“Let’s start with an idea.”

In a film exploring the inner workings of an everyday phenomena, Dr. Lloyd Trefethen begins with something at the heart of all scientific investigations: an idea. This idea that surfaces exert forces has been fundamental in the many studies that have looked at instances of surface tension, which in turn have made this idea into a successful hypothesis that continues to provide explanations of the behaviors of many liquids.

Many of us may remember visiting museums when we were kids and creating giant soap films with brilliant displays of iridescent colors. Or perhaps when we visited a park, we saw unimaginably large bubbles being formed from large bubble wands. These fantastic experiments have a firm rooting in ideas that are already familiar to us. In the example of a soap film caught on a wire frame (0:30), work becomes important in describing how to enlarge the surface of the film. Work not only acts when making liquid surfaces as in the case of the soap film, but also in creating solid surfaces. In examining the interactions of a droplet of liquid with a solid surface, work to create the solid surface and minimize system energy must be considered.

Returning to the idea that surfaces exert forces, the continuum equations of fluid mechanics can be used with three boundary conditions. In the case of droplets forming on a solid surface, the boundary conditions describes how where surfaces meet, the contact angle is uniquely determined by the energies associated with the interfaces. With a force balance across surfaces, a second boundary condition states that a curved liquid surface has a higher pressure on the concave side, as can be described by the Young-Laplace equation. A third condition describes that the surface tension variation along a surface is balanced by shear forces in the bounding materials, with surface tension being affected by the types of molecules, electrical conditions at the surface, and temperature of the surfaces.

The many demonstrations contained in this video showcase the varied behaviors of fluids and how these can be described. The following are exciting examples of fluid surface forces in action:

• The pulls of surface tension, drops of milk onto water (15:39)
• Wine tears formed at high surface area regions by evaporation (19:29)
• Oscillating mercury from electrical charges affecting the magnitude of surface tension (21:00)

 

Figure 1. Dropping milk into water creates a crown-like shape as liquid is both pushed upward by the impact and drawn downward by surface tension.

Perhaps you are tired of love triangles. Maybe you cannot get enough of the drama-inducing TV/movie trope. In either case, you have probably never seen one quite like this…

In a video produced by scientists at Universidad Carlos III de Madrid and Universidad Nacional Autónoma de México, a love triangle of the fluids kind takes the stage. In this, we see the special type of interactions that arise in a three-liquid mixture of anethole (anise oil), ethanol and water.

Here’s the backstory:

• Anise oil and ethanol are miscible (they are totally into each other)
• Ethanol and water are miscible (they also have chemistry)
• Water and anise oil do not mix (they just can’t stand each other)

In a solution of 1 part ethanol to 5 parts anise oil, the two liquids readily mix. When a droplet of water is added to the bottom of the mixture, however, the drama starts to unfold. The initial states of the liquids are largely based on density. The colored water droplet (1 g/mL) sits at the bottom of the system while the less dense mixture of anise oil (0.98 g/mL) and ethanol (0.79 g/mL) lie above. There appears not be be even a moment of calm as the separation and mixing processes begin.

The droplet of water begins shaking and growing as ethanol dissolves in it. As this process continues, the surface tension of the interface between the droplet and anise oil environment is altered. Additionally, with ethanol dissolving into the water droplet, density is lowered and the drop begins to move upward. Anise oil microdroplets find their way into the drop and set of additional movements from this interaction. The shaking sets off convective motion into the surrounding liquid, which can be easily viewed. This growth continues until buoyancy forces overcome the surface tension pulling the drop downwards. The growth-detachment cycles continue until all of the water has left the bottom surface. Changing the mixture of the environment to one part ethanol to two parts anise oil shows an enhancement of the mixing and separation processes.

This type of phenomenon is termed the “Ouzo effect.” This is also seen when water is added to anise-based alcoholic drinks like Ouzo or absinthe.

This video is accompanied by a free improvisation, following the love story as it proceeds. A violin represents the alcohol, a clarinet for the anise oil, and percussion for water.

 

Figure 1. The droplet of water having accumulated ethanol and anise micro-droplets grows until buoyancy forces win out. The convective motion in the fluid can be seen around the perimeter of the droplet.

With a continued reliance on oil and other fossil fuels, the need to keep drilling goes on. Accompanying this is the looming risk of oil spills. These spills are not only costly, but also a danger to human lives and marine and coastal environments. Oil spill simulations are notoriously complicated and take significant amounts of time. With new research, however, it appears that fluid mechanics may just save the day– or to be more accurate, days.

In a publicity release from Virginia Tech, Professors Shane Ross and Traian Iliescu have been awarded an NSF grant for developing computational model-based simulation of fluid transport events. The three year project was awarded $200,000 and will serve to produce a faster and more accurate prediction of the rate of spreading of various contaminants in the environment. Their use of computational fluid dynamics will show marked improvements of forecasts for spread in ocean, floodwater and atmospheric environments.

Using reduced order modeling and the Navier-Stokes equation in tandem, Ross and Iliescu aim to create faster modeling in their simulations. By breaking the Navier-Stokes equation into smaller pieces using reduced order modeling, computer should be able to enhance the rate in which calculations can be performed.

While oil spills would benefit greatly from this development, other applications include positional identification in search and rescue scenarios, the spread of smoke and debris in wildfires and volcanic eruptions, and forecasts of plant diseases in the atmosphere. The possibilities extend even further, as Ross hopes that this information can be brought to the general public through a mobile app. With expected yearly wildfires in California, knowing the current state of such hazardous gases in one’s area could have major impacts.

For these researches, this work is incredibly important to them. Iliescu has said, “I believe fluid turbulence is fascinating. It is a part of everyday life, yet still a mystery. My goal is to solve this mystery, or if I can’t, at least develop models that others can use in practical applications.”

With the potential for this work having impacts on such large scales across many areas, new developments in this project will be met with much excitement.

Here is a video of the fieldwork they have performed so far, featuring some great drone shots and some warmer weather.

 

Figure 1. Dr. Shane Ross (left) and Dr. Traian Iliescu (right) discussing fluid models.  

As major incidents can occur at practically any step of a chemical or manufacturing process, it is of the utmost importance to have the necessary process safety systems in place. A company owes it to their employees to ensure that an operating system maintains its integrity and hazardous substances are handled appropriately.

In the oil and gas industry, “process safety” is often used interchangeably with “asset integrity.” In the associated asset integrity procedures, hazardous releases, structural failure and the loss of stability are often considered.

In this industry, key performance indicators (KPIs) are used to measure how a system is currently performing and what can be expected of its future performance. This method of continuously checking for improvements in a process typically uses three metrics:

1. Leading indicators: maintain the strengths of barriers through forward-looking metrics indicating the performance of current safety measures
2. Lagging indicators: measure the degree of barrier defects and their consequences, based on incidents that should be reported
3. “Near Miss” indicators: incident-based metrics that provide indicators for potentially more severe incidents

These metrics are brought together into a process safety metric pyramid (Figure 1) which assesses how these should be incorporated into the larger process.

As I will be working at a liquefaction plant for natural gas next summer, I expect to learn much more about KPIs while on the job!

Sources: AIChE, IOGP

Figure 1. The process safety metric pyramid bringing together leading, lagging and “near miss” indicators.

Is there a limit to how far we should go to stop the earth from warming?

In a lecture given by Professor Frank Keutsch from Harvard University on September 18, 2018, this question was explored in the context of solar geoengineering. To meet the goal of limiting the global mean temperature rise to 2oC from the pre-Industrial era, significant changes must be made very soon.

The three major response options focus on mitigation, adaptation and geoengineering. Investigation of the latter has accumulated interest for its ability to treat the problem quickly. Reflective aerosols is one geoengineering technology that is both fast and cheap. Operating on the level on only several billion dollars per year to implement globally, aerosols could be put into place on a short timescale. Since the cause of the problem is not actually addressed, this form of solar geoengineering would only serve as a method of buying humanity more time. To avoid hitting a crucial tipping point, this technology could spare us from the worst impacts of a warming globe. How to justify a technology with such large uncertainty, however, becomes a point of contention.

With a well-mixed atmosphere, anything that is introduced to the skies should be expected to have potential impacts around the world. Natural experiments as found during volcanic eruptions have shown lowering of the tropospheric temperature in addition to a decrease in water concentrations. While temperatures may have been lowered, there was also a significant impact to the hydrological cycle. In using sulfate aerosols, secondary effects such as ozone destruction and oxidant chemical cycle disruption. The use of titania (TiO2), alumina (Al2O3), nano-diamonds, and calcite (CaCO3) have also been explored in small-scale experiments, each with their own list of potentially negative effects.

Whether this research should be continued is even under question. Does the potential need for this technology one day take precedence over the mammoth unknowns it brings?

It seems that only time will tell.