An Action due to Thermal Inequilibrium

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An Action due to Thermal Inequilibrium

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Every member of earth wants it for A Refresh
.... A Natural Happening ..
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A Wake-up Call to Earth
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A Means of Generating Primary Wealth on Earth

• Development and ripening of vegetable substances
  demand the light and the heat of the Sun.
• The source of energy to the Organic Sphere.
• The energy of winds and water originate from the
  heat of the Sun.
• The winds arise from air currents due to the
  heating of the air by the Sun on Earth's surface.
• In order to fall, water must first be raised - by
  evaporation, which due to the heat of the Sun
  persists at the surface of the seas and Earth.
• Hence the heat of the Sun maintains all
  meteorological, climatic, geological and organic
  processes of Earth.

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The Sun enlightens Every Life

• Kowsalya supraja Rama poorva sandhya
  pravarthatheUthishta narasardoola karthavyam
  daivamahnikam

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A Natural Engineering Process for the Existence,
Growth and Performance.

• A True Design Reason behind Existence of Natural
  Systems..
• A Strong Design Modification for the Performance
  of Artificial Systems.

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The Engineering Process Responsible for Evolution
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The Geometry of Natural Products

• An orange is about double the diameter of a
  lemon, but could in principle hold eight times
  more juice in volume.
• Same goes for Elephants.
• Elephants are warm blooded tetrapods.
• Warm blooded animals desire to remain at an
  isothermal body temperature of 35 to 42 C
  (varies between animals).
• The body temperature is maintained at the desired
  value with a built-in thermo-regulatory
  mechanism.
• This mechanism either releases the excess heat
  produced in the metabolism or
• triggers the body to generate higher metabolic
  rate at times, when the body temperature falls
  below the desired value.

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Why I Am Different ?
?
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Geometry of An Elephent ?!?!?!

• A bigger warm blooded animal should in principle
  generate more metabolic heat energy simply
  because it has more volume hence more flesh and
  cells.
• This metabolic heat release has to be regulated
  if it is excess only through the heat transfer
  across the skin surface area.
• Firstly, in such a situation, having a fur coat
  of a hair structure is the least desired thing
  and hence Elephants are mostly bald.
• The hotter the climate in which they live, the
  balder they are.
• Secondly, Elephants have large ears which are
  packed with capillary structure through which
  sizable quantity of blood flows.
• The ear flaps of the elephant serve as an
  enormous convection fin - a flapping one at that
  - to enhance heat transfer from the elephant body
  to the environment.

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Classification of Elephants
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Mammoths, living in a cold tundra region, have
fur coats and small hairy ears.
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An Exotic Artificial Device

• The basic invention is due to other sciences
• The final and reliable existence is due to Heat
  Transfer

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The Pentium 4 Processor
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Basic Location on A Mother Board
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Heat Sinks for Pentium 4
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Pentium 4 While Performing
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Heat Sinks of Cooling of Electronics
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Heat Sinks Guided Flow
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Heat Sinks Guided Flow with Different Fin Shapes
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Heat Sinks Curious Paired Video
Card-Motherboard Design
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What is Heat Transfer?

• Thermal energy is related to the temperature of
  matter.
• For a given material and mass, the higher the
  temperature, the greater its thermal energy.
• Heat transfer is a study of the exchange of
  thermal energy through a body or between bodies
  which occurs when there is a temperature
  difference.
• When system and its surroundings are at different
  temperatures, thermal energy transfers from the
  one with higher temperature to the one with lower
  temperature.
• Thermal Energy always travels from hot to cold.
• This spontaneous act is called Heat Action or
  Heat Transfer.

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Heat Transfer Between System Surroundings

• Heat transfer is typically given the symbol Q,
  and is expressed in joules (J) in SI units.
• The rate of heat transfer is measured in watts
  (W), equal to joules per second, and is denoted
  by q.
• The heat flux, or the rate of heat transfer per
  unit area, is measured in watts per area (W/m2),
  and uses q" for the symbol.

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Heat Transfer What Happens to the System ?

• The thermal energy of the system may decrease or
  increase.
• However, temperature may or may not change
• What is the other property, which is directly
  affected by heat transfer?
• Specific Heat?
• Any couple like pressure and volume during work
  transfer?
• Not now .. May be later.

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Modes of Heat Mass Transfer

• Conduction or Diffusion
• Radiation
• Convection

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Thermal conduction through Earth's crust

• Two problems of Geophysics created a concern
  about heat conduction
• To what extent affects the heat of Earth's
  interior by conduction the temperature at the
  surface ?
• How far inward and in what manner propagate daily
  and seasonal temperature variations at Earth's
  surface?
• The answer through the theory of Kelvin to the
  first question is
• A stationary thermal state near Earth's surface,
  which maintains the heat of its interior, demands
  a uniform temperature gradient per metre inwards
  from the surface to the centre, provided all the
  different layers have the same thermal
  conductivity.
• Depending on their locations, temperature
  measurements in bore holes have yielded different
  results, on the average about 1ºC per 33m (medium
  geothermal depth gradient).
• An answer to the second question is best based on
  the observations of the Edinburgh Observatory
  (since 1837).

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Conduction Heat Transfer

• Conduction is a significant mode of transfer when
  system and surroundings consist of solids or
  stationery fluids.
• When you touch a hot object, the heat you feel is
  transferred through your skin by conduction.
• Two mechanisms explain how heat is transferred by
  conduction lattice vibration and particle
  collision.
• Conduction through solids occurs by a combination
  of the two mechanisms heat is conducted through
  stationery fluids primarily by molecular
  collisions.

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Fourier law of heat conduction
A Constitutive Relation

• The rate of heat transfer through the wall
  increases when
• The temperatures difference between the left and
  right surfaces increase,
• The wall surface area increases,
• The wall thickness reduces,
• The wall is changed from brick to aluminum.
• If we measure temperatures of the wall from left
  to right and plot the temperature variation with
  the wall thickness, we get

This is called as Fourier Law of Conduction
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Thermal Image of Laptop Casing
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Graphite Covering
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Thermal Image of Laptop Casing with Graphite cover
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Most General form of Fourier Law of Conduction
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Radiative Mode of Heat Transfer

• Any body (gt absolute zero) emits radiation at
  various wavelengths.
• Transparent bodies radiate energy in spherical
  space.

• Non-transparent bodies radiate energy in
  hemi-spherical space.

• The radiation energy emitted by a body is
  distributed in space at various wavelengths.
• This complex phenomenon requires simplified laws
  for engineering use of radiation.

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Planck Radiation Law

• The primary law governing blackbody radiation is
  the Planck Radiation Law.
• This law governs the intensity of radiation
  emitted by unit surface area of a blackbody as a
  function of wavelength for a fixed temperature.

• The Planck Law can be expressed through the
  following equation.

h 6.625 X 10-27 erg-sec (Planck Constant) K
1.38 X 10-16 erg/K (Boltzmann Constant) C
Speed of light in vacuum
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Stefan-Boltzmann Law

• The maximum emissive power at a given temperature
  is the black body emissive power (Eb).
• Integrating Planks Law over all wavelengths gives
  Eb.

• Driving forces Heat transfer by radiation is
  driven by differences in emissive power
  (proportional to T4.

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Radiation from a Thermodynamic System
The total energy emitted by a real system,
regardless of the wavelengths, is given by

• where esys is the emissivity of the system,
• Asys-surface is the surface area,
• Tsys is the temperature, and
• s is the Stefan-Boltzmann constant, equal to
  5.6710-8 W/m2K4.
• Emissivity is a material property, ranging from 0
  to 1, which measures how much energy a surface
  can emit with respect to an ideal emitter (e 1)
  at the same temperature