Entropy(last day of thermal) 3/17/2015

We derive a formula of entropy, and we found that it is the ratio of the heat and temperature. Next, we listed something in our classroom that increasing entropy, but remain a constant thermal energy. They all have a similarity which is they are all experiencing phase change.

As well as regular p-v diagrams, we draw a T-S diagram to describe the relationship between temperature and entropy of adianadic, isothermal, isovolume and isobaric process.

We have introduced a new kind of engine, Stirling engine. The way it works is due to the difference of temperature of the bottom and top, the air inside the engine and does work, which makes the engine works.

In order to compare the efficiency of the Stirling engine and Carnot engine, we calculate a efficiency of one cycle of a Carnot engine. We use the formula: e = 1-Qc/Qh

We are introduced a new concept, coefficient of performance. The best refrigeration cycle is one that removes the greatest amount of heat  from the inside of the refrigerator for the least expenditure of mechanical work,  The relevant ratio is coefficient of performane. The larger this ratio, the better the refrigerator. 

We are doing a regular heat transfer problem of a heat engine. At this point, we just directly applied the formula and pv = nRT, as well as Q = cmT to solve the Qh.

Later, by giving those amounts of data, we directly apply the formula, we are able to solve the efficiency of the heat engine.

At this problem, we are given that the change of entropy is 0 during the process, thus we just directly applied the formula, change of entropy = Intergral ( dQ/T ) = Intergral ( cmdT/T ) = cmln(Tf/Ti) = 0. Then, after pluging the number, we were able to solve the final temperature.

This is a refrigerator problem. The general idea is almost same to solve a heat engine problem. However, there is a key point we need to be  careful which is the heat we get by multiply COP is Qc not Qc.  

This is the last experiment. By making some bubble and ignite them, we observe a great reaction from the bubble. The conclusion we can draw is as entropy increasing, the system gets less stable.