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Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401Chapter (I)Introduction1.1- Energy sourcesThe energy sources can be of two types:1. Renewable or non conventional energy resources2. Non-renewable or conventional energy resources1. Renewable energy resources Solar energyWind energyTidal energyOcean tides and waves energyFlowing of stream of water2. Non-renewable energy resources Coal, coke, etcPetroleumNatural gasNuclear power1.2-FuelsFuel is defined as any material which when burnt will produce heat.commonly used are as follows: Various fuelsSolid fuels (Wood, peat, lignite, bituminous coal and anthracite coal)Liquid fuels (Petroleum and its derivatives)Gaseous fuels (CNG, LPG, etc)1.3- Types of Power Plants1.2.3.4.5.Steam Power PlantGas turbine Power PlantsCombined Cycle Power GenerationNuclear Power PlantsHydroelectric Power plant1.4- Steam TablesSteam tables commonly consist of two sets of tables of the energy transfer properties ofwater and steam: saturated steam tables and superheated steam tables. Both sets oftables are tabulations of pressure (P), temperature (T), specific volume (v), specificinternal energy (u), specific enthalpy (h), and specific entropy (s). The followingnotation is used in steam tables.T : temperature (oC)P : pressure (kPa)v : specific volume (m3/kg) Dr. Rahim K. Jassimu: specific internal energy (kJ/kg)h: specific enthalpy (kJ/kg)s: specific entropy (kJ/kg K)8

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401DefinitionsSubcooled or compressedSaturated liquidWet (mixture)Saturated vaporSuperheatedQuality (x)WaterDTSubcooled water (A)Saturated liquid (B) (x 0)Evaporation of saturated liquid (B-C) (x 0 1)Wet steam (F) (x )Dry Saturated steam (C) ) (x 1)Superheated steam (D)x BFCAvapour masstotal masss1.5- The enthalpy-entropy diagramThe Mollier diagram, shown in Figure 1.1, is a chart on which enthalpy (h) versusentropy (s) is plotted. It is sometimes known as the h-s diagram and has anentirely different shape from the T-s diagrams. The chart contains a series of constanttemperature lines, a series of constant pressure lines, a series of constant quality lines,and a series of constant superheat lines. The Mollier diagram is used only when qualityis greater than 50% and for superheated steam.Figure 1.1 Dr. Rahim K. Jassim9

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401Example 1.1Heat is transferred to a dry saturated steam at 193 oC until it’s superheated by 167 oC,while the pressure remains constant, determine h.Example 1.2Steam at 300 oC and 0.5 MPa is expanded in a reversible adiabatic process (isentropic)to 0.01 MPa, determine h and x. Dr. Rahim K. Jassim10

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 4011.6- Thermodynamics reviewWe have already discussed the first law of thermodynamics: control volume in appliedthermodynamics and heat transfer subject.1.6.1- Conservation of mass and the control volumeThe conservation of mass is one of the most fundamental principles in nature. We are allfamiliar with this principles, and it is not difficul to understand. For closed systems, theconservation of mass principles is implicitly used by requiring that the mass of thesystem remains constant during a process. For control volumes (see Figure 1.2),however, mass can cross the boundaries, and so we must keep track of the amount ofthe mass entering and leaving the control volume (see Figure 1.2). The conservation ofmass principle for the control volume (CV) undergoing a process can be expressed as m CV m i m eThe average rate of change of mass within the control volumedmCV m& i m& edttotaltotal net change in mass within mass entering mass leaving control volume control volume control volume (1.1)me2 kg m CVFigure 1.2mi 3 kg5 kgEquation (1.1) for the conservation of mass is commonly termed the Continuity Equation.While this form of the equation is sufficient for the majority of applications inthermodynamics, it is frequently rewitten in terms of local fluid properties in the study offluid dynamics and heat transfer.Let us consider one further aspect of mass flow across a control volume. For simplicity,we assume that a fluid is flowing uniformaly inside a pipe or duct, as shown in Figure1.3. Dr. Rahim K. Jassim11

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401VAFlowdsFigure (1.3)We wish to examine the flow in terms of the amount of mass crossing the surface Aduring the time interval δt . As seen from the figure above, the fluid moves a distanceds during this time, and therefore the volume of fluid crossing surface A is A ds.Consequently, the mass crossing surface A is given byδm A dsvIf both sides of the above expression is devided by δt and take the limit δt 0 , theresult is& mAVv(1.2)Where V is the fluid velocity m/sA cross sectional area m21.6.2-The First law of Thermodynamics for a Control VolumeThe first law of thermodynaocs for a control mass, which consists of a fixed quantity ofmass is expressed as1Q2 E 2 E1 1W2This expression can be written as a rate equation dE V 2 V 2 Q& c.v. m& i hi i g Z i 10 3 c.v m& e he e g Z e 10 3 W& c.v. (1.3) dt 2 2 The first application of the first law of thermodynamics for the control volume will be todevelop a suitable analytical model for SSSF operation of devices such as turbines,compressors, nozzles, boilers, heat excangers, etc.SSSF assumptionsdmc.v. 0dtanddE c.v. 0dtThen, equations (1.1 and 1.3) can be written, m& m&i Dr. Rahim K. Jassime12

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401 V 2 V 2 Q& c.v . m& i hi i g Z i 10 3 m& e he e g Z e 10 3 W& c.v . 2 2 In many applications of SSSF model have only one flow stream entering and one leavingthe control volume. Thenm& i m& e m&(1.4) Vi 2 Ve2 3& &&Qc.v . m hi g Z i 10 m he g Z e 10 3 W& c.v. 2 2 (1.5)Rearranging this equation, we have V 2 V 2 q hi i g Z i 10 3 he e g Z e 10 3 w 2 2 (1.6)where, by definition,q Q& c.vm&and Dr. Rahim K. Jassimw W& c.vm&(1.7)13

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 4011.6.3- Power CyclesTwo important area of application for SSSF or cylinder/piston boundary work processesof thermodynamics are power generation and refrigeration systems. Both systemsare accomplished by operating on a thermodynamic cycles. These cycles are generallydivided into two categories: power cycles and refrigeration cycles.The systems used to produce a net power output are often called engines (i.e. steampower plant, internal combustion engine and gas turbine) and the thermodynamic cyclesthey operate on are called power cycles. Whereas, the systems used to producerefrigeration are called refrigerators, air conditioners, or heat pumps, and thethermodynamic cycles they operate on are called refrigeration cycles.Thermodynamic cycles can be categories to: Closed cycles and open cycles. In closedcycles, the working fluid is returned to the initial state at the end of the cycle and isrecirculated (i.e. steam power plant, refrigerators) . In open cycle, the working fluid isrenewed at the end of each cycle (i.e. internal combustion engine, gas turbine).In this course, the focus will be only on power cyclesIn gas power cycle, the working fluid remains a gas throughout the entire cycle. Internalcombustion engine, gas turbines are familiar examples of devices that operate on gascycles. Analysis of these cycles are rather complex. To simplify the analysis to amanageable level, we utilize the following assumptions, commonly known as the air –standard assumptions.1. The working fluid is air that continuously circulates in a closed loop and alwaysbehaves as an ideal gas.Some important relationsdu C vo dT(1.8 a)dh C po dT(1.8 b)P2 V1 P1 V2 T2 P2 T1 P1 kwhere k k 1k V 1 V2 C poC vo(1.9 a)k 1(1.9 b)Also, the specific heat of air is constant and is evaluated at 25oC2. All the processes that make up the cycle are internally reversible3. The combustion process is replaced by a heat addition process from external anexternal source (Figure 1.4).4. The exhaust process is replaced by a heat rejection process that restores theworking fluid to its initial state. Dr. Rahim K. Jassim14

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401Figure (1.4)1.6.4 - Reciprocating enginesThe basic components of a reciprocating engine are shown in Figure 1.5. The pistonreciprocates in the cylinder between two fixed positions called the top dead center(TDC)—the position of the piston when it forms the smallest volume in the cylinder—andthe bottom dead center (BDC)—the position of the piston when it forms the largestvolume in the cylinder. The distance between the TDC and the BDC is the largestdistance that the piston can travel in one direction, and it is called the stroke of theengine. The diameter of the piston is called the bore. The air or air-fuel mixture is drawninto the cylinder through the intake valve, and the combustion products are expelledfrom the cylinder through the exhaust valve.The minimum volume formed in the cylinder when the piston is at TDC is called theclearance volume (Figure 1.6). The volume displaced by the piston as it movesbetween TDC and BDC is called the displacement volume. The ratio of the maximumvolume formed in the cylinder to the minimum clearance volume is called thecompression ratio ( r ) of the engine:r Vmax V BDC Vmin VTDC Dr. Rahim K. Jassim(1.10)15

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401Figure (1.5)Figure (1.6)Notice that the compression ratio is a volume ratio and should not be confused with thepressure ratio.Another term frequently used in conjunction with reciprocating engines is the MeanEffective Pressure (MEP). It is a fictitious pressure which, if it acted on the pistonduring the entire power stroke, would produce the same amount of net work as thatproduced during the actual cycle (Figure 1.7). That is,Wnet., MEP X piston area X stroke MEP X displacement volumeMEP Wnetwnet Vmax Vmin v max v min(1.11)The mean effective pressure can be used as a parameter to compare the performancesof reciprocating engines of equal size. The engine that has a larger value of MEP willdeliver more net work per cycle and thus will perform better.Figure (1.7) Dr. Rahim K. Jassim16

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 4011.6.4.1- Otto CycleThe air standard Otto cycle is an ideal cycle approximates a spark-ignition internalcombustion engine (IC). This cycle is shown on P-v and T-s diagrams of Figure (1.8).Process 1-2 is an isentropic compression (s c) of the air as the piston moves from BDCto TDC.Process 2-3 heat is added at constant volume while the piston is momentarily at rest atthe TDC point. (This process corresponds to the ignition of the fuel air mixture by thespark and subsequent burning in the engine).Process 3-4 is an isentropic expansion (s c), andProcess 4-1 is the heat rejection of heat from the air while the piston is at BDC (v c).The thermal efficiency of this cycle is found as follows,ηth ,Otto T T1 4 1 Tm C vo (T4 T1 )Q 1 L 1 1 1QHm C vo (T3 T2 ) T T2 3 1 T2 WnetQH(1.12)Processes 1-2 and 3-4 are isentropic, and v2 v3 and v4 v1. ThusT2 V1 T1 V2 k 1 V 4 V3 k 1 T3T4(1.13)Therefore,T3 T4 T2 T1(1.14)andηth ,Otto 1 T111 k 1 (r ) 1 k 1T2(r )(1.15)wherer V1 V4 V2 V3(1.16)Example 1.3An ideal Otto cycle has a compression ratio of 8. At the beginning of the compressionprocess, the air is at 100 kPa and 17 oC, and 1800 kJ/kg of heat is transferred to airduring the constant-volume heat addition process. Determinea- the maximum temperature and pressure that occur during the cycle.b- the net work outputc- the thermal efficiency, andd- the mean effective pressure for the cycle Dr. Rahim K. Jassim17

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401Solution. Dr. Rahim K. Jassim18

Mechanical Engineering TechnologyPower Plant Engineering and Economy MET 401(a)(b)Figure (1.8)1.6.4.2- The Diesel CycleThe air-standard Diesel cycle is shown in Figure 1.9. This is the ideal cycle for the dieselengine, which is also called the compression-ignition engine.The Diesel cycle is the ideal cycle for Cl reciprocating engines. The Cl engine, firstproposed by Rudolph Diesel in the 1890s, is very similar to the S

1. Basic thermodynamics of power cycles and combustion processes 2. Conduction, convection and radiation heat transfer CO-REQUISITE: None COMPUTER USAGE: Use of computer programs in power plant calculations TEXT AND MATERIALS: Textbook: 1. Power Plant Engineering. by Nag, P.K