Concept of heat engine

Heat engine -: Heat engine is a device which converts part of heat into work , and also re-jected some amount of heat to the surroun-ding source and sink .

Source ----- E ------ sink 

(Q1=Qs)       |        ( Q2= Qr)

                  Work

Q1 = Q2 + w 

W = Q1 - Q2  ------ eq. 1

Efficiency = w / Q1 

Eff.  = Q1 - Q2 / Q1

Eff.  = 1 - ( Q2 / Q1 )

Eff.  = 1 - ( Qr / Qs )

* Relationship between coefficient of         heat pump and cop of refrigeration-:

Working between some temperature limits-

Cop ( heat pump)   =  Q1 / ( Q1 - Q2) 

Cop ( refrigeration)   Q2 / ( Q1 - Q2 )

=     Q1        ×    Q1 - Q2  

   Q1- Q2               Q2

Cop ( H.P.)     =  Q1 / Q2

Cop ( R.f.)

Cop ( H.P )  -  Cop ( R.f.) = 1

      Q1      -         Q2      = 1

 Q1- Q2        Q1 - Q2 

Q1  -  Q2     = 1 .

Q1  -  Q1

Thermodynamics defination

Thermodynamics equilibrium -:

A system said to be exist in a state of thermo - dynamics equilibrium, when no change in microscopic properties .

Microscopic properties-:

1. Mechanical -: Equality of force.

2. Physical -: Equilibrium of temperature. 

3. Chemical -: Equilibrium of chemical com - position .

 Pure substance -: A substance is said to be     pure substance, if it is homogeneous chemical composition and homogeneous is chemical .

 Steam         H2 + o2        H2 + o

-----------        -----------        -----------

Water             H2o            water

( pure)        ( not pure )   ( not pure)

Adiabatic process -: A process is said to be adiabatic if there is no heat transfer from the system or to the system. 

Generalise equation for adiabatic process--

 PV^r = c ( r = adiabatic index)

 W = P1.V1 - P2.V2 / r - 1

Polytropic  process-: In adiabatic process there is no hear transfer only work transfer,

But in polytropic process there is heat trans-fer as well as worktransfer. 

Generalise equation for polytropic process--

   PV ^ n = c   ( n = polytropic index ) 

    r = Cp / Cv
   Cp - Cv = R                                                               W ( polytropic ) = P1.V1 - P2.V2/ n-1
   (r > 1 ,   n > 1 ,   r > n ).

Wet region-: It is the region where vapour and liquid exest in equilibrium. 

In this case- T ( actual) = T ( saturated)

Dry ice -: Dry ice , that is called solid co2 , when exposed to 1 atmospheric pressure , it 

Vaporized directly without absorbing latent heat of sublimation.                                                                             The slop of sublimation and vaporization is positive. Also slop of fusion is positive or all the case except water.

Triple point  -:  The triple point is a point   where all three phases co- exist. the triple   point of water is 4.58 mm(p) of Hg and tem-

 Perature is 0.01 ° C or 237.16 K.

Perceptual motion machine -1 and Heat transfer

Perceptual motion machine-1 -: perceptual motion machine, which devo-loped works continuously without absorbing some other form of energy, if sach a machine is develop -  ed it would first law of thermo-dynamics. 

 Q = 0 --- PMM -1 --- w

PMM -1 is impossible. 

dv = m.Cv.dT ,      

dH = m.Cp.dT

Here  U = f ( t )

Heat transfer -: 

Heat transfer in various non - flow process--

1. Constant volume process -:

Heat transfer in a constant volume process for a closed system is equal to change in thermal energy .

dQ = du + P. dv

When , v = Constant,  dv = 0 dw = 0

Then dQ = dv

2.  Constant pressure process-: 

Heat transfer for a constant pressure process is equal to change in Enthalpy. 

dQ = du + P. dv

When , P = Constant 

dQ = du + P ( dv )   , dQ = d ( u + Pv )

dQ = dH

3. Isothermal process-: 

When an ideal gas undergoes isothermal process , heat transfer is equal to work .

dQ = du + P.dv

When , T = Constant  if  u = f ( t ) du = 0

dQ = dw .

Thermodynamics MCQ - 05

Q.1 At very high pressure , an ideal gas as compared to a real gas occupies ______.

A. Same volume 

B. More volume 

C. Less volume 

D. None of these 

Ans-: B

Q.2 Superheated vapour behaves like ___.

A. As steam 

B. Exactly as gas 

C. Water

D. Approximately as a gas

Ans-: D

Q.3 Which law states that , the specific heat of a gas remain constant at all temperature and pressure?

A. Regnault's law

B. Boyle's law 

C. Joules law 

D. Avogadro's law

Ans-: A

Q.4 Thermocouple based on the ____.

A. Temperature of two bodies

B. Atmospheric pressure 

C. See - back effect 

D. Atmospheric temperature 

Ans-: C

Q.5 Air contains following parts of the oxygen. ( on the weight basis )

A. 24 

B. 23

C. 30

D. 73

Ans-: B

Q.6 In thermodynamics cordinates properties of substance like , pressure, temperature and density are ______.

A. Real function 

B. Point function

C. Cyclic function 

D. Thermodynamics function 

Ans-: B

Q.7 which of the following is not a path function?

A. Heat

B. Work 

C. Kinatic energy 

D. Thermal conductivity 

Ans-: D

Q.8 In a cycle heat us rejected at____.

A. Constant pressure 

B. Constant temperature 

C. Constant volume

D. All of the above 

Ans-: A

Q.9  Flow of steam through a nozzle is ___.

A. Constant flow

B. Adiabatic flow

C. Isothermal flow

D. Constant pressure flow

Ans-: B

Q.10 The ratio of number of moles of a gas to total number of moles is known as _____.

A. Ideal gas 

B. Mole fraction 

C. Enthalpy 

D. Molecular ratio

Ans-: B

Q.11 Real gas follows,  PV = nRT ?

A. Yes 

B. No

C. At constant temperature 

D. At constant pressure 

Ans-: No 

Q.12 The region where vapour and liquid exest in equilibrium is called ___.

A. Hot region 

B. Wet region

C. Cold region

D. None of these 

Ans-: B

Q.13 Solid "Co2" is also known as _____.

A. Dry solid 

B. Dry ice 

C. Dry Co2

D. Dry gas 

Ans-: B

Q.14 The triple point is a point , where ___.

A. Two phases co - exist 

B. Three phases co - exist 

C. No phase co - exist 

D. None of these 

Ans -: B

Q.15 Triple point of water is ____.

A. 4.58 mm(p) of Hg

B. 0

C. 45.8 mm (p) of Hg

D. 1 

Ans -: A

Physical meaning of entropy and Enthalpy

Entropy is a measure of molecular dis - oderness or randomness, greater is the disorderness lesser the efficiency.                    " Entropy change of univers "

  ds >or = dQ/ T

  ds (universe) > or = 0 

( universe is a isolated system)

ds ( system) + ds ( surrounding) > or = 0

Entropy of the system can increase or decrease or it can remain constant. Similarly the entropy of surrounding can increase or decrease or it can remain constant but " the overall change in Entropy of univers can never decrease.

Q. What is source and sink?

Ans-: source-: source is a reservoir, which supplies thermal energy without undergoing any temperature change .

Sink -: It is a reservoir which absorb thermal energy without undergoing any temperature change. 

Enthalpy -: In thermodynamics the term " u + Pv " is taken as Enthalpy. 

H = u + Pv

It is an extensive property and generally express in " KJ".

Specific Enthalpy  H/m = h = KJ/Kg

Zeroth law and thermometer

Zeroth law of thermodynamics -:

Zeroth law of thermodynamics is that , when a body "A" is in thermal equilibrium with body "B" and the body "B" is in thermal equilibrium with body "C" , then automatically body "A" will be in thermal equilibrium with body " C".

       The concept of the thermometer  is based on the " zeroth law of thermodynamics "

Thermometer -: Thermometer is a device or a measuring instrument which is used to measure temperature ( how hot or cold some- thing is ).

Types of thermometer--

1. Resistance thermometer 

2. Thermo couple -: It is based on the see - back effect .

3. Constant volume gas thermometer-:

    It is works on the pressure change .

4. Constant pressure gas thermometer-:

    It is works on the change in volume. 

Throttling process

Throttling process -: when steam is pass from a respectable path such as partially opened valve , it's pressure reduces but the entropy of the steam remian constant this prcess is known as throttling process.

                In this process there is no change in Enthalpy from state one to state two , h1 = h2

,no work is done and process is adiabatic ,

 Q= 0.

Concept of entropy

First law of thermodynamics says that energy is constant, it does not give any direction for a particular process. 

           But the second law of thermodynamics gives direction of processe  the concept of entropy hence second law of thermdynamics also known as "directional law " .

Thermodynamics MCQ- 04

Q.1 Real gas follows which relation ?

A. PV= nRT

B. PV×compressbility factor = nRT

C. (PV)^n = RT

D. PV^n = C

Ans-: B

Q.2 1 bar is =_______.

A. 1.0197 kgf/cm^2 or 750.06 mm Hg

B. 735.6 mm Hg

C. 100 mm Hg 

D. 1.033 kgf/cm^2 or 760 mm Hg

Ans-: A

Q.3 According to james law ____.

A. Q = W/J

B. W = Q/J

C.  J = Q/W

D. W = J/Q 

Ans-: D 

Q.4 At constant pressure, when a liquid boils , the following parameter increases?

A. Enthalpy 

B. Entropy 

C. Temperature 

D. Kinetic energy 

Ans-: B

Q.5 For which process work done is zero ?

A. Constant volume 

B. Free expansion 

C. Throttling 

D. All of the above 

Ans-: D

Q.6 No liquid exists as liquid at ____.

A. Zero temperature 

B. Zero pressure 

C. Vacuum 

D. In space 

Ans-: B

Q.7 Temperature of a gas produced due to ____.

A. It's heating value 

B. Kinetic energy of molecules 

C. Surface tension of molecules 

D. Enthalpy 

Ans-: A

Q.8 According to Gay- lussac law, for a perfect gas, the absolute pressure of given mass varies directly as ___.

A. Temperature 

B. Pressure 

C. Absolute temp. , if volume is kept constant

D. All of the above 

Ans-: C

Q.9 The smallest quantity ehich take part in a chemical reaction is known as _.

A. Molecule

B. Atom

C. Carbon

D. None of these

Ans-: A

Q.10 The ratio if brake or actual work done to the indicated work done is called ?

A. Relative efficiency 

B. Mechanical efficiency 

C. Total efficiency 

D. Thermal efficiency 

Ans-: B

Q.11 For complete combustion an axcess quantity of air required in order to permit intimate mixing of fuel with oxygen is known as ___.

A. Excess fuel 

B. Excess air 

C. Oxygen 

D. All of the above 

Ans-: B

Q.12 According to Boyle's law ___.

A. PV = 0

B. PV = Constant 

C. PV = 1

D. PV = 1/2

Ans -: B

Q.13 According to first law of thermodynamics total energy of univers remain _______.

A. Constant 

B. Increases

C. Decreases

D. Zero 

Ans-: A

Q.14 In isolated system __.

A. Matter can not interchange 

B. Energy can not interchange 

C. Matter and energy can interchange 

D. A+B

Ans-: D

Q.15 In open system ___.

A. Energy can interchange 

B. Matter can  interchange 

C. A+B 

D. Energy and matter can not interchange 

Ans-: C

Heat

Heat-: Heat is a form of energy that can be move between two things when one of them is hotter then the other.

         In other words, the amount of thermal energy in a system is also known as heat.

Q. What is sensible heat ?

Ans-: The heat required to raise the temperature of 1kg of liquid from 0°C to the boilling point. Sensible heat is denoted by"h".

                   Sensible heat is related to changes temperature of gas or object with no changes in phase .

Thermodynamics MCQ-03

Q.1 The zeroth law of thermodynamics deals with ______.

A. Conversion of heat and mass

B. Reversibility of a process

C. Introduction of concept of entropy 

D. Transitivity of thermal equilibrium 

Ans-: D

Q.2 Which of the following defined specific fuel consumption?

A. Fuel consumption per hour 

B. Fuel consumption per km

C. Fuel consumption per hr per BPH

D. Fuel consumption per BPH

Ans-: C

Q.3 Combustion of gases fuels deals with _____.

A. Dalton's law

B. Avogadro's hypothesis 

C. Krichhoff's law

D. Boyle's law

Ans-: B

Q.4 A substance above critical temperature exists as_____.

A. Solid

B. Liguid

C. Vapour 

D. Supersaturated fluid

Ans-: D

Q.5 When a vapour condenses into a liquid then ____.

A. It evolves heat

B. It absorbs heat

C. No change in heat

D. Its temperature rises

Ans-: A

Q.6 On which cycle constant pressure gas cycle work ____. 

A. Otto cycle 

B. Brayton cycle

C. Rankine cycle 

D. Dual cycle 

Ans-: B

Q.7 Entropy is defined by which law?

A. Gas law 

B. First law of thermodynamics 

C. Second law of thermodynamics 

D. Zeroth law of thermodynamics 

Ans-: C

Q.8 Water is a______.

A. Substance 

B. Liquid 

C. Compound 

D. mixture 

Ans -: C

Q.9 When the cut off is _______ efficiency of diesel cycle is maximum.

A. Increased

B. Zero

C. Decreased 

D. Maximum 

Ans-: B

Q.10 Total heat of a substance is also known as ____. 

A. Entropy 

B. Calorific value 

C. Enthalpy

D. Specific heat of substance 

Ans-: C

Q.11 Heat is rejected,  In a cycle ____.

A. At constant pressures 

B. At constant volume 

C. At constant temperature 

D. At constant Enthalpy 

Ans-: A

Q.12 In the barometric reading sudden fall is the sign off approaching ____.

A. Cold wave 

B. Rain

C. Strom

D. Fine weather 

Ans-: C

Q.13 Unit of universal gas constant is ___.

A. Nm/kg mole °k

B. Nm/ kg

C. Nm/kg °k 

D. N/m/ °k 

Ans-: A

Q.14 How many value of specific heat solid and liquid have?

A. 1

B. 2

C. 3

D. 5

Ans-: 1

Q.15 In closed system ____.

A. No interchange of matter 

B. Only energy cross the boundaries 

C. Boundary can move or change position 

D. All of these 

Ans-: D 

Thermodynamics MCQ-02

Q.1 A perfect gas follows which law?

A. Joules law

B. Boyle's law

C. Charles law

D. Gay -lussac law

E.  All off the above

Ans-: E

Q.2 S.I. unit of mass is ________.

A. Tonne

B. Gram

C. Kg

D. Newton

Ans-: B

Q.3 which is general gas equation?

A. PV^n = C

B. PV= nRT

C. PV= mRT

D. Cp- Cv = R/J

Ans-: C

Q.4 S.I. unit of pressure ______.

A. Bars 

B. Kg/cm^2

C. Pascal 

D. Mm of water column 

Ans-: C

Q.5 How many law's fully determined behaviour of gases? 

A. 1 law

B. 2 law

C. 5 law

D. 4 law

Ans-: D

Q.6 Ice and water form a mixture of_____.

A. Open system 

B. Closed system 

C. Heterogeneous system 

D. Isolated system 

Ans-: C

Q.7  1 N/m^2 is equal to _____.

A. 5 watt 

B. 3 watt

C. 2 watt

D. 1 watt

Ans-: D

Q.8 The unit of entropy is _____.

A. Nm/kg sec

B. J/°k

C. J/kg °k

D. J/kg

Ans-: C

Q.9 which of the following is not the property of the system?

A. Density

B. Pressure 

C. Heat

D. Temperature 

Ans-: C

Q.10 In kg one calorie us equal to _____.

A.  .0427

B.  4.27

C.  427

D.  42.7

Ans-: A

Q.11 Who developed first law of thermodynamics?

A. Kelvin

B. Joule

C. Carnot 

D. Charles

Ans-: B

Q.12 Charles law is ___. ( P is constant )

A. V=T=Constant

B. V×T×Constant 

C. V/T = Constant

D. None of these

Ans -: C

Q.13 Measurement of temperature is based on ____.

A.  Thermodynamics properties 

B.  Zeroth law of thermodynamics 

C.  First law of thermodynamics 

D.  Joules law 

Ans -: B

Q.14 At  0° C value of entropy taken as___.

A.  1

B. -1

C.  Zero 

D.  2

Ans -: C

Q.15 Thermal power plants work on which cycle?

A. Rankine cycle 

B. Otto cycle 

C. Joules cycle 

D. Carnot cycle 

Ans -: A

Thermodynamics MCQ-01

Q.1 The unit of temperature in S.I. unit _____.

A. Kelvin     

B. Celsius

C. Centigrade 

D. All of the above 

Ans.: A

Q.2 The unit of energy _____.

A. Joule/sec

B. Watt

C. Joule

D. Erg

Ans.: C 

Q.3 Erg is unit of ______.

A. Energy

B. Electric power 

C. Heat

D. Work

Ans.: B

Q.4 How many fundamental units ___.

A. 5

B. 7

C. 6

D. 9

Ans.: B

Q.5 what is the S.I. unit of power?

A. Erg

B. Newton

C. Joule

D. Watt

Ans.: D

Q.6 what is the S.I. unit of time?

A. Hour

B. Minute

C. Second

D. Day

Ans.: C

Q.7 Length is measured in ______.

A. Meter/sec

B. Km/hour

C. Meter 

D. All of the above

Ans.: C

Q.8 Internal energy of a substance depend on _______.

A. Volume 

B. Entropy 

C. Temperature 

D. Pressure 

Ans.: C

Q.9 First law of thermodynamics define ___.

A. Conservation of mass.

B. Conservation of energy.

C. Conservation of heat.

D. None of the above. 

Ans.: B

Q.10 In S.I. unit 1 bar is equal to  ____. 

A. 1 kN/m^2

B. 1×10^5 N/m^2

C. 1×10^4 N/m^2

D. 1×10^6 N/m^2

Ans.: B

Q.11 What is the value of Barometric pressure?

A. 100 mm Hg

B. 1 mm Hg 

C. 735.6 mm Hg

D. 760 mm Hg

Ans.: D

Q.12 In which cycle air refrigerators work? 

A. Otto cycle 

B. Carnot cycle 

C. Reversed joule cycle

D. Diesel cycle

Ans.: C 

Q.13  1 KWH of energy is equal to _____.

A. 3600 joule 

B. 3600 kJ 

C. 100 J

D. 36000 KJ

Ans.: B 

Q.14  which of the following measured in calorie ? 

A. Work

B. Entropy

C. Specific heat

D. Quantity of heat 

Ans.: D

Q.15 What is the unit of universal gas constant? 

A. Watts/°k

B. Erg/°k 

C. Erg cm/° k

D. None of the above 

Ans.: D

Thermodynamic laws

Thermodynamics:

It is deals with relation between work, heat and other form or energy.

It gives many relationships between properties  of matter and efficiencies of various processes.

 

First law of thermodynamics:- 

First law of thermodynamics concern with conservation of energy.

According to law energy can neither be created or nor be destroyed. It can transform only one form to another form .

The total sum of all energy in the universe remain constant. 

Thermodynamics second law :-- 

According to kelvin - plank statement no cyclic process is possible whose result is the flow of heat from a single heat reservoir and the performance of an equivalent amount of work on a work reservoir.

According to second law , In a cyclic device heat abstract continuously from a single reservoir , is totally convert to mechanical work is impossible.