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Questions and Answers
The room temperature decreases when electric energy is consumed by a device.
The room temperature decreases when electric energy is consumed by a device.
False
Kinetic energy can be described using the equation KE = $\frac{1}{2}mv^2$.
Kinetic energy can be described using the equation KE = $\frac{1}{2}mv^2$.
True
Potential energy is calculated using the formula PE = $mgz$.
Potential energy is calculated using the formula PE = $mgz$.
True
The total energy of a system is the sum of only kinetic energy.
The total energy of a system is the sum of only kinetic energy.
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Microscopic forms of energy are related to molecular activity and structure.
Microscopic forms of energy are related to molecular activity and structure.
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Intensive properties depend on the size or extent of the system.
Intensive properties depend on the size or extent of the system.
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Equilibrium refers to a state of unbalanced forces within a system.
Equilibrium refers to a state of unbalanced forces within a system.
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An isothermal process occurs at a constant volume.
An isothermal process occurs at a constant volume.
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Specific properties are extensive properties per unit mass.
Specific properties are extensive properties per unit mass.
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A vacuum flask and a dewar flask serve the same purpose.
A vacuum flask and a dewar flask serve the same purpose.
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In an isobaric process, the temperature of the system remains constant.
In an isobaric process, the temperature of the system remains constant.
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An isochoric process occurs with no change in pressure.
An isochoric process occurs with no change in pressure.
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In a thermodynamic cycle, the initial state coincides with the final state.
In a thermodynamic cycle, the initial state coincides with the final state.
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A mixture of liquid and gaseous air is considered a pure substance.
A mixture of liquid and gaseous air is considered a pure substance.
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The work done (W) calculated using $W = 60 \cdot 9.81 \cdot 0.05 + \frac{1}{2} \cdot 50000 \cdot 0.052 + 100000 \cdot \pi \cdot 0.12 \cdot 0.05$ results in 249 J.
The work done (W) calculated using $W = 60 \cdot 9.81 \cdot 0.05 + \frac{1}{2} \cdot 50000 \cdot 0.052 + 100000 \cdot \pi \cdot 0.12 \cdot 0.05$ results in 249 J.
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In thermodynamics, a negative change in internal energy (∆U) indicates that the system has absorbed more energy than it has done work.
In thermodynamics, a negative change in internal energy (∆U) indicates that the system has absorbed more energy than it has done work.
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Molecules in a gas are arranged in a particular order and do not collide with each other.
Molecules in a gas are arranged in a particular order and do not collide with each other.
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A pure substance can exist in different phases while maintaining the same chemical composition.
A pure substance can exist in different phases while maintaining the same chemical composition.
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Vapour is the British English spelling of vapor.
Vapour is the British English spelling of vapor.
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Latent heat is the total heat required during a phase change.
Latent heat is the total heat required during a phase change.
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The latent heat of vaporization of water is 2256.5 kJ/kg.
The latent heat of vaporization of water is 2256.5 kJ/kg.
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The temperature changes during the melting process due to added heat energy.
The temperature changes during the melting process due to added heat energy.
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Specific volume of gas is denoted by the symbol vf.
Specific volume of gas is denoted by the symbol vf.
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During boiling, heat is required to vaporize the substance.
During boiling, heat is required to vaporize the substance.
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The quality of a mixture is the ratio of the mass of liquid to the total mass.
The quality of a mixture is the ratio of the mass of liquid to the total mass.
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Superheated steam does not exist in the saturated liquid-vapour region.
Superheated steam does not exist in the saturated liquid-vapour region.
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The equation for heat transfer is $Q = mC_v(T_2 - T_1)$ for constant volume processes.
The equation for heat transfer is $Q = mC_v(T_2 - T_1)$ for constant volume processes.
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The formula for volume flow rate is $Q = A imes t$.
The formula for volume flow rate is $Q = A imes t$.
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Specific heat changes with temperature is represented by the equation $Q = m C_p(T_2 - T_1)$.
Specific heat changes with temperature is represented by the equation $Q = m C_p(T_2 - T_1)$.
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The first law of thermodynamics applies only to systems at equilibrium.
The first law of thermodynamics applies only to systems at equilibrium.
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In the formula for volume flow rate, $ rac{Volume}{Time}$ is equal to $A imes v$.
In the formula for volume flow rate, $ rac{Volume}{Time}$ is equal to $A imes v$.
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Bernoulli's equation is applicable only to compressible fluids.
Bernoulli's equation is applicable only to compressible fluids.
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The term $ rac{C_p}{C_v}$ can represent the ratio of specific heats, denoted as $eta$.
The term $ rac{C_p}{C_v}$ can represent the ratio of specific heats, denoted as $eta$.
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In steady flow, the energy analysis can include entropy considerations.
In steady flow, the energy analysis can include entropy considerations.
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In an adiabatic process, the change in internal energy is represented as $\Delta U = Q$.
In an adiabatic process, the change in internal energy is represented as $\Delta U = Q$.
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For an isolated system, the first law of thermodynamics states that $\Delta U = 0$.
For an isolated system, the first law of thermodynamics states that $\Delta U = 0$.
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The equation for an isobaric process is $\Delta U = Q - P(V_f - V_i)$.
The equation for an isobaric process is $\Delta U = Q - P(V_f - V_i)$.
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In an isothermal process, the internal energy change is given by $\Delta U = Q - W$.
In an isothermal process, the internal energy change is given by $\Delta U = Q - W$.
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The first law of thermodynamics can be simplified to $\Delta U = Q - W$ for any thermodynamic process.
The first law of thermodynamics can be simplified to $\Delta U = Q - W$ for any thermodynamic process.
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Joule’s Law states that the internal energy of an ideal gas depends on both temperature and volume.
Joule’s Law states that the internal energy of an ideal gas depends on both temperature and volume.
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For isovolumetric processes, the change in internal energy is $\Delta U = Q$.
For isovolumetric processes, the change in internal energy is $\Delta U = Q$.
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The work done by the system is considered positive in the first law of thermodynamics expression $\Delta U = Q - W$.
The work done by the system is considered positive in the first law of thermodynamics expression $\Delta U = Q - W$.
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Study Notes
Course Information
- Course title: 5ENT1129 Thermodynamics for Aerospace
- Lecturer: Dr. Burhan Saeed
- University: University of Hertfordshire (UH)
Lecture 1 - Introduction to Thermodynamics
- Thermodynamics derives from Greek words "therme" (heat) and "dynamis" (power)
- Thermodynamics is a study of energy and its transformations, encompassing various aspects of life and engineering systems.
- Two main approaches exist in thermodynamics: classical (macroscopic) and statistical (microscopic)
- Classical approach focuses on the average behaviour of a large group of particles, while the statistical approach investigates individual particle behaviour
- Terminology: system, surroundings, boundary
- A system can be classified as open, closed, or isolated.
- Open systems can exchange both mass and energy with their surroundings (e.g., human body, boiler).
- Closed systems can only exchange energy with the surroundings, not mass (e.g., pressure cooker, home heating system).
- Isolated systems can't exchange either mass or energy with their surroundings (e.g., the universe).
Systems with moving boundaries
- In systems with moving boundaries, the boundary itself can change size, impacting the calculations of the system.
Properties of systems
- System properties can be intensive (independent of mass like temperature, pressure, density) or extensive (dependent on mass such as total mass, total volume).
- Intensive properties are often expressed per unit mass.
Density and Specific Gravity
- Density (ρ): Mass per unit volume (kg/m³)
- Specific volume (v): Volume per unit mass (m³/kg)
- Specific gravity (SG): Ratio of density of a substance to density of water (dimensionless)
- Specific weight (γs): Weight per unit volume(N/m³)
- Relations between all the given quantities
State and Equilibrium
- Equilibrium state: Properties of a system have fixed values throughout.
- Equilibrium criteria: Thermal equilibrium (same temp throughout), Mechanical equilibrium (no pressure changes with time), Phase equilibrium (mass of each phase reaches equilibrium and stays there), Chemical equilibrium (chemical composition doesn't change).
Processes and Cycles
- Quasi-equilibrium process: System undergoes infinitesimal changes, remaining close to an equilibrium state.
- Process diagrams: Diagrams that graphically represent processes, helping to visualize work done.
- Isothermal processes: Constant temperature.
- Isobaric processes: Constant pressure.
- Isochoric processes: Constant volume.
- Cycles: Processes where the system returns to its initial state.
The first law of thermodynamics
- Energy conservation: Energy cannot be created or destroyed; it can only change form or location.
- ΔU = Q - W
- U: Internal energy of the system
- Q: Heat transferred into the system.
- W: Work done by the system.
Adiabatic processes
- A process in which no heat exchange with the surrounding takes place (q = 0).
Energy transfer and heat
- Heat is a form of energy transfer due to a temperature difference.
- Rate of heat transfer is dependent on temperature difference.
Energy transfer by work
- Work is a form of energy transfer associated with a force acting through a distance.
- Work is done when a force causes movement.
- Different types of work can be done, including shaft work, boundary work etc.
Different forms of energy
- Kinetic energy (KE): Energy of motion
- Potential energy (PE): Energy of position
- Internal energy: microscopic/molecular energy (U)
Steady and uniform processes
- Stationary flows: No accumulation of mass, energy, or other thermodynamic properties in the control volume.
- Steady conditions: Properties remain unchanged over time at every point within the control volume.
- Steady flow processes: Flows steadily through a control volume, fluid properties can change from point to point.
Reverse and Irreversible Process
- Reversible Processes: Process that can be reversed without leaving any trace on the surroundings.
- Irreversible processes: Processes that are not reversible.
Unit of Measure for Temperature
- Units: Kelvin (K)
- Relation to Celsius (°C) (°C=K−273.15)
Temperature Scales – Celsius and Fahrenheit
- Celsius scale (0 degrees is the freezing point of water, 100 degrees is the boiling point of water)
- Fahrenheit scale (32 degrees is the freezing point of water, 212 degrees is the boiling point of water)
- Conversion formulas between Celsius and Fahrenheit
Understanding the First Law of Thermodynamics
- Conservation of energy. The change in energy of a system is equal to the sum of the energy transferred to or from the system as heat and work
- AU = Q - W
Adiabatic processes
- No heat transfer occurs in adiabatic processes
The First Law of Thermodynamics– Examples
- In the absence of work interactions, the energy change of a system is equal to the net heat transfer.
Properties of Fluids
- Different states (solid, liquid, gaseous) of a pure substance with phase changes that occur between them.
Recap
- First law of thermodynamics
- Energy transfer in the form of heat and work
- Change in internal energy (ΔU) = Q – W, for a closed system.
- Generalisation to open systems involves rates of heat transfer to and from the system and shaft work.
- The steady flow energy equation, and the effect of mechanical devices: pumps, turbines, valves, and nozzles.
Various thermodynamic cycles
- Different types of cycles like Isothermal, Isobaric, Isochoric, Adiabatic, Isentropic, Isenthalpic cycles and their components along with the thermodynamic properties. (e.g., Rankine cycle, Diesel cycle, Ericson cycle etc.)
Heat Engine Processes
- Different cycles commonly encountered in real heat engines along with their components. (e.g., Carnot thermodynamic cycles, Rankine Cycle, Diesel, Otto, etc.)
Recap of Thermodynamic Processes
- Summary points of thermodynamic processes
Thermodynamics
- Key concepts of thermodynamics; Extensive, intensive and specific properties.
Thermodynamic Property Tables
- Extensive tabulations of thermodynamic property data for various substances (e.g., water/steam tables, ideal gas properties of air).
- Steam tables provide the saturation temperature and pressure values of a pure substance.
- Superheated water gives properties of superheated steam.
Enthalpy
- A combination of internal energy (U) and pressure-volume product (PV).
- Enthalpy is a thermodynamic property.
- Useful in steam turbine analysis: specific enthalpy (h) and total enthalpy (H)
Saturated Liquid and Vapour States
- Properties of saturated liquid and vapour substances.
- Tables are available for many substances.
Linear Interpolation
- Numerical technique to find intermediate values between existing data points in thermodynamic property tables
Heat Pump
- Working on principle similar to a refrigerator
- Purpose is to heat a system by transferring thermal energy from a cold reservoir to a hot reservoir.
- Examples, applications and basic components
Refrigeration Systems
- Working on a similar principle to a heat pump but with the goal of cooling rather than heating.
- Examples, applications, basic components
Entropy
- Thermodynamic property that quantifies the irreversibility associated with a system undergoing a process.
- Measure how random/disordered a system is. A system's tendency towards increased entropy.
The Second Law of Thermodynamics
- Thermodynamic processes are directional; they can occur spontaneously in a certain direction but not in the opposite direction.
- The total entropy of an isolated system can only increase over time or remain constant in ideal cases.
- Statements of Second Law.
- Relation between the first and second laws.
Specific Heat
- Molar Heat Capacity (intensive) of gases and fluids at constant pressure & constant volume, along with its derivation.
Ideal Gas – Equations of State
- Definition and nature of ideal gases
- Derivation of the equation of state, PV=nRT, which relates pressure(P), volume(V), number of moles(n) and absolute temperature(T)
The adiabatic process of an ideal gas
- PV^k = constant
- Derivation of the equation
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Description
Test your understanding of key thermodynamics concepts, including kinetic and potential energy, the laws of energy conservation, and different types of processes such as isothermal and isobaric. This quiz covers definitions, formulas, and practical applications related to energy in systems.
