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bthm sub topic list to check on status
basic thermo quick recap hand written notes
These notes largely follow flow of book by PK Nag, page numbers are mentioned where I could not fill in due to paucity of time
A set of solved questions from previous year Engineering Service Exams.. Good for quick recap
ESE solved
Consider a system going from state 1 to 2 by path A and coming back from state 2 to 1 in possible paths B and C.
bthm sub topic list to check on status
basic thermo quick recap hand written notes
These notes largely follow flow of book by PK Nag, page numbers are mentioned where I could not fill in due to paucity of time
A set of solved questions from previous year Engineering Service Exams.. Good for quick recap
ESE solved
Zeroth Law of
thermodynamics[basis of temperature measurement]
When a body A is in thermal equilibrium with a body B and
also separately with a body C, then B and C will be in thermal equilibrium with
each other
5 types of
thermometers
Type
|
Thermometric property
|
Details
|
Constant Volume gas
|
Pressure
|
|
Constant pressure gas
|
Volume
|
|
Electrical resistance
|
Resistance
|
Platinum wire is one of the Wheatstone bridge arms
|
Thermocouple
|
Thermal emf
|
Seebeck effect, is quick to catch up as the junction
bead is small
|
Hg in glass
|
Length
|
Before 1954, ice point and steam point were used as fixed
points and temperature was inter or extrapolated based on the measurement, but
after 1954 proportionality is used with fixed point at 273.16K which is triple
point of water and is easily reproducible
For higher temperatures(above Gold point 1064 degC),
optical method is used where wavelength of radiation is measured and using
Planck’s equation temperature is
calculated
ITS-90 is a revised temperature scale that was adapted in
1990, has added more fixed points so that scale conforms with the temperature
scale based on 2nd law of thermodynamics(Kelvin scale)
System types:
Closed, Isolated, Open
Adiabatic wall is impermeable to heat flow while
diathermic wall allows heat flow
Types of
processes:Isochoric, Isobaric/isopiestic, isothermal, isentropic, adiabatic
(should plot these on T-s, p-V and remember index of each
process(n) used in pVn=constant
Intensive
properties are independent of mass/size of system, while extensive are dependent
Energy is
capacity of doing work and is either in storage(internal energy) or is in
transit(work or heat transfer). Internal energy is a point function and a
property, but energy transfer occurs at boundary of system and is usually a
path function.
Heat transfer is a boundary phenomenon that occurs by
virtue of temperature difference
Work transfer occurs in many ways—displacement(pdV),
shaft work ,film surface area change, axial pull, magnetization, flow work,
paddle work. In general for these, inexact differential
work=intensive.d(extensive) for ex. dW=p.dV
1st law
of thermodynamics
Heat and work are different forms of the same entity
called energy which is conserved
For a closed system undergoing a cycle: ∑W=J. ∑Q
Proof of energy
being a property
Consider a system going from state 1 to 2 by path A and coming back from state 2 to 1 in possible paths B and C.
Then, for each we can write, Q-W=∆E
Now for the cycle A-B, we can write ∑W= ∑Q and same for
cycle A-C, which then leads to ∆EA = -∆EB = -∆EC
So, E is not dependent on path B or C and is a point
function or a property.
Internal energy components: macroscopic(macro KE mV2/2
and macro PE mgh) + microscopic (molecular motion, vibration, chemical, nuclear
etc)
PMM1 perpetual
motion machine type 1 is one that produces work continuously without any other
form of energy disappearing at the same time, violating 1st law
1st law
applied to flow processes
Control volume: a specific region in space under
consideration, Control surface: surface of CV
Steady flow: rates of flow of mass and energy are
constant(not changing with time)
Steady state: any thermodynamic property not changing
with time at a particular location
For a flow process there is:
Mass balance, m1=m2 and
Energy balance, first balancing work transfer(work
transfer=external work+flow work) Eqn 1:
Assuming there is no accumulation of energy in the
system, energy in = energy out then Eqn 2:
Where , e=ek+ep+u =
V2/2 +Zg + u ---(3)
When we put eqn (3) and (1) in (2) we can
combine u with pv terms and we get h(enthalpy), thus we get the SFEE or steady flow energy equation
With bit of moving terms around, we can
write the differential form of the same as
Furthermore, applying conditions of a
inviscid incompressible(ρ=constant) flow without work and heat transfer,
internal energy remaining constant, we end up with Bernoulli equation
Application
|
Conditions
|
Equation
|
Nozzles diffusers
|
dQ=0, dW=0, dZ=0
|
h1+ V12/2=h2
+V22/2
|
Throttling devices
|
dQ=0, dW=0, dZ=0, V1, V2
too small
|
h1=h2
|
Turbine/compressor
|
Well insulated, velocities often small,
dZ=0
|
h1=h2-Wx/m
|
Heat exchanger
|
Well insulated, small velocities, dZ=0
|
mch1+ mhh2=
mch3+ mhh4
|
The above equations are good to know but
there is another big category from where many interesting questions are often
asked, which is on tank charging/discharging.
These are beyond SFEE and are sometimes
called Variable flow problems.
The
general equation (which
becomes simpler applying conditions given in question) is:
2nd law
of thermodynamics
1st law says heat(low grade) and work(high grade) are energy itself, only different forms, but 2nd law clarifies that they are not completely interchangeable
1st law says heat(low grade) and work(high grade) are energy itself, only different forms, but 2nd law clarifies that they are not completely interchangeable
Kelvin-Planck statement: It is impossible for a heat
engine to produce net work in a complete cycle if it exchanges heat only with
body at a single fixed temperature
Clausis statement: It is impossible to construct a device
which, operating in a cycle, will produce no effect other than the transfer of
heat from a cooler to a hotter body
Proof of equivalence of the two statements
1.
2.
Reversible process: is carried out infinitely slowly with
an infinitesimal gradient, so that every state passed thru by system is an
equilibrium state
Causes of irreversibility:
--lack of equilibrium during the process(finite gradient)
like heat transfer thru finite temperature difference, free expansion, lack of
pressure equilibrium
--involvement of dissipative effects like friction,
paddle wheel work transfer, electricity thru resistor
Types of irreversibility:
--internal: caused by internal dissipative effects,
within the system ex friction, turbulence, electrical resistance, magnetic hysteresis
--external: occurs at system boundaries, like heat thru
finite ∆T, chemical concentration gradient, pressure gradient
So, Conditions for reversibility:
--system is at all times inifinitesimally near a state of
thermodynamic equilibrium and
--in absence of dissipative effect of any form
Carnot cycle
Processes, equations, diagram
CSE2003A2b30--solved
CSE2005A2a30--solved
CSE2005A1a20 --solved
CSE2010A2a20--solved
CSE2007A1a20--solved
CSE2005A2a30--solved
CSE2005A1a20 --solved
CSE2010A2a20--solved
CSE2007A1a20--solved
Carnot’s theorem and proof:
Of all heat engines operating between a given constant
temperature source and a given constant temperature sink, none has higher
efficiency than a reversible engine
Absolute thermodynamic temperature scale based on Carnot
cycle:
Proof of ideal gas temperature=Kelvin temperature
3rd law of thermodynamics:
Nernst statement: It is impossible for any method to lead
to isotherm of T=0 in a finite number of steps
Also stated that entropy of a system at absolute zero is
a well defined constant, which later came to be zero, found using statistical
mechanics(S-S0=kBlnΩ. kB is Boltzmann constant and Ω is
number of microstates consistent with the macroscopic configuration
Fowler-Guggenheim statement: It is impossible by any
procedure, no matter how idealized, to reduce any system to the absolute zero
of temperature in a finite number of operations
Entropy
Proof that 2 reversible adiabatic paths cant cross each
other
Clausius theorem
Proof of entropy being a property
Clausius inequality
Entropy change in an irreversible process
Entropy principle and its applications
Entropy transfer with heat flow
Entropy generation in a closed system
Entropy generation in an open system
Property relations combining 1st and 2nd
laws:
Exergy
Exergy of a system at a given state is the maximum work
that can be extracted from it till it reaches the state of thermodynamic
equilibrium with its surroundings
It provides a measure of the quality of energy(at higher
temperature, quality of same quantity of energy is higher than one at lower
temperature)
Exergy of heat input in a cycle:
Decrease in exergy when heat is transferred thru a finite
∆T
Exergy of a finite body at temperature T
Exergy POV: 1st law says energy quantity is
conserved, and 2nd law says energy quality always degrades
Proof that maximum work is done in a reversible process
Proof that work done in all reversible processes is the
same
Exergy of a closed system
Exergy of a steady flow system
Exergy in chemical reactions and Gibb’s function
Irreversibility
Irreversibility and Guoy-Stodola Theorem
Exergy balance
Exergy balance for closed system
Exergy principle
Exergy balance for a steady flow system
2nd law efficiency
Properties of pure
substances
p-V-T diagrams of water
Terminology: critical point, vapour pressure
NBP normal boiling point=temperature at which vapour
pressure=760mm
Saturation pressure and temperature
Critical point of water
p-V, p-T, T-s. h-s(Mollier) diagram for pure substance
Measurement of steam quality
Throttling calorimeter
Separating and throttling calorimeter
Electrical calorimeter
Properties of
gases-EOS equations of state
Ideal gas equation
Proof of Joule’s law u=f(T)
Variation of Cp with temperature for various
substances
Entropy change of an ideal gas
Processes, equations, expressions for ∆h, ∆u, W
--Reversible adiabatic
--reversible isothermal
--polytropic
Equations of state:
Van der Waal
Virial expansions
Law of corresponding states, Boyles’ temperature
Dalton’s law of partial pressures
Amagat’s law of additive volumes
Properties of gas mixtures, u,h,Cp, S
Maxwell relations and
others
Maths of it
Maxwell’s equations
CSE2015A2c10
TdS equations
Difference in heat capacities
Ratio of heat capacities
Energy equation
Joule-Kelvin effect
Clausius Clapeyron equation
Thermodynamic properties from an EOS
Types of equilibrium, conditions of stability
Rankine cycle,
efficiency, heat rate, steam rate
Reheat cycle
Ideal regenerative cycle
Reheat-regenerative cycles
Binary vapour cycles
Coupled cycles
Cogneration plant
Gas power cycles
Carnot 1824
Stirling 1827
Ericsson 1850
Otto 1876
Diesel 1892
Dual
Lenoir/pulse jet
Atkinson
Brayton
Aircraft
propulsion
Turbojet
Turbofan
Turboprop
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