Tyler's Take on Fluid Mechanics

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Seminar: Catalytic Conversion of Carbon Dioxide to Fuels and Chemicals

On December 9,2015, I had the opportunity to attend a seminar called Catalytic Conversion of Carbon Dioxide to Fuels and Chemicals given by Columbia’s very own Professor Jingguang Chen. Being in that room listening to Professor Chen, I couldn’t help but recall my days in Material and Energy Balance sophomore year in 825 with Professor Chen. In comparison to sophomore year, Professor Chen seemed a lot more enthusiastic and comfortable presenting some of the topics of his research. His talk was slightly informal and engaging. The premise of his presentation was providing enough information on the subject matter in order to spark something his audience to think and possibly contribute to the solution for carbon dioxide problems. 

He began his presentation by showing a graph of experimental data of the increase of atmospheric concentration of carbon dioxide over time. As a result of this increase in carbon dioxide concentration, the ocean is becoming more acidic and temperature is increasing. Most people solely focus on the temperature increases in regards to  carbon dioxide concentration; however, Professor Chen emphasized ocean acidification. The most shocking example he gave was of sea butterflies dissolving in 45 days. The further acidification of the ocean would destroy aquatic diversity and sources of food for people all over the world.

After he clearly defined the problem and its societal impact, he outlined current solutions. The first solution he gave was sequestration, the burial of carbon dioxide in the ground. That option is fine and dandy until there is an earthquake and then what? That process is also very expensive so a cheaper and less risky and solution is more desirable. 

The second method was to convert the carbon dioxide into other chemicals such as carbon monoxide, methanol, and methane. A conversion to carbon monoxide could lead to a 40% reduction in carbon dioxide and the Fischer Tropsch reaction could convert carbon monoxide into fuels liquid fuels. Conversion to methanol results a 0.1% reduction in carbon dioxide, a value far too small to rely on to solve this issue. 

Professor Chen’s research focuses on conversion and specifically the Discovery of Active, Selective, and Low-Cost Catalyst for conversion. He mainly focused on conversion by heterogeneous catalysis; however, he briefly discussed the work his team has done regarding conversion by electrocatalysis. 

In regards to heterogeneous catalysis, he used different catalysts to get different results. For example, in order convert carbon dioxide into methane, a bimetallic catalyst was used. The conversion is a two step process that requires a certain catalyst (acquired from his team’s database of materials) for hydrogenation followed by scission to yield methane. 

In order to convert carbon dioxide to carbon monoxide, his team used in-situ techniques over a carbide catalyst. I was a little lost during this part in the talk because the techniques were not as straightforward as the other. It would have been helpful if he spent maybe a minute longer on this topic but what I took away from it was that there was a direct reaction that isolated oxygen on the surface of the material and then the hydrogenation step to yield carbon monoxide. 

Another method discussed was the roadblocks to reducing the concentration of carbon dioxide through hydrogen gas reduction. The main problem is that 95% of hydrogen gas comes from hydrocarbon based feed stock but the feedstock generates carbon dioxide as a by-product. In an effort to reduce carbon dioxide, more carbon dioxide is created, offsetting the intention of the efforts. 

He briefly touched on low cost electrocatalysts in acid electrolytes and hybrid processes before concluding his presentation. He concluded by review the pros and cons of each of the possible conversions previously discussed with factors like product value, geographic location, selectivity, and yield all in mind.

Finally, he proposed the final question of “What should we do?” from the perspective of chemical engineers. Should we sequestrate the carbon dioxide or should we convert it? If we convert it, how so? These were the questions that he left us with along with a quote from one of his advisors: Chemical Engineers should create opportunities and solve problems critical society’s well being.” That quote reiterated why myself and so many others were there sitting in that room. Our jobs as engineers aren’t just to solely theorize topics in material balance or thermodynamics. We must apply those those theories and our create abilities to solve the problems of tomorrow. 

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The Hajj Stampede: A Fluid Dynamic Problem

The Hajj, the Pilgrimage to the Holy city of Mecca, was home to one of the greatest fluid dynamic disasters in 2015. Mina has had this fluid dynamics problem for the last few years, though a solution has yet to be found. The fluid that is causing so many problems in Mina is comprised of people. 

Before reading this article, I had never thought of people in terms of fluid dynamics. I never drew that connection that this article laid out. This idea is not a new one and stampedes have been happening since the late 1900s. 

Now that I have the connection between people and fluids in my mind, I can’t help but think of the different effects and mechanism that cause turbulence, or in our case deadly stampedes. 

Using the equation for the Reynold’s Number derived in my last blog post, I was able to explore the different effects of different variable. 

The article stated that the number of deaths have risen due to the shear number of pilgrims that have decided to make the pilgrimage. This data correlates with the the fluid dynamic equation for the Reynold’s Number because as the number of pilgrims increase, so does the density which would increase the turbulence and increase the deaths. 

The death toll reached over a thousand people in 2015. The casualties almost alway occur at the Jamarat Bridge, the site where turbulence seems to begin. The flow before the Jamarat Bridge is fairly laminar and unidirectional. The laminar flow becomes less steady as a result of obstacles: turns, narrow doors, and people falling. Moreover, turbulence is introduced when two flows from different directions, or multiple directions collide. 

Different solutions have been implemented such as making the bridge multilevel with multiple exits but the transition to turbulence has yet to be solved. This solution would make sense because it is increasing the diameter of the roads that can be used by the pilgrims which should reduce Reynold’s Number and the turbulence. However, unlike fluids that we may deal with in our fluid mechanics class, human are not uniform in our size, ability, awareness, and balance which causes our Reynold’s number equation to break down a little bit. 

With an increase in people comes an increase in density and the density reaches a point where people are so tightly packed that any small disturbance, or movement put a force on surrounding bodies. The force could lead to someone falling and when someone falls, a hole forms. The creation of a hole gives rise to eddies and vortices of people falling into the hole and people avoid the hole at all cost by going around it. The hole creates a ripple effect as those who try to go around it exert more force on the people outside of the hole which results in more holes and more turbulent flow. 

The severity of understanding fluid dynamics is even more important now that human lives are are stake. 

http://www.wired.com/2015/09/hajj-stampede-fluid-dynamics-problem/

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Fluid Mechanics in Medicine

I vaguely remember around this time my freshman year I decided that I wanted to be pre-med, a decision that I would soon renege on just two months later. I realized that medicine just wasn’t for me and I expected this video to overwhelm me with biology terminology that would lull me sleep. Surprisingly, I stayed awake the entire time and enjoyed the entire video. The connections that this video drew between medicine an fluid mechanics sparked a newfound interest in medicine in me. 

The video began by covering topics that we had already covered in our Transport I class such as the Reynold’s Number and turbulent flow. The main goal of the video, stated at the beginning, was to understand how flow, vessel diameter, and blood viscosity impact the generation of heart murmurs and bruits. 

The narrator built the definition of turbulent flow off of the definition of laminar flow which allowed for a segway to better understand Reynold Numbers and transitions into turbulent flow. 

In the application to medicine, we first looked at how turbulent flow is more likely when the diameter increase but only in the case of when the velocity is constant. However, in blood vessels, the velocity of blood flow rarely stays constant due because the diameter of the blood vessel varies along its length. In keeping with the equation of continuity (A1xV1=A2xV2), as the diameter across the length of a blood vessel decreases, the risk of turbulence increases because the degree of the velocity change is to the square of the diameter. (for example, if the diameter decreases by a factor of 3, the velocity will increase by a factor of 9.) 

Moreover, I also learned about the effects of turbulent flow in a blood vessel. When the blood goes from laminar to turbulent flow, the eddies and vortices transform the kinetic energy into sound waves which reveal themselves to us as murmurs, often found in the heart, and bruits, often found in arteries. The video also gave short sound clips of different types of murmurs. For example, one murmur was of a blood vessel suffering from an infection that made the heart beat faster than it should. 

We derived the following equation in order to delve into the mechanisms hat lead to murmurs and bruits: 

The first variable that we ruled out was an increase in the density because it does not occur naturally. Next, we looked at an increase in blood flow which could come about due to infections such as sepsis, hyperthyroidism (speeds up your heartbeat), and exercise. A decrease in the diameter of the blood vessel would be the result of a valvular disease or vasculitis. Lastly, anemia would cause a decrease in the viscosity of blood because the blood does not have enough healthy red blood cells. I enjoyed this part of the video because it made this equation more than just numbers and shows that variables are also interconnected. 

Another interesting topic that this video touched on was how how turbulent flow relates to asthma attacks. During an asthma attack, the airways become constricted (the diameter of the airways become smaller) leading to a higher likelihood of turbulence. Therefore, the question to be asked during an asthma attack is how can we best get rid of this turbulence. The video explained the traditional way by increasing the diameter. What I found most interesting was the experimental approach of decreasing the density of air inhaled. Research has been done on Heliox, a breathing gas made of 70% helium and 30% oxygen, and has a significantly lower density than that of air. Inhaling Heliox instead of air would would decrease the turbulence and thereby reduce the effects of the asthma attack. Unfortunately, Heliox is expensive and has small technical issues that keep it from being used. 

https://www.youtube.com/watch?v=FZYnewBWUoc

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A New Coat: Making Oil Spill Clean Ups Faster and More Efficient

On March 24, 1989, the Exxon Valdez crashed into the Bligh Reef and thus began the second largest oil spill in the United States. A total of approximately 38 million gallons of oil was spilled. This oil spill was way before my time and when I saw the numbers, I was shocked.

However, I was more shocked to find that the biggest oil spill in U.S history happened during my time, less than 5 years ago on April 20, 2010. The BP oil spill, as it is more commonly known, was a result of an explosion of the Deep Water Horizon oilrig. A total of approximately 210 gallons were spilled.

The aftermath and the environmental impact have been topics of discussion. One of the main questions is how to make oil spill cleanups faster and more efficient. P.S Brown, O.D.L.A Atkinson, and J.P.S Badyal from the Department of Chemistry Science Laboratories at Durham University try to the tackle this issue in their research, Ultrafast Oleophobic-Hydrophilic Switching Surfaces for Antifogging, Self-Cleaning, and Oil-Water Separation published on April 30, 2014. A common way of cleaning up oil spills is by using absorbents to collect the oil; however, this method is inefficient because it also collects a lot of water too. Moreover, another process must be employed in order to extract the oil from the absorbent. The research team at Durham University has developed an oleophobic-hydrophilic coating that can be applied to metal mesh that will allow the water from an oil-water mixture to filter through and repel the oil off to the sides. Initially I found this article on ScienceDaily but the details were scarce so I decided to take a look at the published research paper to get a better understanding. Although the paper was fairly complex and beyond the scope of my coursework, I was able to gather some important details that were essential to the discovery and were touched on in our Transport Phenomena class. The oleophobic-hydrophilic surfaces that the team analyzed were polyelectrolyte flouro-surfactants. The polyelectrolyte flouro-surfactant allows for a “switch” of the surface-water interaction due to a hydrophilic realignment that creates a film that the water can penetrate through but the oil cannot penetrate through because of its size.

Time-scales, an important topic in our class, were are major setback for previous research on this topic. Earlier attempts took a few minutes for the water to go through the fluorinated top layer but this method takes roughly 10 seconds for the water to drain through. The new method uses copolymer-flouro-surfactant complexes to create a film with the desired time scale to pass through. As I was reading through the research paper, I found a set of pictures that reminded me of the pancake syrup-spreading problem from our third homework assignment. Water droplets were applied to glass slides with a coating of copolymer flouro-surfactants. The water droplets were allowed to spread across the film until it came to equilibrium which happened in less than 10 seconds.

In our homework problem, the speed at which the water droplet spread was a function of the height of the water droplet; however, for this more advanced topic, more variables must be taken into account such as hydrophilic factors, molecular analysis, and the water contact angle. A similar method was carried out using hexadecane droplets; however, when these droplets hit the flouro-surfactant complex surface there was negligible change in the hexadecane contact angle that shows that the film is oleophobic. This discovery also lends itself to applications of antifogging and self-cleaning. Since oils such as hexadecane stay contained to their droplets they are easy remove with a water rinse which increases its transparency and its ability to clean. Finally, they applied a rougher version of the flouro-surfactant to steel mesh creating 2 different length scales, the pores of the steel mesh and film roughness, that make it more difficult for the oil to go through. The water was allowed to go through the mesh while the oil ran off into another compartment. By scaling this process up, future oil spills could be cleaned up a lot quicker and more efficiently creating safer methods to protect the environment.

Brown P.S., Atkinson O.D.L.A, Badyal J.P.S. 2014.Ultrafast Oleophobic-Hydrophilic Switching Surfaces for Antifogging, Self-Cleaning, and Oil-Water Separation. American Chemical Society Applied Materials and Interfaces.6.United Kingdom.

Link to researh paper: http://pubs.acs.org/doi/pdf/10.1021/am500882y

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Visualization of Flow

          As a self-proclaimed visual learner, I found this video helpful in understanding the underpinning of the mathematical models used in fluid mechanics. Mathematical models for many flow patterns would be difficult to derive without an intuitive sense and visual evidence of flow patterns based on system geometry. The first half of this video emphasizes the different techniques for flow visualization such as the hydrogen bubble method and the dye method which both use open surface water channels. The video employed the hydrogen bubble experiment to define key terms such as path lines, streak lines, flow fields, timelines, and streamline. These definitions and their correlations allowed for a more meaningful discussion regarding the difference between steady and transient flow with a further elaboration on the transient flow. Unlike the steady state, the transient flow has more complicated streamline from which to derive mathematical models. For example, the video illustrates a fluid flowing in time with an oscillating barrier. The flow pattern was difficult to understand at first because there was so much going on. However, the video deconstructed the flow pattern into its simplest form by first showing only path line for one particle at one time and then another directly after and so on and so forth. This breakdown allowed me to see the non-coinciding streak lines over time while also getting a better understanding of the transient flow. 

          Another positive aspect about this video is that whenever the topics seemed to get slightly more difficult to understand theoretically, the video introduced more visuals to aid in understanding. For example, the next topic discussed was the laminar boundary layer exemplified by a flow enclosed by two parallel walls and the how the velocity drops off near the walls. This concept pretty easy to understand, however, when the angle of the channel began to open up, the flow pattern began to change. The laminar boundary layer became a turbulent boundary layer with the flow near the walls a lot thicker and less steady. As the angle continued to get larger, the slower moving part began to near the wall began to accumulate and then move up. This accumulation causes a stall in the flow, however; after the pressure changes, the washes out and then builds up again. The gradual build up of ideas in this situation is indicative of how early fluid mechanical models were created and give insight to how flow patterns can be made more efficient. Through many trials of holding the flow constant and adjusting the angle of the walls, the video helped me understand divergence angle boundaries in which to minimize stall by way of creating smaller and separate channels.

           The video also illustrated another method of flow visualization through dye injection. The video emphasized laminar flow and transient flow throughout the early parts of the video as mutually exclusive. I liked how the video introduced the laminar turbulent transition in the context of the dye injection because it allowed me to correlate a concept with a methodology that will help me better remembers the concept. Lastly, I found this video extremely helpful in getting a more intuitive sense of flow patterns.

https://www.youtube.com/watch?v=nuQyKGuXJOs

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In the Beginning: Rheological Behavior of Fluids

           I watched the video about Rheological Behavior of Fluids from the National Science Foundation mere hours after my first Transport Phenomena I class with Professor McNeill and I must say that this video helped solidify key concepts of fluid through live experiments and real life examples.  The video introduced me to new vocabulary such as rheology, inviscid fluid, and memory fluid, all topics that we touched on briefly during class. The narrator presents the material in a clear and concise way that assumes that people watching it, like myself, have little to no prior knowledge of fluids. The flow of content progresses gradually especially at the beginning of the video where the narrator explains the basic assumptions of behind the stress deformation relation and their accompanying models such as Euler’s and Navier-Stokes’s Equation.

          The theories and concepts around inviscid and Newtonian fluids explained in the video were fairly straightforward and needed little to no experimental elaboration; however, for the “non-Newtonian” fluids that did not adhere to the aforementioned models. Luckily, he offered numerous demonstrations for “non-Newtonian” fluids that had larger molecules. The demonstrations were extremely helpful in his examination of viscosity, elasticity, and memory fluids. The narrator defined “non-Newtonian”  (or Memory Fluids) as having a fading memory as illustrated by the ball and the hand crank experiment. The ball exhibited characteristics of an elastic solid but in actuality it was a fluid because after 45 minutes it turned into a puddle. Similarly with the hand crank and can of “non-Newtonian” fluid, the crank was turned and the fluid acted as best it could on its memory of its “solid state”. However, when the crank was turned and held in that position longer, the fluid adjusted a lot less. These two experiments along with the other few illustrated how the yield value of a material and the history of the deformation gradient lead to the stress being a non-linear function. 

           The second half of the video left the more challenging topics with less explanations and demonstration that were difficult to interpret in black and white. The narrator briefly touched on shear thinning (pseudo-plastic) and shear-thickening (dilatant) before diving into the effects of non-linearity of normal stress. The more complicated experiment in last few minutes offered not so detailed information regarding further understanding of the material because the narrator was stating facts and not explaining them. However, end of the video drives home the point that the degree to which “non-Newtonian” fluids occur depends on material and flow situations. Overall, I found the video extremely helpful in visualizing introductory fluid concepts.

https://www.youtube.com/watch?v=Ol6bBB3zuGc