Slide 1Slide 2MOVING BOUNDARY WORKSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9ENERGY BALANCE FOR CLOSED SYSTEMSSlide 11Slide 12Slide 13Slide 14SPECIFIC HEATSSlide 16INTERNAL ENERGY, ENTHALPY, AND SPECIFIC HEATS OF IDEAL GASESSlide 18Slide 19Slide 20Specific Heat Relations of Ideal GasesSlide 22Slide 23Slide 24Slide 25Internal Energy ChangesSlide 27Slide 28SummaryCHAPTER 4 ENERGY ANALYSIS OF CLOSED SYSTEMSLecture slides byMehmet KanogluCopyright © The McGraw-Hill Education. Permission required for reproduction or display.Thermodynamics: An Engineering Approach 8th EditionYunus A. Çengel, Michael A. BolesMcGraw-Hill, 20152Objectives•Examine the moving boundary work or P dV work commonly encountered in reciprocating devices such as automotive engines and compressors.•Identify the first law of thermodynamics as simply a statement of the conservation of energy principle for closed (fixed mass) systems.•Develop the general energy balance applied to closed systems.•Define the specific heat at constant volume and the specific heat at constant pressure.•Relate the specific heats to the calculation of the changes in internal energy and enthalpy of ideal gases.•Describe incompressible substances and determine the changes in their internal energy and enthalpy.•Solve energy balance problems for closed (fixed mass) systems that involve heat and work interactions for general pure substances, ideal gases, and incompressible substances.3MOVING BOUNDARY WORKMoving boundary work (P dV work): The expansion and compression work in a piston-cylinder device.Quasi-equilibrium process: A process during which the system remains nearly in equilibrium at all times.Wb is positive  for expansionWb is negative  for compression4The boundary work done during a process depends on the path followed as well as the end states.The area under the process curve on a P-V diagram is equal, in magnitude, to the work done during a quasi-equilibrium expansion or compression process of a closed system.5Boundary Work for a Constant-Pressure Process6Boundary Work for a Constant-Volume ProcessWhat is the boundary work for a constant-volume process?7Boundary Work for an Isothermal Compression Process8Boundary Work for a Polytropic ProcessFor ideal gas9Expansion of a Gas against a Spring10ENERGY BALANCE FOR CLOSED SYSTEMSEnergy balance for any system undergoing any processEnergy balance in the rate formThe total quantities are related to the quantities per unit time isEnergy balance per unit mass basisEnergy balance in differential formEnergy balance for a cycle11Energy balance when sign convention is used: (i.e., heat input and work output are positive; heat output and work input are negative).Various forms of the first-law relation for closed systems when sign convention is used.The first law cannot be proven mathematically, but no process in nature is known to have violated the first law, and this should be taken as sufficient proof.12Energy balance for a constant-pressure expansion or compression processHWUbFor a constant-pressure expansion or compression process:An example of constant-pressure processGeneral analysis for a closed system undergoing a quasi-equilibrium constant-pressure process. Q is to the system and W is from the system.1314Unrestrained Expansion of Water15SPECIFIC HEATSSpecific heat at constant volume, cv: The energy required to raise the temperature of the unit mass of a substance by one degree as the volume is maintained constant.Specific heat at constant pressure, cp: The energy required to raise the temperature of the unit mass of a substance by one degree as the pressure is maintained constant.Constant-volume and constant-pressure specific heats cv and cp(values are for helium gas).16•The equations are valid for any substance undergoing any process.•cv and cp are properties.•cv is related to the changes in internal energy and cp to the changes in enthalpy.•A common unit for specific heats is kJ/kg·°C or kJ/kg·K. Are these units identical?True or False? cp is always greater than cvFormal definitions of cv and cp.17INTERNAL ENERGY, ENTHALPY,AND SPECIFIC HEATS OF IDEAL GASESJoule showed using this experimental apparatus that u=u(T)For ideal gases, u, h, cv, and cp vary with temperature only.Internal energy and enthalpy change of an ideal gas18Ideal-gas constant-pressure specific heats for some gases (see Table A–2c for cp equations).•At low pressures, all real gases approach ideal-gas behavior, and therefore their specific heats depend on temperature only. •The specific heats of real gases at low pressures are called ideal-gas specific heats, or zero-pressure specific heats, and are often denoted cp0 and cv0.•u and h data for a number of gases have been tabulated.•These tables are obtained by choosing an arbitrary reference point and performing the integrations by treating state 1 as the reference state.In the preparation of ideal-gas tables, 0 K is chosen as the reference temperature.19(kJ/kg)Internal energy and enthalpy change when specific heat is taken constant at an average value201. By using the tabulated u and h data. This is the easiest and most accurate way when tables are readily available. 2. By using the cv or cp relations (Table A-2c) as a function of temperature and performing the integrations. This is very inconvenient for hand calculations but quite desirable for computerized calculations. The results obtained are very accurate. 3. By using average specific heats. This is very simple and certainly very convenient when property tables are not available. The results obtained are reasonably accurate if the temperature interval is not very large.Three ways of calculating u and hThree ways of calculating u.21Specific Heat Relations of Ideal GasesThe cp of an ideal gas can be determined from a knowledge of cv and R.On a molar basisThe relationship between cp, cv and RSpecific heat ratio•The specific ratio varies with temperature, but this variation is very mild. •For monatomic gases (helium, argon, etc.), its value is essentially constant at 1.667. •Many diatomic gases, including air, have a specific heat ratio of about 1.4 at room temperature.dh = cpdT and du = cvdT22Heating of a Gas in a Tank by Stirring23Heating of a Gas by a Resistance Heater24Heating of a Gas at Constant Pressure25INTERNAL ENERGY, ENTHALPY, ANDSPECIFIC HEATS OF SOLIDS AND LIQUIDSIncompressible substance: A substance whose specific volume (or