1. ENGR 2213 Thermodynamics F. C. Lai School of Aerospace and Mechanical Engineering University of Oklahoma

2. Basic Concepts Process Path The series of equilibrium states through which a system passes during a process To describe a process completely, one needs to specify the initial and final states of the process, as well as the path it follows Steady State Properties of the system does not change with time Cycle A sequence of processes that begins and ends at the same state

3. Intensive Properties Continuum Hypothesis - A substance is viewed to be a continuous, homogeneous matter ● Specific volume ● Pressure ● Temperature

4. Specific Volume Density Specific volume V’ is the smallest volume for which the matter can be Considered a continuum

5. Pressure - the normal force exerted by a fluid per unit area For a fluid at rest, pressure at a given point is the same in all direction. The pressure in a fluid increases with depth as a result of the weight of the fluid.

6. Pressure depth pressure Atmosphere P atm ●● ●● ●● APAPA B PBPB Water tank

7. Pressure depth pressure PAPA ●● ●● ●● BPBPB CPCPC Gas tank A

8. Pressure Absolute Pressure - the actual pressure at a given position - it is measured relative to absolute vacuum (i.e., absolute zero pressure) - reading from a pressure-measuring device Relative Pressure ● Gage pressure ● Vacuum Pressure

9. Pressure Gage Pressure pressure in the system > local atmospheric pressure P g = P - P atm Vacuum Pressure pressure in the system < local atmospheric pressure P v = P atm - P P = P g + P atm P = P atm - P v

10. Pressure Measuring Devices Manometer U-tube containing a fluid such as mercury, water, alcohol, or oil Gas h 12 P = P 1 = P 2 Force Balance AP 2 = AP atm + W = AP atm + (ρAh)g P 2 = P atm + ρgh ΔP = P 2 – P atm = ρgh

11. Pressure Measuring Devices Barometer - A device used to measure the atmospheric pressure - Discovered by Torricelli h 12 P atm = P 1 = P 2 Force Balance AP 2 = (ρAh)g P 2 = P atm = ρgh ●●

12. Pressure Standard Atmosphere The pressure produced by a column of mercury 760 mm (29.92 in.) in height at 0ºC under standard gravitational acceleration (g = 9.807m/s 2 ) If a water column were used, ρ Hg = 13,595 kg/m 3 it would require a height of 10.3 m

13. Temperature - a concept originates with our sense perceptions Properties of materials that change with temperature in a repeatable and predictable way Thermometric Properties Thermometric Substances Substances that exhibit thermometric property

14. Temperature Device thermocouple liquid-in-glass thermometer PropertySubstance volumemercury, alcohol electromotive force copper-constantan platinum-platinum & rhodium RTD-resistance temperature device electrical resistance platinum, nickel, copper

15. Temperature Device gas thermometer thermistor PropertySubstance electrical resistance semiconductors pressurehelium, hydrogen Gas thermometer is used as a standard temperature measuring device worldwide by bureaus of standards and research labs.

16. Temperature Scales Reference Points ● ice point a mixture of ice and water which is in equilibrium with air saturated with vapor at 1 atm pressure ● steam point a mixture of liquid water and water vapor, with no air, in equilibrium at 1 atm pressure ● triple point the state of equilibrium among steam, ice, and liquid water

17. Temperature Scales Celsius Scale - named after Swedish astronomer A. Celsius Ice point 0 ºC Steam point 100 ºC Triple point0.01ºC Ice point 0 ºC Steam point 100 ºC Triple point0.01ºC 100 divisions

18. Temperature Scales Fahrenheit Scale - named after German instrument maker G. Fahrenheit Ice point 32 ºF Steam point 212 ºF Triple point 32.02ºF Ice point 32 ºF Steam point 212 ºF Triple point 32.02ºF 180 divisions ºF = 1.8 (ºC) + 32

19. Temperature Scales A Sportsman’s Scale Ice point49 ºS Steam point 76 ºS 27 divisions

20. Temperature Scales Absolute Temperature Scale Gas A Gas B Gas C Gas D P T (ºC) Absolute Zero -273.15 ºC -459.67 ºF

21. Absolute Temperature Scales Kelvin Scale Ice point 0 ºC273.15 K Steam point 100 ºC373.15 K Triple point0.01ºC373.16 K K = ºC + 273.15 ºC = K - 273.15 Ice point 0 ºC273.15 K Steam point 100 ºC373.15 K Triple point0.01ºC373.16 K

22. Absolute Temperature Scales Rankine Scale Ice point 32 ºF491.67 K Steam point 212 ºF671.67 K Triple point 32.02ºF491.69 K R = ºF + 459.67 ºF = R – 459.67 Ice point 32 ºF491.67 K Steam point 212 ºF671.67 K Triple point 32.02ºF491.69 K

23. Absolute Temperature Scales The magnitudes of each division in K and ºC are equal The magnitudes of each division in R and ºF are equal Always use the absolute pressure in the Thermodynamics equations. Always use the absolute temperature in the Thermodynamics equations.

24. Zero th Law of Thermodynamics Two systems in thermal equilibrium with a third system are in thermal equilibrium with each other AC BC AB

25. Zero th Law of Thermodynamics First formulated by R. H. Fowler in 1931. Since the so-called First and Second Law of Thermodynamics were formulated much earlier, and since in a logical development of the subject it must be stated before them, it has been agreed to designate it as the Zero th Law.