Project: Stirling Engine
The final project for my thermodynamics course was a Stirling Engine. We fabricated parts from technical drawing by using mills and lathes in the machine shop, which gave us familiarity with CNC machines and interpreting technical drawings. The Stirling Engine efficiency can be modeled by the Carnot efficiency, assuming an idealized cycle with a regenerator (a flywheel in our case.) The ideal Carnot efficiency is defined as, (Tsource - Tsink)/Tsource, which indicates that a greater efficiency is achieved with a greater difference in temperature between the source and the sink. Work can be extracted through the cycle as shown through the efficiency of the first law of thermodynamics: Qin = Qout + Work.
To increase the temperature difference in the piston chamber (and therefore the efficiency) I created a water-cooling apparatus from copper tubing, which I attached to a pump in jar of ice water.
The mechanics of the Stirling Engine involve two pistons: displacement and power, as well as a flywheel which acts as a regenerator. As the end of the heat transfer cylinder (the one with the copper coils) is heated from to the flame, air expands and pushes both the displacement and power piston, creating the initial movement of the flywheel. The motion of the flywheel then moves the displacement piston to shift the air into the heat sink region of the cylinder. As air cools in the heat sink, the volume decreases and both pistons are drawn inward. This shifts air to the heat source, where it is heated and expands, thus driving the work piston and the displacement piston, and the cycle repeats.