For this entry, I will elaborate more about 2nd Law of Thermodynamics.
In class, Dr taught us about the differences between 1st Law and 2nd Law of Thermodynamics. In 1st Law, I learned that energy cannot be created or destroyed but it can be converted from one form to another form which means that energy can only be conserved. For 2nd Law, it is about energy systems have tendency to increase their enropy rather than than decreasing them. In 2nd Law, quality is more important than quantity. There are 3 engineering systems that implement the 2nd Law of Thermodynamics which are Heat Engines, Heat Pumps, and also Refrigerator.
For Heat Engines, what we want is Work net output and what we need is Q input. By dividing work with Q input, we will get the thermal efficiency of the Heat Engines. Example of system that uses Heat Engine is Power Plant. Besides Heat Engine, I learned about Heat Pumps where it is a reverse process of Heat Engines. So the thermal efficiency of Heat Pumps or the Coefficient of Performance(COP) is Q output divided by Work net input. We must bear in mind that the COP of Heat Pump must be larger than 1. If it is less than unity,then our calculation is totally wrong.
Next is about Refrigerator. The working fluid used in Refrigerator is called Refrigerant. The objective of a Refrigerator is to remove Q heat from the refrigerated space. To calculate the COP of the Refrigerator we must divide QL with Work net input. The value of COP for Refrigerator is also larger than 1.
As a conclusion for this topic, we must deeply understand about the differences between Heat Engines, Heat Pumps, and Refrigerator. If we could not know their differences, it will become a problem for us to answer any questions. I hope I can answer any question given to me during Tests or Examinations.