01 Thermodynamic Properties Concept Overview
THERMODYNAMIC PROPERTIES | CONCEPT OVERVIEW The topic of PROPERTIES OF SINGLE-COMPONENT SYSTEMS can be referenced on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
CONCEPT INTRO: THERMODYNAMICS is the study of energy, energy transformations, and its relation from one form via the interactions within thermodynamic systems. Thermodynamics focuses heavily on heat, temperature, and pressure, and the relationship a mechanical process or chemical reaction will have on a system, and the changes in energy that are accompanied by various interactions. A THERMODYNAMIC PROPERTY is an attribute of a system to which a value can be assigned to describe the system. A defining characteristic of a property is that the value can be stated at a given time independently of its values at any other time, and independently of the process by which the system arrived at its state. The topics of NOMENCLATURE AND STATE FUNCTIONS (PROPERTIES) can be referenced under the topic of THERMODYNAMICS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
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The STATE OF A MEDIUM is the properties of that medium that can be divided into two major categories: 1. INTENSIVE PROPERTIES are properties independent of mass. Examples of intensive properties are pressure, βπβ, density, βπβ, and temperature, βπβ. 2. EXTENSIVE PROPERTIES are properties proportional with the mass of the system. Examples of extensive properties are volume, (π), total enthalpy, (π»), total internal energy, (π), and mass, (π). STATE PROPERTIES are properties dependent upon the thermodynamic state of the system and are independent of the path the system takes to reach that state. Some state properties are ππππ π π’ππ π , π‘πππππππ‘π’ππ π , π πππππππ π£πππ’ππ π£ , πππ‘πππππ energy (U), enthalpy (H), entropy (S), Gibbs free energy (G), Helmholtz free energy (A), and heat capacities at constant pressure (πΆ: ) and constant volume (πΆ< ). MASS, (π), is the measure of a substanceβs or systemβs quantity. It is expressed in units of pound-mass (πππ) and kilograms (ππ). SPECIFIC PROPERTIES are properties determined by dividing the value of an extensive property by the mass of the system. A specific property is commonly denoted by the lower case version of the letter used to represent the extensive property. Examples of specific properties are: β’ specific volume, (π) β’
enthalpy, (β)
β’ entropy, (π )
β’ internal energy, (π’) Made with
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The FORMULA FOR SPECIFIC VOLUME can be referenced under the topic of STATE FUNCTIONS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The SPECIFIC VOLUME is the volume occupied by a unit mass of substance. It is expressed in units of ft D /lbm or mD /kg. It is calculated as the total volume divided by the mass:
π=
π π
Where: β’ π is the volume of the system in units of ft D or mD β’ π is the mass of the system in units of lbm or kg β’ π is the specific volume of the system in units of ft D /lbm or mD /kg The FORMULA FOR DENSITY can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. DENSITY π is the mass π divided by the volume (π) or the inverse of the specific volume (π£).
π =
π 1 1 = ππ π = π£ π π
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The formula for PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. PRESSURE, (π), is defined as the force per unit area normal to the force:
π=
πΉ π΄
Pressure is measured as GAUGE PRESSURE, the difference between ABSOLUTE and the ATMOSPHERIC. Gauge pressure is either positive or negative (vacuum). The AMBIENT PRESSURE is pressure at which the vapor pressure is equal to the surrounding pressure. This is the pressure at which a liquid boils.
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The formula for ABSOLUTE PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We use the following formula to relate absolute pressure, atmospheric pressure, and gauge pressure. πOPQ = πORS + πUOVUW Where: πOPQ = Absolute Pressure πORS = Atmospheric Pressure πUOUW = Gauge Pressure (positive or negative) The topic of TEMPERATURE is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We must memorize this formula and understand its application independent of the NCEES Supplied Reference Handbook. TEMPERATURE, (π), is the thermodynamic property of a substance that depends on the energy content. A variance, or difference in temperature, (π₯π), is required for heat energy to flow. A TEMPERATURE SCALE is a unit measurement system for determining the kinetic energy of the particles in a material. For the purposes of the FE Exam, the four commonly used temperature scales that we should be familiar with are: Fahrenheit, Celsius, Rankine, and Kelvin.
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The FAHRENHEIT TEMPERATURE SCALE is based on 32Β°πΉ for the freezing point of water and 212Β°πΉ for the boiling point of water. A degree on the Fahrenheit scale represents 1/180 of the temperature range between the freezing and boiling points of water. The CELSIUS TEMPERATURE SCALE is based on 0Β°πΆ for the freezing point and 100Β°πΆ for the boiling point of water. A degree on the Celsius scale represents 1/100 of the temperature range between the freezing and boiling points of water. The ABSOLUTE TEMPERATURE SCALE is a commonly used scale of temperature units in thermodynamic problems, and is given in units of Rankine (Β°R) and Kelvin (K). As there are no negative temperatures on the absolute temperature scale, the coldest theoretical temperature is ABSOLUTE ZERO, which is represented as 0 K on the Kelvin temperature scale and 0Β°π on the Rankine Scale. Absolute zero represents the temperature at which the thermal motion of atoms and molecules reaches its minimum. The KELVIN TEMPERATURE SCALE is the absolute temperature scale used in the International Engineering Systems and SI System of units. The Kelvin scale of temperature uses Celsius degree from absolute zero, and is based on 0 K being defined as absolute zero. The RANKINE TEMPERATURE SCALE is the absolute temperature scale used in the American Engineering System and in the English System of Units. The Rankine scale of temperature uses Fahrenheit degrees from absolute zero, and is based on 0Β°π being defined as absolute zero.
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The formulas for the UNIT CONVERSIONS OF TEMPERATURE can be referenced under the topic of UNITS on page 1 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The formula for converting a Celsius temperature to degrees Fahrenheit is expressed using the following expression: π` = 1.8 πc + 32 Where: β’ π` is the temperature given in degrees Fahrenheit(Β°πΉ) β’ πc is the temperature given units of degrees Celsius (Β°πΆ) The formula for converting a Fahrenheit temperature to degrees Celsius is expressed using the following expression: πc = (π` β 32)/1.8 Where: β’ π` is the temperature given in degrees Fahrenheit(Β°πΉ) β’ πc is the temperature given units of degrees Celsius (Β°πΆ)
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The formula for converting a Fahrenheit temperature to the Absolute Temperature Scale in units of degrees Rankine (Β°π ) is expressed using the following expression: πe = π` + 459.67
π₯πe = π₯π`
Where: β’ πe is the temperature given in degrees Rankine (Β°π ) β’ π` is the temperature given in degrees Fahrenheit(Β°πΉ) The formula for converting a Celsius temperature to the Absolute Temperature Scale in units of Kelvin (πΎ) is expressed using the following expression: πl = πc + 273.15
π₯πl = π₯πc
Where: β’ πm is the temperature given in units of Kelvin (πΎ) β’ πc is the temperature given units of degrees Celsius (Β°πΆ)
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NOMENCLATURE: The topic of NOMENCLATURE can be referenced under the topic of STATE PROPERTIES OF SINGLE-COMPONENT SYSTEMS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. ENERGY is the ability to do work. When the work is actually being done, the energy is considered KINETIC, and when the work is waiting to be done and there is the potential do work, the energy is considered POTENTIAL. Energy is always conserved, it is neither created nor destroyed, but is transformed from one form to another. POTENTIAL ENERGY (ππΈ) is the energy that results from an objectβs position or arrangement of parts that can be come kinetic energy. The measurement of potential energy in an object is calculated based on the objectβs mass, height, or distance. Potential energy is given in units of Joules (J). KINETIC ENERGY (πΎπΈ) is the energy that results from an objectβs motion. The measurement of kinetic energy in an object is calculated based on the objectβs mass and velocity. Kinetic energy is given in units of Joules (J). INTERNAL ENERGY (π) accounts for all of the energy of a substance, representing the sum of the kinetic and potential energies of the mass comprising the system. HEAT ENERGY (π) is the energy transferred across the boundaries of a system because of the temperature difference. Heat energy is the result of the movement of atoms, molecules, or ions transferring from one solid, liquid, or gas to another.
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WORK (π) is the process of transferring energy across the boundaries of a system in the form of mechanical energy across the boundaries of a system, and is not a system state property. A SIMPLE SUBSTANCE is a substance that is macroscopically homogeneous and is isotropic. A PURE SUBSTANCE is a substance that has a definite and constant composition whose properties are homogeneous. HOMOGENEOUS indicates that the properties of a material are uniform throughout. ISOTROPIC indicates that there is no preferred spatial direction in which any interaction will behave differently than if applied from any other spatial direction. ENTROPY is the energy which is no longer available to perform useful work. SPECIFIC ENTHALPY is represented by the equation β = π’ + ππ = π»/π and is given in units of Btu/lbm or kJ/kg. SPECIFIC ENTROPY is represented by βπ β and given in units of π΅π‘π’/πππ-π or ππ½/ππ-πΎ. It is represented by the equation π = π/π. SPECIFIC HEAT AT CONSTANT PRESSURE is represented by πΆx and given in units of π΅π‘π’/πππ-π or ππ½/ππ-πΎ. SPECIFIC HEAT AT CONSTANT VOLUME is represented by βπΆy β and given in units of π΅π‘π’
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CONCEPT EXAMPLE: The following problem introduces the concept reviewed within this module. Use this content as a primer for the subsequent material.
A pressure gage on the receiver of an air compressor gives a reading of 0.22 πππ (gage). What is the absolute pressure of the tank, in units kPa, if the surrounding atmospheric pressure is 101 πππ? A. 121 B. 221 C. 321 D. 421
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SOLUTION: The TOPIC OF STATE FUNCTIONS (PROPERTIES) can be referenced under the topic of THERMODYNAMICS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We are given: β’ Gage Pressure πUOUW = 0.22 MPa β’ Atmospheric Pressure: πORS = 101 kPa The for ABSOLUTE PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We use the following formula to relate absolute pressure, atmospheric pressure, and gauge pressure. πOPQ = πORS + πUOUW
πOPQ
10D πππ = 0.22 πππ + 101 πππ = 321 πππ 1 πππ
Therefore, the correct answer choice is C. πππ ππ·π.
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CONCEPT INTRO: THERMODYNAMICS is the study of energy, energy transformations, and its relation from one form via the interactions within thermodynamic systems. Thermodynamics focuses heavily on heat, temperature, and pressure, and the relationship a mechanical process or chemical reaction will have on a system, and the changes in energy that are accompanied by various interactions. A THERMODYNAMIC PROPERTY is an attribute of a system to which a value can be assigned to describe the system. A defining characteristic of a property is that the value can be stated at a given time independently of its values at any other time, and independently of the process by which the system arrived at its state. The topics of NOMENCLATURE AND STATE FUNCTIONS (PROPERTIES) can be referenced under the topic of THERMODYNAMICS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
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The STATE OF A MEDIUM is the properties of that medium that can be divided into two major categories: 1. INTENSIVE PROPERTIES are properties independent of mass. Examples of intensive properties are pressure, βπβ, density, βπβ, and temperature, βπβ. 2. EXTENSIVE PROPERTIES are properties proportional with the mass of the system. Examples of extensive properties are volume, (π), total enthalpy, (π»), total internal energy, (π), and mass, (π). STATE PROPERTIES are properties dependent upon the thermodynamic state of the system and are independent of the path the system takes to reach that state. Some state properties are ππππ π π’ππ π , π‘πππππππ‘π’ππ π , π πππππππ π£πππ’ππ π£ , πππ‘πππππ energy (U), enthalpy (H), entropy (S), Gibbs free energy (G), Helmholtz free energy (A), and heat capacities at constant pressure (πΆ: ) and constant volume (πΆ< ). MASS, (π), is the measure of a substanceβs or systemβs quantity. It is expressed in units of pound-mass (πππ) and kilograms (ππ). SPECIFIC PROPERTIES are properties determined by dividing the value of an extensive property by the mass of the system. A specific property is commonly denoted by the lower case version of the letter used to represent the extensive property. Examples of specific properties are: β’ specific volume, (π) β’
enthalpy, (β)
β’ entropy, (π )
β’ internal energy, (π’) Made with
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The FORMULA FOR SPECIFIC VOLUME can be referenced under the topic of STATE FUNCTIONS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The SPECIFIC VOLUME is the volume occupied by a unit mass of substance. It is expressed in units of ft D /lbm or mD /kg. It is calculated as the total volume divided by the mass:
π=
π π
Where: β’ π is the volume of the system in units of ft D or mD β’ π is the mass of the system in units of lbm or kg β’ π is the specific volume of the system in units of ft D /lbm or mD /kg The FORMULA FOR DENSITY can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. DENSITY π is the mass π divided by the volume (π) or the inverse of the specific volume (π£).
π =
π 1 1 = ππ π = π£ π π
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The formula for PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. PRESSURE, (π), is defined as the force per unit area normal to the force:
π=
πΉ π΄
Pressure is measured as GAUGE PRESSURE, the difference between ABSOLUTE and the ATMOSPHERIC. Gauge pressure is either positive or negative (vacuum). The AMBIENT PRESSURE is pressure at which the vapor pressure is equal to the surrounding pressure. This is the pressure at which a liquid boils.
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The formula for ABSOLUTE PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We use the following formula to relate absolute pressure, atmospheric pressure, and gauge pressure. πOPQ = πORS + πUOVUW Where: πOPQ = Absolute Pressure πORS = Atmospheric Pressure πUOUW = Gauge Pressure (positive or negative) The topic of TEMPERATURE is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We must memorize this formula and understand its application independent of the NCEES Supplied Reference Handbook. TEMPERATURE, (π), is the thermodynamic property of a substance that depends on the energy content. A variance, or difference in temperature, (π₯π), is required for heat energy to flow. A TEMPERATURE SCALE is a unit measurement system for determining the kinetic energy of the particles in a material. For the purposes of the FE Exam, the four commonly used temperature scales that we should be familiar with are: Fahrenheit, Celsius, Rankine, and Kelvin.
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The FAHRENHEIT TEMPERATURE SCALE is based on 32Β°πΉ for the freezing point of water and 212Β°πΉ for the boiling point of water. A degree on the Fahrenheit scale represents 1/180 of the temperature range between the freezing and boiling points of water. The CELSIUS TEMPERATURE SCALE is based on 0Β°πΆ for the freezing point and 100Β°πΆ for the boiling point of water. A degree on the Celsius scale represents 1/100 of the temperature range between the freezing and boiling points of water. The ABSOLUTE TEMPERATURE SCALE is a commonly used scale of temperature units in thermodynamic problems, and is given in units of Rankine (Β°R) and Kelvin (K). As there are no negative temperatures on the absolute temperature scale, the coldest theoretical temperature is ABSOLUTE ZERO, which is represented as 0 K on the Kelvin temperature scale and 0Β°π on the Rankine Scale. Absolute zero represents the temperature at which the thermal motion of atoms and molecules reaches its minimum. The KELVIN TEMPERATURE SCALE is the absolute temperature scale used in the International Engineering Systems and SI System of units. The Kelvin scale of temperature uses Celsius degree from absolute zero, and is based on 0 K being defined as absolute zero. The RANKINE TEMPERATURE SCALE is the absolute temperature scale used in the American Engineering System and in the English System of Units. The Rankine scale of temperature uses Fahrenheit degrees from absolute zero, and is based on 0Β°π being defined as absolute zero.
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The formulas for the UNIT CONVERSIONS OF TEMPERATURE can be referenced under the topic of UNITS on page 1 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The formula for converting a Celsius temperature to degrees Fahrenheit is expressed using the following expression: π` = 1.8 πc + 32 Where: β’ π` is the temperature given in degrees Fahrenheit(Β°πΉ) β’ πc is the temperature given units of degrees Celsius (Β°πΆ) The formula for converting a Fahrenheit temperature to degrees Celsius is expressed using the following expression: πc = (π` β 32)/1.8 Where: β’ π` is the temperature given in degrees Fahrenheit(Β°πΉ) β’ πc is the temperature given units of degrees Celsius (Β°πΆ)
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The formula for converting a Fahrenheit temperature to the Absolute Temperature Scale in units of degrees Rankine (Β°π ) is expressed using the following expression: πe = π` + 459.67
π₯πe = π₯π`
Where: β’ πe is the temperature given in degrees Rankine (Β°π ) β’ π` is the temperature given in degrees Fahrenheit(Β°πΉ) The formula for converting a Celsius temperature to the Absolute Temperature Scale in units of Kelvin (πΎ) is expressed using the following expression: πl = πc + 273.15
π₯πl = π₯πc
Where: β’ πm is the temperature given in units of Kelvin (πΎ) β’ πc is the temperature given units of degrees Celsius (Β°πΆ)
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NOMENCLATURE: The topic of NOMENCLATURE can be referenced under the topic of STATE PROPERTIES OF SINGLE-COMPONENT SYSTEMS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. ENERGY is the ability to do work. When the work is actually being done, the energy is considered KINETIC, and when the work is waiting to be done and there is the potential do work, the energy is considered POTENTIAL. Energy is always conserved, it is neither created nor destroyed, but is transformed from one form to another. POTENTIAL ENERGY (ππΈ) is the energy that results from an objectβs position or arrangement of parts that can be come kinetic energy. The measurement of potential energy in an object is calculated based on the objectβs mass, height, or distance. Potential energy is given in units of Joules (J). KINETIC ENERGY (πΎπΈ) is the energy that results from an objectβs motion. The measurement of kinetic energy in an object is calculated based on the objectβs mass and velocity. Kinetic energy is given in units of Joules (J). INTERNAL ENERGY (π) accounts for all of the energy of a substance, representing the sum of the kinetic and potential energies of the mass comprising the system. HEAT ENERGY (π) is the energy transferred across the boundaries of a system because of the temperature difference. Heat energy is the result of the movement of atoms, molecules, or ions transferring from one solid, liquid, or gas to another.
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WORK (π) is the process of transferring energy across the boundaries of a system in the form of mechanical energy across the boundaries of a system, and is not a system state property. A SIMPLE SUBSTANCE is a substance that is macroscopically homogeneous and is isotropic. A PURE SUBSTANCE is a substance that has a definite and constant composition whose properties are homogeneous. HOMOGENEOUS indicates that the properties of a material are uniform throughout. ISOTROPIC indicates that there is no preferred spatial direction in which any interaction will behave differently than if applied from any other spatial direction. ENTROPY is the energy which is no longer available to perform useful work. SPECIFIC ENTHALPY is represented by the equation β = π’ + ππ = π»/π and is given in units of Btu/lbm or kJ/kg. SPECIFIC ENTROPY is represented by βπ β and given in units of π΅π‘π’/πππ-π or ππ½/ππ-πΎ. It is represented by the equation π = π/π. SPECIFIC HEAT AT CONSTANT PRESSURE is represented by πΆx and given in units of π΅π‘π’/πππ-π or ππ½/ππ-πΎ. SPECIFIC HEAT AT CONSTANT VOLUME is represented by βπΆy β and given in units of π΅π‘π’
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CONCEPT EXAMPLE: The following problem introduces the concept reviewed within this module. Use this content as a primer for the subsequent material.
A pressure gage on the receiver of an air compressor gives a reading of 0.22 πππ (gage). What is the absolute pressure of the tank, in units kPa, if the surrounding atmospheric pressure is 101 πππ? A. 121 B. 221 C. 321 D. 421
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SOLUTION: The TOPIC OF STATE FUNCTIONS (PROPERTIES) can be referenced under the topic of THERMODYNAMICS on page 87 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We are given: β’ Gage Pressure πUOUW = 0.22 MPa β’ Atmospheric Pressure: πORS = 101 kPa The for ABSOLUTE PRESSURE can be referenced under the topic of FLUID MECHANICS on page 103 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. We use the following formula to relate absolute pressure, atmospheric pressure, and gauge pressure. πOPQ = πORS + πUOUW
πOPQ
10D πππ = 0.22 πππ + 101 πππ = 321 πππ 1 πππ
Therefore, the correct answer choice is C. πππ ππ·π.
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