UNIT 2 : SECOND LAW, ENTROPY AND AVAILABILITY1.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.c.5.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% 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.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?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.What is the corollaries of carnot theorem?(1). All the reversible engines operating between the two given thermal reservoirs with fxedtemperature have the same efciency.(2). The efciency of any reversible heat engine operating between two reservoirs is independentof the nature of the working fuid and depends only on the temperature of the reservoir.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?(1). To know the feasibility of process.(2). 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.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.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.34.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 ones35.Write the equation forClausius inequalityClausius inequality is given by,When a system performs a reversible cycle, thenbut when the cycle is not reversibleUNIT 3 :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 .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.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 partially evaporated and having water particles in suspension is called wetsteam.The steam which 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.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 where all the three phases that is, solid, liquid andvapour to 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. Sometimes called a sub-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.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.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.List the advantages of reheat cycle.Marginal increase in thermal efciency. Increase in work done per kg of steam which results in reduced size of boiler andauxiliaries for the same output. We can prevent theturbine from erosion.29.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.30.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 .31.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 calledavailability OrThe 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.32.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.33.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.