Heat Processes (Sixth Day)

Spring 2015
12th of March's Class

This is a thermoelectric cooler, it functions as a machine that changes heat energy into electrical energy through the difference in temperature. The bottom part of the apparatus has a metal plating in the shape of the letter 'U'.

Since it is in the shape of 'U', it has two ends to the metal plate. Each side is supposed to be immersed in water of different temperature for the apparatus to work. Using the difference in temperature, it can generate electricity that is subsequently transformed into kinetic energy. This can be seen as the hypnodisk attached at the top of the apparatus started to spin after some time in the water.

The professor then asked us to make a prediction of what will happen if the temperatures were switched. The image that is posted below shows our prediction.

We then found out that it turns out like our prediction. The hypnodisk would spin the other way if the position of hot and cold water is switched.

Professor Mason then brought out a machine that could supply electrical energy. He removed the kinetic portion of the thermoelectric cooler, which is the hypnodisk, and connected that machine to the thermoelectric cooler.

He was trying to demonstrate to us that the process can be done in reverse, that means that with a supply of electrical energy, the thermoelectric cooler could produce heat energy in the form of differing temperature in the metal plate.

Image attached below shows what he is doing.

Pink arrow shows the machine's portion that will be putting in electrical energy into the thermoelectric cooler.

Orange arrow shows the thermoelectric cooler with the hypnodisk removed. This is the location that electrical energy is supplied to the thermoelectric cooler.

Yellow arrow shows the metal plating that will generate heat. One of the ends would get hotter, while the other would get colder.

The professor then gave us real-life examples of how the technology of thermoelectric cooler has been used in the past. It was used as a source of energy for launched satellites. By placing a chunk of Uranium, the heat radiated from Uranium would be converted into electrical energy for the satellite.

However it's use has since been stopped since the amount of Uranium they used to place into the satellite would be equivalent to a small nuclear bomb. If the satellite had exploded while launching, it would have spread radiation over a large radius of area. Hence, its use has been stopped till recently, where they only use small amount of Uranium.

The image above shows the derivation of Cv, specific heat when the Volume would remain constant. This is the case only when the process is isochoric and the gases involved are monoatomic.

After getting the Cv, professor Mason wanted to teach us the way to derive Cp too, the specific heat ratio for when the pressure remains constant.

Using Work and Heat's equations, we describe the change in temperature in respective equations. After that, we equate them to each other, and single out the Cp.

Cp is then equals to [Q/(p delta V)]*R

By the relationships:
U = Q - (p delta V)
U = (3/2) nRT
(p delta V) = nRT

Q is then equals to (5/2) nRT

[Q/(p delta V)]*R then equals [(5/2) nRT] / [nRT] * R

The [nRT] cancels each other out, leaving Cp to equal (5/2)R

Professor Mason then guided us to derivate the Work Done in adiabatic process. The first step is to find an equation that can describe the final pressure of the process. We can do this by using the (PV initial) = (PV final), which will result in p final being described as (PV initial) / (V final).

Then we integrate it  and at the end of the integration, we would obtain the formula that describes Work Done in adiabatic process.

Professor Mason then gave us a sample problem to work on. And the image attached below is how we attempted to solve it, though it was really messy as there were a lot of workings.

Upon completion of the exercise, we were introduced to how the pistons work in an engine. There are 4 steps to completing 1 engine cycle. Intake, Compression, Power and Exhaust.

Intake
The intake valve opens up, and the piston moves down, pulling in the gas and increasing the gas' volume.

Compression
Intake valve closes, and piston is moving up, increasing pressure, decreasing volume.

Power
When the piston is close to the top, a spark plug would ignite the gas causing an explosion as the piston is moving down. As the piston is pushed down by the force of the explosion, the momentum opens up the exhaust valve.

Exhaust
The piston moves upward, pushing the expanded gas out into the exhaust valve.

Below is a short video that depicts how the piston works. (Partly)

Professor Mason then asked us how to increase the power output of an engine, and asked us to make a guess on it. The image below is how we answered his question.