Zeroth Law of Themodynamics

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Zeroth Law of Themodynamics

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

An Universal Law for Measurement
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Zeroth Law of Thermodynamics

• Every system in this universe spontaneously move
  towards equilibrium with surroundings.

• If A and C are in thermal equilibrium with B,
  then A is in thermal equilibrium with C. Maxwell
  1872
• Practically this means that all three are at the
  same temperature.
• A basis for comparison of effect of temperatures.
  

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Demonstration of Zeroth Law
If the substance that composes the system is in
thermal equilibrium, the temperature will be the
same throughout the entire system, and we may
speak of the temperature as a property of the
system

• When Two bodies have equality of temperature with
  a third body, they in turn have equality of
  temperature with each other.

BRASS
Copper
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Construction of A Thermometer
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Thermometers with Electrical Output
Liquid in Glass Thermometer
Thermocouple Thermometer
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How Long it takes to achive Zeroth Law?
Conservation of Energy during a time dt
Heat in Change in energy of thermocouple
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Sudden Immersion of Thermometer in a Known
Constant Temperature System
Define Time constant
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Response of A Thermo-couple in A Constant
Temperature System
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Response of A Thermo-couple in A Ramp Temperature
System
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Format of Examinations

• Minor Examinations each of one hour duration.
• Major Examination Two hours duration.
• All the examinations are open hand written
  notes examinations.
• All kinds of your own hand written notes are
  allowed to be used during examinations. (Class
  notes, Tutorial notes, etc.)
• No printed or photocopied material is allowed.
• Printed copies of my lectures are also not
  allowed.
• Hand outs supplied by me are allowed.

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Weightage of examinations

• A Grand total of 200 points will be considered.
• Following distribution is sued for individual
  evaluations
• Minor-1 30
• Minor 2 40
• Major 70
• Tutorial notes evaluation 30
• Assignments 30

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Extension of Zeroth Law
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Mechanical Equilibrium

• When Two bodies have equality of pressure with a
  third body, they in turn have equality of
  pressure with each other.

Oxygen Cylinder
LPG Cylinder
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Mechanical Equilibrium of A Finite size System

• If a system is in mechanical equilibrium, there
  is no changing tendency for the pressure at any
  point.
• There will be a variation in pressure with
  elevation because of the influence of
  gravitational forces, although under equilibrium
  conditions there will be no tendency for the
  pressure at any location to change.
• In many thermodynamic problems, this variation in
  pressure with elevation is so small that is can
  be neglected.

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Chemical Equilibrium

• A system is in chemical equilibrium when there is
  no tendency for the quantities of species to
  change.
• When Two bodies have equality of concentration
  with a third body, they in turn have equality of
  concentration with each other.

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Chemical Sensors
Can we selectively detect chemicals? Can we also
detect classes of chemicals? An electronic
tongue or nose!
Chemical Sensors covers a wide category of
devices used to monitor, measure, test, analyse
concentration.
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Control Methods for Forest Fire
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Thermodynamic Equilibrium

• When a system is in equilibrium regarding all
  possible changes of state, we say that the system
  is in Thermodynamic Equilibrium.
• The properties of a system can be measured, when
  system is at equilibrium.
• Definition of a system using certain observable,
  macroscopic properties is known as description
  of The state.
• Some familiar ones are temperature, pressure, and
  density.
• How many properties are required to completely
  describe the state of a system?

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State Postulate

• The state postulate for a simple, pure substance
  states that the equilibrium state can be
  determined by specifying any two independent
  intensive properties.

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Change of State

• Whenever one or more of the properties of a
  system change, we say that a change in state has
  occurred.

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Change of State

• Whenever one or more of the properties of a
  system change, we say that a change in state has
  occurred.

Change of state due to an infinitesimal
deviations from thermodynamic equilibrium can be
precisely identified.
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Economics of Change of State

• Every change of state of a system consumes
  resource (Energy).
• Detail record of a change of state is essential
  to efficiently use a given resource.
• Keeping a record of change of state of a system
  is called as detailing the process in
  thermodynamics.

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Economics of Utilization of Energy
Why So? The paths followed are different
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Thermodynamic Process

• The path of succession of states through which
  the system passes is called the process.
• Quasi-equilibrium process is a collection of
  changes, in which the deviation from
  thermodynamic equilibrium is infinitesimal.
• All the states the system passes through during a
  quasi-equilibrium process may be considered
  equilibrium states.

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Process Executed by A Control Volume