Energy and Heat Transfer AOS 101 Section 301 - Feb 16 2009

Heat, Temperature, and Energy Transfer Some basic definitions: Temperature – Related to the energy content of an object. In a gas, the temperature is defined as the average kinetic energy of the gas particles.

Heat, Temperature, and Energy Transfer Some basic definitions: Heat – Related to the energy transfer between two objects. Heat is the transfer of energy from a warm object to a cool object, obeying the 2nd Law of Thermodynamics: “Things fall apart”

Heat, Temperature, and Energy Transfer Important Note: Temperature =/= Heat You cannot “feel” the temperature of an object, only the heat exchange between yourself and that object. It is related to the object’s temperature, but not the same thing.

HOT COLD Temp

ENERGY TRANSFER HOT COLD Temp

ROOM TEMP ROOM TEMP Temp

More Terms to Know Specific Heat Capacity – This is the ratio of the amount of energy 1 Kg of a substance requires in order to change its temperature by 1 Kelvin: Q C = T C = Specific Heat Capacity Q = Energy (J) Δ T = Change in Temperature (K)

Some Sample Specific Heat Capacities: Air 1.0035 Water 4.1813 Diamond 0.5091 Glass 0.8400 Ice 2.050 Aluminum 0.897 Helium 5.1932

Kinds of Energy Transfer There are four kinds of energy transfer: Conduction Convection Advection Radiation

Kinds of Energy Transfer There are four kinds of energy transfer: Conduction Convection Advection Radiation Conduction, Convection, and Advection require some kind of medium to act through – Radiation does not.

Kinds of Energy Transfer There are four kinds of energy transfer: Conduction Convection Advection Radiation Air is a poor conductor of heat, therefore Convection, Advection, and Radiation all play large roles in the atmosphere, while Conduction is less important.

Kinds of Energy Transfer Advection Energy can be transferred from one region to another through the transport of warm or cool air from one place to another – Advection of temperature Cyclones are especially good at this:

L Cool air from the pole is being advected to the south Warm air from the tropics is being advected to the north

L Uniformly cold near the pole Strong temperature contrast exists along a narrow line Uniformly warm in the tropics

L Uniformly cold near the pole Warm Front Cold Front Uniformly warm in the tropics

L L L L

L L L L “Wave Train”

Kinds of Energy Transfer Convection Energy can be transferred when a fluid is forced to vertically mix, allowing hot and cold portions of the fluid to make contact and even the temperature out “Hot air rises and cold air sinks”

Convection In the atmosphere, convection occurs when relatively warm air is below relatively cool air, forcing the warm air to rise and cold air to sink – “overturning” Overturning can occur by warming the air at the surface OR cooling the air above

Lake Effect Snow

Lake Effect Snow “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Cold Warm N S

Cold air from the land is advected over the warm water surface Lake Effect Snow “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Cold air from the land is advected over the warm water surface Cold Warm N S

Warm air is now underneath cold air, leading to convective overturning Lake Effect Snow “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Warm air is now underneath cold air, leading to convective overturning Cold Warm Cold N S

Lake Effect Snow “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Rising warm air creates strong convective clouds and snow – “Lake Effect” snow Cold N S

Videos of Convection Convection Video 1 http://www.youtube.com/watch?v=QpriSb6uN4A Convection Video 2 http://www.youtube.com/watch?v=1gvHpO26Xv4&feature=related Convection Video 3 http://www.youtube.com/watch?v=H1sS1TmXF38&feature=related

Kinds of Energy Transfer Radiation Energy can be transmitted from one object to another through emission and absorption of electro-magnetic waves The Earth-Atmosphere-Sun system is the most important aspect of this kind of energy transfer for meteorology

Earth-Atmosphere-Sun System

Earth-Atmosphere-Sun System Sun is at ~6000 K, and emits shortwave radiation to the atmosphere Sun Earth Atmosphere

Earth-Atmosphere-Sun System Atmosphere is selectively transparent to solar radiation, allowing it to pass through to the Earth, where it is absorbed Sun Earth Atmosphere

Earth-Atmosphere-Sun System Earth heats up and emits longwave radiation outward, some of which is selectively absorbed by the atmosphere, also heating the atmosphere (the rest escapes to space) Sun Earth Atmosphere

Earth-Atmosphere-Sun System Atmosphere heats up and emits longwave radiation both toward the Earth, and away from the Earth into space Sun Earth Atmosphere

Earth-Atmosphere-Sun System Earth has TWO sources of radiation heating the surface: the Sun AND the atmosphere. This is why the Earth is warmer than 0oF Sun Earth Atmosphere

Earth-Atmosphere-Sun System The more longwave radiation the atmosphere absorbs from the Earth, the more longwave radiation is radiated back to Earth – “Greenhouse Effect” Sun Earth Atmosphere

Radiation In general, when radiation strikes an object, it can be:

Radiation In general, when radiation strikes an object, it can be: Transmitted – radiation passes through the object without being absorbed

Radiation In general, when radiation strikes an object, it can be: Transmitted – radiation passes through the object without being absorbed Absorbed – radiation is retained by the object and stored energy is manifest as an increase in temp.

Radiation In general, when radiation strikes an object, it can be: Reflected – radiation bounces off of object and travels in a new direction Transmitted – radiation passes through the object without being absorbed Absorbed – radiation is retained by the object and stored energy is manifest as an increase in temp.

Radiation In general, when radiation strikes an object, it can be: Reflected – radiation bounces off of object and travels in a new direction Transmitted – radiation passes through the object without being absorbed Absorbed – radiation is retained by the object and stored energy is manifest as an increase in temp. Scattered – radiation strikes a small object and reflects in all directions (though not necessarily equally)

Rtotal=Rtrans+Rabs+Rref+Rscat Radiation When radiation strikes an object, it MUST do one or more of these things. There is no radiation that is not transmitted, absorbed, reflected, or scattered: Rtotal=Rtrans+Rabs+Rref+Rscat Reflected – radiation bounces off of object and travels in a new direction Transmitted – radiation passes through the object without being absorbed Absorbed – radiation is retained by the object and stored energy is manifest as an increase in temp. Scattered – radiation strikes a small object and reflects in all directions (though not necessarily equally)

What About Latent Heat? Technically, there are five forms of energy transfer to consider: Conduction Convection Radiation Advection

What About Latent Heat? Technically, there are five forms of energy transfer to consider: Conduction Convection Radiation Advection Latent Heat

What About Latent Heat? Technically, there are five forms of energy transfer to consider: Conduction Convection “Sensible Heat” Radiation Advection Latent Heat

What About Latent Heat? “Sensible Heat” – Energy transfer via the manipulation of temperature – an object becoming warmer or colder due to the absorption or emission of thermal energy. Heat transfer you can sense. Latent Heat – Energy transfer via the manipulation of the phase state of water. Heat transfer latent to the state of water.

Heating Ice Into Water Vapor Temp Energy supplied to ice causes ice to increase in temperature – sensible heat Time

Heating Ice Into Water Vapor Temp Ice reaches melting point, and supplied energy now forces ice to melt – absorbing latent heat Time

Heating Ice Into Water Vapor Ice has completely melted into water, and now supplied heat increases water temperature – sensible heat Temp Time

Heating Ice Into Water Vapor Temp Water reaches boiling point and uses supplied energy to convert to water vapor – absorbing latent heat Time

Heating Ice Into Water Vapor Temp Water boils completely, and supplied energy now increases temperature of water vapor – sensible heat Time

Sensible heat transfer Sensible heat transfer Sensible heat transfer Heating Ice Into Water Vapor Sensible heat transfer Sensible heat transfer Sensible heat transfer Temp Latent heat transfer Latent heat transfer Time