MEL 242 : Heat and Mass Transfer

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MEL 242 Heat and Mass Transfer

• P M V Subbarao
• Associate Professor
• Mechanical Engineering Department
• IIT Delhi

Every member of earth wants it for A Refresh
.... An Essential Phenomenon in all Energy
Interactions . A First level Engineering for
Existence ..
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A Wake-up Call to Earth
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A Means of Generating Wealth on Earth

• Development and ripening of vegetable substances
  demand the light and the heat of the Sun, which
  therefore must be viewed as the source of energy
  as far as its nature is organic.
• The energy of winds and water originate from the
  heat of the Sun.
• 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
  and the winds arise from air currents due to the
  heating of the air by the Sun on Earth's surface.
  
• Hence the heat of the Sun maintains all
  meteorological, climatic, geological and organic
  processes of Earth.
• Where does it come from?
• It is obvious to suspect that it arises out of
  chemical processes between the elements,
  contained in the Sun (spectral analysis).

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ONE TIME RESOURCE
SOLAR ENERGY
INCOMING RESOURCE
CO2 H2O
PHTOSYNTHESIS
SOLAR RADIATION
WINDS
VEGETATION
VELOCITY
CHEMICAL ENERGY
THERMAL
WAVE
WIND ENERGY
CLOUDS
OCEAN THERMAL ENERGY
FOSSILIZATION
RAINS
HYDRO ENERGY
COAL
FOSSIL FUEL
PETROLEUM
NATURAL GAS
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Energy Cycle in Living Things
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A Natural Engineering 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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Why I Am Different ?
?
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Reasons Explanations

• It is A Problem of Geometry.
• 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.
• A major difference between warm and cold blooded
  creatures is that warm blooded ones can generate
  by metabolism, the required heat energy to
  maintain their body temperature while the cold
  blooded ones require external heat sources like
  the Sun, to maintain their body temperature.
• Elephants also are warm blooded tetrapods.
• Warm blooded animals desire to remain at an
  isothermal body temperature of 35 to 42 C
  (varies between animals).

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• In mammals and birds a highly active metabolism
  generates the required exothermic heat in their
  cells.
• This heat is fed to the internal energy of the
  body, which results in the desired body
  temperature.
• 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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External Design Variations to Control Body
Temperature

• Warm blooded animals retain their heat by
  insulating their body against the environment by
  growing hair and feathers.
• The hair traps a small layer of air around it as
  thermal insulation (air is a very poor heat
  conductor - k 0.02 W/m.K).
• This is one reason polar bears are furry.
• This is also possible reason why we humans go
  bald. More on this in a later post.
• On the other hand, warm blooded animals when
  faced with the need to release the excess
  metabolism generated heat energy, seek cool
  environment and divert their blood flow to the
  surface of their skin.
• This ensures higher heat transfer rate to the
  cooler environment from their body and maintains
  the body temperature at a constant value.
• When such a direct sensible cooling is not
  sufficient to remove the excess heat, an
  evaporative cooling mechanism aids in case of
  mammals with large quantities of reservoir
  fluids.
• In other words, under such conditions, humans
  sweat.

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Geometry of An Elephent ?!?!?!

• Now to connect the geometry part that we
  discussed earlier.
• In light of the above features, 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.
• Whenever there is excess heat that needs to be
  released, warm blood flows through these
  capillaries, while the elephant chooses a cold
  spot (like that of a shade) and uses the
  favorable thermal gradient to release the excess
  heat.
• In other words, 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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Reliable and Guaranteed Location in A Desktop