THERMODYNAMICS OVERVIEW Thermodynamics Thermodynamics is the study of the relationship between all forms of Energy beginning historically with the relationship between Heat and Work. Laws of Thermodynamics ( fundamental observations) Mass Balance (should be a law) Mass can not be created or destroyed and is conserved. First Law Heat and work are equivalent Property energy is defined Energy can change form, can not be destroyed, and is conserved Second Law Heat can not be converted completely to work. Property entropy defined. Ideal and actual heat engine efficiency. THERMODYNAMICS IN DESIGN Thermodynamic Analysis – Process Analysis Thermodynamic analysis is the first step in energy system design. Through Thermodynamic Analysis the required mass flows, volume flows, temperatures and pressures are established. Performance is determined. ENERGY SYSTEMS Gasoline Engines Food Processing Plants Diesel Engines Rocket Engines Steam Power Plants Air Conditioning Systems Chemical Plants Refrigeration Systems Compression Systems Heating Systems Gas Liquefaction Gas Turbine Engines Thermodynamics Concepts Thermodynamic System Properties State Point Process Cycle Heat Work Energy First Law - Energy Balance lead the analysis HEAT WORK Thermodynamic System MASS Control Volume 3 Types of SYSTEMS Closed Open Unsteady Heat added to a system and Work done by a system are positive (+) by convention. Concepts System CLOSED THERMODYNAMIC SYSTEM Properties NON FLOW SYSTEM State Point Process A MASS OF MATERIAL. Cycle Heat and Work can cross the system boundaries. Mass can not. Work Heat Examples: A closed tank. A piston cylinder. A balloon OPEN THERMODYNAMIC SYSTEM Concepts System STEADY FLOW THERMODYNAMIC SYSTEM Properties State Point A FIXED REGION IN SPACE Process Mass, heat and work can Cycle cross the system boundaries. Examples: turbine, compressors, boilers, heat exchangers Mass in Mass out Heat Work Concepts System Properties UNSTEADY FLOW THERMODYNAMIC SYSTEM State Point Process Cycle A VARIABLE MASS Mass, heat and work can cross the system boundaries Examples: Work A filling tank. Heat An emptying tank Piston-Cylinder Filling Mass Concepts System Properties State Point Process Cycle The mass of water is a closed thermodynamic system. Heat(+) is added to the closed thermodynamic system from the surroundings system. Work (+) is done by the closed thermodynamic system on the surroundings system. Concepts System Properties State Point Process Cycle The boiler, turbine, condenser and pump are open thermodynamic systems Heat (+) is transferred into the open boiler system from the surroundings system. Work (+) is done by the open turbine system on the surrounding system. Heat (-) is rejected from the condenser open system to the surrounding system. Work(-) is done on the open pump open system by the surroundings system. CONCEPTS Thermodynamic Properties System Temperature Properties Pressure State Point Volume Process Internal Energy Cycle Enthalpy Entropy Temperature −o F, o C, absolute, o K, oR o F =1.8×o C + 32. o K=o C + 273.15 o R=o F + 459.69 p Pressure − kPa, atmospheres, bar, lb/in 2 Absolute pressure = Gage pressure + Ambient pressure v SpecificVolume − m3/kg,ft3/lb ρ Density − kg/m3 ,lbm/ft3 V Volume − m3 ,ft3 V = mass× v CONCEPTS Thermodynamic Properties System u SpecificInternalEnergy − kJ/kg, BTU/lb Properties du = c dT State Point v Process c − specifc heat at constant volume, v Cycle kG/jg, m3/kgo C, BTU/lbmo F U InternalEnergy − kJ, BTU h Specific Enthalpy − kJ/kg, BTU/lbm h = u + pv dh = cpdT o o cpspecific heat at constant pressure, kJ/kg C, BTU/lbm F H Enthalpy − kJ, BTU H = m× h s Specific Entropy − kJ/kgo C, BTU/lbmo F S Entropy − kJ/ oK S = m×s PRESSURE Pabs = Patm + Pgage Force Units - force = mass x acceleration 2 1 N =1 kg• 1 m/sec 2 1 lbf = lbm • gc ft/sec 2 9.807 N =1 kg• 9.807 m/sec 2 1 lbf = lbm •32.174 ft/sec 1 1 lb = slugs Mass is measured indirectly by measuring the m 32.174 2 gravitational force it exerts. l kg mass weighs 1 lbf = l slug •1 ft/sec 2 2 9.807 N at an acceleration of 9.807m/sec 1 lbm weighs 1 lbf at an acceleration of 32.174ft/sec Energy Units - force x distance, mass and temperature change 1 J =1N •1m 1ftlbf =1lbf •1ft o o Calorie −1 g water at 15 C raised 15 C o o BTU −1 lbm water at 60 F raised 1 F 1 J = 4.1868 calories 1BTU = 778 ftlbf 1 kJ = 4.1816 kg water at 15o C raised15o C Power Units - energy per time 1watt −1J/sec 1HP = 550ftlbf /sec 1kw −1kJ/sec 1kw = .7457HP Concepts System THERMODYNAMIC STATE POINT Properties State Point Process Properties are measured. Cycle Equations and models are fitted (T,p,v,u,h,s) to the data resulting in : Tables of Property Values Equations of State Computer property modules ordinate Two properties define the property state point of a single phase fluid. One property defines the abscissa property state point of a multiphase fluid. THERMODYNAMIC PROCESS Concepts A thermodynamic process is an interaction between a thermodynamic system and System its surroundings which results in a change in the state point of the system Properties State Point Reversible Process Process A process is reversible if the state points of all affected thermodynamic systems, including the external system Cycle or surroundings, are returned to their original state point values. Examples: - movement of a frictionless pendulum - transfer of work to potential energy without loss - movement of a frictionless spring Irreversible Process A process which can not be reversing bringing all the affected thermodynamic properties back to their original values is irreversible. Examples: - applying brakes to a moving wheel - mixing hot and cold water - transfer of heat through a finite temperature difference THERMODYNAMIC CYCLE CONCEPTS System A thermodynamic system undergoes Properties a cycle when the system is subjected to a series State Point of processes and all of the state point Process properties of the system are returned to their Cycle initial values. Q = ∑Qprocess cyclenet cycle p W = Wprocess cyclenet ∑ cycle First Law initial point v ∫δQ = ∫δW δ is an inexact differential, a deriviative that is path dependent. Concepts Thermodynamic Problem Solving Technique System 1. Problem Statement 4. Property Diagram Properties Carbon dioxide is contained in a cylinder state points - processes - cycle with a piston. The carbon dioxide is compressed T3,p3 State Point with heat removal from T1,p1 to T2,p2. The gas is then heated from T2, p2 to T3, p3 at constant Q Process p volume and then expanded without heat transfer to W the original state point. Cycle T2,p2 T1,p1 W Q 2. Schematic v 5. Property Determination 1 2 3 T p v 3. Select Thermodynamic System p u open - closed - control volume h s a closed thermodynamic system T2,p2 composed to the mass of carbon dioxide in the cylinder v 6. Laws of Thermodynamics Q=? W=? E=? material flows=? CO2.