Engineering Expert Witness Blog

     Last week we followed Dorothy through the forest and watched Scarecrow transform from a fire trap to a robust fire-retardant fiberglass composition with the help of materials science.  This week we’ll explore the magical world of thermodynamics, and nobody knows thermodynamics like the Great and Powerful Oz.  In fact, he’s a real “Wiz” at it! 

     But seriously, thermodynamics is one of those out-of-sight, out-of-mind things that we take for granted in our daily lives.  Without thermodynamics we wouldn’t have modern conveniences like electricity, air conditioning, or anything with a motor, like the cars we can’t seem to do without.  The world would essentially be in the Dark Ages again. 

     Often referred to as “thermo” among mechanical engineers, thermodynamics is the science that deals with heat and work in processes used in power plants, refrigeration compressors, and engines.  Thermo also deals with the properties of substances that absorb and release heat energy, things like water (steam), refrigerants, and fuels (coal, gasoline, natural gas, etc.).

     In thermodynamics there are basically two laws that must be obeyed.  The first law states that energy cannot be created or destroyed, it can only be transformed from one form into another.  An example of this principle at work would be when you gas up your car.  According to the first law of thermodynamics, the chemical energy that is released when gasoline is burned by the engine must add up to the work energy put out by the engine to move all its parts and accelerate the car.  The first law sets up an energy accounting system, so to speak.  This principle makes it possible to analyze and design engines, refrigeration equipment, etc. 

     The second law of thermodynamics states that it is impossible to build something that is 100% efficient.  So, going back to the car example above, the second law tells us that we must also account for things like the heat energy lost to the atmosphere from the hot engine parts and the fumes leaving through the exhaust pipe.  This heat energy essentially wastes gasoline and doesn’t do any useful work, but it is a real phenomenon which must be dealt with when doing engineering design work.

     Thermodynamics can be broken down into different subsets, including power cycle analysis, refrigeration cycle analysis, stoichiometry, and psychrometrics. We’ll begin exploring these next time.

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