1	Thermodynamics I Asst.Prof.Dr.Denpong Soodphakdee Department of Mechanical Engineering
2	Pure Substance Fixed chemical composition throughout There are three phases Solid Liquid Gas Phase can be changed from one to another.
3	Phase-Change Processes of Pure Substances Compressed Liquid :- not about to vaporize Saturated Liquid :- about to vaporize Saturated Vapor :- about to condense Saturated Liquid-Vapor Mixture :- liquid and vapor phases coexist Superheated vapor :- not about to condense
4	Phase-Change Processes of Pure Substances T-v diagram for the heating process of water at constant pressure.
5	Property Diagrams for Phase-Change Processes Critical point (the point at which the saturated liquid and saturated vapor states are identical) Saturated liquid line Saturated vapor line Compressed liquid region Superheated vapor region Saturated liquid-vapor mixture region or wet region
6	Property Diagrams for Phase-Change Processes :: T-v Diagram
7	Property Diagrams for Phase-Change Processes :: P-v Diagram
8	Property Diagrams for Phase-Change Processes :: P-v Diagram
9	Property Diagrams for Phase-Change Processes :: P-v Diagram
10	Property Diagrams for Phase-Change Processes :: P-T Diagram
11	Property Diagrams for Phase-Change Processes :: P-v-T Surface
12	Property Diagrams for Phase-Change Processes :: P-v-T Surface
13	Enthalpy Enthalpy is a combination property Enthalpy per unit mass
14	Saturated Liquid and Saturated Vapor States
15	Saturated Liquid and Saturated Vapor States
16	Example A mass of 200 gm of saturated liquid water is completely vaporized at a constant pressure of 100 kPa. Determine the volume change of the water.
17	Saturated Liquid-Vapor Mixture To analyze the mixture of saturated liquid and saturated vapor, the proportions of the liquid and vapor phases in the mixture needs to be known.
18	Saturated Liquid-Vapor Mixture Saturated Liquid-Vapor Mixture
19	Saturated Liquid-Vapor Mixture Average value of specific volume and quality
20	Saturated Liquid-Vapor Mixture Average of internal energy, enthalpy and other properties
21	Example A rigid tank contains 10 kg of water at 90 °C. If 8 kg of the water is in the liquid form and the rest is in the vapor form, determine (a) the pressure in the tank and (b) the volume of the tank.
22	Example An 80-L vessel contains 4 kg of refrigerant-12 at a pressure of 160 kPa. Determine (a) the temperature of the refrigerant, (b) the quality, (c) the enthalpy of the refrigerant, and (d) the volume occupied by the vapor phase.
23	Superheated Vapor Lower pressures (P < P_sat at a given T) Higher temperatures (T > T_sat at a given P) Higher specific volumes (v > v_g at a given P or T) Higher internal energies (u > u_g at a given P or T) Higher enthalpies (h > h_g at a given P or T)
24	Example Determine the temperature of water at a state of P = 0.5 MPa and h = 2890 kJ/kg.
25	Compressed Liquid Variation of properties in compressed liquid with pressure is very mild. A general approximation is to treat compressed liquid as saturated liquid at the given temperature.
26	Compressed Liquid Higher pressures (P > P_sat at a given T) Lower temperatures (T < T_sat at a given P) Lower specific volumes (v < v_g at a given P or T) Lower internal energies (u < u_g at a given P or T) Lower enthalpies (h < h_g at a given P or T)
27	Example Determine the internal energy of compressed liquid water at 80°C and 5 MPa, using (a) data from the compressed liquid table and (b) saturated liquid data. What is the error involved in the second case?
28	Reference State and Reference Values The value of u, h, and s can not be measured directly. They are calculated relatively between thermodynamic properties, not the value at that state. Reference state will give the reference value of zero. Example reference state: Water : saturated liquid at 0.01°C R134a : saturated liquid at -40°C
29	The Ideal-Gas Equation of State Any equation that relates the pressure, temperature, and specific volume of a substance is call an equation of state. Property relations that involves other properties of a substance at equilibrium state are also called equation of state.
30	The Ideal-Gas Equation of State The vapor phase of a substance is call a gas when it is above the critical temperature. Vapor usually implies a gas that is not far from a state of condensation. At low pressures the volume of a gas is proportional to its temperature.
31	The Ideal-Gas Equation of State The gas constant R is determine from
32	Example Determine the mass of the air in a room whose dimension are 4m´5m´6m at 100 kPa and 25°C.
33	Compressibility Factor A Measure of Deviation from Ideal-Gas Behavior
34	Compressibility Factor A Measure of Deviation from Ideal-Gas Behavior The deviation from ideal-gas behavior at a given temperature and pressure can accurately be accounted for by a correction factor called compressibility factor, Z.
35	Compressibility Factor A Measure of Deviation from Ideal-Gas Behavior
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