An Experimental Study on Bubble Growth in Laponite RD as Thixotropic Yield Material.

Yiping Zhang,Yongchao Zhou,Mengxian Hu

doi:10.3390/ma13132887

Abstract

The growth and release of the leading major bubble at the tip of a needle in the thixotropic yield material Laponite RD was different from subsequent minor bubbles. The gas injection experiments combined with high-speed camera were conducted. The results showed that the shape of the major bubbles transformed from an inverted carrot shape to an inverted teardrop shape, while the shape of the minor bubbles tended to be elliptical. In addition, the pressure of bubble emergence consisted of hydrostatic pressure, capillary pressure, and cracking pressure. The major and minor bubbles differed only in the cracking pressure. The pressure when the minor bubble detached could be estimated from the lateral hydrostatic pressure. It can be deduced from dimensionless numbers that buoyancy and viscous forces were, respectively, the main driving force and resistance of bubble growth. The yield stress of Laponite RD and inertial force at the initial moment resulted in distinctive behavior of the major bubble. In addition to the viscosity resistance, surface tension, and hydrostatic pressure had a non-negligible influence on minor bubbles and still accounted for 10–20% of the total resistance in the later stage but less than 5% in major bubble growth.

Highlights

Bubbling behavior is a fundamental problem of two-phase gas–liquid flow and is widely encountered in various engineering applications, especially in the fields of energy, chemicals, and environment such as methanol fuel cells [1,2], sewage treatment [3,4], frictional drag reduction [5,6], and gas–liquid contactors [7,8]
Laponite RD powder was a synthetic silicate with the same refractive index as water
Laponite RD powder was manufactured by Southern Clay Products Inc. (TX, USA)

Summary

Introduction

Bubbling behavior is a fundamental problem of two-phase gas–liquid flow and is widely encountered in various engineering applications, especially in the fields of energy, chemicals, and environment such as methanol fuel cells [1,2], sewage treatment [3,4], frictional drag reduction [5,6], and gas–liquid contactors [7,8]. It is worth noting that bubbles on the scale of a few micrometers to a few hundred micrometers in Newtonian fluids are relatively easier to study, because they are almost spherical shape and not deformed. Some scholars have studied the bubbling behavior of a single gas escaping from the orifice of non-Newtonian fluids and found

Methods

Results

Conclusion