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Third Semester Mechanical Engineering

ENGINEERING THERMO DYNAMICS (ME 2202)

1. What do you understand by pure substance?

A pure substance is defned as one that is homogeneous and invariable

in

chemical composition throughout its mass.

2. Defne thermodynamic system.

A thermodynamic system is defned as a quantity o matter or a region

in space,

on hich the analysis o the problem is concentrated.

!. "ame the di#erent types o system.

1. $losed system %only energy transer and no mass transer&

2. 'pen system %(oth energy and mass transer&

!. )solated system %"o mass and energy transer&

*. Defne thermodynamic equilibrium.

) a system is in +echanical, hermal and $hemical -quilibrium then

the system

is in thermodynamically equilibrium. %or&

) the system is isolated rom its surrounding there ill be no change inthe

macroscopic property, then the system is said to eist in a state o

thermodynamic equilibrium.

/. What do you mean by quasi0static process?

-quilibrium state

uasi0static process

)nfnite sloness is the characteristic eature o a quasi0static process.

A quasistatic process is that a succession o equilibrium states. A

quasi0static process is also called as reversible process.

. Defne 3ath unction.

he or4 done by a process does not depend upon the end o the

process. )t

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depends on the path o the system ollos rom state 1 to state 2.

5ence or4 is

called a path unction.

6. Defne point unction.

hermodynamic properties are point unctions. he change in a

thermodynamic

property o a system is a change o state is independent o the path

and depends

only on the initial and fnal states o the system.

7. "ame and eplain the to types o properties.

he to types o properties are intensive property and etensive

property.

Intensive Property: )t is independent o the mass o the system.

E!"p#e:

pressure, temperature, specifc volume, specifc energy, density.

Etensive Property: )t is dependent on the mass o the system.

E!"p#e:

8olume, energy. ) the mass is increased the values o the etensive

propertiesalso increase.

9. -plain homogeneous and heterogeneous system.

he system consist o single phase is called homogeneous system and

the system consist o more than one phase is called heterogeneous

system.

1:. What is a steady ;o process?

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surroundings. here is no mass transer and energy transer. According

to frst

la o thermodynamics as d = d> dW@ d> = d dW@ d = :, dW

= :,

here ore d> = : by integrating the above equation > = constant,

thereore the

internal energy is constant or isolated system.

12. )ndicate the practical application o steady ;o energy equation.

1. urbine, 2. "oBBle, !. $ondenser, *. $ompressor.

1!. Defne system.

)t is defned as the quantity o the matter or a region in space upon

hich e

ocus attention to study its property.

1*. Defne cycle.

)t is defned as a series o state changes such that the fnal state is

identical ith

the initial state.

1/.

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When to systems are separately in thermal equilibrium ith a third

system then

they themselves are in thermal equilibrium ith each other.

2:. What are the limitations o frst la o thermodynamics?

1. According to frst la o thermodynamics heat and or4 are

mutually

convertible during any cycle o a closed system. (ut this la does not

speciy the possible conditions under hich the heat is converted into

or4.

2. According to the frst la o thermodynamics it is impossible to

transer

heat rom loer temperature to higher temperature.

!. )t does not give any inormation regarding change o state or

hether the

process is possible or not.

*. he la does not speciy the direction o heat and or4.

21. What is perpetual motion machine o frst 4ind?

)t is defned as a machine, hich produces or4 energy ithout

consuming anequivalent o energy rom other source. )t is impossible to obtain in

actual

practice, because no machine can produce energy o its on ithout

consuming

any other orm o energy.

22. Defne $lausius statement.

)t is impossible or a sel0acting machine or4ing in a cyclic process, to

transer

heat rom a body at loer temperature to a body at a higher

temperature ithout

the aid o an eternal agency.

2!. What is 3erpetual motion machine o the second 4ind?

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A heat engine, hich converts hole o the heat energy into

mechanical or4 is

4non as 3erpetual motion machine o the second 4ind.

2*. Defne elvin 3lanc4

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he miing o to substances and combustion also leads to

irreversibility. All

spontaneous process is irreversible.

!1. -plain entropy?

)t is an important thermodynamic property o the substance. )t is the

measure o

molecular disorder. )t is denoted by

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he entropy o an isolated system can never decrease. )t alays

increases and

remains constant only hen the process is reversible. his is 4non as

principle

o increase in entropy or entropy principle.

!6. What are the important characteristics o entropy?

1. ) the heat is supplied to the system then the entropy ill increase.

2. ) the heat is reFected to the system then the entropy ill decrease.

!. he entropy is constant or all adiabatic rictionless process.

*. he entropy increases i temperature o heat is loered ithout or4

being done as in throttling process.

/. ) the entropy is maimum, then there is a minimum availability or

conversion in to or4.

. ) the entropy is minimum then there is a maimum availability or

conversion into or4.

!7. What is reversed carnot heat engine? What are the limitations o

carnot cycle?

1. "o riction is considered or moving parts o the engine.

2. here should not be any heat loss.!9. Why Gan4ine cycle is modifed?

he or4 obtained at the end o the epansion is very less. he or4 is

too

inadequate to overcome the riction. hereore the adiabatic epansion

is

terminated at the point beore the end o the epansion in the turbine

and pressure decreases suddenly, hile the volume remains constant.

*:. "ame the various vapour poer cycle.

$arnot cycle and Gan4ine cycle.

*1. Defne eEciency ration.

he ratio o actual cycle eEciency to that o the ideal cycle eEciency is

termed

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as eEciency ratio.

*2. Defne overall eEciency.

)t is the ratio o the mechanical or4 to the energy supplied in the uel.

)t is also

defned as the product o combustion eEciency and the cycle

eEciency.

*!. Defne specifc steam consumption o an ideal Gan4ine cycle.

)t is defned as the mass ;o o steam required per unit poer output.

**. "ame the di#erent components in steam poer plant or4ing on

Gan4ine cycle. (oiler, urbine, $ooling oer or $ondenser and 3ump.

*/. What are the e#ects o condenser pressure on the Gan4ine $ycle?

(y loering the condenser pressure, e can increase the cycle

eEciency. he

main disadvantage is loering the bac4 pressure in rease the etness

o steam.

)sentropic compression o a very et vapour is very diEcult.

*. +ention the improvements made to increase the ideal eEciency o

Gan4ine cycle.

1. Hoering the condenser pressure.2.

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*9. What are the advantages o reheat cycle?

1. )t increases the turbine or4.

2. )t increases the heat supply.

!. )t increases the eEciency o the plant.

*. )t reduces the ear on the blade because o lo moisture content in

H3 state o the turbine.

/:. Defne latent heat o evaporation or -nthalpy o evaporation.

he amount o heat added during heating o ater up to dry steam

rom boiling

point is 4non as Hatent heat o evaporation or enthalpy o

evaporation.

/1. -plain the term super heated steam and super heating.

he dry steam is urther heated its temperature raises, this process is

called as

superheating and the steam obtained is 4non as superheated steam.

/2. -plain heat o super heat or super heat enthalpy.

he heat added to dry steam at 1::o$ to convert it into super heated

steam at the temperature sup is called as heat o superheat or super

heat enthalpy./!. -plain the term critical point, critical temperature and critical

pressure.

)n the 0< diagram the region let o the aterline, the ater eists as

liquid. )n

right o the dry steam line, the ater eists as a super heated steam.

)n beteen

ater and dry steam line the ater eists as a et steam. At a

particular point, the ater is directly converted into dry steam ithout

ormation o et steam. he point is called critical point. he critical

temperature is the temperature above hich a substance cannot eist

as a liquid, the critical temperature o ater is !6*.1/o$. he

corresponding pressure is called critical pressure.

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/*. Defne dryness raction %or& What is the quality o steam?

)t is defned as the ratio o mass o the dry steam to the mass o the

total steam.

//. Defne enthalpy o steam.

)t is the sum o heat added to ater rom reeBing point to saturation

temperature

and the heat absorbed during evaporation.

/. 5o do you determine the state o steam?

) 8Ivg then super heated steam, 8= vg then dry steam and 8J vg then

et steam.

/6. Defne triple point.

he triple point is merely the point o intersection o sublimation and

vapourisation curves.

/7. Defne heat o vapourisation.

he amount o heat required to convert the liquid ater completely

into vapour

under this condition is called the heat o vapourisation.

/9. -plain the terms, Degree o super heat, degree o sub0cooling.

he di#erence beteen the temperature o the superheated vapourand the

saturation temperature at the same pressure. he temperature

beteen the saturation temperature and the temperature in the sub

cooled region o liquid.

:. What is the purpose o reheating?

he purpose o reheating is to increase the dryness raction o the

steam passing

out o the later stages o the turbine.

1. Defne )deal gas.

)t is defned as a gas having no orces o intermolecular attraction.

hese gases

ill ollo the gas las at all ranges o pressures and temperatures.

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2. Defne Geal gas.

)t is defned, as a gas having the orces o attraction beteen

molecules tends to

be very small at reduced pressures and elevated temperatures.

!. What is equation o state?

he relation beteen the independent properties such as pressure,

specifc volume and temperature or a pure substance is 4non as the

equation o state.

*.

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9. -plain DaltonKs la o partial pressure.

he pressure o a miture o gases is equal to the sum o the partial

pressures o

the constituents. he partial pressure o each constituent is that

pressure hich

the gas ould epect i it occupied alone that volume occupied by the

mitures at

the same temperatures. m = mAm(m$LL. = Mmi

mi = mass o the constituent.

3=3A3(3$LL. = M3i, 3i the partial pressure o a constituent.

6:.

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he total pressure eerted in a closed vessel containing a number o

gases is equl to the sum o the pressures o each gas and the volume

o each gas equal to the volume o the vessel.

6/. 5o does the 8ander WaalKs equation di#er rom the ideal gas

equation o state?

he ideal gas equation p8=mG has to important assumptions,

1. here is little or no attraction beteen the molecules o the gas.

2. hat the volume occupied by the molecules themselves is negligibly

small

compared to the volume o the gas. his equation holds good or lo

pressure and high temperature ranges as the intermolecular attraction

and

the volume o the molecules are not o much signifcance.

As the pressure increases, the inter molecular orces o attraction and

repulsion

increases and the volume o the molecules are not negligible. he real

gas deviate considerably rom the ideal gas equation

Op%aP82&Q%80b& = G

6. What is humidifcation and dehumidifcation?he addition o ater vapour into air is humidifcation and the removal

o ater

vapour rom air is dehumidifcation.

66. Di#erentiate absolute humidity and relative humidity.

Absolute humidity is the mass o ater vapour present in one 4g o dry

air.

Gelative humidity is the ratio o the actual mass o ater vapour

present in one 4g o dry air at the given temperature to the maimum

mass o ater vapour it can ith hold at the same temperature.

Absolute humidity is epressed in terms o 4gP4g o dry air. Gelative

humidity is epressed in terms o percentage.

67. What is e#ective temperature?

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he e#ective temperature is a measure o eeling armth or cold to

the human

body in response to the air temperature, moisture content and air

motion. ) the

air at di#erent D( and G5 condition carries the same amount o heat

as the heat carried by the air at temperature and 1::R G5, then the

temperature is

4non as e#ective temperature.

69. Gepresent the olloing psychrometric process using s4eleton

psychrometric

chart? a& $ooling and dehumidifcation, b& -vaporative cooling.

7:. Defne Gelative humidity.

)t is defned as the ratio o partial pressure o ater vapour %p& in a

miture to the

saturation pressure %ps& o pure ater at the same temperature o

miture.

71. Defne specifc humidity.

)t is defned as the ratio o the mass o ater vapour %m s& in a given

volume to themass o dry air in a given volume %ma&.

72. Defne degree o saturation.

)t is the ratio o the actual specifc humidity and the saturated specifc

humidity at

the same temperature o the miture.

7!. What is de point temperature?

he temperature at hich the vapour starts condensing is called de

point

temperature. )t is also equal to the saturation temperature at the

partial pressure o ater vapour in the miture. he de point

temperature is an indication o

specifc humidity.

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7*. What is meant by dry bulb temperature %D(&?

he temperature recorded by the thermometer ith a dry bulb. he dry

bulb

thermometer cannot a#ected by the moisture present in the air. )t is

the measure

o sensible heat o the air.

7/. What is meant by et bulb temperature %W(&?

)t is the temperature recorded by a thermometer hose bulb is

covered ith

cotton ic4 %et& saturated ith ater. he et bulb temperature may

be the

measure o enthalpy o air. W( is the loest temperature recorded by

moistened bulb.

7. Defne de point depression.

)t is the di#erence beteen dry bulb temperature and de point

temperature o air vapour miture.

76. What is meant by adiabatic saturation temperature %or&

thermodynamic et bulb temperature?

)t is the temperature at hich the outlet air can be brought intosaturation state by

passing through the ater in the long insulated duct %adiabatic& by the

evaporation o ater due to latent heat o vapourisation.

77. What is psychrometer?

3sychrometer is an instrument hich measures both dry bulb

temperature and et bulb temperature.

79. What is psychrometric chart?

)t is the graphical plot ith specifc humidity and partial pressure o

ater vapour

in y ais and dry bulb temperature along ais. he specifc volume o

miture,

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et bulb temperature, relative humidity and enthalpy are the

properties appeared

in the psychrometric chart.

9:. Defne sensible heat and latent heat.

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5elmholtB unction is the property o a system and is given by

subtracting the

product o absolute temperature %& and entropy %&.

5elmholtB unction = > &, enthalpy%5&, entropy %