Fluid Dynamics: Space Edition

A report came out this week from the International Space Station concerning a new joint plan from the Center for the Advancement of Science in Space (CASIS) and the National Science Foundation to conduct fluid dynamics research in space. The initative is a continutation of CASIS’ efforts to expand educational and commercial research opportunities in space and will fund up to 1.8 million dollars in research grants.

They claim that the space environment provides a unique opportunity to study otherwise commonplace scientific phenomena from a new perspective. The question is how do fluids behave given the absence of forces like hydrostatic pressure and gravity. The project has potential for advancements in the understanding of fluid dynamics such as “capillary flow, diffusion,.... and surface tension.” Their hope is to discover useful knowledge that will help industry and academia alike.

While I’m amazed about the idea that this space research could eventually lead to knowledge that’s taught in the chemical engineering department in 20 years, I’m also slightly skeptical of any plans to advance science research by a great amount. Don’t get me wrong, I understand the implications involved- maybe we’ll find a new relationship that describes a behavior we thought we knew really well. But I feel that frequently, science is done for the sake of science and that the bridge between research and industry is quite weak. I say this from my limited personal experience of working in a lab myself.

Space flight is a vestige of Cold War one-uppery with the Soviet Union and serves many nationalist and entertainment (?) interests. Projects like these make me wonder if the promise of scientific advancements in space isn’t just the novelty of space shuttles under the guise of true research; I’m not convinced that finding water or bacteria on mars is a great use of resources.

Questions that linger on my mind about the scientific process in space:

• How will research expectations influence experimental results given the relatively high stakes of just one chance to conduct an experiment in space?

• Will there be a way to reproduce these results in a rigorous manner?

• Would the 1.8 million dollars be better spent on fluid dynamics research on earth?

• If we do make an interesting observation in space, how do we know that this information will be useful on earth (where gravitational forces persist)?

Tianjin Chemical Warehouse Explosions

Image Courtesy of the Guardian.com

When do chemical catastrophes occur and how do we prevent them?

The Tianjin chemical warehouse explosions that occurred on August 12th this year are a prime example of why process safety is so necessary to the chemicals industry today. With 173 dead and many more injured, you have to wonder, how did this happen? The answer to that question remains a mystery. On-site investigators were not able to determine the cause of the explosion, however I suspect that negligence, like for many situations, is the cause. To make matters worse, first responders attempted to extinguish the chemical fires with water. This was a major oversight on the part of the fire department considering the potential for pyrophoric chemicals to be stored on site. Other chemicals such as sodium cyanide and potassium nitrate present on large quantities pose serious health hazards to the surrounding community due to the risk of inhalation or water contamination.

It is known that China’s chemical industry has been rapidly expanding in the last 15 years and that the safety regulations that usually accompany this industry have lagged behind. This is not China’s first chemical explosion in 2015 and according to CNN it is a drop in the pan when compared to the total number of occupational deaths in China last year (68,061 deaths).

I think the only answer to a situation like this is tougher enforcement of safety regulations, accompanying fines and potential business closures. Businesses are profit-minded and will only consider the costs of their negligence when there is a tangible consequence to unsafe working conditions.

While not a chemical plant, I see many parallels to the Tianjin fires in my own residence hall.

Recently, there was a fire in my residence hall due to an irresponsible resident on the floor above mine. He had his candle burning at 5:30 AM that Thursday morning (before my Thermo quiz) and woke up from a nap to find that half of his room was in flames and that smoke was filling the space rapidly. Instead of doing the reasonable thing, shutting his door and window, exiting the room, and pulling the fire alarm, he opted to stay in the room and attempted to put out the fire himself. Not only did he fail to do the reasonable thing, but he also ended up making the fire worse when he tried to extinguish it with mouthwash instead of the fire extinguisher less than 30 feet away from his room; obviously not a chemical engineering student as the primary ingredient in mouthwash is the ever-flammable alcohol.

All this to say that the reason for this fire was the alignment of two or more unmitigated risk factors. I happen to know this resident personally and there were at least two contributions to the risk; this happened during the first round of midterms and he was getting very little sleep AND his natural disposition is to deal with problems himself and to not ask for help. So in his exhaustion from studying, he lights a soothing candle before dozing off and a fire ensues. What normally would have been a manageable accident became out of control as he chose to deal with the problem his own way, releasing plumes of smoke into the hallway and putting others at an even greater risk of injury.

I still think to myself today; what would have happened if there was one more unmitigated risk factor at play? What if the fire alarms weren’t working that morning? I live less than five feet away from him in a room directly beneath his. What could have happened to me?

This is why Columbia Housing doesn't allow candles in the residence hall, students are encouraged to get sleep during midterms, and everyone is informed of the proper procedures for dealing with fires. In my mind, scale is the only difference between fires in a residence hall and fires at a chemical plant.

References:

1. "Tianjin Explosion: China Sets Final Death Toll at 173, Ending Search for Survivors." The Guardian. 12 Sept. 2015. Web. 13 Dec. 2015.

2. "Tianjin Explosion Exposes Toxic Chemicals in China - CNN.com." CNN. Cable News Network, 17 Aug. 2015. Web. 13 Dec. 2015.

3. "3,000 Tonnes of Dangerous Chemicals Were Stored at Tianjin Explosion Site, Say Police." Hong Kong Free Press. 18 Aug. 2015. Web. 13 Dec. 2015.

Cavitation in the Wake of an Underwater Bullet

In this video, Destin was hoping to continue his investigation on guns underwater. He opted to use an AK-47 and a high-resolution, 27,450 frames-per-second camera in a swimming pool. At normal video speed, you cannot see the bullet exit the gun but you can see the disturbance in the fluid around it. The bullet travels about 5 to 6 feet before being completely slowed by the water.

In the slow motion of the video, we observe a more sophisticated fluid motion. As the bullet leaves the chamber, a cloud of disturbance traces the bullet’s trajectory in three regimes: gunpowder, water jet, and bow shock. We learn that each bubble undergoes volume oscillations due to momentum and pressure forces as well as the balancing of mechanical energy. After collapsing, the bubbles never become as large as they were in the first moment after the bullet passed because of energy dissipation.

Destin explains how this bubble phenomena is dictated by the Rayleigh-Plesset equation shown below

where P_B(t) is the pressure within the bubble, P_∞(t) is the pressure at a distance infinitely far from the bubble, L is the density of the liquid, R(t) is the radius of the bubble, v_L is the kinematic viscosity and S is the surface tension of the bubble. The phenomena characterized by the Rayleigh-Plesset equation is called cavitation.

In practice, the reason that the bubble forms in the first place is because the fluid around the bullet when gains kinetic energy from the velocity of the bullet and pushes the fluid to expand outwards. The bubble eventually stops expanding as the kinetic energy turns into potential energy and the pressure difference inside and outside of the bubble is great. The pressure gradient of low pressure inside the bubble and high pressure outside the bubble then forces it to compress.

Destin kindly annotated the fluid disturbance in the image above where each bubble is a result of a process of the firing mechanism. One explanation as for why the leftmost bubble looks smoother than the right bubbles is that the flow around the bullet in this region best resembles laminar flow due to a smaller velocity as dictated by the reynold’s number

Re=ρvd/μ

While I am from Texas, I’ve only shot a gun once in my life and it too was an AK-47. Guns don’t interest me terribly but gun safety does. Some of the appeal of this video is the strategy behind jumping in water when being shot at- this information could come in handy one day. This video also piqued my interest because it was related to a 2010 Mythbusters episode where they did a similar experiment in which they discovered that an even bigger gun--- a 50 caliber sniper lost all velocity at 3 feet into water.

References:

1. Leighton, T.G. (2007) Derivation of the Rayleigh-Plesset equation in terms of volume. Southampton, UK, Institute of Sound and Vibration Research, University of Southampton, 26pp. (ISVR Technical Reports, 308).

Fundamentals of Boundary Layers

In the Fluid Dynamics video, Fundamentals of Boundary Layers, we learn how fluids behave upon encountering an obstacle. In general, a boundary layer is formed when a fluid with viscosity passes a solid plate. The video consists of black and white montage of fluid experiments along boundary layers with accompanying narration.

Throughout the video we observe the formation of formation of boundary layers. While this phenomena was mentioned in class with reference to the Blasius Problem, I found it difficult to visualize the actual physical representation. To see demonstrated by real fluids that the boundary layer grows along the length of the boundary was a valuable addition to my intuitive knowledge of transport phenomena. The proportion given below, and the physical phenomena it represents, is shown in the video

δ/l ∝ v/(U_o l)

where δ is the boundary layer thickness, l is the distance along the length of the boundary, v is dynamic viscosity and U_o is the free stream velocity.

One class concept that I learned to think about in a different way was the relationship between vorticity and the boundary layer. The video describes the local boundary layer thickness as a measure of the vorticity that has diffused away from the plate. Prior to this insight I had thought of vorticity as strictly a measure of fluid spin and the boundary layer as a function of only velocities and the distance along the boundary.

One section of the video that I was able to relate to more than others was the demonstration of fluid motion around an elongated cylinder. Near the end of the video, an airplane wing is shown to give the example more relevance. I happen to thoroughly enjoy airplanes and airplane rides; oftentimes I sit near the wings so I can watch as they glide through the air. It was interesting to look at this commonplace example of fluid passing around an object as vortex generation and the disturbance of an otherwise laminar flow.

Dr. Christina Chan Colloquia

Dr. Christina Chan graduated from Columbia with an undergraduate degree in chemical engineering. She went on to earn her doctorate at the University of Pennsylvania and do postdoc research at Massachusetts General Hospital before assuming her current position at Michigan State University. Dr. Chan is most interested in researching systems biology to better understand the pathways and mechanisms utilized in diseases and how they can be employed for therapeutic purposes. Dr. Chan explained at the beginning of her talk how there are two ways to go about treating diseases: a systems biology approaches or a tissue engineering approach. The talk was divided into two parts where she treated each of of these methods.

We were first presented with an application of systems biology, the correlation between saturated fats and diseases. Dr. Chan explained that with the technology we have now, we can take genes and predict the likelihood of diseases based on their identity. In Dr. Chan’s lab she uses both bottom-up and top-down methods to better understand the relationship between genetics and disease states. According to Dr. Chan, by the bottom-up approach, large amounts of data are processed and used to model predictive algorithms while the top-down approach involves “data mining.” This part of the talk was confusing because it seems that both of the descriptions are of the bottom-up approach and I would be curious to know what precisely Dr. Chan meant when she said top-down.

Dr. Chan also talked about the different effects of prestretched and unstretched surfaces when culturing cells. She explained that depending on the cell being cultured, one surface might yield more growth than the other. The difference was most pronounced in spinal cord regeneration where it was important that axons be made thicker than other cells. Dr. Chan found that when the cells were placed on a stretched surface, they aligned in such a way as to imitate protein (muscle) cells. A diagram similar to one that Dr. Chan showed during her presentation is shown above.

Dr. Chan’s research discussed in the colloquia, while interesting, had much to do with biomedical and computer science applications for a limited scope of cell culturing problems. I still can’t identify one main thread that would connect her talk to the field of chemical engineering. She works at the Chemical Engineering and Materials Science Department at Michigan State University so I would surmise that this falls under the latter subject and that her other projects account for her chemical engineering focus.

Overall, I think Dr. Chan’s research is significant and constitutes a new strategy for how to manipulate cell growth for optimal performance. Her examples given are substantial; in particular, I was impressed with the spinal cord regeneration anecdote. Dr. Chan realizes the practical applications of her work and goes so far as to prescribe a new way of thinking about systems biology and cell culturing. Far from being out of touch with the larger world of research, the questions Dr. Chan is investigating pair well with a paper written earlier this year on the same topic with mice.

Reference:

1. Arulmoli, Janahan. "Static Stretch Affects Neural Stem Cell Differentiation in an Extracellular Matrix-dependent Manner." Scientific Reports 5 (2015). Nature. Macmillan Publishers Limited. Web. 25 Nov. 2015.