Energy and Heat Transfer - PowerPoint PPT Presentation

Loading...

PPT – Energy and Heat Transfer PowerPoint presentation | free to download - id: 7f1c6d-ZjRjM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Energy and Heat Transfer

Description:

Energy and Heat Transfer AOS 101 Discussion Sections 302 and 303 www.spirit-alembic.com – PowerPoint PPT presentation

Number of Views:93
Avg rating:3.0/5.0
Slides: 34
Provided by: Alex4324
Learn more at: http://aos.wisc.edu
Category:
Tags: energy | heat | moist | transfer

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Energy and Heat Transfer


1
Energy and Heat Transfer
  • AOS 101 Discussion Sections 302 and 303

2
Energy
  • Energy is the capacity to do work
  • Work is done on something when it is either
    pushed, pulled, or lifted over some distance
  • Kinds of energy
  • Kinetic energy
  • KE ½mv2
  • Potential energy
  • PE mgh
  • Mechanical energy
  • Chemical energy
  • Thermal energy
  • Radiant energy

3
Laws of Thermodynamics
  • 1st Law of Thermodynamics
  • Energy cannot be created or destroyed
  • Energy lost during one process must equal the
    energy gained during another
  • 2nd Law of Thermodynamics
  • Heat can spontaneously flow from a hotter object
    to a cooler object, but not the other way around
  • The amount of heat lost by the warm object is
    equivalent to the heat gained by the cooler
    object

4
Conservation of Energy
5
Heat
  • Heat is a form of energy and is the total
    internal energy of a substance
  • Revisiting the 1st law
  • States that heat is really energy in the process
    of being transferred from a high temperature
    object to a lower temperature object.
  • Heat transfer changes the internal energy of both
    systems involved
  • Heat can be transferred by
  • Conduction
  • Convection
  • Advection
  • Radiation

6
Heat Capacity and Specific Heat
  • Heat capacity of a substance is the ratio of heat
    absorbed (or released) by that substance to the
    corresponding temperature rise (or fall)
  • Specific heat
  • The heat capacity of a substance per unit mass
  • Can be thought of a measure of the heat energy
    needed to heat 1 g of an object by 1ºC
  • Different objects have different specific heat
    values

7
Specific Heat
  • 1 g of water must absorb about 4 times as much
    heat as the same quantity of air to raise its
    temperature by 1º C
  • This is why the water temperature of a lake or
    ocean stays fairly constant during the day, while
    the temperature air might change more
  • Because of this, water has a strong effect on
    weather and climate

Substance Specific Heat (J/gK)
Water (liquid) 4.183
Ice 2.050
Wood 0.420
Sand 0.835
Air 1.012
8
Latent Heat
  • Latent heat is the amount of energy released or
    absorbed by a substance during a phase change

FOR WATER
2260 J/g released
334 J/g released
SOLID
LIQUID
GAS
2260 J/g absorbed
334 J/g absorbed
SOLID
LIQUID
GAS
9
Orange Example
  • Farmers spray their oranges with water when a
    frost event is about to occur
  • Why?
  • When the temperature drops below 32oF, liquid
    water freezes into ice.
  • This liquid to solid phase change causes energy
    to be released to the fruit.
  • Thus, the temperature of the orange remains warm
    enough to prevent ruin.

10
Swimming Pool Example
  • Why do you feel cool when you get out of the
    pool?
  • Drops of liquid water are still on your skin
    after getting out
  • These drops evaporate into water vapor
  • This liquid to gas phase change causes energy to
    be absorbed from your skin

11
Cumulus Cloud Example
  • Formation of clouds
  • Clouds form when water vapor condenses into tiny
    liquid water drops
  • This gas to liquid phase change causes energy to
    be released to the atmosphere
  • Release of latent heat during cloud formation
    drives many atmospheric processes

12
Conduction
  • Conduction is the transfer of heat from molecule
    to molecule within a substance
  • Molecules must be in direct contact with each
    other

13
Thermal Conductivity
  • Thermal conductivity is the measure of how well a
    substance can conduct heat
  • Depends on its molecular structure
  • If it is a bad conductor, it is a good insulator

Substance Thermal Conductivity (W/Km)
Air 0.024
Soil 0.2
Asphalt 0.75
Glass 1.05
Stainless Steel 16
Copper 401
Silver 429
14
Convection
  • Convection is the transfer of heat by the mass
    movement of a fluid (such as water and air) in
    the vertical direction (up and down)

15
Convection
16
Moist Convection
  • As the temperature of an air parcel cools, it may
    reach a point where it reaches saturation (the
    air temperature and dew point are the close to
    the same)
  • Air parcels condense and form a cloud

17
Advection
  • Advection is the transfer of heat in the
    horizontal direction
  • The wind transfers heat by advection
  • Occurs frequently
  • Why is advection important?
  • Important for the formation of precipitation and
    fog

18
Types of Advection
  • Two types
  • Warm air advection (WAA)
  • Wind blows warm air toward a region of colder air
  • Cold air advection (CAA)
  • Wind blows cold air toward a region of warmer air

19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
Radiation
  • Radiation is the travel of energetic particles or
    waves traveling through space or another kind of
    medium to heat it up
  • For Example
  • The suns rays traveling through space and
    reaching the Earth
  • The warmth from a fire pit
  • Radiation back into space from a warm Earth
  • Black Body
  • A perfect absorber and emitter of radiation

23
Radiation, Convection, and Conduction
24
Solar Radiation
  • The suns rays do not hit all areas of the Earth
    the same
  • Factors that determine the amount of solar
    radiation hitting the Earth
  • Position on Earth (latitude, longitude, and
    elevation)
  • Time of day (shown below in UTC)
  • Composition of the atmosphere
  • Amount and thickness of clouds, if any
  • Position of Earth in orbit around the sun (i.e.
    time of year)

25
Solar Radiation
26
Solar Radiation
  • Equinoxes
  • Where day and night are of equal length
  • Vernal Equinox March 20
  • Autumnal Equinox September 23
  • Solstices
  • Summer Solstice June 21
  • Longest day of the year in the Northern
    Hemisphere
  • Where the sun is at its northernmost point from
    the equator
  • Winter Solstice December 21
  • Shortest day of the year in the Northern
    Hemisphere
  • Where the sun is at its southernmost point from
    the equator
  • How radiation changes with latitude and date

27
Solar Radiation Budget
28
Energy Budget
29
Radiation
  • All things with a temperature above absolute zero
    emit radiation
  • Radiation allows heat to be transferred through
    wave energy
  • These waves are called electromagnetic waves
  • Wavelengths of the radiation emitted by an object
    depends on the temperature of that object
  • i.e., the sun mainly emits radiative energy in
    the visible spectrum, and the earth emits
    radiative energy in the infrared spectrum
  • Shorter wavelengths carry more energy than longer
    wavelengths

30
Radiation
  • A photon of ultra-violet radiation carries more
    energy than a photon of infrared radiation
  • The shortest wavelengths in the visible spectrum
    are purple, and the longest are red

31
Types of Radiation
  • Energy can be
  • Absorbed
  • Increasing the internal energy of the gas
    molecules
  • Reflected
  • Albedo is the percentage of the light reflected
    off an object
  • Scattered
  • Light deflected in all directions forward,
    backward or sideways
  • Also called diffused light
  • Transmitted

32
Kirchoffs Law
  • Good absorbers of a particular wavelength are
    good emitters at that wavelength and vice versa
  • Our atmosphere has many selective absorbers
  • Carbon dioxide, water vapor, etc
  • These gases are good at absorbing IR radiation
    but not solar radiation
  • These gases are called greenhouse gases
  • Due to the fact they help to absorb and reemit IR
    radiation back toward the Earths surface thus
    keeping us warmer then we would otherwise be

33
More Examples
  • Energy
About PowerShow.com