Thermodynamics Quiz: Zeroth Law and Pressure

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Questions and Answers

What does the Zeroth Law of Thermodynamics state?

Thermal equilibrium requires direct contact between bodies.

The Zeroth Law can be derived from the First and Second Laws of Thermodynamics.

Two bodies are in thermal equilibrium if they have the same temperature. (correct)

Two bodies in thermal equilibrium can have different temperatures.

In which year was the Zeroth Law of Thermodynamics formulated?

1860

1905

1931 (correct)

1920

How is pressure defined in the context of thermodynamics?

The ratio of force to velocity.

The ratio of mass to volume.

The ratio of force to area. (correct)

The ratio of temperature to heat flux.

What is absolute pressure?

The pressure at a given point relative to a vacuum. Signup and view all the answers

What type of pressure is measured relative to atmospheric pressure?

Gage pressure Signup and view all the answers

Which unit is used to measure pressure?

Pascal Signup and view all the answers

What happens to bodies that are at different temperatures according to the Zeroth Law?

They will exchange heat until they reach the same temperature. Signup and view all the answers

In a formula for pressure, which of the following represents the dimensions of pressure?

[$M L^{-1} T^{-2}$] Signup and view all the answers

What occurs during the phase change from a saturated liquid to a saturated vapour?

The temperature remains constant until the last drop of liquid vapourises. Signup and view all the answers

Which statement accurately describes a compressed liquid?

It exists well below its boiling point. Signup and view all the answers

At what temperature does water exist as a saturated liquid at 1 atm pressure?

100°C Signup and view all the answers

What characterizes the superheated state of a gas?

The temperature of the gas begins to rise with added heat. Signup and view all the answers

During the melting process of a solid, what happens when heat is added?

The temperature remains constant until it has completely melted. Signup and view all the answers

What is the formula used to calculate the volume change when vaporizing water?

ΔV = mvfg where vfg = vg – vf Signup and view all the answers

At what pressure does the volume change for saturated water increase significantly compared to lower pressures?

10,000 kPa Signup and view all the answers

What will happen to the value of vfg as the pressure approaches the critical point?

It decreases significantly Signup and view all the answers

Using the values provided, what is the calculated ΔV for 10 kg of saturated water at 1 kPa?

1292 m3 Signup and view all the answers

Which value for vf is correct when examining 0.2 MPa?

0.0011 m3/kg Signup and view all the answers

What is the interpolated value for vfg at 260 kPa based on the tabulated values?

0.717 m3/kg Signup and view all the answers

What is the freezing point of water on the Kelvin scale?

273.15 K Signup and view all the answers

What is the boiling point of water on the Fahrenheit scale?

212 oF Signup and view all the answers

What does the calculation of ΔV require for its determination in saturated water vaporization?

Mass and specific volume data Signup and view all the answers

What is the main consequence of performing linear interpolation in thermodynamic property tables?

Better estimation of intermediate values between two known states Signup and view all the answers

Which of the following statements about absolute zero is correct?

It is the lowest temperature possible. Signup and view all the answers

What formula converts Celsius to Kelvin?

K = C + 273.15 Signup and view all the answers

What year was the Kelvin scale established?

1848 Signup and view all the answers

How does the Kelvin scale relate to the Celsius scale?

It is a shifting of the Celsius scale. Signup and view all the answers

If a temperature is measured as 150 oF, what is an equivalent temperature in Celsius?

65.56 oC Signup and view all the answers

What is the highest recorded temperature achieved near absolute zero?

100 picokelvins Signup and view all the answers

What happens to the boiling temperature of water when the pressure is increased?

It increases. Signup and view all the answers

In the context of a T-V diagram, what corresponds to the process of returning to state 1 by cooling the water at constant pressure?

It traces the same path as the heating process. Signup and view all the answers

What is the saturation temperature Tsat defined as?

The temperature at which a pure substance changes phase at a given pressure. Signup and view all the answers

At what pressure does water achieve the maximum point where liquid and vapor can coexist?

22.09 MPa. Signup and view all the answers

Which of the following accurately describes the effects of increasing pressure on the specific volume of a substance?

Specific volume decreases. Signup and view all the answers

What is represented by the horizontal inflection point on the liquid-vapor saturation curve?

The critical point for water. Signup and view all the answers

What characterizes the process of reversing the heating process of water at constant pressure when retracing to state 1?

The amount of heat released matches the heat added during heating. Signup and view all the answers

Which of the following statements about the temperature-volume (T-V) diagram for water under constant pressure is accurate?

It reveals the relationship between boiling point and pressure. Signup and view all the answers

What condition is necessary for work to be performed on the boundary of a system?

There must be a force acting on the boundary. Signup and view all the answers

When calculating the shaft work, which equation correctly relates torque, force, and moment arm?

$T = F imes r$ Signup and view all the answers

If a shaft transmits power at a torque of 200 N.m and a rotational speed of 4000 rpm, what does this signify about the shaft's performance?

The power transmitted can be calculated using $P = T imes ext{RPM}$. Signup and view all the answers

According to the definition of work in physics, how is work represented mathematically?

$W = F imes d$ Signup and view all the answers

How is the work done by a gas evaluated in terms of initial and final states on a pressure-volume (PV) diagram?

It depends on the area under the curve between two states. Signup and view all the answers

When a gas transitions between two states (P1, V1) and (P2, V2), how is the work done related to the path taken?

Work done depends on the specific path taken between the states. Signup and view all the answers

In the context of shaft power, how can pressure be related to area and force?

$F = P imes A$ Signup and view all the answers

Which expression correctly represents the integral form of work as derived from pressure and volume?

$W = igg(rac{F}{A}igg) imes V$ Signup and view all the answers

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 is derived from Greek words "therme" (heat) and "dynamis" (power)
Thermodynamics is encountered in many aspects of life and engineering systems
Two approaches in thermodynamics:
- Classical (macroscopic) approach: studies the average behavior of a large group of particles without studying individual particle behavior.
- Statistical (microscopic) approach: studies the average behavior of a large group of individual particles.
System: a region in space that encloses a quantity of matter
Surroundings: everything outside the system
Boundary: separates the system from its surroundings; has zero thickness and can move.

System Types

Open system: can exchange energy and mass with the surroundings (e.g. boiler, human body, rocket nozzle)
Closed system: can exchange energy but not mass with the surroundings (e.g. pressure cooker, home heating system)
Isolated system: cannot exchange energy or mass with the surroundings (e.g. universe, Dewar flask)

Properties of a System

Any characteristic of a system is called a property
Extensive Property: depends on the size or extent of the system (e.g. total mass, total volume)
Intensive Property: does not depend on the size or extent of the system (e.g. temperature, pressure)
Specific Property: extensive property per unit mass (e.g. specific volume, specific total energy, specific heat capacity)

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 the density of water at a specified temperature (often 0°C or 20°C)
Specific weight (Ys): weight per unit volume (N/m³)

State and Equilibrium

State: all the properties have fixed values throughout the system.
Equilibrium state: no unbalanced potential or driving force can change the system
Thermal equilibrium: no heat transfer between systems
Mechanical equilibrium: no pressure change with time
Phase equilibrium: mass of each phase reaches an equilibrium level and stays there.
Chemical equilibrium: chemical composition does not change with time

Processes and Cycles

Quasi-equilibrium process: change in a system undergoes from one equilibrium state to another, the system remains infinitesimally close to an equilibrium state at all times.
Process diagram: shows the relationship between two properties during a process.
Isothermal process: occurs at constant temperature (e.g. boiling of water in open air)
Isobaric process: occurs at constant pressure
Isochoric/isovolumetric process: occurs at constant volume
Adiabatic process: occurs with no heat transfer (e.g. compression/expansion in compressors/turbines)

Assessments

Timed Assessment 1: computer-based test (20%)
Lab Coursework: Heat Pump experiments (20%)
Final Timed Assessment: multiple-choice and open questions (60%)

Lecture 2 - Energy Conservation

Different forms of energy: thermal, mechanical, kinetic, potential, electric, magnetic, chemical, and nuclear.
Total energy of a system on a unit mass basis is denoted by e (kJ/kg).
Macroscopic energy: related to the motion of a system, e.g., potential energy, kinetic energy
Microscopic energy/Internal Energy (u or Eint): related to the molecular structure of the system and the degree of molecular activity e.g sensible energy, latent energy, chemical energy, nuclear energy.

Energy Transfer and Heat, Work

Heat transfer: transfer between two systems (or a system and its surroundings) due to temperature difference.
Heat transfer is a form of energy
Work transfer: energy transfer associated with a force acting through a distance
Work is energy
Q is heat

Formal Sign Convention on Heat and Work

Heat transfer to a system is positive (Q>0)
Heat transfer from a system is negative (Q<0)
Work done by a system is positive (W>0)
Work done on a system is negative (W<0)

First Law of Thermodynamics

Energy can not be created or destroyed, only transformed
Change in total energy of system = Heat added to system − Work done by system ($\Delta$U = Q − W)
Adiabatic process: a process where there is no heat transfer (Q = 0)

Adiabatic Process

Definition: A process during which there is no heat transfer.
Two ways to be adiabatic: Well insulated, No temperature difference.

Ideal Gas Eqaution Of State

PV = nRT
- P = Pressure (measured in Pascal)
- V = Volume (measured in m³)
- n = number of moles(measured in mol)
- R = Universal Gas Constant (8.314 J/mol·K)
- T = Absolute temperature (measured in K)

Specific Heat

Specific heat at constant volume (cv): energy required to raise the temperature of a unit mass by one degree at constant volume
Specific heat at constant pressure (cp): energy required to raise the temperature of a unit mass by one degree at constant pressure
- For monoatomic gas (e.g., Helium, Neon, Argon): cv=3/2 R and Cp= 5/2 R
- For diatomic gas (e.g., Hydrogen): cv=5/2 R and Cp = 7/2 R

Adiabatic process of an ideal gas

PV^k = constant ; k = _cp/_cv
T.V^k-1 = constant

Different process on the PV (Clapeyron) plane

Energy Analysis Steady Flow Control Volume

Volume flow rate: the volume of fluid passing a point per unit time (Q = AV)
Mass flow rate: the mass of fluid passing a point per unit time (m = ρQ = ρAV)
Steady flow: a process in which the properties at a fixed point in the control volume do not change with time, steady flow processes are often encountered in turbines, compressors, nozzles, diffusers, heat pumps, and refrigerators.

Flow Work or Flow Energy

Enthalpy [kJ/kg]: the sum of internal energy plus flow energy (h = u + pv)
Total Enthalpy [kJ]: the sum of total energy plus flow energy (H = U+PV)
Mass flow rate is often important when dealing with steady flow (m = ρ Q)
The heat transfer rate and the work transfer rate must be considered

Efficiency and Power

Mechanical efficiency
Turbine efficiency
Compressor efficiency
Heat pump efficiency
The power calculations are based on energy transfer

Heat Pump Application, Refrigerators

Entropy, Thermodynamic Processes

Entropy is a thermodynamic property that quantifies the irreversibility of thermodynamic processes
In general , $ΣS_{system} + ΣS_{surr} > 0$ (Entropy of the universe always increases)

Reversible Processes

A process where the system & surroundings are returned completely to their original state at the end of the process.
Ideally, many processes in thermodynamic systems are reversible.
The theoretical limit for real processes,

Factors that Contribute to Irreversibility

Friction (heat generation)
Heat transfer between bodies with finite thermal capacities.
Mixing and chemical reactions

The Carnot Cycle

Series of four reversible processes that constitute a theoretical heat engine cycle.
- Reversible adiabatic compression
- Reversible isothermal heating/expansion
- Reversible adiabatic expansion/compression

Carnot Cycle Thermal Efficiency

Carnot Heat Engine η =1 - (T_cold/T_hot)
A Carnot heat engine is a theoretical heat engine that operates on the Carnot cycle and is fully reversible.
The efficiency of a heat engine must always be less than a Carnot cycle engine when operating between the same two reservoirs.

Reversed Carnot Cycle

Exactly the same as the Carnot cycle but the heat and work interactions are reversed

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Description

Test your knowledge on the Zeroth Law of Thermodynamics and concepts of pressure. This quiz covers key principles, definitions, and phenomena related to thermodynamics. Ideal for students looking to grasp the fundamentals of heat transfer and pressure measurements.