Know Your Thermodynamic Systems

P M V SubbaraoProfessor

Mechanical Engineering Department

I I T Delhi

A Thorough Understanding of Your System will Make you An Outstanding Innovator…

What is Inside Your System?

• Every Learner is a Blind Person.

First Level of Knowledge about System : Substance & Purity

• Matter: Distinct chemical species.

– single component – pure substance

– two components – binary system

• A pure substance can become a binary system:

– example: water or steam under normal conditions is a single component; but at very high temperatures, H2O dissociates and becomes a two-component system – the components are H and O (binary)

• A binary system can be treated as a single component:

– O2 and N2 in air under normal conditions can be considered as a single component, “air”.

• Multi-component systems: three or more interacting chemical species

Nature of Substance working for Extrasomatic Cause

• Any substance working for Extrasomatic cause is titled as working susbstance in thermodynamics.

• Simple working Substance

• A simple system is one in which the effects of motion, viscosity, fluid shear, capillarity, anisotropic stress, and external force fields donot affect the primitive characteristics.

• Homogeneous Substance:

• A substance that has uniform thermodynamic properties throughout is said to be homogeneous.

• Pure Substance:

• A working substance which has a homogeneous and invariable chemical composition and may exist in more than one phase is titled as Pure Substance.

Superiority of A Thermodynamic Device

• A thermodynamic device can be identified as a superior device, if pure substance works inside this device to satisfy the extrasomatic needs with better efficiency & Eco-affability.

• Better efficiency is achieved when lower quantities of resource is consumed by this device.

• Eco-affability is achieved when lower levels of damage is made to surroundings by this device.

• How to select a right substance as working substance???

New Ideas for Same Desire

• Development of A Display system for A Computer

What fundamental quality of the substance is to be identified to select right candidate as working substance?

Knowledge of Substance for Design of Artificial Heart Valves

Second Level of Knowledge : Phases

• Phase: A phase is state of aggregation.

• A substance in a given phase will have the same physical properties throughout.

• How many different phases can we think of?

– Vapor, Liquid and Solid (many different forms depending on crystal symmetry)

New Phases

• Liquid Crystal

Nematic, Smectic and Cholesteric

• Plasma (electrons separated from nuclei)

• Super fluid (e.g., Liquid He)

• Glass (actually a fluid state)

• A system may have any number of solid phases, any number of liquid phases, but usually only one gas phase.

Is this knowledge Sufficient ???

What More ????

How to do Engineering with this Knowledge????

“ When you can measure what you are speaking about, and express it in numbers,

you know something about it; but when you cannot measure it in numbers, your knowledge

is of a meagre and unsatisfactory kind . . . ”.

•-- Lord Kelvin

Great Benefits through Quantitative Description of Change of Phase

Evaporator/Freezer

Condenser

Compressor

The Methodology of Quantification of Knowledge

• Thermodynamics deals with changes in the system.

• Measures for identifying these changes are necessary.

• This will help in estimating the ability of the system.

• The measures are generally based on some characteristics.

• The numerical values of characteristics will completely describe the system.

Numerical Description of Substance

• The behavior of a system may be numerically described in either a microscopic or a macroscopic point of view.

• Microscopic Description.

Microscopic Description of A System

• A System consists of Substance.

• A collection of Atoms or molecules.

• Each Atom/molecule can be described by its position, velocity, mass….

• Every characteristic of a substance is due to these kinematic properties of atoms/molecules.

• Collective description of atoms/molecules is the description of System.

• Each atom requires three equations for the description of position and three equations for the description of velocity.

• Computationally very intensive.

• Sciences namely, Kinetic Theory and Statistical Thermodynamics use Probability Theory to get a representative numerical description.

• This is a true description of system but impractical.

Quantification of Knowledge thru Microscopic Description

What is the Engineering Sense of this Peculiar Velocity?

• Useful in computing average kinetic energy of atoms in a system.

n

ii

n

iii

m

vm

1

1

2

21

• When atoms/molecules collide they tend on the average, to equalize kinetic energy spreads equally over all atoms.

• Same may happen when molecules of one system collide with molecules of another system.

• This describes a natural tendency of a system to reach equilibrium with surroundings.

• Can we promote this tendency?