THERMODYNAMICS Course no. ME22002 Section 1 Dr. Sourav Mitra Room No. 204 (first floor) Department of Mechanical Engineering 1 THERMODYNAMICS: Properties of Pure substance 2 T-v diagram for isobaric heating of water 3 T-v chart for water 4 T-v chart for water Isobars 4 T-v chart for water Isobars Isotherms 4 T-v chart for water Isobars Isotherms 4 T-v chart for water 5 T-v chart for water As we increase pressure the twophase region shortens 5 T-v chart for water As we increase pressure the twophase region shortens 5 Critical point 6 Critical point The point at which the saturated liquid and saturated vapor states are identical 6 Critical point The point at which the saturated liquid and saturated vapor states are identical The corresponding temperature is called critical temperature and pressure is called critical pressure. 6 P-v chart for water 7 P-v chart for water Isobars 7 P-v chart for water Isobars 7 P-T chart for water 8 P-T chart including solid phase 9 P-T chart including solid phase A-B: Melting/freezing A B 9 P-T chart including solid phase A-B: Melting/freezing A B C C-D: Boiling/condensation D 9 P-T chart including solid phase A-B: Melting/freezing B A C C-D: Boiling/condensation D E-F: Sublimation/deposition E F 9 P-v-T chart for water 10 P-v-T chart for water 10 P-v-T chart for water 10 P-v-T chart for substance that contract on freezing 11 P-v-T chart for substance that contract on freezing 11 P-v-T chart for substance that contract on freezing 11 Application of triple point Ptr & Ttr are fixed for a pure substance 12 Application of triple point Ptr & Ttr are fixed for a pure substance The cell is filled with pure deionized water and then evacuated. The top portion is not air but water vapor 12 Application of triple point Ptr & Ttr are fixed for a pure substance Vapor Liquid Cool using dry ice Ice The cell is filled with pure deionized water and then evacuated. The top portion is not air but water vapor 611.73 Pa 0.01°C Can be used for calibration of sensors 12 Application of triple point Ptr & Ttr are fixed for a pure substance Vapor Liquid Cool using dry ice Ice The cell is filled with pure deionized water and then evacuated. The top portion is not air but water vapor 611.73 Pa 0.01°C Can be used for calibration of sensors If you achieve 3 phases simultaneously, then Ptr , Ttr is obtained. 12 Application of triple point Ptr & Ttr are fixed for a pure substance Vapor Liquid Cool using dry ice Ice The cell is filled with pure deionized water and then evacuated. The top portion is not air but water vapor 611.73 Pa 0.01°C Can be used for calibration of sensors If you achieve 3 phases simultaneously, then Ptr , Ttr is obtained. What is the problem in using freezing point and boiling point of water? 12 Significance of critical point Pcr Tcr 13 Significance of critical point Suppose you are in vapor region with T<Tcr One can liquefy the vapor by the action of pressure alone Pcr Tcr 13 Significance of critical point Suppose you are in vapor region with T<Tcr One can liquefy the vapor by the action of pressure alone Pcr Suppose you are in vapor region with T>Tcr Liquefaction of the vapor by the action of pressure alone is impossible !! Tcr 13 Significance of critical point Suppose you are in vapor region with T<Tcr One can liquefy the vapor by the action of pressure alone Pcr Suppose you are in vapor region with T>Tcr Liquefaction of the vapor by the action of pressure alone is impossible !! Tcr Critical temp: the temperature beyond which vapor cannot be liquefied by the action of pressure alone 13 Significance of critical point Pcr Tcr 14 Significance of critical point Suppose you are in vapor region with P<Pcr One can liquefy the vapor by the action of temperature alone Pcr Tcr 14 Significance of critical point Suppose you are in vapor region with P<Pcr One can liquefy the vapor by the action of temperature alone Pcr Suppose you are in vapor region with P>Pcr Liquefaction of the vapor by the action of temperature alone is impossible !! Tcr 14 Significance of critical point Suppose you are in vapor region with P<Pcr One can liquefy the vapor by the action of temperature alone Pcr Suppose you are in vapor region with P>Pcr Liquefaction of the vapor by the action of temperature alone is impossible !! Tcr Critical temp: the pressure beyond which vapor cannot be liquefied by the action of temperature alone 14 Significance of critical point Supercritical fluid Pcr Tcr 15 Significance of critical point Supercritical fluid Pcr Tcr Fluid with temperature greater than critical temperature and pressure higher than critical pressure is called “Supercritical Fluid” 15 Quality or dryness fraction of vapor 16 Quality or dryness fraction of vapor 16 Quality or dryness fraction of vapor x vg v 16 Quality or dryness fraction of vapor v 1 x v f xvg x vg v Mixture specific volume: v 16 Quality or dryness fraction of vapor vapor fraction within the saturated mixture 17 Quality or dryness fraction of vapor vapor fraction within the saturated mixture Saturated vapor: x = 1 Saturated liquid: x = 0 17 Quality or dryness fraction of vapor vapor fraction within the saturated mixture Quality is an intensive property Saturated vapor: x = 1 Saturated liquid: x = 0 17 Quality or dryness fraction of vapor vapor fraction within the saturated mixture Saturated vapor: x = 1 Saturated liquid: x = 0 Quality is an intensive property Can be used with other independent intensive property like P or T for defining state of saturated mixture 17 Quality or dryness fraction of vapor vapor fraction within the saturated mixture Saturated vapor: x = 1 Saturated liquid: x = 0 Quality is an intensive property Can be used with other independent intensive property like P or T for defining state of saturated mixture Are x and v independent intensive properties ? 17 Ideal and Real gas 18 Ideal and Real gas Ideal gas assumption: Molecules are far apart hence no intermolecular forces 18 Ideal and Real gas Ideal gas assumption: Molecules are far apart hence no intermolecular forces Low density gases 18 Ideal and Real gas Ideal gas assumption: Molecules are far apart hence no intermolecular forces Low density gases • • But what constitutes low density? By how much does an actual gas at a given pressure and temperature deviate from ideal-gas behavior? 18 Ideal and Real gas Ideal gas assumption: Molecules are far apart hence no intermolecular forces Low density gases • • But what constitutes low density? By how much does an actual gas at a given pressure and temperature deviate from ideal-gas behavior? Error between ideal gas and experimental measurements for saturated and superheated water vapor 18 Ideal and Real gas Ideal gas assumption: Molecules are far apart hence no intermolecular forces Low density gases • • But what constitutes low density? By how much does an actual gas at a given pressure and temperature deviate from ideal-gas behavior? Error between ideal gas and experimental measurements for saturated and superheated water vapor High temperatures or very low pressure 18 Compressibility factor P0 Reduced pressure: PR = P/Pcr Reduced temperature: TR = T/Tcr 19 Compressibility factor • Bring in a factor called “compressibility factor” to define the deviation: Pv/RT=Z P0 Reduced pressure: PR = P/Pcr Reduced temperature: TR = T/Tcr 19 Compressibility factor • Bring in a factor called “compressibility factor” to define the deviation: Pv/RT=Z • • Z=1 (ideal gas) Any value of Z (real gas) P0 Reduced pressure: PR = P/Pcr Reduced temperature: TR = T/Tcr 19 Compressibility factor • Bring in a factor called “compressibility factor” to define the deviation: Pv/RT=Z • • Z=1 (ideal gas) Any value of Z (real gas) P0 vreal = ZRT/P videal = RT/P So Z = vreal/videal Reduced pressure: PR = P/Pcr Reduced temperature: TR = T/Tcr 19 Compressibility factor • Bring in a factor called “compressibility factor” to define the deviation: Pv/RT=Z • • Z=1 (ideal gas) Any value of Z (real gas) P0 vreal = ZRT/P videal = RT/P So Z = vreal/videal • • • Z=1 (no Inter-Molecular force) Z<1 (attractive forces) Z>1 (repulsive forces) Reduced pressure: PR = P/Pcr Reduced temperature: TR = T/Tcr 19 Compressibility factor Compressibility factor for nitrogen • • • Z=1 (no Inter-Molecular force) Z<1 (attractive forces) Z>1 (repulsive forces) 20 Property tables and charts P-h chart of steam Steam table We don’t need these charts and tables Use electronic tool to obtain this database 21
