Engines and the Four Thermodynamic Processes

At the start of class we did a computer assignment which showed the connections between Volume, Pressure, and Temperature. We also used the formula P1V1/T1=P2V2/T2 to solve for certain variables.

This graph shows the 4 processes. The isothermal explanation in the picture is not correct though, it should state that there is a gradual inverse change in both Pressure and Volume that prevents a change in temperature.

Our assumption for heating up a rubberband was that it would expand. In reality it shrinks when heated because it is a polymer.

This is our engine composed of a rubber band, ramp and hairdryer. We would move the can to the lift, heat the band, place the can on the next conveyor, cool the band, then repeat.

This picture shows where heat is added and where work is done. Lifting the can and placing the can on the other conveyor are both examples of work. Heat is added when we heat the band to shrink it.

This is the formula for Work and for Efficiency of a heat engine.

This picture shows a cycle that is isobaric on the top and bottom and isochoric on the left and right. We found internal energy at each stage with the formula E = 3/2 * PV. We then subtracted to find the change in internal energy. Net work is zero in this situation because the change in volume is the same, one being positive and one being negative.

This is a more clear picture of the same problem. We also solved for Q in this picture. To solve for Q we put the work and the change in energy together (Q = E+W). Q simply equaled the change in energy when volume was constant.

The above 3 pictures are of an experiment Professor Mason did in which a beaker was submerged first in cold water, left at room temperature, then placed in hot water. This is similar to an engine cycle.

The above picture shows what the graph should have looked like if we could have completed the experiment properly.

The above two pictures show how we found change in energy, Q, and subsequently W from the experiment. All net energies were 0. The white board picture shows our energy calculations in green and black, the mass calculation in blue, and the Q calculations in red.