Thermodynamics 1

Only available on StudyMode
  • Download(s) : 64
  • Published : April 8, 2013
Open Document
Text Preview
ENGINEERING THERMODYNAMICS FOR YEAR I ELECTRICAL

1
INTRODUCTION AND THE FIRST LAW OF THERMODYNAMICS

All living things depend on energy for survival, and modern civilizations will continue to thrive only if existing sources of energy can be developed to meet the growing demands.

Energy exists in many forms, from the energy locked in the atoms of matter itself to the intense radiant energy emitted by the sun.

Many sources of energy exist: many are known, some perhaps unknown; but when an energy source exists, means must first be found to transform the energy into a form convenient to our purpose.

The chemical energy from the combustion of fossil fuels (oil. coal, gas) and waste (agricultural, industrial, domestic) is used to produce heat which is converted to mechanical energy in turbines or reciprocating engines.

Uranium atoms are bombarded asunder and the nuclear energy released is used as heat.

The potential energy of large masses of water is converted into electrical energy as it passes through water turbines on its way from the mountains to the sea.

The kinetic energy of the wind is harnessed by windmills to produce electricity.

The energy of the waves of the sea is converted into electrical power by floating Turbines.

The tides produced by the rotation of the moon produce electrical energy by flowing through turbines in large river estuaries.

Hot rocks and trapped liquids in the depths of the earth are made to release their energy to be converted to electricity.

The immense radiant energy of the sun is tapped to heat water or by suitable device is converted directly into electricity.

Figure 1.1shows the various energy sources and the possible conversion paths with the more important transfers shown as bold.

Macroscopic versus microscopic viewpoint
A microscopic viewpoint is used to attempt to understand a process or system by considering the particle nature of matter. This viewpoint might focus on molecules, atoms or even an electron and nucleus. A complete description would require an enormous effort with suitable approximations. A macroscopic consideration addresses the appropriate observable averages of the microscopic phenomena. For example, the microscopic momentum transfer between gas molecules and a surface is observed on the macroscopic level as gas pressure on the surface. Clearly, the macroscopic viewpoint is of direct consequence to the engineer. Classical thermodynamics is a macroscopic science.

The fundamental statements or laws concern the macroscopic properties of matter. Any atomic or microscopic concept must be exhibited in the macroscopic behavior of the system. This does not imply that a microscopic viewpoint is inappropriate for thermodynamics. A clear understanding of macroscopic phenomena is often possible through microscopic concepts. Yet the overriding goal of engineering thermodynamics is to address macroscopic properties. This course stresses the fundamental concepts from a macroscopic viewpoint. References are made to microscopic behavior where it is helpful to clearly present the material. Applied thermodynamics is the science on the relationship between heat, work, and the properties of systems.

It is concerned with the means necessary to convert heat energy from available sources such as fossil fuels into mechanical work.

A heat engine is the name given to a system which by operating in a cyclic manner produces net work from a supply of heat.

The laws of thermodynamics are natural hypotheses based on observations of the world in which we live.

It is observed that heat and work are two mutually convertible forms of energy and this is the basis of the First Law of Thermodynamics.

It is also observed that heat never flows unaided from an object at a low temperature to one at a high temperature, in the same way that a river never flows unaided uphill.

This observation is the basis of the Second Law of...
tracking img