Questions and Answers
Which of the following is an intensive property?
Throttling is which type of process?
Why is temperature of a gas produced due to?
kinetic energy of molecules
What is the temperature at which a system goes under a reversible isothermal process without heat transfer?
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What is the work done for a constant volume process?
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When there is no heat exchange between two bodies at the same temperature, they are said to be in:
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What is another name for total heat of a substance?
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What is the universal gas constant in SI units equal to?
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Which of the following processes is also known as an isometric process?
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Molar specific heat of an ideal gas depends on which two factors?
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An adiabatic process is one in which the temperature of the gas changes.
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A frictionless quasi static process is called a ____________ process.
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Match the following with their characteristics:
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Which law of thermodynamics forms the basis of the measurement of temperature?
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Which of the following is the extensive property of a thermodynamic system?
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Heat and work are classified as which type of properties?
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A _________ system is exemplified by a jet engine.
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Internal Energy is a function of only pressure.
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Which of the following statements about an ideal gas is false?
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The area under the T-S diagram curve at any thermodynamic process represents:
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What is enthalpy?
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Enthalpy is the addition of internal energy i.e. $\Delta Q = T.dS$ and product of pressure volume. $H = U + PV$. The area under the P-V diagram curve at any thermodynamic process represents ______ done.
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Isolated system indicates both mass and energy of substance cross the boundary.
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In an isothermal process, the internal energy:
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In a free expansion process, which of the following statements is true?
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Which of the following are intensive properties?
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Which of the following is NOT an extensive property?
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Of the following, which quantity is a 'path function'?
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Which of the following is the property of a system?
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What is the latent heat of ice?
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Specific heat is the amount of heat required to raise the temperature by what unit?
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Ice kept in a well-insulated thermoflask is an example of which system?
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Which of the following is an extensive property?
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What is the end temperature after 24 hours in a thermally insulated room undergoing a hyperbolic process with initial temperature of 50°C?
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In the Pressure-Volume (P-V) diagram, what does the area under the process line represent?
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An adiabatic process is always reversible.
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The correct formula for converting temperature units from Celsius (C) to Fahrenheit (F) is ______.
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What is the gas constant (R) defined as in thermodynamics?
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Which of the following variables controls the physical properties of a perfect gas?
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Heat transfer occurs due to temperature difference.
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The amount of heat required to raise the temperature of 1 kg of water by 1°C is called ________.
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Which statement correctly describes the relation between specific heat at constant pressure (Cp) and specific heat at constant volume (Cv)?
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What is the equivalent Fahrenheit reading for a temperature of 40°C?
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In a steady flow process, which of the following statements is true?
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What is a quasi-static process?
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Temperature and pressure of a perfect gas are intensive properties.
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The work done in the expansion of a gas from volume $V_1$ to $V_2$ under constant pressure 'P' is equal to P(V2 – V1).
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Match the expansion properties with their correct description:
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Heat addition to a system at constant volume will increase its:
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What is the final temperature of a perfect gas when heated at constant pressure till its volume is doubled from 270ºC?
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What is the ratio of Cp to Cv of a perfect gas?
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Which gas among the following has the highest adiabatic index?
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What is 100ºC in Fahrenheit?
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The temperature at which the volume of a gas becomes zero is called ____________.
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What causes the pressure exerted on the walls of a container by gas molecules?
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What are the fixed points for the Celsius temperature scale?
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What are the values of Cp and Cv for a particular ideal gas with R = 0.280 kJ/kgK and γ = 1.375?
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Study Notes
Thermodynamics
- Zeroth law of thermodynamics forms the basis of measurement of temperature.
- This law states that when two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.
Basic Concepts
- Throttling process is a constant enthalpy process or isenthalpic process.
- Characteristics of throttling process:
- No work transfer
- No heat transfer
- It is irreversible process
- It is isenthalpic process
Properties
- Extensive property: Volume is an example of an extensive property.
- Properties can be classified on the basis of size/extent of the system.
Heat and Work
- Heat and work are path functions.
- They are denoted by dynamic path, so they are inexact and imperfect differential.
Thermodynamic System
- Thermodynamic system is a region in space upon which the study/analysis is focused.
- Boundary is the separation between system and surrounding.
Types of Systems
- Open System: Mass and energy transfer take place across the boundary. (e.g. Turbine, pump, piston-cylinder arrangement with valve)
- Closed System: No mass transfer, but energy transfer takes place. (e.g. Rigid closed container with conductive walls, piston cylinder arrangement without valve)
- Isolated System: No mass and energy transfer takes place. (e.g. Universe, hot fluid in perfect insulated flask/container)
Control Volume
- Control volume in a thermodynamic system refers to a fixed region in space for thermodynamic study.
- Examples of control volume systems include turbine impeller, pump, compressor, etc.
Closed Thermodynamic System
- A closed thermodynamic system is one in which there is no mass transfer, but energy transfer exists.
Internal Energy
- Internal energy is a function of temperature only for an ideal gas.
- It represents the total energy associated with molecules.
- Internal energy for an ideal gas is given by the equation U = mCvT.
Enthalpy
- Enthalpy is the addition of internal energy and product of pressure volume. (H = U + PV)
- It is a compound property.
- Enthalpy for an ideal gas is given by the equation dH = mCpdT.
Isolated System
- Isolated system indicates that both mass and energy of substance do not cross the boundary.
- Examples of isolated systems include thermos flask, casserole, and universe.
Adiabatic Process
- A process in which no heat crosses the boundary of the system is called an adiabatic process.
- First law of thermodynamics for closed system is given by the equation ∂Q = dU + ∂W.
- In an adiabatic process, ∂Q = 0, so ∂W = -dU.
Polytropic Process
- Under certain polytropic process, value of n = 1 corresponds to isothermal process.### Thermodynamic Properties
- Intensive properties: independent of the mass of the system, e.g. pressure, temperature, specific enthalpy, specific volume, specific energy, density, etc.
- Extensive properties: dependent on the mass of the system, e.g. volume, energy, enthalpy, entropy, etc.
- Note: Each specific extensive property is intensive.
Thermodynamic Processes
- Free expansion process: no heat is supplied or rejected, and no external work is done.
- Q1-2 = 0, W1-2 = 0, and du = 0
- P decreases, V increases, T remains constant (ideal gas)
- Throttling process: an irreversible process with no change in enthalpy, and no work done.
- Isothermal process: a process where temperature remains constant.
- Adiabatic process: a process where no heat enters or leaves the system.
- Isobaric process: a process where pressure remains constant.
- Isochoric process: a process where volume remains constant.
- Isentropic process: a process where entropy remains constant.
Thermodynamic Systems
- Isolated system: a system where there is no heat transfer or work done.
- Examples: Thermos flask, Casserole, etc.
- Open system: a system where there is heat transfer or work done.
- Examples: Centrifugal pump, Pressure cooker, etc.
Ideal Gas
- Universal gas constant: 8314 J/kg-mole K or 8.314 kJ/kg-mole K.
- Ideal gas equation: PV = nRT.
- Charles' law: V1 / T1 = V2 / T2.
Temperature and Heat
- Temperature: a measure of the average kinetic energy of gas particles.
- Heat: a form of energy transferred from one body to another due to a temperature difference.
- Absolute zero: the lowest possible temperature, at which all particles come to rest.
Work and Energy
- Work done: the product of pressure and volume change.
- Internal energy: the total energy of a system, including kinetic energy, potential energy, and potential energy.
- Enthalpy: the total energy of a system, including internal energy and the product of pressure and volume.
- Specific enthalpy: the enthalpy per unit mass of a system.
Miscellaneous
- The ratio of two specific heats of air is 1.41.
- Density of water is maximum at 4°C.
- The heat absorbed or rejected during a polytropic process is equal to (γ - n) / (γ - 1) × workdone.### Thermodynamics
Adiabatic Process
- A process in which no heat enters or leaves the gas.
- The change in internal energy is equal to the work done.
- Expressed by the relation, PVγ = constant, where γ is the isentropic index.
- For monoatomic gas, γ = 1.67, for diatomic gas, γ = 1.4, and for polyatomic gas, γ = 1.33.
Types of Processes
- Reversible process: can be reversed bringing both the state of the system and the surroundings to the initial condition without any other inputs.
- Irreversible process: cannot be reversed without any external inputs.
- Isentropic process: a reversible adiabatic process.
- Isenthalpic process: an irreversible adiabatic process.
- Polytropic process: the most commonly used process in practice, governed by the law PVn = Const.
Laws of Thermodynamics
- The second law of thermodynamics: heat transfer occurs from a body at a higher temperature to a body at a lower temperature.
Thermodynamic Properties
- Internal energy (U): a state function, a property of the system.
- Enthalpy (H): a state function, a property of the system.
- Specific heat: the amount of heat required to raise the temperature of a unit mass of a substance by one degree.
- Specific heat at constant pressure (Cp): the amount of heat required to raise the temperature of a unit mass of a substance by one degree at constant pressure.
- Specific heat at constant volume (Cv): the amount of heat required to raise the temperature of a unit mass of a substance by one degree at constant volume.
Heat Transfer
- Heat transfer occurs due to temperature difference.
- No heat transfer occurs when the temperatures of the two bodies are equal.
P-V and T-S Diagrams
- Area under the process line in the P-V diagram gives the work done.
- Area under the process line in the T-S diagram gives the heat transferred.
Thermodynamic Systems
- Closed system: a system in which the mass of the system remains constant.
- Open system: a system in which the mass and heat energy can be transferred to its surroundings.
- Isolated system: a system in which no heat, work, or matter can be transferred across the boundary.
Thermodynamic Relations
- Cp - Cv = R/J, where R is the gas constant and J is the mechanical equivalent of heat.
- γ = Cp / Cv, where γ is the isentropic index.
Gas Constant
- The gas constant (R) is the work per degree per mass.
- The unit of gas constant (R) is N-m/kg.K or J/kg.K.
- The value of gas constant for air is 287 J/kg.K.
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Description
Understand the fundamentals of thermodynamics, including the zeroth law and its application in measurement. Also, learn about throttling process and its characteristics.