Heat Transfer PPT

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Energy
•
•
•
•
Ability to do work
Many different forms
Conservation of energy (Law)
Transformed: example:
– Radiant to Thermal
– Kinetic to Thermal (friction)
Absolute Zero
• As low as you can go
• -273 degrees Celsius
• All particles stop moving
The Electromagnetic
Spectrum
Light (medium wavelength)
made up of several color components
Infrared (long wavelength)
eg: Heat Escaping from People
UV (short wavelength)
causes sunburn and skin cancer
X-rays (very short wavelength)
Insolation
• SOLAR RADIATION (radiation coming from the
sun)
– Includes different types of radiation (UV/Infrared)
– Visible light makes up the majority of this
radiation
Transmission, Absorption,
and Scattering
• Transmission
– Wave passes through matter
• Scattering
• Absorption
– Wave and energy are absorbed
– Waves absorbed and reemitted
• Diffuse scattering
• Reflection
Refraction
Scattering
• Scattering is the redirection (in all directions)
of light by small particles and gas molecules in
the atmosphere; The result is more light rays
with weaker intensity.
Diffuse Scattering of Sunlight
Scattering of Light
through Reflection
Absorption of Sunlight
by Asphalt
17.2 Heating the Atmosphere
Conduction
• Conduction is the
transfer of heat
through matter
by molecular
activity; Energy is
transferred
through collisions
from one
molecule to
another.
Convection
• Convection is the transfer of heat by the
movement of a mass or substance; It can take
place only in liquids and gases.
Radiation
• Radiation is the transfer of energy (heat)
through space by electromagnetic waves.
Temperature
• Temperature is a
measure of the
average kinetic
energy of individual
atoms or molecules
in a substance.
Heat
• Heat is thermal energy transferred from one
object to another.
(Calories) Joules
• Unit of Energy
• Calories is used in the US
• Joules is metric unit
SPECIFIC HEAT
• The amount of energy needed to
heat 1 gram of a substance by one degree
celsius
Heat is the energy transferred from one object
to another because of a difference in their
temperatures.
Reflection
• Reflection is the process whereby light
bounces back from an object at the same
angle at which is encounters a surface and
with the same intensity.
Three mechanisms of energy transfer as heat are
conduction, convection, and radiation.
Unlike conduction and convection, which need
material to travel through, radiant energy can
travel through the vacuum of space.
When radiation strikes an object, there
usually are three different results.
1. Some energy is absorbed by the object.
2. Substances such as water and air are
transparent to certain wavelengths of
radiation.
3. Some radiation may bounce off the object
without being absorbed or transmitted.
How the atmosphere is heated:
• All objects, at any temperature, emit radiant
energy.
• Hotter objects radiate more total energy per
unit area than colder objects.
• The hottest radiating bodies produce the
shortest wavelengths of maximum radiation.
• Objects that are good absorbers of radiation
are good emitters as well.
Greenhouse Effect
• Greenhouse effect is the heating of Earth’s
surface and atmosphere from solar radiation
being absorbed and emitted by the
atmosphere, mainly by water vapor and
carbon dioxide.
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