ME 109

Heat Transfer

I made a couple great new friends in this class.  Notable ones included Biot, Nusselt, Prandtl, and Rayleigh.  But in all seriousness, who are these people?  We tossed their name-attributed dimensionless numbers around like tennis balls in this class.  While I’m here, I’d also like to point out how easy this Kirchoff guy made it to the scientific history books.  Literally all of his laws just say, “what goes in must come out”.  Genius innit?

 ME 109 is the last of my required Mechanical Engineering courses that dive into the theory behind a cornerstone ME subtopic.  Taught by Professor Costas Grigoropoulos, the course combines topics learned in ME 40 (Thermodynamics) and ME 106 (Fluid Mechanics) and focuses on, you guessed it, the transfer of heat.  The course was very nicely split up between three units, covering the three primary types of heat transfer: conduction, convection, and radiation.  The course had that classic, three-lectures and one-discussion per week schedule.  As well, the three exams were neatly split up between the three units. 

The first two units were on conduction and convection.  Conduction is the transfer of heat by transferring the physical motion of the particles from one body to another.  Conduction accounts for your hand not being able to hold a hot coffee cup.  Conduction was a plain unit, seemingly coming straight out of physics class and using classic calculus techniques to solve problems.  Convection is the transfer of heat by fluid motion.  Convection is why fans work and the sea breeze cools the coast.  Convection was a dumb unit (or rather a dumbed-down unit).  Convection is a complex topic that brings challenges from both thermodynamics and fluids.  However, scared that us undergrads would be too dumb to understand, many of our problems were solved with the help of spoon-fed correlations courtesy of Nusselt, Prandtl, and Rayleigh.  We barely had to do any work aside from looking up the right formula in a table.  Radiation is the transfer of heat through electromagnetic stimulation.  Radiation is why the sun warms us and why the inner coating of your lunch bag is shiny.  Radiation was my favorite unit, largely because of my interest in space.  Out in the vacuum of space, conduction and convection go on sabbatical, as there are no particles to carry kinetic energy.  Out there, radiation is alpha.  This unit was where I finally felt like I learned valuable new information, which is what I take classes for.  A highlight of this unit was the concept of steradians and the view factor, which is basically the concept of radians for a circle extrapolated for spheres.  For more, check out the Food for Thought. 

This class wasn’t exciting.  There were no labs, interesting projects, in-class demos, or anything of the sort.  We just did problems all day.  Problems for homework, discussion, and exams.  Professor Grigoropoulos was also rather dry, no offense.  He would often miss raised hands for 5 minutes at a time, by which either he had already moved on to another topic or the student’s arm got tired.  In a class with just shy of 70 people, steady-state lecture attendance was 5 people.  I personally attended 1 lecture every 3 weeks on average (1 of every 9 lecture).  9 AM was too early to hear my man drone on about his good friend Nusselt.  Worst of all, to nobody’s fault, I found the curriculum rather cookie-cutter, at least up to the radiation unit.  There was no elegance in how some of the problems were to be solved.  Difficulty did not come from problem-solving ingenuity, but from problem length instead.  Wrong answers were typically wrong because students made a calculation error in the middle of a 2-page problem, or the wrong correlation was used.  Speaking of which, I’ve always been uncomfortable using correlations, but that’s just me and my insistence on seeing a fundamental proof for everything.  Nevertheless, at least I come away from this class having learned a handful. 

Food for Thought

Just as a circle has 2pi radians, a sphere has 4pi steradians.  You can think of a steradian as a solid angle.  If a spotlight shines on a screen, the classic cone shape that is made can be quantified by steradians. 

This cone has equal height to diameter (h = 2r).  What how many steradians is the tip of the cone?