An Action due to Thermal Inequilibrium

P M V SubbaraoProfessor

Mechanical Engineering Department

Every member of earth wants it for A Refresh ....A Natural Happening …..

A Wake-up Call to Earth

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.

The Sun enlightens Every Life

•Kowsalya supraja Rama poorva sandhya pravarthatheUthishta narasardoola karthavyam daivamahnikam

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….

The Engineering Process Responsible for Evolution

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.

Why I Am Different ?

?

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.

Classification of Elephants

Indian ElephantAfrican Elephant

Mammoths, living in a cold tundra region, have fur coats and small hairy ears.

An Exotic & Artificial Device……

The basic invention is due to other sciences…

The final and reliable existence is due to Heat Transfer…

The Pentium 4 Processor

Basic Location on A Mother Board

Heat Sinks for Pentium 4

Pentium 4 While Performing

                                                           

                                         

Heat Sinks of Cooling of Electronics

Heat Sinks : Guided Flow

Heat Sinks : Guided Flow with Different Fin Shapes

Heat Sinks : Curious Paired Video Card-Motherboard

Design

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.

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.

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….

Modes of Heat & Mass Transfer

• Conduction or Diffusion

• Radiation

• Convection

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).

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.

Conduction by lattice vibration or Particle Collisions

                                                                                                                               

Fourier law of heat conduction

L

TkA

L

TTkAq coldhot

x

This is called as Fourier Law of 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:

Thermal Image of Laptop Casing

Graphite Covering

Thermal Image of Laptop Casing with Graphite cover

Most General form of Fourier Law of Conduction

dx

dTkqx ''

Tkq ''

kkjkikk zyxˆˆˆ

Radiative Mode of Heat Transfer

• Any body (> 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.

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.

1

12,

5

2

kT

hcb

e

hcTE

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

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

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.

05

2

0 1

12,

d

e

hcdTE

kT

hcb

444

42

15

2TT

khc

hcTEb

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

The total energy emitted by a real system, regardless of the wavelengths, is given by:

4syssurfacesyssysemitted TAQ

• where εsys is the emissivity of the system,• Asys-surface is the surface area, • Tsys is the temperature, and • σ is the Stefan-Boltzmann constant, equal to 5.67×10-8 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 (ε = 1) at the same temperature

Radiation from a Thermodynamic System