MEL344 Introduction

Department of Mechanical Engineering, Indian Institute of Technology Delhi

MEL 344: Refrigeration and

Air-Conditioning

Amit Gupta

Department of Mechanical Engineering

Indian Institute of Technology Delhi

1st Semester 2013-2014


about the course

• to prepare the students to carry out analysis and design

of refrigeration and air-conditioning systems

• prerequisites: thermodynamics, heat and mass transfer,

fluid mechanics

• office hours: Fri 10 AM - 11 AM (tentative) @ II-255

• course website: web.iitd.ac.in/~agupta under “Courses”

MEL 344_lecture1.ppt


Dr. Amit Gupta

• joined the Department of Mechanical Engineering, IIT Delhi,

as Assistant Professor in May 2011

• B.Tech.: Indian Institute of Technology Delhi (2004)

• M.S.: University of Central Florida (2007)

• Ph.D.: University of Central Florida (2009)

• Post-Doctoral Fellow: University of Michigan, Ann Arbor

(2009-2011)

• Research interests: thermodynamics, microfluidics, Li-ion

batteries, micro-air vehicles


evaluation procedure

• “Celebrations of Learning”

• Two minor exams: 35 points each (35x2=70)

• Major exam: 70 points

• Quizzes (approx. 5)*: 10 points

• Lab Sessions: 50 points

• TOTAL: 200 points

• Audit: > 75% attendance & 60% final score (no

exceptions)

* ALL SCORES WILL BE COUNTED


Ground Rules

• Unacceptable activities during a lecture/lab session?

– Text messaging using mobile phone

– Browsing internet on mobile phone

– Emailing using mobile phone

– Calling through your mobile phone

– All of the above


Ground Rules

• Mobile phones SILENT

• 75 % attendance (lesser means a lower grade)

• No disruptive behavior

• Act professionally

• PLAGIARISM is a serious offense

• Honour Code


The Honour Code

• I will not give or receive aid in examinations; that I will not give

or receive unpermitted aid in class work, in preparation of

reports, or in any other work that is to be used by the

instructor as the basis of grading; and

• I will do my share and take an active part in seeing to it that

others as well as myself uphold the spirit and letter of the

Honour Code


Review of Responsibility

Lectures AG

Readings you

Homeworks you

Labs and reports you

Exams you


Course components

• Refrigeration cycles, refrigerants

• Psychrometry, air-conditioning and load

calculations

• Components-compressors, evaporators,

expansion devices, condensers,

dehumidification coils, ducts, fans

• Alternative systems –absorption, steam-

ejector, air

Multi-cylinder Compressor1

Shell-and-tube condenser1

Automatic expansion valve2

Sources: 1Hundy, Trott and Welch; 2Dossat


reading material

• Reference books/literature:

– Refrigeration and Air-conditioning by W.F. Stoecker

and J.W. Jones, McGraw Hill, 2nd edition

– Heating, Ventilating and Air Conditioning Analysis and

Design by McQuiston, Parker and Spitler, Wiley

– Refrigeration and Air-conditioning by R.C. Arora, PHI

– Principles of refrigeration: R.J. Dossat

– Refrigeration and Air-conditioning: Hundy, Trott and

Welch

– Refrigeration and Air-conditioning: C.P.Arora


reading material

– ASHRAE handbooks

– Automotive Air-Conditioning and Climate Control

Systems by Daly, Butterworth-Heinemann

– Fundamentals of Thermodynamics: Sonntag and van

Wylen

– Applied Thermodynamics for engineering

technologists: T.D. Eastop and A. McConkey

– Fundamentals of Engineering Thermodynamics by

Moran and Shapiro

– Thermodynamics: An Engineering Approach by

Cengel and Boles


Definitions

Refrigeration:

• action of cooling; removal

of heat and discarding it

at a higher temperature

Air-conditioning:

• Treating air to control

simultaneously its

temperature, humidity,

cleanliness, and distribution to

meet the comfort requirements

of the occupants of the

conditioned space

Cooling and dehumidifying operations in air-conditioning

Heating, dehumidifying, control of air quality

Industrial (food preservation), chemical, process industries


Relevance

• According to WB, food-grain stock management in

India needs to improve to tackle inflation

Source: The Hindu

Grain storage and preservation in India

Source: The Deccan Herald


Relevance

• According to BBC, more than 1.3 million tonnes of

food grain - worth millions $ - went rotten in storage

over the past decade in India

• “Grain was damaged in warehouses”

• Amount of food grain could have fed over 10 million

people in a year

• According to MD of FCI

"Our storage conditions are not really the same as in the

West, where it is untouched by hand. "


Relevance

• Increasing cost of energy require innovative

approaches to improve efficiency

• Depletion of the ozone layer by CFCs has

resulted in research on newer and safer

refrigerants

• Newer applications, for instance cooling at the

microscale (microchips) cannot be achieved by

merely scaling existing refrigeration systems


In practice

Interior of a cold storage

facility; warehouse

preservation of fruits,

vegetables and meat at -20°C

Once ice-cream is frozen, it

is rapidly hardened to a

storage temperature of

-25°C, thus requiring very low

refrigerant temperature

Slabs of Ice-cream

cold air

Source: Hundy, Trott and Welch

Source: Hundy, Trott and Welch


In practice

Construction: hardening

of raw materials releases

heat which must be

removed to avoid

expansion and stress in

concrete

Drinking fountains: small

refrigeration units chill

drinking water for use as

needed

Source: Stoecker & Jones


In practice

Operation Theatres:

Key factors to be

controlled-Temperature

and humidity.

Clean rooms:

Very low level of environmental

pollutants like dust, microbes,

aerosol particles etc. are allowed.

Cleanliness measured as particles

of micron size per m3


Other applications

• Domestic refrigeration

• Textile industries

• Computer rooms

• Residential air-conditioning

• Air-conditioning of vehicles

• Food storage and distribution


Fundamentals

• Thermodynamic property: an attribute

that can be evaluated quantitatively;

something that matter ‘has’.

• Work and heat transfer can be

evaluated in terms of change in

properties; ‘things’ that are done to/on

the system

• Equilibrium states.

– 2 thermodynamic properties will define a

state.

– For a mixture (e.g. dry air and water

vapor), 3 properties will be required.

Lord Kelvin, who devised the absolute scale for temperature*

*Source: Hundy, Trott and Welch


Basic laws of thermodynamics

• Zeroth law:

– when two bodies have equality of

temperature with a third body, they

in turn have equality of

temperature with each other

• First law:

– during any cycle a system (control

mass) undergoes, the cyclic

integral of heat is proportional to

the cyclic integral of work

A

CB

WQ for a control mass system


System (Closed and Open)

• System: collection of matter within prescribed and identifiable boundaries.

Fluid in the cylinder of a reciprocating engine: “Closed” system*

Fluid in a turbine at any instant: “Open” system*

*Source: Eastop and McConkey


Work

• Classical definition of work:

– Work is done by a system if the sole effect on the

surroundings could be the raising of a weight

– Path function, i.e. depends on the path that the system

follows

– Work done at a moving boundary

V

P 2

1

b a

Consider quasi-equilibrium compression of air

Air

Work done on the system is given by the area a-1-2-b-a, i.e.,

2

1 2

1

W PdV


Heat

• Classical definition:

– Heat: form of energy that is transferred across the

boundary of a system at a given temperature to

another system (surroundings) at a lower temperature

by virtue of the temperature difference between the

two systems

• Transient phenomenon, i.e. a body never

contains heat

• Path function


First law of thermodynamics (contd.)

• How does it change for a

process?

• Consider two separate cycles:

• Subtract:

2P

V

C

A

1

B

1

2

2

1

1

2

2

1

BABA WWQQ A-B:

1

2

2

1

1

2

2

1

BCBC WWQQ C-B:

2

1

2

1

CA WQWQ



• depends only on the

initial and final states => not a

path function (Point function)

• Given by E:

• Property of the mass

WQ

WQdE

• E=Internal energy + Potential energy + Kinetic

energy, i.e.

KEPEUE

2P

V

C

A

1

B



• Integrating

– 1Q2 : heat transferred to the control mass from state 1

to 2

– 1W2 : work done by the control mass during the

process

• For negligible changes in KE and PE, change in

E can be written as change in U

• u: Internal energy intensive property

211221 WEEQ


First law for a control volume (CV)

• Steady flow with a given mass

flow rate through the CV

• Energy entering = Energy leaving

2

11 1 1 1

2

22 2 2 2

2

2

Cm u z g p v Q

CW m u z g p v

• In most problems (unless specified), changes in KE

and PE are negligible.

• Define a new property, specific enthalpy (h): h u pv

Source: Eastop and McConkey


First law for a control volume (CV)

• steady-state, steady-flow process (SSSF)

• Rearranging,

2 2

1 21 1 2 2

2 2

C Cm h z g Q W m h z g

2 2

1 21 1 2 2

2 2

C Ch z g q w h z g


Availability for the Lab Sessions

Name:

Entry number:

Mon Tues Wed Thurs Fri

9:30 AM – 11:30 AM

2PM - 4PM

3PM - 5PM

4PM - 6PM

MEL344 Introduction

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Transcript of MEL344 Introduction