Heat Engines and Cycles

Lab Day 6: Heat Engines and Cycles Experiments
Purpose:

The purpose of this lab was to analyze the different types of heat engines including the carnot engine cycle and determine how to maximize the efficiency of the engine based on how the engines work. We will use the pV diagram in order to consider its four main elements in a high efficiency heat engine cycle.

Experiment:

The first demonstration showed a hypno-disc that is attached to a conductor with two sides where one side is placed with a conductor in cold water consisting of ice and water while the other side is placed in heat. The result showed the disc spinning counter -clockwise. When switched, the results showed the disc spinning in the opposite direction. The question that is proposed is: which part would be cooled and which part will be heated?  As a result, the right side was heated and the left side was cooled, which is the thermoelectric effect in which the voltage itself allows one side to be extremely hotter than the other (confirmed through touching the two sides) without the help of the torch.


The predictions were correct and one side was hotter than the
other when the voltage itself was at work using the conductors

 

The red conductor is the cold while the black
conductor is the hot.
One side is definitely hotter than the other.

In this part, we have a heat engine connected to electricity due to a voltage and this is an example where work is done to produce a temperature difference. As the electricity is run through the conductor, there is work done on the the transfer of heat. As a result, one side is cold and one side is left hot. This is interesting because in reverse, we also have heat engines that produces work due to a temperature difference. A refrigerator is a type of heat engine that is ran in a similar fashion to this experiment where the inside is left cold and the outside is warm where we can use work(done by electricity) to create a temperature difference.

The Cv and Cp was derived where we were able to find the ratio of Cp/Cv.



Further calculations and substitutions

Calculations part 2

We then calculated the symbolic derivations of  work done in an adiabatic process. Below shows calculations to identify the work in functions of pressure and volume using gamma.

Calculations part 1

Calculations part 3

Calculations part 4

 

 

We can calculate the thermal efficiency by identifying this as an ideal gas. The internal energy depends on the

The 4 point cycle: Heat engines represent a parallelogram where it returns to its original

 

Next, we looked at a cylinder where there are different points where the cylinder first goes from a minimum to maximum volume where air is absorbed in which we have constant pressure in the intake of air stage. This is representative of a isobaric process. When we reach a high pressure at its maximum, which is sparked by the ignition of air and gas there is evidence of isochoric process where the volume remains constant. At the last point of the cycle, the air is released and therefore we have a cycle that repeats itself after. The idea of air being compressed in this engine show that it is going through an adiabatic process where the heat is constant.

Heat Engines and

How to increase power

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.

Thermodynamics

Lab Day 4: 3/5/15 First Law of Thermodynamics and Gases

Relationships between Work and Gas:

We analyzed the relationship between work and gas where we found that work is the area under the curve of pressure versus volume. There is also internal energy which is caused by heat. We can see based on this graph that there is no work done when the volume is constant. In fact the work done on the system does depend on its path where the initial and final states are not the only variable.

Area under Pressure vs distance and volume curve

Kinetic Energy Model:

Kinetic Model

For the kinetic energy model, we looked at atoms in a software that collides elastically in a two dimensional box. In fact when we saw that as the volume increases, the amount of collision also decreases in which pressure would decrease. We found that the speed of gas particles could be found using the root mean square speed.

Kinetic Energy Model Derivation Part 1

Kinetic energy Model Derivations part 2

Adiabatic Conditions:

Adiabatic Compression of Gas

There is no change in pressure, but there is change in gas and volume.

Fire Syringe Experiment: Rapid Compression of Gas

Fire Syringe Experiment

In order to analyze the rapid compression of air, we used a device called a fire syringe that when compressed rapidly, the cotton on the bottom would ignite due to the compressed air.

Apparatus: Fire syringe with cotton inside compressed air in adiabatic conditions that sparks at high temperatures.

As a result, as we pushed the syringe down quickly, we observed a rapid spark of fire. We took measurements of the initial states of the syringe including the length of  the air column, inner radius, volume, and temperature. The final temperature was calculated to be  351 degrees K which is incredible in temperature difference. The burning temperature of paper is 451 degrees F. There was no heat exchange where it was adiabatic in a plastic cylinder. Therefore, according to the first law of thermodynamics, the change in internal energy is equal to the negative work being done. So as the volume increases, the temperature and pressure decreases. In this case, as the piston is lowered rapidly causing a rapid decrease in volume is seen to have caused an instant increase in temperature.

Uncertainty and Uncertainty Propagation:

We used a digital caliper to measure the length of the syringe and the inner diameter which accounted for an uncertainty of +/- 0.0001 m. The volume was found using the length measured by the same caliper which should have an uncertainty of approximately 0.0005 m. The temperature was measured with an uncertainty of 0.0005 m.
First Law of Thermodynamics:

First Law of Thermodynamics

Relationship of work,heat,internal energy