3.1

## Hanyang University

Skip to 0 minutes and 16 secondsDuring the 3rd and 4th week in thermodynamics in energy engineering, we are going to be looking at the 2nd law of thermodynamics. This week, we are focusing on the traditional interpretation of entropy and the closely related topics such as heat engines, refrigerators and heat pumps. The 1st law of thermodynamics was the energy principle. Now, the 2nd law is the entropy principle. There are various expressions describing the 2nd law. The most historical interpretation is on the efficiency of conversion from heat to work. According to the 2nd law of thermodynamics, we cannot completely convert heat into work and there is always limitation. We cannot get 100 % conversion efficiency. It’s by nature. Energy becomes less usable over time.

Skip to 1 minute and 11 secondsTherefore, while the total amount of energy remains constant by the 1st law, the quality of energy decreases over time by the 2nd law. We are going to be looking at why the 2nd law is the entropy principle, what the entropy is and how the entropy is related to the useful energy. We are going to prove that the total entropy of universe increases or remains constant by solving the entropy changes for reversible and irreversible processes. Then, we are going to talking about the heat engines, refrigerators and heat pumps to demonstrate the relationship between the 2nd law and conversion efficiency from heat to work.

# The week ahead

Welcome to the Third week of the course. We are going to introduce the second law of thermodynamics.

Last week, we overviewed the first law of thermodynamics: the energy principle. Now, the second law is the entropy principle. There are various expression describing the second law. During this week, we focus on the traditional interpretation of entropy and the closely related topics such as heat engines, refrigerators and heat pumps.