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CH1 INTRODUCTION AND BASIC CONCEPTS

BASIC CONCEPTS OF THERMODYNAMICSEXAMPLE 11 Spotting Errors from Unit Inconsistencies

While solving a problem, a person ended up with the following

equation at

some stage:

where E is the total energy and has the unit of kilojoules. Determine

how to

correct the error and discuss what may have caused it.

EXAMPLE 12 Obtaining Formulas from Unit onsi!erations

tank is filled with oil whose density is!"#$ kg%m&. 'f the volume of

the tank is (

) m

&

, determine the amount of mass m in the tank.

EXAMPLE 1" #$e %eig$t of One Poun!&Mass

*sing unity conversion ratios, show that +.$$ lbm weighs +.$$ lbf on

earth -ig. ++&/.

+


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EXAMPLE 1' E(pressing #emperature )ise in *ifferent Units

During a heating process, the temperature of a system rises by

+$01. E2press this rise in temperature in 3, 0-, and 4.

EXAMPLE 1+ Absolute Pressure of a ,acuum $amber

vacuum gage connected to a chamber reads #." psi at a location

where the atmospheric pressure is +5.# psi. Determine the absolute

pressure in the chamber.

EXAMPLE 1- Measuring Pressure .it$ a Manometer

manometer is used to measure the pressure in a tank. 6he fluid

used has a specific gravity of $."#, and the manometer column

height is ## cm, as shown in -ig. +57. 'f the local atmospheric

pressure is 87 k9a, determine the absolute pressure within the tank.

)


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EXAMPLE 1/ Measuring Pressure .it$ a Multiflui!

Manometer

6he water in a tank is pressuried by air, and the pressure is

measured by a multifluid manometer as shown in -ig. +58. 6he

tank is located on a mountain at an altitude of +5$$ m where the

atmospheric pressure is "#.7 k9a. Determine the air pressure in the

tank if h+$.+ m, h)$.) m, and h&$. m. 6ake the densities of

water, oil, and mercury to be +$$$ kg%m&, "#$ kg%m&, and +&,7$$

kg%m&, respectively.

&


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EXAMPLE 10 Measuring Atmosp$eric Pressure .it$ a

arometer

Determine the atmospheric pressure at a location where the

barometric reading is ;5$ mm


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@olar ponds are small artificial lakes of a few meters deep that are

used to store solar energy. 6he rise of heated and thus less dense/

water to the surface is prevented by adding salt at the pond bottom.

'n a typical salt gradient solar pond, the density of water increases

in the gradient one, as shown in -ig. +##, and the density can be

e2pressed as

where r$ is the density on the water surface, is the vertical

distance measured downward from the top of the gradient one, and

< is the thickness of the gradient one. -or


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replotted in -ig. +7+. Determine the air pressure in the tank using

EE@. lso determine what the differential fluid height h&would be for

the same air pressure if the mercury in the last column were

replaced by seawater with a density of +$&$ kg%m&.

1" n office worker claims that a cup of cold coffee on his table

warmed up to "$01 by picking up energy from the surrounding air,

which is at )#01. 's there any truth to his claim? Does this process

violate any thermodynamic laws?

11/ What is the difference between intensive and e2tensive

properties?

124 Define the isothermal, isobaric, and isochoric processes.

1" 1onsider two identical fans, one at sea level and the other on

top of a high mountain, running at identical speeds.


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1'0 1onsider a ;$>kg woman who has a total foot imprint area of

5$$ cm). @he wishes to walk on the snow, but the snow cannot

withstand pressures greater than $.# k9a. Determine the minimum

sie of the snowshoes needed imprint area per shoe/ to enable her

to walk on the snow without sinking.

1+/ gas is contained in a vertical, frictionless pistoncylinder

device. 6he piston has a mass of 5 kg and a cross>sectional area of

cm). compressed spring above the piston e2erts a force of 7$ A

on the piston. 'f the atmospheric pressure is 8# k9a, determine the

pressure inside the cylinder.

1/1E 6he pressure in a natural gas pipeline is measured by the

manometer shown in -ig. 9+;+E with one of the arms open to the

atmosphere where the local atmospheric pressure is +5.) psia.

Determine the absolute pressure in the pipeline.

;


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1/- 1onsider a double>fluid manometer attached to an air pipe

shown in -ig. 9+;7. 'f the specific gravity of one fluid is +&.##,

determine the specific gravity of the other fluid for the indicated

absolute pressure of air. 6ake the atmospheric pressure to be +$$

k9a.

CH3 PROPERTIES OF PURE SUBSTANCES

PROPERTIES OF PURE SUBSTANCES

"


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EXAMPLE 31 Pressure of Saturate L!"u! !# a Ta#$

A rigid tank contains 50 kg of saturated liquid water at 90C. Determine the pressure

in the tank and the volume of the tank.

EXAMPLE 3% Te&'erature of Saturate (a'or !# a C)*!#er

A pistonclinder device contains ! ft"of saturated water vapor at 50#psia pressure.

Determine the temperature and the mass of the vapor inside the clinder.

EXAMPLE 33 (o*u&e a# E#er+) C,a#+e ur!#+ E-a'orat!o#

A mass of !00 g of saturated liquid water is completel vapori$ed at a constant

pressure of %00 k&a. Determine 'a( the volume change and ')( the amount of energ

transferred to the water.

EXAMPLE 3. Pressure a# (o*u&e of a Saturate M!/ture

A rigid tank contains %0 kg of water at 90C. *f + kg of the water is in the liquid form

and the rest is in the vapor form, determine 'a( the pressure in the tank and ')( the

volume of the tank.

EXAMPLE 30 Pro'ert!es of Saturate L!"u!(a'or M!/ture

An +0#- vessel contains kg of refrigerant#%"a at a pressure of %/0 k&a. Determine

'a( the temperature, ')( the qualit, 'c( the enthalp of the refrigerant, and 'd( the

volume occupied ) the vapor phase.

EXAMPLE 3 I#ter#a* E#er+) of Su'er,eate (a'or

Determine the internal energ of water at !0 psia and 00.

8


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EXAMPLE 32 Te&'erature of Su'er,eate (a'or

Determine the temperature of water at a state of &0.5 1&a and h!+90 k23kg.

EXAMPLE 3 A''ro/!&at!#+ Co&'resse L!"u! as Saturate L!"u!

Determine the internal energ of compressed liquid water at +0C and 5 1&a, using

'a( data from the compressed liquid ta)le and ')( saturated liquid data. 4hat is the

error involved in the second case

EXAMPLE 3 A''ro/!&at!#+ Co&'resse L!"u! as Saturate L!"u!

Determine the internal energ of compressed liquid water at +0C and 5 1&a, using

'a( data from the compressed liquid ta)le and ')( saturated liquid data. 4hat is the

error involved in the second case

EXAMPLE 34 T,e Use of Stea& Ta5*es to Deter&!#e Pro'ert!es

Determine the missing properties and the phase descriptions in the following ta)le for

water6

EXAMPLE 316 Mass of A!r !# a Roo&

Determine the mass of the air in a room whose dimensions are m 7 5 m 7/ m at %00

k&a and !5C.

EXAMPLE 311 T,e Use of 7e#era*!8e C,arts

+$


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Determine the specific volume of refrigerant#%"a at % 1&a and 50C, using 'a( the

ideal#gas equation of state and ')( the generali$ed compressi)ilit chart. Compare the

values o)tained to the actual value of 0.0!%89/ m"3kg and determine the error

involved in each case.

EXAMPLE 31% Us!#+ 7e#era*!8e C,arts to Deter&!#e Pressure

Determine the pressure of water vapor at /00 and 0.5%"% ft"3l)m, using 'a( the

steam ta)les, ')( the ideal#gas equation, and 'c( the generali$ed compressi)ilit chart.

EXAMPLE 313 D!ffere#t Met,os of E-a*uat!#+ 7as Pressure

&redict the pressure of nitrogen gas at %85 : and v 0.00"85 m"3kg on the )asis

of 'a( the ideal#gas equation of state, ')( the van der 4aals equation of state, 'c( the

;eattie#;ridgeman equation of state, and 'd( the ;enedict#4e))#


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3.C *s there an difference )etween the intensive properties of saturated vapor at a

given temperature and the vapor of a saturated mi=ture at the same temperature

332 A pistonclinder device contains 0.+5 kg of refrigerant# %"a at ?%0C. he

piston that is free to move has a mass of %! kg and a diameter of !5 cm. he local

atmospheric pressure is ++ k&a. @ow, heat is transferred to refrigerant#%"a until the

temperature is %5C. Determine 'a( the final pressure, ')( the change in the volume of

the clinder, and 'c( the change in the enthalp of the refrigerant#%"a.

30% A rigid vessel contains ! kg of refrigerant#%"a at +00 k&a and %!0C.

Determine the volume of the vessel and the total internal energ.

30. A 0.5#m"

vessel contains %0 kg of refrigerant#%"a at !0C. Determine 'a( the

+)


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pressure, ')( the total internal energ, and 'c( the volume occupied ) the liquid

phase.

3 A pistonclinder device initiall contains steam at ".5 1&a, superheated )

5C. @ow, steam loses heat to the surroundings and the piston moves down hitting a

set of stops at which point the clinder contains saturated liquid water. he cooling

continues until the clinder contains water at !00C. Determine 'a( the initial

temperature, ')( the enthalp change per unit mass of the steam ) the time the piston

first hits the stops, and 'c( the final pressure and the qualit 'if mi=ture(.

342 A %#m"tank contains !.+% kg of steam at 0./ 1&a. Determine the temperature

of the steam, using 'a( the idealgas equation, ')( the van der 4aals equation, and 'c(

the steam ta)les.

CH% ENER7Y9 ENER7Y TRANSFER9 AND 7ENERALENER7Y ANALYSIS

CH. ENER7Y ANALYSIS OF CLOSED SYSTEMS

CH0 MASS AND ENER7Y ANALYSIS OF CONTROL(OLUMES MASS AND ENER7Y ANALYSIS OF CONTROL (OLUMESTHISFIRST LA: OF THERMODYNAMICSEXAMPLE %1 A Car Po;ere 5) Nu


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An average car consumes a)out 5 - of gasoline a da, and the capacit of the fuel tank

of a car is a)out 50 -. herefore, a car needs to )e refueled once ever %0 das. Also,

the densit of gasoline ranges from 0./+ to 0.8+ kg3-, and its lower heating value is

a)out ,000 k23kg 'that is, ,000 : of heat is released when % kg of gasoline is

completel )urned(. Buppose all the pro)lems associated with the radioactivit and

waste disposal of nuclear fuels are resolved, and a car is to )e powered ) #!"5. *f a

new car comes equipped with 0.%#kg of the nuclear fuel #!"5, determine if this car

will ever need refueling under average driving conditions 'ig. !9(.

EXAMPLE %% :!# E#er+)

A site evaluated for a wind farm is o)served to have stead winds at a speed of +.5

m3s 'ig. !%0(. Determine the wind energ 'a( per unit mass, ')( for a mass of %0 kg,

and 'c( for a flow rate of %%5 kg3s for air.

EXAMPLE %3 Bur#!#+ of a Ca#*e !# a# I#su*ate Roo&

A candle is )urning in a well#insulated room. aking the room 'the air plus the candle(

as the sstem, determine 'a( if there is an heat transfer during this )urning process

and ')( if there is an change in the internal energ of the sstem.

EXAMPLE %. Heat!#+ of a Potato !# a# O-e#

A potato initiall at room temperature '!5C( is )eing )aked in an oven that is

+5


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maintained at !00C, as shown in ig. !!%. *s there an heat transfer during this

)aking process

EXAMPLE %0 Heat!#+ of a# O-e# 5) :or$ Tra#sfer

A well#insulated electric oven is )eing heated through its heating element. *f the entire

oven, including the heating element, is taken to )e the sstem, determine whether this

is a heat or work interaction.

EXAMPLE % Heat!#+ of a# O-e# 5) Heat Tra#sfer

Answer the question in =ample !5 if the sstem is taken as onl the air in the oven

without the heating element.

+#


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EXAMPLE %2 Po;er Tra#s&!ss!o# 5) t,e S,aft of a Car

Determine the power transmitted through the shaft of a car when the torque applied is

!00 @ E m and the shaft rotates at a rate of 000 revolutions per minute 'rpm(.

EXAMPLE % Po;er Nees of a Car to C*!&5 a H!**

Consider a %!00#kg car cruising steadil on a level road at 90 km3h. @ow the car

starts clim)ing a hill that is sloped "0 from the hori$ontal 'ig. !"5(. *f the velocit

of the car is to remain constant during clim)ing, determine the additional power that

must )e delivered ) the engine.

+7


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EXAMPLE %4 Po;er Nees of a Car to A


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EXAMPLE %1% Heat!#+ Effe


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+0 4 of electricit 'ig. !50(. he lights in the classroom are kept on for %! hours a

da and !50 das a ear. or a unit electricit cost of 8 cents per k4h, determine

annual energ cost of lighting for this classroom. Also, discuss the effect of lighting

on the heating and air#conditioning requirements of the room.

EXAMPLE %1. Co#ser-at!o# of E#er+) for a# Os

Stee* Ba**

he motion of a steel )all in a hemispherical )owl of radius h shown in ig. !5% is to

)e anal$ed. he )all is initiall held at the highest location at point A, and then it is

released. >)tain relations for the conservation of energ of the )all for the cases of

frictionless and actual motions.

EXAMPLE %10 Cost of Coo$!#+ ;!t, E*e


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he efficienc of cooking appliances affects the internal heat gain from them since an

inefficient appliance consumes a greater amount of energ for the same task, and the

e=cess energ consumed shows up as heat in the living space. he efficienc of open

)urners is determined to )e 8" percent for electric units and "+ percent for gas units

'ig. !58(. Consider a !#k4 electric )urner at a location where the unit costs of

electricit and natural gas are G0.093k4h and G0.553therm, respectivel. Determine

the rate of energ consumption ) the )urner and the unit cost of utili$ed energ for

)oth electric and gas )urners.

EXAMPLE %1 Perfor&a#


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EXAMPLE %12 Cost Sa-!#+s Asso

A /0#hp electric motor 'a motor that delivers /0 hp of shaft power at full load( that

has an efficienc of +9.0 percent is worn out and is to )e replaced ) a 9".! percent

efficient high#efficienc motor 'ig. !/%(. he motor operates "500 hours a ear at

full load. aking the unit cost of electricit to )e G0.0+3k4h, determine the amount of

energ and mone saved as a result of installing the high#efficienc motor instead of

the standard motor. Also, determine the simple pa)ack period if the purchase prices

of the standard and high#efficienc motors are G5!0 and G5%/0, respectivel.

)+


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EXAMPLE %1 Reu

A geothermal power plant in @evada is generating electricit using geothermal water

e=tracted at %+0C, and reinected )ack to the ground at +5C. *t is proposed to utili$e

the reinected )rine for heating the residential and commercial )uildings in the area,

and calculations show that the geothermal heating sstem can save %+ million therms

of natural gas a ear. Determine the amount of @>= and C>! emissions the

geothermal sstem will save a ear. ake the average @>= and C>! emissions of gas

furnaces to )e 0.008 kg3therm and /. kg3therm, respectivel.

EXAMPLE %14 Heat Tra#sfer fro& a Perso#

Consider a person standing in a )ree$ room at !0C. Determine the total rate of heat

transfer from this person if the e=posed surface area and the average outer surface

temperature of the person are %./ m! and !9C, respectivel, and the convection heat

transfer coefficient is / 43m!E C 'ig. !85(.

% A wind tur)ine is rotating at %5 rpm under stead winds flowing through the

tur)ine at a rate of !,000 kg3s. he tip velocit of the tur)ine )lade is measured to )e

!50 km3h. *f %+0 k4 power is produced ) the tur)ine, determine 'a( the average

velocit of the air and ')( the conversion efficienc of the tur)ine. ake the densit of

))


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air to )e %."% kg3m".

EXAMPLE .1 Bou#ar) :or$ for a Co#sta#t=(o*u&e Pro


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EXAMPLE .0 E*e


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Determine 'a( the final temperature and ')( the final pressure of the helium gas.

EXAMPLE .4 Heat!#+ of a 7as 5) a Res!sta#


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correction given ) q. "+.

EXAMPLE .1% Coo*!#+ of a# Iro# B*o


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EXAMPLE .10 Los!#+ :e!+,t 5) S;!t


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.1% A mass of !. kg of air at %50 k&a and %!C is contained in a gas#tight,

frictionless pistonclinder device. he air is now compressed to a final pressure of

/00 k&a. During the process, heat is transferred from the air such that the temperature

inside the clinder remains constant. Calculate the work input during this process.

.% A pistonclinder device initiall contains 0.!5 kg of nitrogen gas at %"0 k&a

and %!0C. he nitrogen is now e=panded isothermall to a pressure of %00 k&a.

Determine the )oundar work done during this process.

.3 An insulated pistonclinder device contains 5 - of saturated liquid water at a

constant pressure of %85 k&a. 4ater is stirred ) a paddle wheel while a current of + A

flows for 5 min through a resistor placed in the water. *f one#half of the liquid is

evaporated during this constantpressure process and the paddle#wheel work amounts

)"


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to 00 k2, determine the voltage of the source. Also, show the process on a v

diagram with respect to saturation lines.

.4 A room is heated ) a )ase)oard resistance heater. 4hen the heat losses from

the room on a winter da amount to /500 k23h, the air temperature in the room

remains constant even though the heater operates continuousl. Determine the power

rating of the heater, in k4.

EXAMPLE 01 :ater F*o; t,rou+, a 7are# Hose No88*e

A garden hose attached with a no$$le is used to fill a %0#gal )ucket. he inner

diameter of the hose is ! cm, and it reduces to 0.+ cm at the no$$le e=it 'ig. 59(. *f it

)8


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takes 50 s to fill the )ucket with water, determine 'a( the volume and mass flow rates

of water through the hose, and ')( the average velocit of water at the no$$le e=it.

EXAMPLE 0% D!s


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min after the stead operating conditions are esta)lished, and the cross#sectional area

of the e=it opening is + mm!. Determine 'a( the mass flow rate of the steam and the

e=it velocit, ')( the total and flow energies of the steam per unit mass, and 'c( the

rate at which energ leaves the cooker ) steam.

EXAMPLE 0. De


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flow rate of the air is 0.0! kg3s, and a heat loss of %/ k23kg occurs during the process.

Assuming the changes in kinetic and potential energies are negligi)le, determine the

necessar power input to the compressor.

EXAMPLE 02 Po;er 7e#erat!o# 5) a Stea& Tur5!#e

he power output of an adia)atic steam tur)ine is 5 14, and the inlet and the e=it

conditions of the steam are as indicated in ig. 5!+.

'a( Compare the magnitudes of h, ke, and pe.

')( Determine the work done per unit mass of the steam flowing through the tur)ine.

'c( Calculate the mass flow rate of the steam.

EXAMPLE 0 E/'a#s!o# of Refr!+era#t=13.a !# a Refr!+erator


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Consider an ordinar shower where hot water at %0 is mi=ed with cold water at

50. *f it is desired that a stead stream of warm water at %%0 )e supplied,

determine the ratio of the mass flow rates of the hot to cold water. Assume the heat

losses from the mi=ing cham)er to )e negligi)le and the mi=ing to take place at a

pressure of !0 psia.

EXAMPLE 016 Coo*!#+ of Refr!+era#t=13.a 5) :ater


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EXAMPLE 013 Coo$!#+ ;!t, a Pressure Coo$er

A pressure cooker is a pot that cooks food much faster than ordinar pots )

maintaining a higher pressure and temperature during cooking. he pressure inside

the pot is controlled ) a pressure regulator 'the petcock( that keeps the pressure at a

constant level ) periodicall allowing some steam to escape, thus preventing an

e=cess pressure )uildup.

&ressure cookers, in general, maintain a gage pressure of ! atm 'or " atm a)solute(

inside. herefore, pressure cookers cook at a temperature of a)out %""C 'or !8%(

instead of %00C 'or !%!(, cutting the cooking time ) as much as 80 percent while

minimi$ing the loss of nutrients. he newer pressure cookers use a spring valve with

several pressure settings rather than a weight on the cover.

A certain pressure cooker has a volume of / - and an operating pressure of 85 k&a

gage. *nitiall, it contains % kg of water. Heat is supplied to the pressure cooker at a

rate of 500 4 for "0 min after the operating pressure is reached. Assuming an

atmospheric pressure of %00 k&a, determine 'a( the temperature at which cooking

takes place and ')( the amount of water left in the pressure cooker at the end of the

process.

&5


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03C Does the amount of mass entering a control volume have to )e equal to the

amount of mass leaving during an unstead#flow process

0 A hair drer is )asicall a duct of constant diameter in which a few laers of

electric resistors are placed. A small fan pulls the air in and forces it through the

resistors where it is heated. *f the densit of air is %.!0 kg3m "at the inlet and %.05

kg3m"at the e=it, determine the percent increase in the velocit of air as it flows

through the drer.

01% A desktop computer is to )e cooled ) a fan whose flow rate is 0." m "3min.

Determine the mass flow rate of air through the fan at an elevation of "00 m where

the air densit is 0.8 kg3m". Also, if the average velocit of air is not to e=ceed %%0

m3min, determine the diameter of the casing of the fan.

012 Consider a "00#- storage tank of a solar water heating sstem initiall filled

with warm water at 5C.

4arm water is withdrawn from the tank through a !#cm diameter hose at an average

velocit of 0.5 m3s while cold water enters the tank at !0C at a rate of 5 -3min.

Determine the amount of water in the tank after a !0#minute period. Assume the

pressure in the tank remains constant at % atm.


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036 Air enters an adia)atic no$$le steadil at "00 k&a, !00C, and "0 m3s and leaves

at %00 k&a and %+0 m3s. he inlet area of the no$$le is +0 cm!. Determine 'a( the

mass flow rate through the no$$le, ')( the e=it temperature of the air, and 'c( the e=it

area of the no$$le.

00. Argon gas enters an adia)atic tur)ine steadil at 900 k&a and 50C with a

velocit of +0 m3s and leaves at %50 k&a with a velocit of %50 m3s. he inlet area of

the tur)ine is /0 cm!. *f the power output of the tur)ine is !50 k4, determine the e=it

&7


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temperature of the argon.

0


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KA1&- /! uel Consumption


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high#temperature source at /5!C and reects heat to a low#temperature sink at "0C.

Determine 'a( the thermal efficienc of this Carnot engine and ')( the amount of heat

reected to the sink per ccle.

KA1&- // A Fuestiona)le Claim for a


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KA1&- /+ 1alfunction of a


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/!% An automo)ile engine consumes fuel at a rate of !+ -3h and delivers /0 k4 of

power to the wheels. *f the fuel has a heating value of ,000 k23kg and a densit of

0.+ g3cm", determine the efficienc of this engine.

/!+ A coal#)urning steam power plant produces a net power of "00 14 with an

overall thermal efficienc of "! percent. he actual gravimetric airfuel ratio in the

furnace is calculated to )e %! kg air3kg fuel. he heating value of the coal is !+,000

k23kg. Determine 'a( the amount of coal consumed during a !#hour period and ')(

the rate of air flowing through the furnace.

/"!C A heat pump is a device that a)sor)s energ from the cold outdoor air and

transfers it to the warmer indoors. *s this a violation of the second law of

thermodnamics =plain.

/8 Determine the C>& of a heat pump that supplies energ to a house at a rate of

+000 k23h for each k4 of electric power it draws. Also, determine the rate of energ

a)sorption from the outdoor air.

/5% A heat pump is used to maintain a house at a constant temperature of !"C. he

house is losing heat to the outside air through the walls and the windows at a rate of

/0,000 k23h while the energ generated within the house from people, lights, and

appliances amounts to 000 k23h. or a C>& of !.5, determine the required power

input to the heat pump.

/55


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section of a household refrigerator at %!0 k&a with a qualit of !0 percent and leaves

at %!0 k&a and ?!0C. *f the compressor consumes 50 4 of power and the C>& the

refrigerator is %.!, determine 'a( the mass flow rate of the refrigerant and ')( the rate

of heat reected to the kitchen air.

/59C 4h are engineers interested in reversi)le processes even though the can

never )e achieved

/8% A Carnot heat engine operates )etween a source at %000 : and a sink at "00 :.

*f the heat engine is supplied with heat at a rate of +00 k23min, determine 'a( the

thermal efficienc and ')( the power output of this heat engine.

/90 A Carnot refrigerator operates in a room in which the temperature is !5C. he

refrigerator consumes 500 4 of power when operating and has a C>& of .5.

Determine 'a( the rate of heat removal from the refrigerated space and ')( the

temperature of the refrigerated space.

/95 A heat pump is used to maintain a house at !!C ) e=tracting heat from the

outside air on a da when the outside air temperature is !C. he house is estimated to

lose heat at a rate of %%0,000 k23h, and the heat pump consumes 5 k4 of electric

power when running. *s this heat pump powerful enough to do the o)

5)


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CH2 E#tro')

E#tro')EXAMPLE 21 E#tro') C,a#+e ur!#+ a# Isot,er&a* Pro


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A pistonclinder device initiall contains " l)m of liquid water at !0 psia and 80.

he water is now heated at constant pressure ) the addition of "50 ;tu of heat.

Determine the entrop change of the water during this process.

EXAMPLE 20 Ise#tro'!< E/'a#s!o# of Stea& !# a Tur5!#e

Bteam enters an adia)atic tur)ine at 5 1&a and 50C and leaves at a pressure of %.

1&a. Determine the work output of the tur)ine per unit mass of steam if the process is

reversi)le.

EXAMPLE 2 T,e T=S D!a+ra& of t,e Car#ot C)


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EXAMPLE 2 E

h3r( and the facilit pas G0.0853k4h for electricit.

EXAMPLE 24 E#tro') C,a#+e of a# Iea* 7as

Air is compressed from an initial state of %00 k&a and %8C to a final state of /00 k&a

and 58C. Determine the entrop change of air during this compression process )

using 'a( propert values from the air ta)le and ')( average specific heats.

EXAMPLE 216 Ise#tro'!< Co&'ress!o# of A!r !# a Car E#+!#e

5#


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Air is compressed in a car engine from !!C and 95 k&a in a reversi)le and adia)atic

manner. *f the compression ratio I%3I! of this engine is +, determine the final

temperature of the air.

EXAMPLE 211 Ise#tro'!< Co&'ress!o# of a# Iea* 7as

Helium gas is compressed ) an adia)atic compressor from an initial state of % psia

and 50 to a final temperature of "!0 in a reversi)le manner. Determine the e=it

pressure of helium.

EXAMPLE 21% Co&'ress!#+ a Su5sta#

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the increase of entrop principle is satisfied.

EXAMPLE 214 E#tro') 7e#erate ;,e# a Hot B*o A MEASURE OF :OR? POTENTIAL

EXER7Y> A MEASURE OF :OR? POTENTIALEXAMPLE 1 Ma/!&u& Po;er 7e#erat!o# 5) a :!# Tur5!#e

A wind tur)ine with a %!#m#diameter rotor, as shown in ig. +/, is to )e installed at a

location where the wind is )lowing steadil at an average velocit of %0 m3s.

Determine the ma=imum power that can )e generated ) the wind tur)ine.

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EXAMPLE % E/er+) Tra#sfer fro& a Fur#a


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EXAMPLE . Irre-ers!5!*!t) ur!#+ t,e Coo*!#+ of a# Iro# B*ofor residential )uildings that have an efficienc of %00 percent 'ig. +%9(. Assuming

an indoor temperature of !%C and outdoor temperature of %0C, determine the

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second#law efficienc of these heaters.

EXAMPLE 2 :or$ Pote#t!a* of Co&'resse A!r !# a Ta#$

A !00 m"rigid tank contains compressed air at % 1&a and "00 :. Determine how

much work can )e o)tained from this air if the environment conditions are %00 k&a

and "00 :.

EXAMPLE E/er+) C,a#+e ur!#+ a Co&'ress!o# Pron a da when the temperature of the outdoors is 0C, the house is maintained

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at !8C. he temperatures of the inner and outer surfaces of the )rick wall are

measured to )e !0C and 5C, respectivel, and the rate of heat transfer through the

wall is %0"5 4. Determine the rate of e=erg destruction in the wall, and the rate of

total e=erg destruction associated with this heat transfer process.

EXAMPLE 11 E/er+) Destru


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EXAMPLE 1 E/er+) Destro)e ur!#+ M!/!#+ of F*u! Strea&s

4ater at !0 psia and 50 enters a mi=ing cham)er at a rate of "00 l)m3min, where it

is mi=ed steadil with steam entering at !0 psia and !0. he mi=ture leaves the

cham)er at !0 psia and %"0 , and heat is )eing lost to the surrounding air at 080

at a rate of %+0 ;tu3min 'ig. +/(. @eglecting the changes in kinetic and

potential energies, determine the reversi)le power and the rate of e=erg destruction

for this process.

EXAMPLE 12 C,ar+!#+ a Co&'resse A!r Stora+e S)ste&

A !00 m"

rigid tank initiall contains atmospheric air at %00 k&a and "00: and is to

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)e used as a storage vessel for compressed air at % 1&a and "00: 'ig. ++(.

Compressed air is to )e supplied ) a compressor that takes in atmospheric air at &0

%00 k&a and 0"00 :. Determine the minimum work requirement for this process.

31 he radiator of a steam heating sstem has a volume of !0 - and is filled with

superheated water vapor at !00 k&a and !00C. At this moment )oth the inlet and the

e=it valves to the radiator are closed. After a while it is o)served that the temperature

of the steam drops to +0C as a result of heat transfer to the room air, which is at

!%C. Assuming the surroundings to )e at 0C, determine 'a( the amount of heat

transfer to the room and ')( the ma=imum amount of heat that can )e supplied to the

room if this heat from the radiator is supplied to a heat engine that is driving a heat

pump. Assume the heat engine operates )etween the radiator and the surroundings.

3 An insulated pistonclinder device contains ! - of saturated liquid water at a

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constant pressure of %50 k&a. An electric resistance heater inside the clinder is turned

on, and electrical work is done on the water in the amount of !!00 k2. Assuming the

surroundings to )e at !5C and %00 k&a, determine 'a( the minimum work with which

this process could )e accomplished and ')( the e=erg destroed during this process.

.4 An ordinar egg can )e appro=imated as a 5.5cm diameter sphere. he egg is

initiall at a uniform temperature of +C and is dropped into )oiling water at 98C.

aking the properties of egg to )e M%0!0 kg3m" and Cp"."! k23kg E C, determine

how much heat is transferred to the egg ) the time the average temperature of the

egg rises to 80C and the amount of e=erg destruction associated with this heat

transfer process. ake 0!5C.

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CH1% THERMODYNAMIC PROPERTY RELATIONS THERMODYNAMIC PROPERTY RELATIONSEXAMPLE 1%1 A''ro/!&at!#+ D!ffere#t!a* @ua#t!t!es 5) D!ffere#

"00 k&a.

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EXAMPLE 1%0 E-a*uat!#+ t,e ,f+ of a Su5sta#

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)ehavior.

1%1. Consider an ideal gas at 00 : and %00 k&a. As a result of some distur)ance,

the conditions of the gas change to 0 : and 9/ k&a. stimate the change in the

specific volume of the gas using 'a( q. %!" and ')( the ideal#gas relation at each

state.

1%10 sing the equation of state &'v a(


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1%..C he pressure of a fluid alwas decreases during an adia)atic throttling

process. *s this also the case for the temperature

1%0.C 4hat is the enthalp departure

1%0C 4h is the generali$ed enthalp departure chart prepared ) using &

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