Wednesday, June 23, 2010

Chemical Engineering as a career

This post gives a short synopsis of the slide show for the summer engineering program at Notre Dame for 6/23/10.  Here is a pdf of the slides that are posted on one of my webpages .

The slide show describes a little about the traditional chemical industries with the example of fluidized catalytic cracking, which is used to increase the gasoline and diesel fuel yield from crude oil.  Wikipedia has an excellent article on this subject (http://en.wikipedia.org/wiki/Fluid_catalytic_cracking).

I talked about Arrhenius kinetics and showed the equation.  The slideshow on this topic is available here.  It is actually one of my favorite lectures that I have ever given as you can see why the rule of thumb of doubling of a reaction rate with a 10 C rise in temperature has to be the case for reactions that occur on time scales that are useful for industrial processes and why if you want to run a profitable chemical process, you need a catalyst that gets the activation energy down in the range of 25 kcal/mole.

For the kinetics part of the talk I used lightsticks to show the effect of temperature.  One was at room temperature and one was cooled with ice (with added salt).  There was a noticeable difference in brightness, which lasted only a few minutes.  A question that could be asked, that I did not answer in class, is if we would expect the temperatures to equalize on this time scale.  This is easily checked using the principles of Transport Phenomena, specifically transient heat conduction.  The governing equation for a cylinder heating up would be the "heat equation", which is a parabolic partial differential equation.  For the estimation that we want, there is no need to solve the equation, but to note that if the thermal diffusivity for the liquid in the lightstick is about 10^-7 m^2/s (the value for water), then the time scale for relaxation of the temperature would be the radius of the lightstick (or actually the tube inside of it) squared, divided by the this value of thermal diffusivity.  If the radius of this inner tube is about .5 cm. (.005 cm), then the time scale is 250s or about 4 minutes.  This matches extremely well!

The soda pop demonstration showed the the fizzing of a shaken bottle occurs because the gas that is present in the bottle is broken into lots of little bubbles than all can grow.  Because it is difficult to spontaneously create bubbles in a liquid, just opening the cap, without shaking, does not allow a lot of transfer of CO2 from the liquid to the gas.  The process of creating a new phase, within another phase is called nucleation.  Homogeneous nucleation usually require considerable superheat or supersaturation.  You can observe bubble nucleation when boiling water on a stovetop.  Note that before boiling occurs, bubbles form on the bottom of the pan in scratches and other places where air has been trapped when the water was added.  This process of bubble formation is heterogeneous nucleation.

The lecture proceeded to talk about roles for chemical engineers in renewable energy (new materials and material processing for solar and wind) and other topics.

The last part of the class presentation addressed the role of chemical engineers in medicine.  Topics discussed were tissue engineering (the video was from Scientific American Frontiers about a decade ago) and new drug delivery devices and constructs.

There is much additional information in the slide show about the chemical engineering undergraduate curriculum and careers for chemical engineers.



 

Tuesday, June 22, 2010

Thoughts on the oil spill and energy sources

This post describes the essence of the session that I had with students in the summer engineering program at Notre Dame.  The primary threads are how engineers might think of the issue of energy and how the oil spill intersects with the larger societal challenges.

I started by showing a live video link of the oil well with the gas and oil gushing out.  You can find these on the BP web page (http://www.bp.com/genericarticle.do?categoryId=9033572&contentId=7062605); different camera views come and go.  The view that we looked at was intended to show the dispersant being added to the well effluent.  I noted that it was not clear if the actions to date had increased or decreased the amount of oil and gas that are entering the ocean, but that it is certainly possible that by cutting off the riser, more total flow is occurring up the well.  The current collection values of approximately 25,000 bbl/day could be less than 1/3 of what the well is capable of producing.

The rest of the session is available as a pdf at:http://web.me.com/mjm7357/.  

This is a quick snapshot into this problem and just examines some barriers to renewable fuels -- in an attempt to explain why the current mix leans so heavily on fossil fuels.  Although not written in the slides, I did state that the challenge for the future is to lower solar to levels matching coal and gas, not to raise everything to match solar.