Thermodynamics

Chapter 4ENERGY ANALYSIS OF CLOSED SYSTEMSIn Chap. 2, we considered various forms of energy andenergy transfer, and we developed a general relation forthe conservation of energy principle or energy balance.Then in Chap. 3, we learned how to determine the thermodynamicsproperties of substances. In this chapter, we applythe energy balance relation to systems that do not involve anymass flow across their boundaries; that is, closed systems.We start this chapter with a discussion of the movingboundary work or P dV work commonly encountered in reciprocatingdevices such as automotive engines and compressors.We continue by applying the general energy balancerelation, which is simply expressed as E in E out E system , tosystems that involve pure substance. Then we define specificheats, obtain relations for the internal energy and enthalpy ofideal gases in terms of specific heats and temperaturechanges, and perform energy balances on various systemsthat involve ideal gases. We repeat this for systems thatinvolve solids and liquids, which are approximated as incompressiblesubstances.ObjectivesThe objectives of Chapter 4 are to:• Examine the moving boundary work or PdV workcommonly encountered in reciprocating devices such asautomotive engines and compressors.• Identify the first law of thermodynamics as simply astatement of the conservation of energy principle for closed(fixed mass) systems.• Develop the general energy balance applied to closedsystems.• Define the specific heat at constant volume and the specificheat at constant pressure.• Relate the specific heats to the calculation of the changesin internal energy and enthalpy of ideal gases.• Describe incompressible substances and determine thechanges in their internal energy and enthalpy.• Solve energy balance problems for closed (fixed mass)systems that involve heat and work interactions for generalpure substances, ideal gases, and incompressiblesubstances.| 165