Thermodynamics 2 Instructor: Engr. John Harvey V. Bequio, ME, RMP Review of Thermodynamics 1 What is Thermodynamics? Branch of physical sciences that treats of various phenomena of energy and the related properties of matter, especially of the laws of transformation of heat into other forms of energy and vice versa. Thermodynamic System - refers to the quantity of matter or certain volume in space chosen for the study. Thermodynamics 2 Review of Thermodynamics 1 Thermodynamic Surroundings - all matter and space outside the system. Thermodynamic Boundary - a real/imaginary surface that separates the system from its surroundings. It can be fixed or movable. Thermodynamic Properties: 1) Intensive Property - As you change the amount of substance, the property does not change. Independent on its mass. 2) Extensive Property - Property varies with amount. Dependent on its mass. Thermodynamics 2 Review of Thermodynamics 1 Working Substance - a substance to which heat can be stored and from which heat can be extracted. Pure Substance - is a working substance whose chemical composition remains the same even if there is a change in phase. Ex. Water, Ammonia, Freon-12 Ideal Gas - is a working substance that remains in the gaseous state during its operating cycle and whose equation of state is PV=mRT. Ex. Air, Oxygen Gas, Nitrogen Gas, Carbon Dioxide. Thermodynamics 2 Review of Thermodynamics 1 Properties of a Working Substance 1. Mass and Weight Mass - a property of matter that constitutes one of the fundamental physical measurements or the amount of matter a body contains. Weight - the force acting on a body in a gravitational field, equal to the product of its mass and the gravitational acceleration of the field. 2. Volume - amount of space occupied by, or contained in a body and is measured by the no. of cubes a body contains Thermodynamics 2 Review of Thermodynamics 1 3. Temperature - Degree of hotness and coldness. Thermodynamics 2 Review of Thermodynamics 1 4. Pressure - force per unit area. 5. Specific Volume, Density and Specific Weight Density - Mass per unit volume Specific Volume - volume per unit mass Specific Weight - force on gravity or weight per unit volume 6. Internal Energy - Heat energy due to the movement of the molecules within the substance brought about its temperature. Thermodynamics 2 Review of Thermodynamics 1 7. Flow work - work due to the change in volume. 8. Enthalpy - the total heat and heat content of a substance which is equal to the sum of the internal energy of a body and the product of pressure and specific volume. 9. Entropy - measure of randomness of the molecules of a substance or measures the fraction of the total energy of a system that is not available for doing work. Thermodynamics 2 Review of Thermodynamics 1 Work, Heat, and Power Work - the quantity of energy transferred from one system to another Heat - energy in transit from a high-temperature object to a lower temperature object. Power - the amount of energy transferred per unit time. Thermodynamics 2 Review of Thermodynamics 1 Laws of Thermodynamics 1. First Law of Thermodynamics: Total Energy Entering the System = Total Energy Leaving the System 2. Second Law of Thermodynamics Kelvin Planck statement applied to the heat engine: "It is impossible to construct a heat engine which operates in a cycle and receives a given amount of heat from a high-temperature body and does an equal amount of work." Clausius statement applied to the pump: "It is impossible to construct a heat pump that operates without an input work." Thermodynamics 2 Review of Thermodynamics 1 Note: The most efficient operating cycle is the Carnot Cycle. 3. Third Law of Thermodynamics: "The entropy of a substance of absolute zero temperature is zero." 4. Zeroth Law of Thermodynamics: "If two bodies have the same temperature as a third body, they have the same temperature with each other." Ideal Gases - An Ideal gas is a substance that has the equation of state. Ideal Gas Laws Boyle's Law - Constant Temperature Charles' Law - Constant Pressure Gay-Lussac's Law - Constant Volume Thermodynamics 2 Review of Thermodynamics 1 Processes Involving Ideal Gases: ❖ ❖ ❖ ❖ ❖ ❖ ❖ ❖ Reversible Process: No friction Loss Adiabatic Process: No heat loss, no heat gain Constant enthalpy process or Adiabatic Throttling Process Constant Entropy Process or Isentropic Process Constant Volume Process or Isometric/Isochoric/Isovolumic Process Constant Pressure Process or Isobaric Process Constant Temperature Process or Isothermal Process Polytropic Process Thermodynamics 2 Module 1: Steam Properties What is a Pure Substance? It is defined as a working substance whose chemical composition remains the same even if there is a change in phase. Note: Pure substances do not behave like ideal gases. Properties of a Pure Substance: Pressure Temperature Specific Volume Internal Energy Enthalpy Entropy Thermodynamics 2 Module 1: Steam Properties Saturation Temperature The temperature at which liquids start to boil and vapors start to condense. Subcooled Liquid One which has a temperature lower than the saturation temperature corresponding to the existing pressure. Thermodynamics 2 Module 1: Steam Properties Subcooled Liquid One which has a temperature lower than the saturation temperature corresponding to the existing pressure. Thermodynamics 2 Module 1: Steam Properties Compressed Liquid One which has a pressure higher than the saturation pressure corresponding to the existing temperature. Thermodynamics 2 Module 1: Steam Properties Saturated Liquid Liquid at the saturations (saturation temperature or saturation pressure) which has a temperature equal to the boiling point corresponding to the existing pressure. Pure Liquid. Thermodynamics 2 Module 1: Steam Properties Saturated Vapor Vapor is at the saturation conditions (saturation temperature or saturation pressure). No moisture content. Thermodynamics 2 Module 1: Steam Properties Superheated Vapor It is a vapor having a temperature higher than the saturation temperature corresponding to the existing pressure. Thermodynamics 2 Module 1: Steam Properties Superheated Vapor It is a vapor having a temperature higher than the saturation temperature corresponding to the existing pressure. Thermodynamics 2 Module 1: Steam Properties Degrees of Superheat, °SH Difference between the actual temperature of superheated vapor and the saturation temperature for the existing pressure. Thermodynamics 2 Module 1: Steam Properties Degrees of Subcooled, °SB Difference between the saturation temperature for the given pressure and the actual subcooled liquid temperature. Thermodynamics 2 Module 1: Steam Properties Wet Vapor Combination of saturated vapor and saturated liquid. Quality, x The quality of wet vapor or wet steam is the percent by weight that is a saturated vapor. Percent Moisture, y The percent moisture of a wet vapor is the percent by weight that is a saturated liquid. Latent Heat of Vaporization The amount of heat required to change the mass of boiling water to the mass of steam. This same amount of heat is released when the mass of steam is condensed back into the mass of water. Thermodynamics 2 Module 1: Steam Properties Critical Point It represents the highest pressure and highest temperature at which liquid and vapor can coexist in equilibrium. Sensible Heat It is a heat that causes a change in temperature without a change in phase. Latent Heat It is a heat that causes a change in phase without a change in temperature. Thermodynamics 2 Module 1: Steam Properties STEAM TABLE: How to Use It? It is used to determine the thermodynamic properties of water including Vapor, Liquid, and Solid Phases. We will be using 3 tables: Saturation-Temperatures Tables, Saturation-Pressures Tables, and Superheated Vapor Tables Thermodynamics 2 Module 1: Steam Properties STEAM TABLE: Thermodynamics 2 Module 1: Steam Properties Thermodynamics 2 Module 1: Steam Properties STEAM TABLE: Saturation-Temperatures Tables Thermodynamics 2 Module 1: Steam Properties STEAM TABLE: Saturation-Pressures Tables Thermodynamics 2 Module 1: Steam Properties STEAM TABLE: Superheated Vapor Tables Thermodynamics 2 Module 1: Steam Properties Temperature and Pressure Saturation Tables are used when the condition is either saturated or wet. Example: Water at 200°C at 1.5538 MPa Thermodynamics 2 Module 1: Steam Properties As mentioned above, saturation occurs when the temperature is equal to the existing pressure. Look at the table and notice that at a temperature of 200°C the saturation pressure is 1.5538 MPa which means that the temperature in the example is equal to the existing pressure. Since it is denoted as "water", therefore the condition is Saturated Liquid. 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