MEL140

Report
MEL140
Lectures 1 & 2
Course outline
Topic
Number of Lectures
Introduction and basic concepts
2
Energy, energy transfer and
the first law of thermodynamics
2
Properties of pure substances
3
Energy analysis of closed systems
3
Mass and Energy analysis of open systems
5
The second Law of thermodynamics
6
Entropy and the second law
5
Exergy or Available Energy
4
Thermodynamic property relations
4
Air standard cycles
2
Vapor power cycles
4
Refrigeration cycles
2
Total
42
Course outline (contd.)
Textbook:
Cengel, Y.A., and Boles, M.A., Thermodynamics an Engineering Approach, Tata
McGraw-Hill., New York, 7th Edition.
References:
Moran, M.J., and Shapiro, H.N., Fundamentals of Engineering Thermodynamics,
John Wiley, New York, Sixth edition.
P. K. Nag, Engineering Thermodynamics, Tata Mcgraw-Hill, 2005.
Evaluation policy:
Minor 1: 20
Minor 2: 20
Major: 40
Projects and assignments: 20
Attendance Policy:
• 75% and above with or without medical certificate.
• Only IIT Delhi medical certificate can be used for application for Re-minor.
• Audit Criteria: B and above, with same attendance policy.
What is thermodynamics?
• Study of energy transformations and its effects on
matter.
• Although thermodynamics is applicable to any kind of
energy transformation historically, concepts and rules of
thermodynamics evolved from attempts to understand how
energy from “hot” bodies could be harnessed for useful
purposes. Hence, “heat” plays an important role.
• “Effects on matter” how the “condition” of a given
amount of matter changes as energy is transferred into or
out of it is also an important aspect of thermodynamics.
System and surroundings
• System: a region chosen for
thermodynamic analysis
• Surroundings: The part of the
universe other than the
system
• Boundary: The real or
imaginary surface separating
the system from its
surroundings.
Types of system
• Closed system: energy but no mass crosses its boundary.
–
Everyday examples: cup of tea with air-tight lid; pressure-cooker before its
first whistle.
• Open system: mass and energy both cross its boundary.
– Everyday examples: open cup of hot tea; pressure-cooker after its first
whistle; car; hair (blow) dryer; human body (see pic).
heat
Types of system (continued)
• Isolated system: neither energy nor mass
crosses its boundary.
• Everyday example:
a perfect thermos flask
• Conceptual example:
– Universe (system + surroundings)
Nerdy (engineering) examples of open systems
Air being drawn and compressed into a
tank using a motor-plus-compressor set
(mass enters as air through the boundary
shown; electrical energy from the
electricity mains enters the boundary
shown). This system does not operate
“on and on”; once charged a valve at the
entry to the tank (not shown) is closed and
the “compressed air” is reserved for later
use such as pumping bicycle tyres.
Boiler burns fossil fuels to
produce steam for a power
plant. Keep and eye on what
(energy/mass) crosses which
part of the boundary. The boiler
is designed to operate “on and
on”.
Alert: Alternative and confusing
engineering terminology
• The term “control volume” is commonly used
as an alternative terminology for “open system”;
but occasionally for “system”. Here, control
means “kontrol”, which is German for “accounting”;
Tip: forget the English usage of control, please.
• The word system is occasionally used to
imply a closed system.
Pure substance
• A pure substance has the same chemical
composition throughout.
• Are the following pure substances:
–
–
–
–
–
Ice
A mixture of water and water vapor
Air
Oil in contact with water
A gaseous mixture containing N2,O2,H2O, CO2
obtained from burning kerosene
– Liquid air in contact with gaseous air
– Sea Ice in contact with sea water
Alert: in chemistry a pure substance is defined such that it consists of one
component (chemical species) and therefore must be “non-mixture”. We follow a
different definition (see above) in engineering thermodynamics.
Phases
• A region within matter with distinct molecular arrangement that is homogeneous
throughout that region which is separated from other regions (if any) by distinct
boundary surfaces.
• Physical properties (like density and refractive index) of each phase is different;
macroscopically these properties “jump” across certain boundary surfaces known
as “phase boundaries”.
The three principal phases:
Solid
Liquid
Gas
How many phases in?
1.
2.
3.
4.
5.
Ice
A mixture of water and water vapor
Air
Oil in contact with water
A gaseous mixture containing N2,O2,H2O,
CO2 obtained from burning kerosene
6. Liquid air in contact with gaseous air
7. Sea Ice in contact with sea water
Ans. (1) 1, (2) 2 ,(3) 1, (4) 2, (5) 1, (6) 2 (7) 2

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