Thermal Dynamics and Heat Transfer

ASTECTraining Program

Copyright 2007 Insulating Coatings Corporation

1. The Concept of Heat2. Heat Transfer (I)3. Heat Transfer (II)4. Processes in Radiation5. Term Definitions6. ASTEC – Thermal Properties7. ASTEC – The Total Solution

TrainingProgram

The Concept of Heat(Thermodynamics)

Module 1

Module 1Thermodynamics

Thermodynamics:

1. Energy is always conserved; it is never lost.2. Heat always travels from a “hot” region to a “colder” region.

Therefore, the issue is:• Flow of Heat• Heat Flow•Heat Transfer

Module 1Thermodynamics

Module 1Thermodynamics

Heat Transfer

Radiation ~ Electromagnetic Waves

Conduction ~ Molecule Movement

Convection ~ Air Current

Module 1Thermodynamics

• Conduction

• Convection

• Radiation

Heat Transfer Modes

Heat transfer for conductionand for convection is directly proportional to the driving temperature differential. Double the difference to double the heat transfer rate ( T1 – T2 )

Module 1Thermodynamics

• Conduction

• Convection

• Radiation

Heat Transfer Modes

Heat transfer by radiation is proportional to the fourth power of the temperature difference ( T1

4 – T24 ).

Small changes in temperature can create relatively large changes in radiation heat transfer rates.

Heat Transfer (I)(Modes / Electromagnetics)

Module 2

Module 2Heat Transfer (I)

Heat Flows Only by…

•Conduction Intensity of conduction

•Convection Amount of convection

•Radiation Rate of radiation[reflectivity, absorption, and transmissivity]

Module 2Heat Transfer (I)

CONDUCTION

•Direct heat flow through matter resulting from a physical contact.

• Transmission of heat by molecular motion.

Module 2Heat Transfer (I)

CONVECTION

•Transfer or transportation of heat which is within a gas or liquid.

“Free convection”“Forced convection”

Module 2Heat Transfer (I)

RADIATION

•Transmission through space of energy by means of electromagnetic rays of varying wavelengths (λ)and cycles (Hertz).

Module 2Heat Transfer (I)

Wavelength, λ (μ m) for

c = 3 x 108 m/s

Module 2Heat Transfer (I)

Module 2Heat Transfer (I)

Terminology

G Irradiation (solar/thermal radiation)Radiant flux incident per unit area W/m2

ε Emissivity (thermal radiation)Rate of radiation emanating from Numericthe surface of an object compared to the rate of radiation emanating from a “black body”

Module 2Heat Transfer (I)

Terminology

ρ (Radiant) reflectance (Numeric)Ratio of reflected radiant flux ρGto incident radiant flux

α (Radiant) absorptance (Numeric)Ratio of absorbed radiant flux αGto incident radiant flux

τ (Radiant) transmittance (Numeric)Ratio of transmitted radiant flux τGto incident radiant flux

Module 2Heat Transfer (I)

Heat Transfer (II)(Electromagnetics and Infrared Energy)

Module 3

Module 3Heat Transfer (II)

The sun radiates energy to the earth through 93

million miles of space by means of rays of many different wavelengths.

Module 3Heat Transfer (II)

RADIATION

186,286 miles/sec or 300,000 km/sec

SOLAR RADIATION SPECTRUM

Module 3Heat Transfer (II)

Very Low FrequencyLow Frequency Medium FrequencyHigh FrequencyVery High FrequencyUltra High FrequencySuper High FrequencyExtra High Frequency

Infrared (Heat rays)• NIR 0.75 to 3• MIR 3 to 6• FIR 6 to 15• XIR 15 to 1000

Visible raysUltraviolet raysX raysGamma RaysCosmic Rays

SOLAR RADIATION SPECTRUM

Module 3Heat Transfer (II)

Radiation Spectrum

Infrared rays Visible rays Ultraviolet rays

0.76 to 100 μ m 0.75 to 0.4 μ m 0.4 micron to 100 A(feels warm) (visible light) (causes sunburn)

Radiation Intensity

• The closer to the sun a body is, the more rays it will intercept.

• Closer to the sun, the intensity can be so great that we could not survive.

Module 3Heat Transfer (II)

• A 7 story building is exposed to more radiation on the walls than on the roof.

• A single story building receives 70% of it’s radiation on the roof.

Module 3Heat Transfer (II)

Radiation Exposure

Radiation: Solar and Thermal

•Solar•Emanating from the sun•High energy content•Short wavelength, High frequency

•Thermal•Emanating from every object in the universe•Low energy content•Long wavelength, Low frequency

Module 3Heat Transfer (II)

Every Exposed Surface

…Of every object…In the universe…With a temperature…Above absolute zero…Gives off infrared rays…In varying amounts

Module 3Heat Transfer (II)

Absolute Zero

Module 3Heat Transfer (II)

Absolute Zero

Module 3Heat Transfer (II)

ABSOLUTE ZERO

Module 3Heat Transfer (II)

Everything AboveAbsolute Zero…

Radiates Energy inthe form of infrared

heat rays.

Module 3Heat Transfer (II)

Infrared (thermal) heat rays travel…

Module 3Heat Transfer (II)

•Away from every point on the surface.•In a straight line.•In any direction.•With the greatest intensity perpendicular to the surface.•With the least intensity parallel with the receiving surface (zero intensity).

Module 3Heat Transfer (II)

The radiation from a metal roof, a concrete surface or other opaque material originates within a few microns of the surface; hence emissivity (the rate of radiation emitted by a given surface) is a function of the surface state of a material rather than of its bulk properties.

For this reason, the emissivity of a coated or painted surface is characteristic of the coating rather than of the underlying surface.

Processes in Radiation(ρ, α, τ, and ε)

Module 4

Module 4Processes in

Radiation

ReflectivityAbsorptivity

Transmissivity

Module 4Processes in

Radiation

What’s a Black Body?

•A theoretical body•With properties such that…•It will absorb all (100%) radiation falling on its surface•Reflecting and transmitting none•But it will emit radiation depending on its absolute temperature.

Module 4Processes in

Radiation

Black Body Radiation

Module 4Processes in

Radiation

Absorbs all radiation(energy converts to heat)

•Allows no convection•Reflects no radiation•Transmits no radiation

In-coming irradiation(energy)

Emits radiation (depending on its absolute temperature)

(Absorptivity) + (Reflectivity) + τ (Transmissivity) = 1

Black Body Radiation

Module 4Processes in

Radiation

A + R + T = 1

Since there is no Reflectivity R = 0&Since there is no Transmissivity T = 0ThenAbsoptivity must equal one A = 1

(Absorptivity) + (Reflectivity) + τ (Transmissivity) = 1

Black Body Radiation

Module 4Processes in

Radiation

Absorbs all radiation(energy converts to heat)

•No Reflectivity•No Transmissivity•No Convection

In-coming irradiation(G)

Emits ( ε ) all radiation

If all in-coming G (energy) is absorbed,

then all in-coming G (energy) is emitted, therefore ε = 1

Kirchoff’s Identity

Emissivity ( ε )

• The rate at which radiant heat energy is emitted by a given surface.

• “The ratio of the thermal radiation from unit area of a surface to the radiation from unit area of a full emitter (black body) at the same temperature”

• It is a physical property… just like weight, color, shape, etc.

• All materials have an emissivity ranging from zero to one (100%).

Module 4Processes in

Radiation

Emissivity ( ε )

• The rate of radiation emanating from a surface. (the emissivity of an object’s surface is related to the ability of that surface to absorb heat rays.)

• Total Emissive Power of a Black Body:

Eb = σT4

Module 4Processes in

Radiation

Total Emissive Power of a Black Body

Module 4Processes in

Radiation

Eb = σT4

q = quantity of heat ( J )

σ = Stefan – Boltzmann constant

T = temperature K˚ or temperature R˚

Joule ( 1 J = 1 Watt/s )

Sigma: a constant = 0.1714 x 10-8 Btu/h-ft2 or 5.669 x 10-8 W/m2

K˚ = Celsius ˚ + 273.15˚ or R ˚ = Fahrenheit ˚ + 459.7˚

Common Power Units

Module 4Processes in

Radiation

1 watt = 3.412 Btu/hr1 Watt/s = 1 Joule1 Btu/s = 1.055 Watts1 Cal/s = 4.19 Watts1 Ft-lb./s = 1.36 Watts1 Btu = 1050 Joules1 Joule = 0.2389 Cal1 Cal = 4.186 Joules

Grey Body Radiation

•A grey body is a non-ideal emitter or an imperfect radiator.•A grey body will:

•absorb some of the energy it will receive.•reflect some of the energy it will receive. •emit the energy it absorbs.

•A grey body is opaque: τ = 0

Module 4Processes in

Radiation

Model of a Grey Body Radiation

Module 4Processes in

Radiation

Absorbs all radiation(energy converts to heat)

In-coming irradiation (G)

Emitted ( ε ) energy

Reflected energy

Convected energy

Grey Body Radiation

Module 4Processes in

Radiation

A + R + T = 1

Since there is no Transmissivity T = 0thenReflectivity + Absorptivity = 1 A + R = 1

(Absorptivity) + (Reflectivity) + τ (Transmissivity) = 1

Since there is Reflectivity R = > 0thenAbsorptivity must be: A = < 0thereforeEmissivity must be less than 1 ε = < 1

Emissive Power of a Grey Body

•Real surfaces emit less radiation than ideal “black body” surface.

•The ratio of actual emissive power [E] to the emissive power of a black body at the same temperature [Eb] is called the emissivity.

•It is defined byε = E/Eb

Module 4Processes in

Radiation

Energy Economics

•Office worker requires 200 ft2

•Salary: $30,000/yr•Value of services: $150/ ft2

•Cost of Energy: $2.25/ ft2 (1985 $)

Module 4Processes in

Radiation

Term Definitions(Physics)

Module 5

Module 5Term Definitions

Definitions of Terms

•Absorptivity•British Thermal Unit (Btu)•Conductance (C factor)•Conductivity (K factor)•Emissivity •Reflectivity•Resistance (R factor)•U Factor

Module 5Term Definitions

Absorptivity

• The fraction of thermal radiation incident on a surface which is absorbed.

Module 5Term Definitions

British Thermal Unit

• The amount of heat needed to raise the temperature of 1lb. Water 1 degree Fahrenheit.

Module 5Term Definitions

Conductance (C Factor)

• The rate of heat flow in Watts per square meter Kelvin (W/m2K) of any material whether homogeneous or non-homogeneous.

Module 5Term Definitions

Conductivity (k Factor)

• Thermal conductivity, k, is the rate of conduction

heat transfer per unit area for a temperature gradient of 1˚ C/m ( or 1˚ F/ft).

•The units for k are W/(m ˚C) *or Btu/(h ft ˚F)+.

•Thermal conductivity (k) measures the rate of heat transfer through a material from face to face. Calculate for any material by multiplying the thickness in meters by the appropriate k value.

Emissivity

• Ratio of the radiation emitted by a surface to the radiation emitted by a black body at the same temperature.

Module 5Term Definitions

Reflectivity

• The fraction of thermal radiation incident on a surface which is reflected.

Resistance (R Factor)

• Resistance to heat flow is the reciprocal of C, k, or U:

• 1/C, 1/k, 1/U

•The smaller the C, k, or U factor fraction, and the larger the R factor, the better the insulation against heat transfer by conduction.

Module 5Term Definitions

U Factor

• The rate of heat flow or “overall coefficient of heat transmission” in Btus in one hour through one sq. ft. area of the entire depth of ceiling, roof, wall, or floor, including insulation if any, which will result from a 1˚ F temperature difference between the air inside and the air outside.

Module 5Term Definitions

ASTEC Thermal Properties

Module 6

Module 6ASTEC Thermal

Properties

ASTEC Thermal Properties

Module 6ASTEC Thermal

Properties

Reflectivity: 86.9%

ASTEC Thermal Properties

Module 6ASTEC Thermal

Properties

Absorptivity: 13.1%

ASTEC Thermal Properties

Module 6ASTEC Thermal

Properties

Emissivity: 90.1%

ASTEC The Total Solution

Module 7

Module 7ASTEC

The Total Solution

Module 7ASTEC

The Total Solution

Heat Transfer

• The best way to reduce heat transfer:Prevent it from entering the building.

• The best wat to manage heat transfer:Re-emit it quickly.

Module 7ASTEC

The Total Solution

Customer Requirements

• Energy saving radiant heat barrier•Reduced heat transfer•Better heat management•Reduced cooling load•Protection against ultra-violet degradation• Long lasting waterproofing protection

Module 7ASTEC

The Total Solution

Customer Requirements

• Roof structural integrity• No chipping, no cracking, no flaking• Corrosion control• Environmentally friendly products• Economical solutions•Attractive and clean finish•Long life cycle

Module 7ASTEC

The Total Solution

Customer Requirements

• Low installation cost• Brand name recognition• Low roof maintenance• Product warranty• Labor warranty• Increased roof longevity

Module 7ASTEC

The Total Solution

Meeting Customer’s Needs

• ASTEC is more than a mere coating:•Exterior Radiant Insulation & Finish System

• ASTEC greatly reduces radiant heat transfer:•High solar reflectivity of 0.87

• ASTEC efficiently manages heat transfer•High thermal emissivity of .91

Module 7ASTEC

The Total Solution

Meeting Customer’s Needs

ASTEC’s radiant heat barrier…

• Reduces surface temperatures by as much as 20˚ C

• Reflects between 80% and 87% or radiant heat (p = 0.80 to 0.87)

• Limits radiant heat absorption between 15% and 20% (α= 0.14 to 0.20)

• Reduces energy consumption by as much as 40%

Module 7ASTEC

The Total Solution

Meeting Customer’s Needs

• ASTEC’s high density ceramic components:• Resists ultra-violet degradation• Maintains its color

• ASTEC products are water based

•ASTEC provides an aesthetic architectural appearance.

Module 7ASTEC

The Total Solution

Meeting Customer’s Needs

• ASTEC’s metal primer seal inhibits corrosion and prevents oxidation from air and humidity.

• ASTEC’s waterproofing membrane retains its flexibility and monolithic structural integrity.

Module 7ASTEC

The Total Solution

Meeting Customer’s Needs

• ASTEC’s lower surface temperature provides:• Thermal shock protection• Longer roof life cycle

• ASTEC is a world leader• Applied on structures in more than 30 countries.

Module 7ASTEC

The Total Solution

Meeting Customer’s Needs

• ASTEC is easy to maintain and easy to repair

•Ten (10) year warranty

•ASTEC is applied by trained and authorized applicators only

•Astec Dealers offer an optional “certified” roof maintenance program

Module 7ASTEC

The Total Solution

Cost Analysis / Financial Benefits

• Cost effective installation

•Low cost maintenance

•Easy do-it-yourself repair

•Energy Conservation

Module 7ASTEC

The Total Solution

Cost Analysis / Financial Benefits

• Lower roof repair cost • Longer roof life• Environmentally friendly materials• Fire safe products: self extinguishing• Sound attenuation features• Mildew resistant qualities

Module 7ASTEC

The Total Solution

ASTEC Strengths

• Over 20 year proven performance

•Over 300 million square feet of applied products

• Fully tested in independent laboratories

• Accepted, approved and specified by several government agencies in various countries.

•ISO 9001 – 2000 Registered Manufacturing

Module 7ASTEC

The Total Solution

ASTEC Strengths

• Prestigious client references•Industrial sector•Commercial sector•Petrochemical sector•Residential Sector•Military sector

• All marketing claims are scientifically substantiated

Module 7ASTEC

The Total Solution

ASTEC Strengths

• All dealers are professionally trained

• ASTEC Dealers have full time dedicated staff

• Labor and Product warranty

• Worldwide leadership and international recognition

Module 7ASTEC

The Total Solution

Next Steps

• Check our references

• Verify our claims

• Compare us with the competition

• Contact your local ASTEC Dealer for a free estimate