First and Second Law of Thermodynamics Chapter Five First and Second Law of Thermodynamics

First Law of thermodynamics States that: “Energy cannot be created or destroyed BUT it can be changed from one form to another”

Therefore: The first law of thermodynamics is an expression of the conservation of energy principle. Energy can cross the boundaries of a closed system in the form of heat or work.

or

Example: On a hot summer day, a student turns his fan on when he leaves his room in the morning. When he returns in the evening, will the room be warmer or cooler than the neighboring rooms? Why? Assume all the doors and windows are kept closed. Answer: Warmer. Because energy is added to the room air in the form of electrical work.

Watt (J/s)=VI

Type 2 Turbine and Compressors:

The Second Law of Thermodynamics

“processes occur in a certain direction, not in just any direction”. Second Law of Thermodynamics states that: “processes occur in a certain direction, not in just any direction”. Physical processes in nature can proceed toward equilibrium spontaneously: 1. Water flows down a waterfall. 2. Gases expand from a high pressure to a low pressure. 3. Heat flows from a high temperature to a low temperature.

HEAT ENGINES We can convert work to heat directly and completely (rubbing your hand), but converting heat to work requires the use of some special devices. These devices are called heat engines

Characteristics of Heat Engines Heat engines can be characterized by these statements They receive heat from a high-temperature source (solar energy, oil furnace, nuclear reactor, etc.). They convert part of this heat to work (usually in the form of a rotating shaft). They reject the remaining waste heat to a low-temperature sink (the atmosphere, rivers, etc.). They operate on a cycle.

Types of Heat Engines The term heat engine is often used in a broader sense to include work producing devices that do not operate in a thermodynamic cycle. Engines that involve internal combustion such as gas turbines and car engines fall into this category. These devices operate in a mechanical cycle but not in a thermodynamic cycle since the working fluid (the combustion gases) does not undergo a complete cycle. Instead of being cooled to the initial temperature, the exhaust gases are purged and replaced by fresh air-and-fuel mixture at the end of the cycle.

Steam Power Plant

Which one is more efficient or 1 2

1 hp=2545 Btu/h