CHAPTER1: Basic Definitions, Zeroth, First, and Second Laws of Thermodynamics 1.1. Definitions What does thermodynamic mean? It is a Greeks word which means a motion of the heat. Water is a liquid substance Liquid is a fluid substance which is structured in a little close atoms and molecules. Air is a gas substance Gas is a fluid substance which is structured in a less close atoms and molecules. What does Newtonian fluid mean? Newtonian fluids is the fluids in which shear stress is directly proportional to deformation rate, such as water, oil, air, etc. What does Non-Newtonian fluid mean? Non-Newtonian fluids is the fluids in which shear stress is not directly proportional to deformation rate, such as toothpaste, ketchup, etc. γ = du dy [s 1 ] = Shear rate Fig.1.1 Shear stress vs shear rate What does the viscosity mean, classify the type of the viscosity? The viscosity is a material properties which resists any external force. The viscosity can be distinguished into two types: 1. Kinematic viscosity is a substance property. 2. Dynamic viscosity is the ability of a matter to resist a body s motion. 1
1.2. Theories (Basic Concepts) Before discussing the behavior of the fluid, the basic concepts is to understand employing Newton s laws in case of the fluid flow. 1.2.1. Newton s First Law: W = mg Where m is a the mass of a substance, g is thegravitational acceleration (g = 9.81 m ft or 32.2 s2 s 2) 1.2.2. Newton s Second Law A body moves in a uniform velocity unless is exerted by an external force. F = ma Where, m is the mass of a body and a is the acceleration a = dv dx, the velcoity is v = dt dt. 1.2.3. Normal and shear stress: The normal stress is the normal force acts perpendicular on a body s surface area. σ = F A The shear stress is the tangential force acts on a body s surface area. τ = F A 1.2.4. First Law of thermodynamics (Conservation of Energy) The conservation of energy is also called first law of thermodynamics says The energy can t be created or destroyed, but it can change from form to anther forms of energy Closed System: the amount of mass in a system is fixed but the volume changes. Q k k W k k = E, ΔE = ΔU + ΔPE + ΔKE Open system: the amount of the mass flowrate in a system changes but the volume is fixed, i.e. mass flowrate crosses a system boundary. 2
Q i i + W i i Conservation of Mass + H i + 1 2 m V i 2 + m gz i = Q e e + W e e + H e + 1 2 m V e 2 + m gz e Conservation of mass states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. m t = m e e m i i 1.3. Thermodynamics Properties, Fluid Mechanics and Heat Quantities Concepts: Specific volume is the total volume per unit mass (unit volume/unit mass). v = V m Density is the amount of matter in a body per unit volume (unit mass/unit volume). ρ = m V Specific gravity is the ratio of a substance density to the water density at 4ᵒC. SG = ρ ρ @4 C Sensible heat is the amount of heat required to change the temperature of a substance. Latent heat is the amount of heat required to change the phase. Sublimation is the change from solid to gas without passing through the liquid phase. Pressure is the force exerted on a surface area (force per unit area). Surface tension is the apparent interfacial tensile stress that acts whenever a liquid has a density interface. λ = Force A unit length Entropy is a thermodynamics property which is used to measure of a disorder molecules. S = Q rev T 3
Enthalpy is a thermodynamics property which contains the internal energy of a substance plus the pressure energy. H = U + PV Heat flux is the total rate of heat per unit area. q" = Q A Incompressible fluid is flows in which variations are negligible, such as water, oil, etc. Compressible fluid is flows in which variations are not negligible, such as gases. Units and dimensions Table 1.1 Primary SI Units Table 1.2 Some derived units 4
Table 1.3 Some conversion factors in SI units Define 1. 0 th law of thermodynamics? Ans. If the two bodies are in the thermal equilibrium with a third body, they are also in thermal equilibrium with each other. 2. 1 st law of thermodynamics? Ans. The energy cannot created and destroyed but it changes from form to another 3. 2 nd law of thermodynamics? Ans. The energy has quality as well as a quantity, and actual processes occur in the direction of decreasing quality of energy. 4. A system in thermodynamics? 5. Open system and closed system? 6. Isothermal and adiabatic process? 7. Isobaric and Isochoric process? 8. Isentropic process? 9. Process and State? 10. Specific quantity? 11. Cycle and critical point? 12. A pure substance? 13. Saturated liquid and saturated vapor? 5
14. Compressed liquid? 15. Superheated? 16. Latent and sensible heat? Ans. Latent heat is the amount of heat required to change the phase of a pure substance, and the sensible heat is the amount of heat required change the temperature of a pure substance. 17. Sublimation Ans. A Phase which passes from the solid phase directly into the vapor phase. 18. Nuclear, chemical, and thermal energy? What is a turbine? What is a pump? What is a compressor? Which the following system is closed system or open system? System Open Closed Explain? Vessel Tank Piston Cylinder Compressor Turbine Pump Radiator Condenser Boiler 6
Evaporator Expansion V/V Deaerator Heat Exchanger Heater Define 1. Force, Pressure, Energy, and Power? 2. Torque, Kinetic Energy, Potential Energy, and Mechanical Energy? 3. Enthalpy, Entropy, and Energy? 4. Internal Energy, Total Energy? P T ρ ½ m ½ V P T ρ ½ m ½ V Fig.1.2. Intensive and Extensive Quantities 5. Manometer and Parameter? 6. Work and specific heat? 7. Properties, Extensive properties and Intensive properties? Ans. Intensive properties are those that are independent of the size of a system, and Extensive properties are those whose values depend on the size or extend of the system. 8. Molar mass, mole and molecular weight? 9. Thermal equilibrium, mechanical equilibrium, Phase equilibrium, and chemical equilibrium? 10. A pure substance, Specific properties, density, and mass? Ans. A pure substance is a substance that has a fixed chemical composition, 7
, 11. Path, Process, and Quasi-static (equilibrium) process? Table1.1. Units Conversion Table (UCT) Pressure 1kPa = 100bar 1atm=10.325 kpa 1MPa=1000 kpa 1atm = 14.696 psia Work and Energy 1Btu (British thermal unit) = 1.055 kj 1lbf = 32.174 Ibm. ft/s 2 1hp =2545 Btu/hr Temperature T(K)=T(C)+273 T(R) = T(F)+460 T(R) =1.8T(K) T(F)= 1.8 T(C)+32 Length and Volume 1 m =100cm 1km =1000m 1cm=10 mm 1ft =12 in 1m 3 =1000 Liter L 1cm 3 =0.001 L 1ft 3 =28.32 L 1 in 3 =0.0164 L Time 1 hr (hour) = 3600 sec (second) 1 hr = 60 min (minute) 1s = 1000 ms (millisecond) 8