ENGINEERING THERMODYNAMICS FIRST LAW OF THERMODYNAMICS 1. Defne the term thermodynamics.Thermodynamics is an axiomatic science which deals with the relations among heat, work and properties of system which are in equilibrium. It describes state and changes in state of physical systems.2. What is meant by thermodynamic system? How do you classify it? Thermodynamic system is defned as the any space or matter or group of matter where the energytransfer or energy conversions are studied.It may be classifed into three types.(a)Open system(b)Closed system(c)Isolated system3. What is meant by closed system? Give an example.When a system has only heat and work transfer, but there is no mass transfer, it is called as closedsystem. Example: Piston and cylinder arrangement.4. Defne a open system, Give an example.When a system has both mass and energy transfer it is called as open system.Example: Air Compressor.5. Diferentiate closed and open system. Closed System Open System1. There is no mass transfer.Only heat and work willtransfer.1. Mass transfer will take place, in additionto the heat and work transfer.2. System boundary is fxed one 2. System boundary may or may not change.3. Ex: Piston & cylinder arrangement, Thermal powerplant3. Air compressor, boiler6. Defne an isolated systemIsolated system is not afected by surroundings.There is no heat, work and mass transfer take place.In this system total energy remains constant.Example: Entire Universe7. Defne: Specifc heat capacity at constant pressure. It is defned as the amount of heat energy required to raise or lower the temperature of unit mass ofthe substance through one degree when the pressure kept constant. It is denoted by Cp.8. Defne: Specifc heat capacity at constant volume.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $ENGINEERING THERMODYNAMICS It is defned as the amount of heat energy required to raise or lower the temperature of unit mass ofthe substance through one degree when volume kept constant.9. What is meant by surroundings?Any other matter out side the system boundary is called as surroundings.10. What is boundary?System and surroundings are separated by an imaginary line is called boundary.11. What is meant by thermodynamic property? Thermodynamic property is any characteristic of a substance which is used to identify the state of thesystem and can be measured, when the system remains in an equilibrium state.12. How do you classify the property?Thermodynamic property can be classifed into two types. Intensive or Intrinsic and Extensive and Extrinsic property.13. Defne Intensive and Extensive properties. The properties which are independent on the mass of the system is called intensive properties.e.g., Pressure, Temperature, Specifc Volume etc.,The propertieswhich are dependent on the mass of the system is called extensive properties.e.g., Total energy, Total volume, weight etc.14. Diferentiate Intensive and Extensive properties .Intensive Properties Extensive Properties1. Independent on the mass of thesystemDependent on the mass of the system.2. If we consider part of the system theseproperties remain same.e.g. pressure, Temperature specifcvolume etc.,If we consider part of the system it willhave a lesser value. e.g., Total energy, Total volume, weightetc.,3. Extensive property/mass is known asintensive property --15. What do you understand by equilibrium of a system?When a system remains in equilibrium state, it should not undergo any changes to itsown accord.16. What is meant by thermodynamic equilibrium? When a system is in thermodynamic equilibrium, it should satisfy the following three conditions.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e %ENGINEERING THERMODYNAMICS (a)Mechanical Equilibrium :- Pressure remains constant(b)Thermal equilibrium :- Temperature remains constant(c)Chemical equilibrium : There is no chemical reaction.17. State the First law of thermodynamics applied to a cycle .First of thermodynamics states that when system undergoes a cyclic process the net heat transfer isequal to work transfer.18. Defne: PMM of frst kindPMM of frst kind delivers work continuously without any input.It violates frst law ofthermodynamics, It is impossible to construct an engine working with this principle.19. Defne the term process It is defned as the change of state undergone by a fuid due to energy fow.20. Defne the term Cycle:When a system undergoes a series of processes and return to its initial condition, it is known as cycle.21. What is meant by open and closed cycle.In a closed cycle, the same working substance will recirculate again and again.In a open cycle, thesame working substance will be exhausted to the surroundings after expansion.22. What is meant by reversible and irreversible process?A process is said to be reversible, it should trace the same path in the reverse direction when theprocess is reversed.It is possible only when the system passes through a continuous series ofequilibrium state.If a system does not pass through continuous equilibrium state, then the process is said to beirreversible.23. What is meant by Point and Path function? The quantities which is independent on the process or path followed by the system is known as pointfunctions.Example: Pressure, volume, temperature, etc.,The quantities which are dependent on the process or path followed by the system is known as pathfunctions.Example: Heat transfer, work transfer.24. What is Quasi Static process? The process is said to be quasi static, it should proceed infnitesimally slow and follows continuousseries of equilibrium states.Therefore, the quasi static, it should proceed infnitesimally slow andCompiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e &ENGINEERING THERMODYNAMICS follows continuous series of equilibrium states.Therefore, the quasi static process may be anreversible process.25. Explain Zeroth Law of thermodynamics?Zeroth law of thermodynamics states that when two systems are separately in thermal equilibriumwith a third system, then they themselves are in thermal equilibrium with each other.26. Defne the term enthalpy? Ans: The Combination of internal energy and fow energy is known as enthalpy of the system.It mayalso be defned as the total heat of the substance.Mathematically, enthalpy (H) = U + PVWhere, U internal energyP pressureV volumeIn terms of Cp & T H = mCp (T2-T1)KJ27. Defne the term internal energy Internal energy of a gas is the energy stored in a gas due to its molecular interactions.It is also defnedas the energy possessed by a gas at a given temperature.28. What is meant by thermodynamic work?Work is a transient quantity which only appears at the boundary while a change of state is taking place within a system. Work is something which appears at the boundary when a system changes its state due to the movement of a part of the boundary under the action of a force.29. Defne Heat.Heat is the energy crossing the boundary due to the temperature diference between the system andsurroundings.30. Give the general gas energy equations. dH = dE + dW.31. State the law of conservation of energy Energy can neither be created nor destroyed, but it can be transferred from one form to another.32. Defne entropy of a pure substance. Entropy is an important thermodynamic property, which increases with addition of heat and decreaseswith its removal.Entropy is a function of temperature only.It is an unavailability of energy duringenergy transfer.33. Defne an isentropic process. Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e 'ENGINEERING THERMODYNAMICS Isentropic process is also called as reversible adiabatic process.It is a process which follows the law ofpV = C is known as isentropic process.During this process entropy remains constant and no heatenters or leaves the gas.34. Explain the throttling process.Throttling process involves the passage of a higher pressure fuid through a narrow constriction. Theefect is the reduction in pressure and increase in volume. This process is adiabatic as no heat fowsfrom and to the system, but it is not reversible. It is not an isentropic process. The entropy of the fuidactually increases35. What is the work done in a free expansion process ? Zero36. Defne free expansion process.When a gas expands suddenly into a vacuum through a large orifce is known as free expansionprocess.37. Which property is constant during throttling? Enthalpy38. If in the equation PVn = C, the value of n =INFINITYthen the process is called _______ Constant Volume process 39. The polytropic index (n) is given by ________ n = log (P2/P1)/ log (V1/V2)40. Work transfer is equal to heat transfer in case of ________ process.Isothermal process.41. Write down the characteristic gas equation.Characteristic gas equation is pV = mRTWhere,p = pressureV = VolumeR = Characteristic gas constantT = Temperature.42. What is meant by steady fow process? If the rate of fow of mass and energy across the boundary remains constant during a process , itisknown as steady fow process.43. What is the diference between steady fow and non fow process?Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e (ENGINEERING THERMODYNAMICS During the steady fow process the rate of fow of mass and energy across the boundary remainsconstant.A process may be non-fow in which a fxed mass within the defned boundary is undergoing a change of state. Example : A substance which is being heated in a closed cylinder undergoes a non-fow process44.What is meant by Perpetual motion Machine of frst kind?PMM of the frst kind delivers work continuously without any input. It violates frst law ofthermodynamics. It is impossible to construct an engine working with this principle.45.Defne the term process.It is defned as the change of state undergone by a gas due to energy fow.46.Defne the term cycle.When a system undergoes a series of processes and return to its original condition, It is known ascycle.47.What is Quasi-static process?If the process is said to be quasi-static, It should proceed infnitesimally show and follow continuousseries of equilibrium states. Therefore, the quasi-static process may be a reversible process.48.Defne the term internal energy.Internal energy of the gas is the energy stored in a gas due to its molecular interactions. 49.Defne the term enthalpy.The combination of internal energy and fow energy is known as enthalpy of the system50.Defne zeroth law and frst law of thermodynamics?Zeroth law of thermodynamics states that when two systems are separately in thermal equilibriumwith a third system, then they themselves are in thermal equilibrium with each other.First law of thermodynamics states that when system undergoes a cyclic process, net heat transfer isequal to work transfer. 51.Prove that for an isolated system, there is no change in internal energy.For any isolated system, there is no heat, work and mass transfer. Q=W=0According to frst law of thermodynamics,Q=W+U U=0 Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e )ENGINEERING THERMODYNAMICS 52.What is an adiabatic system ?An adiabatic system is one which is thermally insulated from its surroundings. It can,however, exchange work with its surroundings. If it does not, it becomes an isolated system.53.Distinguish classical (macroscopic ) and statistical (microscopic ) thermodynamics .In this approach a certain quantity of matter is considered without taking into account the eventsoccurring at molecular level. In other words this approach to thermodynamics is concerned with grossor overall behaviour. This is known as classical thermodynamics.The approach considers that the system is made up of a very large number of discrete particlesknown as molecules. These molecules have diferent velocities and energies. The values of theseenergies are constantly changing with time. This approach to thermodynamics which is concerneddirectly with the structure of the matter is known as statistical thermodynamics54.Defne Irreversible process and give examples . The process is said to be an irreversible process if it cannot return the system and the surroundings totheir original conditions when the process is reversed. The irreversible process is not at equilibrium throughout the process. An irreversible process is usually represented by a dotted (or discontinuous) line joining the end states to indicate that the intermediate states are indeterminate .Examples.(i) Relative motion with friction (ii) Combustion(iii) Difusion (iv) Free expansion(v) Throttling (vi)Electricity fow through a resistance(vii) Heat transfer (viii) Plastic deformation.55.Discuss external and internal irreversibilities with examples.External irreversibilities. These are associated with dissipating efects outside the working fuid.Example. Mechanical friction occurring during a process due to some external source.Internal irreversibilities. These are associated with dissipating efects within the working fuid.Example. Unrestricted expansion of gas, viscosity and inertia of the gas.56. Prove that for an isolated system, there is no change in internal energy.For any isolated system, there is no heat, work and mass transfer.Q=W=0According to the frst law of thermodynamics.Q=W+U U=0 Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e *ENGINEERING THERMODYNAMICS SECOND LAW OF THERMODYNAMICS 1.State the Kelvin Plank statement of second law of thermodynamics.Kelvin Plank states that it is impossible to construct a heat engine working on cyclic process,whose only purpose is to convert all the heat energy given to it into an equal amount of work.2.State Clausius statement of second law of thermodynamics.It states that heat can fow from hot body to cold without any external aid but heat cannot fowfrom cold body to hot body without any external aid.3.State Carnots theorem.No heat engine operating in a cyclic process between two fxed temperature, can be moreefcient than a reversible engine operating between the same temperature limits.4.What are the Corollaries of Carnot theorem.a.In all the reversible engine operating between the two given thermal reservoirs withfxed temperature, have the same efciency.b.The efciency of any reversible heat engine operating between two reservoirs isindependent of the nature of the working fuid and depends only on the temperature ofthe reservoirs.5.Defne PMM of second kind.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e +ENGINEERING THERMODYNAMICS Perpetual motion machine of second kind draws heat continuously from single reservoir andconverts it into equivalent amount of work.Thus it gives 100% efciency.6.What is the diference between a heat pump and a refrigerator? Heat pumpis a device which operating in cyclic process, maintains the temperature of a hotbody at a temperature higher than the temperature of surroundings.A refrigerator is a device which operating in a cyclic process, maintains the temperature of acold body at a temperature lower than the temperature of the surroundings.7.What is meant by heat engine?A heat engine is a device which is used to convert the thermal energy into mechanical energy.8.Defne the term COP?Co-efcient of performance is defned as the ratio of heat extracted or rejected to work input.a.COP Heat extractedrejectedWorkinputb.9.Write the expression for COP of a heat pump and a refrigerator?e Temperatur Sink- e Temperatur Sourcee Temperatur Sourcepump Heatof = COPe Temperatur Sink- e Temperatur Sourcee Temperatur SourceorRefrigerat of = COP10.What is the relation between COPHP and COP ref?COPHP = COPref +111.Why Carnot cycle cannot be realized in practical?a.In a Carnot cycle all the four process are reversible but in actual practice there is noprocess is reversible.b.There are two processes to be carried out during compression and expansion.Forisothermal process the piston moves very slowly and for adiabatic process the pistonmoves as fast as possible.This speed variation during the same stroke of the piston isnot possible.c.It is not possible to avoid friction moving parts completely.12.Name two alternative methods by which the efciency of a Carnot cycle can beincreased.a.Efciency can be increased as the source temperature increases.b.Efciency can be increased as the sinktemperature decreases.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e ,ENGINEERING THERMODYNAMICS 13.Why a heat engine cannot have 100% efciency?For all the heat engines there will be a heat loss between system and surroundings.Therefore wecant convert all the heat input into useful work.14.When will be the Carnot cycle efciency is maximum?Carnot cycle efciency is maximum when the initial temperature is 0K.15.What are the processes involved in Carnot cycle.Carnot cycle consist of Reversible isothermal compression isentropic compression reversible isothermal expansion isentropic expansion16.State carnot theorem?No heat engine operating in a cyclic process between two-fxed temperatures can be moreefcient that a reversible engine operating between the same temperature limits.17.Defne PMM of second kind?Perpetual motion machine of second kind draws heat continuously from single reservoir andconverts it into equivalent amount of work, Thus it gives 100 percentage efciency.18.What is meant by heat engine?A heat engine is a device, which is used to convert the thermal energy into mechanical energy.19.Defne the term absolute entropy?The change in entropy of the system with respect to ambient conditions or any other standardreference condition is known as absolute entropy.20.Defne Entropy .Entropy may also be defned as the thermal property of a substance which remains constant when substance is expanded or compressed adiabatically in a cylinder.21.Defne the terms source, sink, and heat reservoir.Source:The part where the heat to be rejected to work absorbing or work developing device iscalled source.Sink:The part which receives heat from work absorbing or work developing device is called sink.Reservoir:The part which supplies or receives heat continuously without change in itstemperature is called as reservoir.22.Defne entropy according to statistical thermodynamics?Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $-ENGINEERING THERMODYNAMICS In statistical thermodynamics, entropy is associated with the notion of disorder and the secondlaw statement that the entropy of an isolated system undergoing a spontaneous process tendsto increase is equivalent to saying that the disorder of the isolated system tends to increase.Entropy is an index of unavailability or degradation of energy.23.Is the second law is independent of frst law? Explain.Yes. The second law is independent of frst law. The second law speaks about the quality ofenergy.24.Defne change of entropy. How is entropy compared with heat transfer and absolutetemperature?The measure of irreversibility when the energy transfer takes place within the system orbetween the system and surrounding is called as change of entropy. It is simply known asunaccounted heat loss.25.Statecorollaries of carnot theorem? The thermal efciency of an irreversible power cycle is always less than the thermalefciency of a reversible power cycle when each operates between the same two thermalreservoirs. All reversible power cycles operating between the same two thermal reservoirs have thesame thermal efciency.26.Can entropy of universe ever decrease ? why?Entropy of universe cannot ever decrease. It will be remain constant or will decrease due toirreversibility.27.What is the essence of the second law of thermodynamics? To know the feasibility of process. To know about the quality of energy.28.Why the performances of refrigerator and heat pump are given in terms of C.O.P andnot in terms of efciency?The performance of any device is expressed in terms of efciency for work developing machines.But heat pump and refrigerator are work absorbing machines. So, the performance of thosedevices based on C.O.P only.29.Commenton the statement The entropy of universe tends to be maximum?If the entropy of universe tends to be maximum, the irreversibility will be more due to frictionbetween moving parts.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $$ENGINEERING THERMODYNAMICS 30.For compression process between same states, which will consume more workreversible or irreversible.Irreversible work will be more in the compression process. Generally for compression, the actualwork given will be higher than the calculated work.31.What are the assumptions made in working of Carnot Engine ?The assumptions made for describing the working of the Carnot engine are as follows : The piston moving in a cylinder does not develop any friction during motion. The walls of piston and cylinder are considered as perfect insulators of heat. The cylinder head is so arranged that it can be a perfect heat conductor or perfect heatinsulator. The transfer of heat does not afect the temperature of source or sink. Working medium is a perfect gas and has constant specifc heat. Compression and expansion are reversible.32.What are the conditions to be satisfed for areversible process ? A reversible process should fulfll the following conditions : The process should not involve friction of any kind. Heat transfer should not take place with fnite temperature diference. The energy transfer as heat and work during the forward process should be identically equal toenergy transfer as heat and work during the reversal of the process. There should be no free or unrestricted expansion. There should be no mixing of the fuids. The process must proceed in a series of equilibrium states.33.Why reversible processes are preferred ?Reversible processes are preferred because the devices which produce work such as engines andturbines, reversible process of the working fuid delivers more work than the correspondingrreversible processes. Also in case of fans, compressors, refrigerators and pumps less power input isrequired when reversible processes are used in place of corresponding irreversible ones34.Write the equation forClausius inequalityClausius inequality is given by,When a system performs a reversible cycle, thenbut when the cycle is not reversibleCompiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $%ENGINEERING THERMODYNAMICS 35.What are the various causes of irreversibility ? Heat transfer through a fnite temperature diference Unrestrained expansion of a gas or liquid to a lower pressure Spontaneous chemical reaction Spontaneous mixing of matter at diferent compositions or states Frictionsliding friction as well as friction in the fow of fuids Electric current fow through a resistance Magnetization or polarization with hysteresis Inelastic deformation36.What are internal and external irreversibilities ?Internal irreversibilities are those that occur within the system.External irreversibilities are those that occur within the surroundings, often the immediatesurroundings.37.Defne an internally reversible process .An internally reversible process is one in which there are no irreversibilities within the system.38. State Clausius inequality The Clausius inequality states that for any thermodynamic cyclewhere Q represents the heat transfer at a part of the system boundary during a portion of thecycle, and T is the absolute temperature at that part of the boundary. The subscript b servesas a reminder that the integrand is evaluated at the boundary of the system executing thecycle. The integral symbolindicates that the integral is to be performed over all parts of theboundary and over the entire cycle.39. State Third law of thermodynamics.The third law of thermodynamics states When a system is at zero absolute temperature,the entropy of system is zero.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $&ENGINEERING THERMODYNAMICS 40.What is available energy ?Available energy is the maximum portion of energy which could be converted into useful work byideal processes which reduce the system to a dead state (a state in equilibrium with the earth andits atmosphere).Or The available energy (A.E.) or the available part of the energy supplied is the maximum workoutput obtainable from a certain heat input in a cyclic heat engine .41.What is unavailable energy ?The theoretical maximum amount of work which can be obtained from a system at any state p1 andT1 when operating with a reservoir at the constant pressure and temperature p0 and T0 is calledavailabilityOrThe minimum energy that has to be rejected to the sink by the second law is called theunavailable energy (U.E.), or the unavailable part of the energy supplied.42.Defne irreversibility. The actual work which a system does is always less than the idealized reversible work, and thediference between the two is called the irreversibility of the process.PROPERTIES OF PURE SUBSTANCE1.Defne latent heat of ice?Total amount of heat added during conversion of ice of zero degree Celsius into water of zerodegree Celsius.2.Defne Sensible heat of water .It is defned as the quantity of heat absorbed by 1 kg of water when it is heated from 0C(freezing point) to boiling point. It is also called total heat (or enthalpy) of water or liquid heatinvariably. 3.DefneLatent heat or hidden heat of water .It is the amount of heat required to convert water at a given temperature and pressure intosteam at the same temperature and pressure. It is expressed by the symbol hfg and its value isavailable from steam tables. The value of latent heat is not constant and varies according topressure variation.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $'ENGINEERING THERMODYNAMICS 4.Defne Dryness fraction (x). The term dryness fraction is related with wet steam. It is defned as the ratio of the mass of actual dry steam to the mass of steam containing it.5.What is pure substance?Pure substance is a substance which has a fxed chemical composition throughout its mass.Examples: Water, nitrogen, carbon-di-oxide, and helium. A pure substance does not have to beof a single chemical element or compound. A mixture of various chemical elements orcompounds is also called as pure substance as long as the mixture is homogeneous.6.What is saturation temperature and saturation pressure?At a given pressure, the temperature at which a liquid boils is called saturation temperature.At the given temperature, the pressure at whichthe liquid boils is called saturation pressure.It is also called as vapour pressure.7.Defne latent heat of vaporization?The amount of heat added during heating of water from boiling point to dry saturated stage iscalled as latent heat of vaporization or enthalpy of vaporization or latent heat of steam.8.Defne the terms boiling point and melting pointBoiling point: It is the temperature at which the liquid starts to change its state from liquid tovapour.Melting point: It is the temperature at which the solid starts to change its state from solid toliquid.9.Defne sensible heat of water?The amount of heat required to raise the temperature of unit mass of water from 0C to thesaturation temperature under a constant pressure. It is denoted by hf.10.Defne the term superheat enthalpy.The heat supplied to the dry steam at saturation temperature, to convert it into superheatedsteam at the temperature Tsup is called superheat enthalpy.11.Defne wet steam and dry steam?The steam which is partially evaporated and having water particles in suspension is called wetsteam.The steam which is fully in evaporated state and is not having any water particles is called drysteam.12.What is meant by superheated steam? And indicate its use.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $(ENGINEERING THERMODYNAMICS If the dry steam is further heated, then the process is called superheating and steam obtainedis known as superheated steam. Uses:Superheated steam has more heat energy and more work can be obtained using it.Thermal efciency increases as the temperature of superheated steam is high.13.Defne triple point and critical point for pure substance?Triple point: Triple point is the state at which all the three phases that is, solid, liquid andvapour are saidto exist in equilibrium. The triple point is merely the point of intersection ofsublimation and vapourisation curves. It must be understood that only on p-T diagram is thetriple point represented by a point.Critical point:It represents the highest pressure and temperature at which the liquid andvapour phases coexist in equilibrium. At the critical point the liquid and vapour phases areindistinguishable that is liquid directly converted into vapour.14.Explain the terms: Degree of superheat, Degree of subcooling.Degree of superheat: It is the diference between superheated temperature and saturatedtemperature at the same pressure.Degree of subcooling:It is the amount by which the water is cooled beyond the saturatedtemperature at the same pressure.15.Defne Saturation temperature and saturation pressreThe phase change temperature corresponding to the saturation pressure. Sometimes called theboiling temperature. The pressure at whichphase change occurs is called saturation pressure. 16.What is Compressed liquid ?Liquid whose temperature is lower than the saturation temperature is called compressed liquid.Sometimes it is called as asub-cooled liquid.17.What is Saturated liquid ? It is the liquid at the saturation temperature corresponding to the saturation pressure. That isliquid about to commence evaporating.18.What is Dry (saturated) vapour , wet vapour and superheated vapour ? Dry Vapour is the vapour which has just completed evaporation. The pressure and temperatureof the vapour are the saturation values. Wet vapour is the mixture of saturated liquid and dry vapour during the phase change.Superheated vapour is the vapour whose temperature is greater than the saturationtemperature corresponding to the pressure of the vapour.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $)ENGINEERING THERMODYNAMICS 19.State phase rule of pure substances?The number of independent variables associated with a multicomponent, multiphase system isgiven by the phase rule. It is also called as Gibbs phase rule.It is expressed by the equation asn=C- +2Where, n = the number of independent variable,c = the number of components, = the number of phases present in equilibrium.20.When saturation pressure increases, what happens to saturation temperature andfreezing point?When saturation pressure increases, then the saturation temperature is increasing and thefreezing point decreasing.21.What is meant by steam power cycles?Thermodynamic cycles which use steam as the working fuid is called steam power cycles.22.What is meant by work ratio? What is the importance of work ratio in vapour cycles? Work ratio is defned as the ratio of network transfer to the positive work transfer. Work ratio afects the actual efciency comparing two cycles with the same idealefciency, the cycle having smaller work ratio would have smaller actual efciency. Higher the work ratio, the SSC is lower, resulting in smaller size plant for the givenoutput.23.What are the efects of condenser pressure on the Rankine cycle?Bylowering the condenser pressure, we can increase the cycle efciency.The maindisadvantage islowering the back pressure increases the wetness of steam. Isentropiccompression of a very wet vapour is very difcult.24.A vapour cycle inherently has two advantages over gas power cycle. What are they? Isothermal heat transfer (evaporation and condensation) is possible in practice. The work ratio is high compared to the gas power cycles.25.Mention the improvements made to increase the ideal efciency of ranking cycle. Lowering the condenser pressure Super heated steam is supplied to the turbine. Increase the boiler pressure to certain limit. Implementing reheat and regeneration in the cycle.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $*ENGINEERING THERMODYNAMICS 26.Name the diferent components in steam power plant working on a rankine cycle.Boiler, Turbine, Cooling Tower or Condenser, and Pump.27.What are disadvantages of reheating?The cost of plant increases due to the reheater and its long connections. It also increases thecondenser capacity due to increased dryness fraction.28.What are the disadvantages of bleeding?Cost of the plant increases and the work done per kg of steam is reduced which results inhigher boiler capacity for given output.29.Defne efectiveness.Efectiveness is defned as the ratio of actual useful work to the maximum useful work. Theuseful output of a system is given by the increase of availability of the surroundings. Theefectiveness of an actual process is always less than unity. Thus efectiveness of a process is themeasure of the extent to which advantage has been taken of an opportunity to obtain useful work.Compiled by Abubakkar ADeparment of Me!anial En"ineerin" #a"e $+