Chapter 4 (propertiesof pure substance)
Download as PPT, PDF0 likes163 views
This document discusses the properties of pure substances during phase changes. It defines key terms like saturation temperature, saturation pressure, sub-cooled liquid, saturated liquid, saturated vapor, and superheated vapor. The document explains that 100°C is the saturation temperature corresponding to a pressure of 101.325 kPa. It also provides diagrams to illustrate the different regions on a T-S and h-S chart during phase changes and defines concepts like quality.
Chapter 4 (propertiesof pure substance)
- 1. PROPERTIES OF PURE SUBSTANCE a - sub-cooled liquid b - saturated liquid c - saturated mixture d - saturated vapor e - superheated vapor Considering that the system is heated at constant pressure where P = 101.325 KPa, the 100C is the saturation temperature corresponding to 101.325 KPa, and 101.325 KPa is the saturation pressure correspon- ding 100C. P P P P P Q 30°C 100°C 100°C 100°C T100°C (a) (b) (c) (d) (e) Q Q Q Q
- 2. Saturation Temperature (tsat) - is the highest temperature at a given pressure in which vaporization takes place. Saturation Pressure (Psat) - is the pressure corresponding to the temperature. Sub-cooled Liquid - is one whose temperature is less than the saturation temperature corresponding to the pressure. Compressed Liquid - is one whose pressure is greater than the saturation pressure corresponding to the temperature. Saturated Liquid - a liquid at the saturation temperature Saturated Vapor - a vapor at the saturation temperature Saturated Mixture - a mixture of liquid and vapor at the saturation temperature. Superheated Vapor - a vapor whose temperature is greater than the saturation temper a b c d e T F Saturated Vapor Saturated Vapor 30°C 100°C t 100°C Saturated Mixture P = C Critical Point T- Diagram
- 3. a b c d e T S F Saturated Vapor Saturated Vapor 30°C 100°C t 100°C Saturated Mixture P = C Critical Point T-S Diagram F(critical point)- at the critical point the temperature and pressure is unique. For Steam: At Critical Point, P = 22.09 MPa; t = 374.136C
- 4. a b c d e T S F Saturated Vapor Saturated Vapor ta tsat te Saturated Mixture P = C Critical Point T-S Diagram tsat - saturation temperature corresponding the pressure P ta - sub-cooled temperature which is less than tsat te - superheated vapor temperature that is greater than tsat
- 5. h-S (Enthalpy-Entropy Diagram) h S t = C (constant temperature curve) P = C (constant pressure curve)F I II III I - subcooled or compressed liquid region II - saturated mixture region III - superheated vapor region Entropy(S): Entropy is that property of a substance that determines the amount of randomness and disorder of a substance. During a process if an amountof heat is taken and is divided by the absolute temperature at which it is taken, the result is called the “Entropy Change” T dQ S
- 6. Quality (x): Lv v Lv v mmm m m mm m x Where: mv – mass of vapor mL – mass of liquid m – total mass x- quality The properties at saturated liquid, saturated vapor, superheated vapor and sub-cooled or compressed liquid can be determined from tables. But for the properties at saturated mixture (liquid and vapor) they can be determined by the equation rc = rf + x(rfg) rfg = rg – rf Where: r stands for any property (, U, h and S) rg – property at saturated vapor (from table) rf – property at saturated liquid Note: The properties at siub-cooled or compressed liquid is approximately equal to the properties at saturated liquid corresponding the sub-cooled temperature.
- 7. Throttling Calorimeter Main Steam Line P1 – steam line pressure To main steam line P2 -Calorimeter pressure h1 = h2 h1 = hf1 + x1(hfg1) Where: 1 – main steam line 2 - calorimeter thermometer
- 8. P1 P2 1 2 T S h = C T-S Diagram Throttling Process P1 – steam line pressure P2 – calorimeter pressure