contact angle (CA), which is calculated with balance between adhesive and cohesive forces on droplet surface. Thermophysical properties of the droplet, the forces acting on the droplet, atmosphere surrounding the droplet and the substrate surface are the main parameters affecting on CA. With nanofluids (NF), nanoparticle concentration and size and shape can modify the contact angle and thus wettability. This study investigates the validity of single-phase CA correlations for several nanofluids with different types of nanoparticles dispersed in water. Geometrical parameters of sessile droplet (height of the droplet, wetting radius and radius of curvature at the apex) are used in the tested correlations, which are based on force balance acting on the droplet surface, energy balance, spherical dome approach and empirical expression, respectively. It is shown that single-phase models can be expressed in terms of Bond number, the non-dimensional droplet volume and two geometrical similarity simplexes. It is demonstrated that they can be used successfully to predict CA of dilute nanofluids’ at ambient conditions. Besides evaluation of CA, droplet shape is also well predicted for all nanofluid samples with ±5% error.

Highlights

Wettability is the property of a solid surface contacted with a liquid within a surrounding fluid and its quantity is defined by the contact angle (CA)
The second model we have considered was proposed by Yonemoto and Kunugi [35] (YK model), which is based on the energy balance for various-sized droplets on a solid surface
The aim of this study was to evaluate the reliability of three theoretical models and one empirical model developed for single-phase liquids for describing the correlation between contact angle, The aim of this study was to evaluate the reliability of three theoretical models and one empirical geometrical parameters and forces/energy balance of nanofluid sessile droplets

Summary

Introduction

Wettability is the property of a solid surface contacted with a liquid within a surrounding fluid (liquid or gas) and its quantity is defined by the contact angle (CA). Wettability is important for the industrial applications such as phase change heat transfer, oil recovery and liquid coating. Contact angle (CA) is the angle between liquid–gas (or liquid–liquid) interface and liquid–solid interface for a droplet on a solid surface. The CA strongly depends on solid, liquid and surrounding fluid properties. If CA is smaller than 90◦ , it means that the liquid wets the solid surface. For CA greater than 90◦ , the liquid has lower wettability. CA is dependent on liquid type and surface properties

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