ARN-310-Unit 1.pdf mechanical meachanical

mechanical

1. J ARN-310
{| | Building Technology: Mechanical

Manish Mishra

Mechanics! &Inausria Engineering Deparment

09-03-2021

syllabus

Credits: 4 Contact Hours: L3 -T1 - PO

Scarce Reference 8 courte
EepecnngThemodjaric: Capel Soles, Tt Mera i

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+ Thermodynamics
Refrigeration

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‘Thermodynamics The science ot
energy.
Energy The abity to cause changes
The name thormodynamicestems ram
e Greek words Here (heat) and
aynamis (ponen.
Conservation of energy principle
During an interaction, energy can change
fom one frm to anober bt the total,
amount of energy remains constant
ergy cannot be created or destayed
‘The first law of thermodynamics. An
expression ofthe conservaton of energy
pnp.
‘Theis aw asserts thet energyis a

thatmodmamie property ias cer

| THERMODYNAMICS AND ENERGY

+ The second law of thermodynamics:

IL asser Wat energy has
well as quantity, and actual

occur n the drecton of decreasing
‘ually of energy

+ Classical thermodynamics: À

macroscopic approach to he study of

‘thermodynamics that does notrequire

‘knowledge ofthe behavior of
\dvidual parle,

+ provides a direct and easy way tothe

solution of ngnoerng problems
thermodynamics À
Ic approach, based onthe
‘erage behavior of large groups of
‘vidual partes,

ent nn

- System. A quantity of matter ra region

‘space chosen fer study.

+ Surroundings. The mass or region

outside tne system

- Boundary The real or imaginary surface

that separates the system fom ts

Surrounaings,

The boundary of a system can be xed or

movable

Systems may be consideredtobe closed
SURROUNDINGS

- Closed system

(Controt mass)

Acad amount

of mass, and no
5 boundary,

BOUNDARY

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+ Open system (control volume) A properly
selected regien in space
usualy encloses a device tat involves
mass ton sor turbine, oF
+ Both mass and energy con cross the
ny ofa control volume.
‘surface The boundaries of a control
icon be realorimagnary

The State Postulate

+ The number of properties
required to fx the state of a
system is given by the state
postulate:

- The state of a simple
compressible system is
completely specified by
two independent, intensive
properties.

‘Simple compressible system:
Ha system involves no
electrical, magnetic,
gravitational, motion, and
surface tension effects.

Nitrogen
T= 25°C
v=09 m4

‘The state of ntrogen is

{xed by two independent,
Intensive properties.

PROCESSES AND CYCLES

Process: Any change that a system undergoes from one equllbrium state
to another

Path The series of states through which a system passes during a
process,

To describo a process competa, one should spect the intial and final
‘sates, as well asthe pat follows and the teractions vt he
Surroundings.

Quasi-stsic or quasi-equilbrium process: When a process proceeds
‘Such a manner thatthe system remains inhntesmaly closet a
Sauru state at allbmes

Empire

Some common popes Pat ne
Slate a process fr ail
Fan propery romans cont
Isothermal process A roces
Isobarte process A process sung)
Isochork {or some) process: A
Ke y remain a
Ieertnalple and isentropic process

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‘cle. Below isa cycle compased of twa processes, À and 8. Alon ss À the
pressure andvelume range em sae | state 2 Tan to complee te cyte. te
Pressure aná volume change am state 2 bac o the nal sate Y ong process à
Keepin ming at al ter Inemasynamıtproparies must as change sa ta

The Steady-Flow Process

Arge number a
fngreenng devices D
Stesdyslou process A
process ug ane a ls
Fins tough conta

as tunes pups

Second Law of Thermodynamics

feat flows from a body a higher
eamperatur toa body at lower
temperature

left in room
Have to expend

temperance

oma point of Water from ‘oi
orpoteatial To getit back to the tank you have to
a lower se a pump ie, you spend energy

‘tent flows from a point of Battery can discharge through

higher potential to lower one a resistance, to get the charge

Yon can mix two gases or liguids. But to separate them yon

have to spend alot of energy
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[ONE way > Srecion and nt

fist and second ans of

armodynamics to pro

MAJOR USES OF THE SECOND LAW

‘The second law may be used to identi the rection of processes.
‘The second law also asserts thet energy has qualtyas well as
quantity

The second law provides the necessary means to determine the
quality as well as the degree of degradation of energy during a
process,

‘The second law of thermodynamics also used to determine the
theoretical its forthe performance of commonly used engineering
Systems, such as heat engines and refigerstors, as well a for
predicting the degree of completion of chemical reactions

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HEAT ENGINES Wichscnpsrewe

‘The devices that convert heat fo work.

1. They receive heat from a high-
temperature source (solar energy, oll
furnace, nuclear reactor, etc)

2. They convert par ofthis heat to work
(usually inthe form of a rotating shaft.)

3. They reject the remaining waste heat to
a lowtemperature sink (he atmosphere,
river, ele)

4. They operate on a cycl

Heat engines and other cyclic devices
usually involve a fluid fo and from which
heat i transferred while undergoing a
cycle. This fui Is called the working,
fluid,

noua of work gut x

The Second Law of Thermodynami
Kelvin-Planck Statement

Planck statement of he
‘The impossity ot having a 100% efficient heat engine isnot due to
ficton or oher dissipative effects tis alimtation that apples to both the
idealized and the actual heat engines

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=

The Second Law of Thermodyna:
Clasius Statement

itis impossible 1o construct a device
that operates in a cycle and produces
no effect other than the transfer of heat
{rom a lower-temperature body to a
higher-temperature body. r
source, such as an cir mato :

net effect onthe surroundings
involves tre consumption of some energy nthe
foxm of work, adétion tothe transfer of heat Ga
trom a colder body to awarmer one
To date, no experiment has been conducte
‘onadicts the second an, anaths should be

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CA. Wan
us

ond iat

aken as sufficient proof of As vahcity E roo e
m use

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REFRIGERATORS AND HEAT PUMP:

Coefficient of Performance

COR COPE + | tor eed values 8 Q 280,

The objective of
eat (2) from th
Desi
CORE = Required
Wen = Qu
o

CARNOT REFRIGERATOR & HEAT PUMP

Any refigerator or heat pump

Per con,
001

CO
1-00

Cart erigeratr or heat pump]
i

D Tru
EN

cor,
cor,

How do you nerese ne COP ota
Comatramgerator or est pump?
en How about tor actual ones?

i ed

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7. 09-03-2021

© Most heat pumps in operation today have a seasonal averaged COP of 2
to3

+ Most existing heat pumps use the col ouside ar asthe heat source in
inter (ar.souros HP).

+ In cold cimstes ther efficiency tops considerably when temperatures are
below the freezing point

+ Air conditioners aro basicaly rfigrators whose reigerated space is a
room era bulidng instead of he food compartment

- The COP ofa refrigerator decreases wit decreasing retigeation
temperature

omicalto refrigerate toa lower temperature nan

Energy efficiency rating (EER): The amount of heat removes
from the cooled space m Bu for 1 Wh (watthour) af electacty

A aie COP,

REFRIGERATORS AND HEAT PUMPS.

a ~The transfer of heat from a ow
ees temperature medum to high
temperature one requires
cial devices called
igerators
Religeratrs he heat engines,
ar cycle devices,

+ The working fhidusedin the
refrigeration cycles called a
refrigerant
The most frequent used
retigeation cycles the vapor.

In a household refrigerator, the freezer compartment where heat is

absorbed by the refigerant serves as the evaporator, and the cols

usually behind the refigerator where heat is dissipated to the kitchen
ir serve as the condenser.

8. ABSORPTION REFRIGERATION SYSTEMS

THE REVERSED CARNOT CYCLE

abe mode fr retrgeraon y esses 29 ond 41
sampression o ugu-vapor mature, unn requees a
‘stil Nand wo phases, and process 4-1 aves me expanion ot
hop moin comet retgeant na ran,

Fans Tun.

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HUMAN COMFORT AND AIR-CONDITIONING [Ef

‘ey, modem airconditioning systems can
eco um, demi, en ana
Conan the sr u
‘The rate of est generation by human body
depends onthe level of he acy. For an
‘average adult mal, is about 87 Wwhen
Sleeping, 115 Wen resting or doing fee
work, and 440 W when doing heavy work

pt work oe wating soy, accua!
arte elected uoay meats asspatea rougn
fsapateg tough convecton ana ragiton 35

In an envronment at 10°C wih 48 kmh
winds feats as cold as an environment at
T°C wth 3 km winds as a resut of the
body-chling effect ofthe air mation the
wind fact)

The com ofthe human woay epenas many on ves factors the (y BU)

temperatura relativo hum, and sr mation

The relative humity acts mé amount ot nesta Dog can despatetnougn

par Mat people prfe a relate Mumia 014019 00%

Air motion removes the warm, moist tt ul up around the body ana replaces
na Ar moon shag be strong enaugh to remove Neat and male
ay one boy but gente enough tobe une

‘tor at act human comfort hettranser raat beeen

{ne Boy andthe suroundng sufaces such ae walls and windows

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Control of
+ Temperature
«> Humidity
Flow
+ Purity

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Thermal Comfort

Skin temperature, tan = 33.7°C
Core temperature, ta = 36.8°C

Comfort conditions: 26°C, 50%RH
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