Thermodynamics Part II and Heat Engines!



Lab Day 5: 3/13/15 Thermodynamic Processes and Heat engines

Purpose: 

The purpose was  to identify the different thermodynamic processes including adiabatic, isothermic, isobaric, and isochoric systems. The main variables of each process were predicted to be constant dependent upon the situation which allowed us to analyze the graph of each system.  The concept of heat engines were presented where the goal is to convert heat energy into work as seen in the efficiency of a mass lifter.

 

Experiments:

The state variables for any thermodynamic system is identified through pressure, volume, temperature, and the moles of gas



We were able to use active physics to do a digital analysis of the interactions of each state variable at work in different systems where a certain variable was held constant.

 

It was identified that in an Isobaric process, there is a constant linear relationship between volume and temperature where pressure is constant. In an isochoric process, the pressure and temperature is changing with constant volume again indicating a constant linear relationship. In isothermic processes, pressure and volume is inversely proportional when temperature is constant.

Heat Engines:
We watched a youtube clip of a simple heat engine where a blow dryer was used to heat a rubber band attached to a hanging weight. As a result, the rubber band moved higher than its original position and the rubber band had shrunk when heated.

The efficiency of a mass lifter was experimented analyzing the mass lifter and a conveyer belt. The system is a cycle where work is used in each part and heat in and heat out is also observed where it goes in a circle and repeats itself allowing for constant movement and work.

This setup is used as a mass lifter of an eraser to observe the heat engine cycle

Graph of mass lifter heat engine: Pressure vs. Volume

Using the ideal gas law and heat we were able to calculate the area of the pV diagram which allowed us to identify the work done in the system.

Conclusion

We identified that each process in thermodynamic system is dependent upon its state variables where when each is constant we can derive different equations that allow for each graph to be representative of the conservation of energy of the first law of thermodynamics. As we looked at the mass lifter heat engine and the rubber band experiment, it is seen that the rubber band is giving heat off to its surroundings and returns to its thermodynamic state. Therefore the work is equal to the heat of hot minus the heat of the cold. As a result when we look at the efficiency of the system we can see that to increase the efficiency, we can lower the ratio between the heat hot over heat cold which will increase the amount of energy produced as a result of the engine cycle.