sph 302 thermodynamics 302 thermodynamics nyongesa f. w., phd. ... thermodynamic concepts ......
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SPH 302
THERMODYNAMICS
Nyongesa F. W., PhD. e-mail: [email protected]
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Course Outline
Lecture 1: Thermodynamic
concepts & Zeroth Law
Lecture 2: 1ST Law
Lecture 3: 2ND Law
Lecture 4: Entropy and 2ND Law
Lecture 5: Thermodynamic potentials
Lecture 6: Phase Changes & Equlibria
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Prerequisites
SPH 203
Calculus
ODE
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Introduction & Overview
Before industrial revolution, machinery were powered by animals
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James watt Steam Engine
1ST Engine (invented1790) to
convert steam to mechanical work - lead to industrial revolution
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Steam Engines of Industrial Revolution
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Steam powered cars
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Steam powered Industries
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Work output
Steam (Heat)
By 19th cent, a new science was born – THERMODYNAMICS
GOAL: Asses efficiency of devices that convert heat work e.g., heat engines
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1ST Diesel Engines -1930s
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Hybrids & gas turbines
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What is Thermodynamics?
Thermo Energy transfer in form of heat
Dynamics Energy transfer in form of mechanical work
Thermodynamics = science that govern energy conversions processes (heat work)
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Why Thermodynamics ?
It gives Laws that govern energy conversion processes
ENERGY
Chemical Thermal
Solar Mechanical
Energy 1 (heat)
Energy 2 (work)
Laws of Thermodynamics
Relationship?
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Food (Energy) input
Waste
Work out
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W
waste
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Heat pumps
Work in
Heat out
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Laws of Thermodynamics
Energy conversions processes are governed by 4 Laws
Zeroth Law:
Gives condition for
thermal equilibrium
between 2 bodies
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First Law :
Defines relationship between heat input (dQ), work (dW) and internal energy (dU) in a system
dQ = dU + dW
dQ dU
dW
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“No animal works continously without eating or wearing out”
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Second Law:
(i) Defines efficiency of processes that convert heat work. i.e., No heat engine with 100% efficiency.
“If you eat, you must shit”.
Fuel Tank Engine
No exhaust
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Food input)
Impossible
Work out
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(ii) Gives direction of natural occurring processes - “Arrow of time”
“Naturally processes proceed in a direction such as to increase Total Entropy (disorder)
of system” Disorder
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Disorder
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Third Law:
Explains behaviour of systems as T absolute zero
As T 0, Entropy change (dS) 0 system becomes orderly E.g., water ice
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Thermodynamic Concepts & Zeroth Law
Thermodynamic concepts Ideal Gas Laws Zeroth Law
Lecture 1
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Objectives
Define thermodynamics
concepts
Explain ideal gas Laws
Explain Zeroth Law and its
significance
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Thermodynamic concepts
Energy conversion processes are studied using concept of thermodynamic system
System – Part of material universe that can be isolated completely from the rest for investigation
SYSTEM + SURROUNDING = UNIVERSE
system sorrounding boundary
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Types of systems
3 main types
(a) Open systems:- Allows exchange of both heat and matter through the boundary. E.g. human digestive system.
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(b) Closed systems:- Allows only exchange of heat with surrounding E.g. refrigerator or Engine
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(c) Isolated System:- No heat or matter exchange occurs with surrounding. The walls are Adiabatic (Adiathermal) E.g. Vacuum flask.
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Thermodynamic Variables:- parameters that describe behavior or state of system i.e., P, T, V & composition ()
Extensive variable:- Dependent on mass/size of the substance present in the system e.g., U, S, V etc.
Intensive variable:- opposite of Extensive
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Heat:- Transfer of thermal energy between systems as result of temp difference
Work:-Transfer of mechanical energy
Both Heat & Work = ways of
transferring energy
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Thermodynamic equilibrium:- When system experiences thermal, mechanical and chemical equilibrium S.T. state variables (P, V, T & ) are const.
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Working substance:- Fluid enclosed in the system that either receives or transfers energy to the surrounding in the form of heat or work.
In Thermodynamics, we use ideal gas as the working substance. WHY?
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Activity
Name the working substance in these systems
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Lecture Evaluation
Explain the difference between
Open & Closed system
Adiabatic & Diathermal Wall
Extensive & Intensive variables
State function and state variable
Heat and work
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1.2
Behavior of Ideal gases
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An ideal gas is an abstraction whose properties represent the limiting behavior of real gases at very low densities/high P.
Assumptions in ideal gas
(i) no intermolecular attractions S.T internal energy is entirely K.E Temp
(ii) Molecules occupy negligible volume
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Behavior of ideal gas depends on T, P and V and obey gas laws:
(a) Boyle’s law:
Compressing a gas
increases P
VP
1
V
P
PV = c
CPV
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(b) Pressure law: Heating a gas increases P
(c) Charles’ Law: Heating a gas increases V
CT
PTP
CT
VTV
T
P
T
V
-273 K
-273 K
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(d) V No. of moles (n) of the gas i.e.
V n
Combining (a) to (d) gives
PV = nRT ……………………..(1.1)
State of a system is given by Eqn of State
Equation of state
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P-V Diagram
From PV = nRT Behaviour/processes of ideal gas is represented on PV diagrams
V
P
PV = c
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Non Ideal (Real) Gas
Characterized by
Gas cannot be compressed to zero volume since gas molecules occupy finite volume and liquefy at low P
Intermolecular attractions
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Eqn of state of real gas is given by
Where a & b molecular attractions & v = molecular volume
nRTnbVv
aP
2
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Activity
State difference between Ideal & Non-ideal gas
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Zeroth law of Thermodynamics
A hot object looses heat to attain thermal equilibrium with surrounding
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“Statement of Zeroth Law”
"If objects A and B are separately in thermal equilibrium with third object C, then A and B are in thermal equilibrium with each other”.
A C
B
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Significance of Zeroth Law
Gives condition for thermal equilibrium between 2 bodies
Introduces concept of temperature and how it is determined.
Temperature = measure of degree of hotness
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Lecture -Evaluation
1. Explain an ideal gas and ideal gas laws
2. State Equation of State
3. State Zeroth Law and its significance