Synopsis: Viscous pull

Scaling laws are a useful way to characterize fluid flow over a wide range of flow rates and experimental conditions. Theorists now explain several earlier experiments by finding a scaling law that describes how a liquid-liquid interface changes shape when driven by viscous forces.
Synopsis figure

Shape transitions are ubiquitous in fluids. Consider for example what happens when a pipe is suspended just above the interface between two liquids. As the pipe begins to suction liquid from the top layer, the liquid flow will pull the interface between the two fluids upwards. As the flow rate through the pipe increases, this interface undergoes a shape transition from a gentle hump to a sharp neck at the point when the pipe starts to draw fluid from the lower liquid.

This type of necking effect can occur, for example, in microfluidic devices where fluids are channeled down extremely narrow passages or in the encapsulation of biological cells. But, researchers have not been able to capture the experimental details of the process with a simple scaling law that holds for different types of liquids and length scales. In a paper appearing in Physical Review Letters, François Blanchette and Wendy Zhang at the University of Chicago in the US treat this problem analytically and resolve the discrepancy between different experiments.

Blanchette and Zhang argue that the part that makes this problem hard to solve—the discontinuous neck that forms at the transition—is in fact, not important. Instead, they show that it is the gentle deflection of the interface far away from the opening of the tube that matters. With this simplifying assumption, they find a simple scaling relation between the critical flow rate at which the shape transition occurs and the height of the pipe above the interface and outline the experimental regimes where this law applies. – Jessica Thomas


Announcements

More Announcements »

Subject Areas

Fluid DynamicsSoft Matter

Previous Synopsis

Semiconductor Physics

Dirt and geometry insulate electrons

Read More »

Next Synopsis

Nuclear Physics

Nuclear star gazing

Read More »

Related Articles

Focus: Detecting Femtonewton Forces in Water
Soft Matter

Focus: Detecting Femtonewton Forces in Water

A new technique builds on previous ones to detect forces in the femtonewton range in water, despite the constant jiggling of water molecules.   Read More »

Synopsis: Droplet Hats
Fluid Dynamics

Synopsis: Droplet Hats

Experiments show that drops can form exotic shapes as they spread out on a surface if they are miscible with the surrounding fluid. Read More »

Focus: Complex Crystals Form from Heterogeneous Particles
Materials Science

Focus: Complex Crystals Form from Heterogeneous Particles

A suspension containing particles with wide-ranging diameters can crystallize into multiple ordered structures. Read More »

More Articles