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INTRODUCTION TO THERMODYNAMICS

By hafeedh Apr 16, 2014 1518 Words
FUNDAMENTALs of thermodynamics
(meg 210)
INTRODUCTION TO THERMODYNAMICS

Applied Thermodynamics is the Science of the inter-relationship between Heat, Work and Properties of Systems. It is concerned with the means necessary to convert heat energy from available sources such as chemical fuel or nuclear piles into mechanical work.

Classical Thermodynamics
This is the transformation of work and heat in relation to the properties of matter on macroscopic or bulk basis.

Statistical Thermodynamics
This is a branch of thermodynamics that deals with the microscopic behaviour of matter consequent to the transformation of work and heat.

Scope of Thermodynamics
Thermodynamics does not concern itself with rate process within a given system rather it looks at the gross change in properties of matter as it goes in and out of a system or what happens before and after a system have undergone a process.

DIMENSIONS & UNITS
In Science a type of question often asked is how much? How big? In order to answer such questions it is important to have systems of measurement which are consistent and understood by all.

DIMENSIONS
Dimension is a property that can be measured such as distance, time, mass, temperature, speed, e.t.c

A UNIT
A unit is a basic division of a measure quantity and it enables one to say how much of the quantity we have.

FUNDAMENTAL UNITS
A set of Fundamental Unit is a set of units for physical quantities from which every other unit can be generated. There are seven basic fundamental Units in the field of Science and Engineering. The units are listed below;

DERIVED UNITS
Derived Units are units that are defined by reference to combinations of the Fundamental units.

FUNDAMENTAL UNITS
There are seven basic fundament units in the field of Science and Engineering.:

SYSTEM OF UNITS
A system of unit is a set of Fundamental units defined for the purpose of measuring all necessary physical quantities.

There are two major systems of units

Metric System
British Imperial System

S.I. unit will be used throughout in this course. S.I. unit is The International System of Units. Adopted by the General Conference of weight and measures in 1960 and consequently endorsed by the International Organization for Standardization. It is a Coherent System – In a Coherent System, all derived unit quantities are formed by the product or quotient of other unit quantities. FUNDAMENTAL CONCEPTS

The following Fundamental Thermodynamic Concepts to be considered in this course at this level are:

Systems
Control Volume
Properties and State of a System
Thermodynamic Process
Heat
Work
Pressure
Temperature
Zerothe Law

THERMODYNAMIC SYSTEM

A system may be defined as a region in space containing a quantity of matter whose behaviour is being investigated. This quantity of matter is separated from its surrounding by a boundary which may be a physical boundary e.g. wall of a vessel.

A system may be defined as a collection of matter within a prescribed and identifiable boundary.

The boundaries are not necessarily inflexible while surrounding is restricted to those portion of matter external to the system which are affected by change occurring within the system Classification of Thermodynamic Systems

Thermodynamic systems can be classified into two basic: Closed System and Open System . Closed System

It is one in which there is no mass transfer across the boundaries. e.g Combustion chamber of an Internal combustion engine. It is a system of fixed mass and identity whose boundaries are determined by the space of the matter occupied in it. . Open System

An open system is one in which there is a transfer of mass of the working substance across the boundaries. e.g. In a gas turbine.

CONTROL VOLUME
A control volume is defined as a fixed region in space where one studies the masses and energies crossing the boundaries of the region.

The concept of a control volume is very useful in analyzing fluid flow problems.

Control Volume
1 2
Properties & state of a system

Properties of a System
All the quantities that identify the State of a system are called Properties. It is classified into two general groups; Extensive and Intensive Properties

Extensive Properties
The Properties of the system, whose value for the entire system is equal to the sum of their values for the individual parts of the system are called extensive properties, e.g. total volume, total mass and total energy of a system are its extensive properties. Intensive Properties

The Properties of the system, whose value for the entire system is not equal to the sum of their values for the individual parts of the system are called intensive properties, e.g. temperature, pressure and density State of a System

In all problems in Applied Thermodynamics we are concerned with energy transfers to or from a system. The state of a system (when the system is in thermodynamic equilibrium) is the condition of the system at any particular moment which can be identified by the statement of its properties, such as pressure, volume, temperature e.t.c. The number of properties required to describe the system depends upon the nature of the system.

Path of Change of State
When a system passes through the continuous series of equilibrium states during a change of state (from the initial state to the final state), then it is known as the path of change of State.

Thermodynamic process
When a system changes its state from one equilibrium state to another equilibrium state, then the path of successive state through which the system has passed is known as thermodynamic process.

Thermodynamic or Cyclic Process
When a process or processes are performed on a system in such a way that the final state is identical with the initial state, it is known as a thermodynamic cycle or cyclic process. hEat

Heat is a form of energy which is transferred from one body to another body at a lower temperature , by virtue of the temperature difference between the bodies.

Surroundings
For example when a body A at a certain temperature, say 50°C, is brought into contact with a body B at a high temperature, say 55°C, then there will be a transfer of heat from B to A until the temperature of A are equal.

When the temperature of A is the same as the temperature of B, no heat transfer takes place between the bodies and they are said to be in thermal equilibrium.

Heat is a form of transient energy which can be identified only when it crosses the boundary of a system. It exist only during transfer of energy into and out of a system.

Heat can never be contained in a body or possessed by a body.

The heat flowing into a system is considered as positive and heat flowing out of a system is considered negative

Heat can be transferred in three distinct ways, i.e. conduction, convection and radiation

S.I unit for heat is the Joule.
work
Mechanical work is defined as the product of a force(F) and the distance (l) moved in the direction of the force.

W = F x l

Work done by the system on its surrounding is considered as positive work, while work on the system by its surrounding is considered as negative work.

Work is observed to be energy in transition. It is never contained in a body or possessed by a body.

S.I unit of work is Nm = 1J

CONTROL VOLUME

WORK DONE

Work done by the fluid on the piston is given by;
dW = F x dl
= P x A x dl
where A is the area of the piston
A x dl = dv
dW = Pdv
؞ work done by the expanding fluid is;

Work done under different conditions

A cylinder contains a given mass of gas at an initial state P1 and V1. Calculate the work done through the piston under the following conditions:

The gas expands steadily as a result of the transfer of heat constant at P1 while the final volume is V2;

When P is Constant

ii. The gas in the cylinder is heated in such a manner that P1V1 = P2V2 = PV = Constant. The final Volume is V2.  
When PV is Constant

P1V1 = P2V2 = PV = c
 
P = c/V

Quasi-Static or Quasi-equilibrium Process

When the process is carried out in such a way that at every instant, the system derivation from the thermodynamics equilibrium is infinitesimal, then the process is known as Quasi-Static or Quasi-equilibrium Process and each state in the process may be considered as an equilibrium state.

Quiz(10mins)

(1) State four thermodynamic processes (2) Give four similarities between Heat and Work

Solution
1) Thermodynamic Processes are;

Cyclic Process
Isobaric Process
Isothermal Process
Isochoric Process
Polytropic Process
Isentropic Process
Adiabatic Process
2) Similarities between Heat & work
i) Heat and Work are both transient phenomena. The systems do not possess heat or work.

Heat and Work are boundary phenomena . They are observed at the boundary of the system.

Heat and Work represent the energy crossing the boundary of the system.

Heat and Work are path function and hence they are inexact differentials. They are written as δQ and δW

Things to read-up
Temperature
Pressure

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