Thermo Semester 1 Flashcards by Leo Silvester

Define Open System Flow Processes

Boundaries are such the working fluid can cross them in addition to heat and work

How well did you know this?

Not at all

Perfectly

What is a thermodynamic system

A region within prescribed boundaries containing a quantity of matter where behaviour is being investigated

How well did you know this?

Not at all

Perfectly

What is a Non-Flow Process

Boundaries are such that only heat and work can cross them. Boundaries formed by a piston and cylinder

How well did you know this?

Not at all

Perfectly

What are boundaries

They separate the working fluid from its surroundings. Can be solid or imaginary

How well did you know this?

Not at all

Perfectly

What can the working fluid be

Can be a liquid, a gas or a vapour or a mixture of gases that do not react with each other

How well did you know this?

Not at all

Perfectly

Define heat

Transfer of energy by virtue of a temperature difference

How well did you know this?

Not at all

Perfectly

Define work

Transfer of energy by virtue of a force moving through a distance

How well did you know this?

Not at all

Perfectly

Simply, what does the zeroth Law of Thermodynamics state?

The concept of temperature, if A and B are in thermal equilibrium and so are B and C, then A and C must also be the same temp

How well did you know this?

Not at all

Perfectly

Simply, what does the First Law of Thermodynamics state?

The foundations of energy conservation principle

How well did you know this?

Not at all

Perfectly

Simply, what does the Second Law of Thermodynamics state?

Distribution of energy changes in an irreversible manner

How well did you know this?

Not at all

Perfectly

Simply, what does the Third Law of thermodynamics state?

Matter cannot be brought to absolute zero in a finite number of steps

How well did you know this?

Not at all

Perfectly

What does the kinetic theory of gases say?

Any gas will expand to fill the space available
A gas consists of many rapidly moving, perfectly elastic, infinitely small molecules which take up negligible space
A gas is homogenous

How well did you know this?

Not at all

Perfectly

What is boyles law

P₁V₁=P₂V2₂
pressure is inversely proportional to volume for a FIXED MASS AND TEMP

How well did you know this?

Not at all

Perfectly

What is Charles Law?

V₁ / T₁ = V₂ / T₂
Volume and Temp are directly proportional for a FIXED MASS AND PRESSURE

How well did you know this?

Not at all

Perfectly

What is the pressure law?

PV₁ / T₁ = P₂ / T₂
Pressure and Temp are directly proportional for a FIXED MASS AND VOLUME

How well did you know this?

Not at all

Perfectly

Name 3 forms of Equation of State?

pV = mRT
pv = RT
p / rho = RT

How well did you know this?

Not at all

Perfectly

What is the equation defining a polytropic process?

pV^n = constant

How well did you know this?

Not at all

Perfectly

What is a constant pressure process called, what is the value of n?

Isobaric, n=0

How well did you know this?

Not at all

Perfectly

What is a constant temperature process called, what is the value of n?

Isothermal, n=1

How well did you know this?

Not at all

Perfectly

What is a constant volume process called, what is the value of n?

Isochoric, n = infinity

How well did you know this?

Not at all

Perfectly

What is a reversible and adiabatic process called, what is the value of n?

Isentropic, n = Cp/Cv = gamma

State the Non Flow Energy Equation (NFEE)

Q₁₂ + W₁₂ = U₂ - U₁
U is the internal energy

What is the internal energy of a system?

the energy the system possesses by virtue of its temperature only

Define a reversible process

Processes that can be reversed so that the system and the surroundings are returned to the original condition after the process and reverse process are carried out

Define an irreversible process

Processes which reversal cannot be carried out without leaving some change to the system or surroundings

What is maximised in a reversible process?

Work

COPY FLASHCARD

∫ Δ γ ṁ ρ N¹² N₁₂

How do you calculate the work done in a reversible process?

W = - ∫p.dV

How can the work be found in a polytropic process?

W = (P₂V₂ - P₁V₁) / n-1 Strictly not valid for n=1

What is specific heat capacity?

The energy required to raise 1kg of a substance by 1K

How can you helpfully imagine heat added to a gas?

Divide it into 2 parts: - Some of the heat is used to raise the temperature at constant volume - Further heat addition causes the gas to expand and do work against the surroundings ( FIRST PART WILL BE SAME NO MATTER THE PROCESS, SECOND WILL VARY ON TYPE OF PROCESS)

What is Internal Energy, U =

ΔU = Q + W = mCvΔT for any process

What is the total energy supplied Q, in a constant volume process?

1. U = Q + W -> Q = U-W 2. U = mCvΔT for any process 3. Work done is expanding the gas, therefore for constant volume, W=0 4. Q = U = mCvΔT

What is the total energy supplied Q in a constant pressure process?

1. U = Q + W -> Q = U-W 2. U = mCvΔT for any process 3. W = - ∫p.dV 4. Q = mCvΔT - -∫p.dV = mCvΔT + ∫p.dV =mCpΔT

How are Cp and Cv related?

Cp = Cv + R

What conclusion can be made from the Joules Experiment?

Internal energy is ONLY a function of temperature not pressure or volume

What pv equation can be written for an isentropic process?

pv^γ = constant

For an isentropic process, how can the specific work done, w be found?

w =(P₂v₂ - P₁v₁) /γ -1 (This makes sense because just divided by mass on both sides to go from W and V, then n=γ for isentropic)

What properties do steady flow processes have?

- Mass flow rate in = mass flow rate out - Transfer of energy (work or heat is at constant rate) - fluid properties do NOT vary with time

What is the equation for the flow of kinetic energy?

KE = 1/2 ṁ C² ṁ = mass flow rate C = velocity

What is the equation for the flow of potential energy?

PE = ṁgz z = height in thermodynamics ṁ = mass flow rate

What is flow work?

Work done on the system to push fluid into the system, or work done by the system to eject the fluid

What are the 4 energy flows that must be considered in an Steady Flow Energy question?

Internal energy (ṁu) Flow Energy (ṁ p / ρ) Kinetic Energy (1/2 ṁ C²) Potential Energy (ṁgz)

How do you calculate the rate of flow work?

ṁ p / ρ

The steady flow energy equation is on the formula sheet, but which terms in it are often neglected?

PE term can usually be neglected ( if z small) KE term important in high speed flows, but often neglected in low speed ones

What is enthalpy?

thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.

What is a stagnation temp?

An imaginary situation where all of the KE is converted into enthalpy and so its the maximum theoretical temp

What equation links static (real) temp and the stagnation temp?

T₀ = T + C²/2Cp T₀ is the stagnation temp T is static temp (Also h₀ = h + C²/2) h is enthalpy

What needs to be specified before finding stagnation pressure?

Isentropic flow