LECTURES IN THERMODYNAMICS Claus Borgnakke CHAPTER 1 For the 8th Edition of: Fundamentals of Thermodynamics Claus Borgnakke, Richard Sonntag John Wiley & Sons, 2013

Chapter 1 Introduction to Thermodynamics Thermodynamic System and Control Volume Properties, Processes and Cycles Units Specific Volume and Density Pressure Energy and Temperature

Introduction to Thermodynamics Theory about energy, its conversion and its effect on substances and devices. Subjects: Thermal systems, devices, components Examples: Steam Power Plant, Air conditioner (A/C) unit, Heater, Boiler, Steam generator, Refrigerator, Engine, Pump, Nozzle, … Subjects: Behavior and Properties of pure substances Examples: When is water (H2O) a solid (ice), liquid or vapor (gas) When air is compressed how much smaller does it become? How much energy is needed to bring cold water to a boil? At what pressure will R-410A (a refrigerant) boil at 35 C (95 F) Subjects: Behavior or characteristics of devices or systems Examples: How big a pump do I need to empty a swimming pool in 1 hour? How much air must I blow into a balloon for a given size? How much work is involved to inflate a flat tire or balloon?

Thermodynamic System and Control Volume Control Volumes Closed control volume: Open control volume: Encloses a fixed amount of mass Mass can enter or leave Also called control mass Notice volume may change Control surface A B Control surface Control volume A + B

Thermodynamic System and Control Volume Closed control volume: Open control volume: Encloses a fixed amount of mass Mass can enter or leave CV: argon, volume can go up Hot air balloon being inflated Filling of a tank Heating at constant volume

Complete system: Power Plant Conversion of fuel energy into electricity and heat Water Loop Heat (Condenser)

Complete system: Refrigerator Refrigerator pushes energy out of a cold space into a warmer space (room) Refrigerant flows in a loop through 4 devices

Properties, Processes and Cycles Phases: Solid, Liquid and Vapor (gas) State: a specific condition expressed by a unique set of property values like P, T and density ρ. Two independent properties are needed to specify a state Intensive properties are independent of mass (P, T, ρ) Extensive properties depend on mass (Mass, Volume, Energy) Process: A change of a substance beginning at state 1 to a final state 2 through a continuous variation of the state. Example: Heat a cup of cold water to be warm water Example: Compress air in a cylinder to a smaller volume (bike pump)

Properties, Processes and Cycles, Continued Process path or type: A specific succession of states is usually given a name that relates to the condition under which this happens. This is given by the way the device behaves as a process equation or device equation. Example: The heating of water in a cup takes place at atmospheric pressure so it is called an isobaric process, pressure is constant. Example: Heating of air in a constant volume container is called an isochoric process, volume is constant. Example: Air is compressed in a piston cylinder while it is maintained at a constant temperature called an isothermal process. Example: Air is compressed in a well insulated piston cylinder so it does not have any heating or cooling called an adiabatic process. The type of process is often dictated by the device behavior and could also be called a device equation.

Properties, Processes and Cycles, Continued Cycle: A process path that ends in the initial state. It can be a complex process or a combination of several simple processes. Example: Water circulating in a steam power plant Example: Refrigerant (like R-134a, R-410A or R-12) circulating in a refrigerator or air-conditioner. Example: Air going through 4 sequential processes in a piston cylinder similar to what happens in a car engine. This is repeated in time. Cycles do not (net) change the working substance which keeps looping in space (flow) or in time. However during the cycle the outside world exchanges energy with the working substance at different conditions during the cycle so the net effect is an energy conversion process.

UNITS SI or English: Units and Conversions: See Table A.1 SI: mass (kg), length (m), time (s), force (N) F = ma has units 1 N = (1 kg) (1 m/s2) = 1 kg m/s2 English: mass (lbm), length (ft), time (s), force (lbf) F = mg has units 1 lbf = (1 lbm) (32.174 ft/s2) = 32.174 lbm ft/s2 Mole: A fixed number of particles (No = 6.022*1023 particles per mol) distinguish between gram mole (mol) and kilomole (kmol). m = n M where m is mass , n = number of moles, M is molecular mass Units and Conversions: See Table A.1

UNITS

UNITS Recall: 1 lbf = 32.174 lbm ft/s2

Specific Volume and Density Specific volume: Volume per unit mass (v) v = V/m limit for small volume Density: Mass per unit volume (ρ) ρ = m/V limit for small volume Typical numbers SI: Liquid water: v ≈ 0.001 m3/kg and ρ ≈ 1000 kg/m3 Atmospheric air: v ≈ 1 m3/kg and ρ ≈ 1 kg/m3 See Tables for a few typical substances. SI: A3, A4, A5 Eng.: F2, F3, F4

Specific Volume and Density, English Units Specific volume: Volume per unit mass (v) v = V/m limit for small volume Density: Mass per unit volume (ρ) ρ = m/V limit for small volume Typical numbers English: Liquid water: v ≈ 0.016 ft3/lbm and ρ ≈ 62.5 lbm/ft3 Atmospheric air: v ≈ 13.7 ft3/lbm and ρ ≈ 0.073 lbm/ft3 See Tables for a few typical substances. SI: A3, A4, A5 Eng.: F2, F3, F4 Density [lbm/ft3]

Concept Questions

Pressure Pressure is force per unit area (normal stress) 𝑃= lim 𝛿𝐴→0 𝛿𝐹 𝛿𝐴 With uniform P, piston at rest (F→ = F←) Fext = P Acyl Units for P 1 Pa = 1 N/m2 1 kPa = 1000 Pa = 1 kN/m2 1 bar = 105 Pa = 100 kPa = 0.1 MPa 1 atm = 101.325 kPa = 14.696 lbf/in2

Pressure

Pressure

Manometer/Barometer Manometer Barometer

Manometer Manometer

Manometer Manometer

Manometer/Barometer Manometers Barometer

Static/dynamic pressure Static pressure in a fluid is only a function of depth below surface with given P. Shape does not matter. Ships or floating objects are displacement hulls. They push a mass of water away that equals their own mass (m = ρV ). A submarine or swimmer is neutrally buoyant when the displaced volume of water has a mass that equals the object mass. The pressure below a speedboat or water ski is a static plus a dynamic pressure part. The water is being pushed away with significant acceleration. P same

Pressure

Pressure Liq water Air Ballast tank Air tanks

Pressure P

Pressure

Manometer/Barometer

Pressure and Manometer Concept Questions Figure 1.13 manometer

Energy and Temperature A diatomic molecule, O2, N2 . 2 modes of rotation (ͼ x, z axis) 1 mode of vibration (in y axis) A H2O molecule, 3 modes of vibration, 3 modes of rotation (not shown)

Temperature

Thermocouples, thermistors