* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Heat Transfer: Conduction, Convection and Latent Heat In addition
Survey
Document related concepts
Passive solar building design wikipedia , lookup
Insulated glazing wikipedia , lookup
Solar water heating wikipedia , lookup
Heat exchanger wikipedia , lookup
Heat equation wikipedia , lookup
Dynamic insulation wikipedia , lookup
Building insulation materials wikipedia , lookup
Intercooler wikipedia , lookup
Copper in heat exchangers wikipedia , lookup
Cogeneration wikipedia , lookup
Hyperthermia wikipedia , lookup
Solar air conditioning wikipedia , lookup
R-value (insulation) wikipedia , lookup
Transcript
Heat Transfer: Conduction, Convection and Latent Heat In addition to radiation, energy can also be transferred in the form of heat: Heat Transfer: Conduction, Convection and Latent Heat In addition to radiation, energy can also be transferred in the form of heat: ● The simple diffusion of heat through a substance as caused by the motions of its molecules is referred to as conduction conduction of heat along a metal rod Heat Transfer: Conduction, Convection and Latent Heat In addition to radiation, energy can also be transferred in the form of heat: ● The simple diffusion of heat through a substance as caused by the motions of its molecules is referred to as conduction ● Air is actually a very inefficient conductor of heat (or equivalently, air is a very good insulator) - As a result, conduction in the atmosphere is only important in the lowest few cm next to the ground ● Heat transfer through the motion of warm and cold air masses from place to place is referred to generally as convection vertical heat transfer due to the rising of a warm air bubble (or thermal) ● Heat transfer through the motion of warm and cold air masses from place to place is referred to generally as convection ● Some terminology: - Heat transfer due to vertical air motions is always referred to as convection - Heat transfer due to horizontal air motions is often referred to more specifically as advection ● In the atmosphere, convection is the main way that heat gets moved from place to place - Convection is much, much more efficient than conduction ● ● Depending on the temperature, water in the atmosphere may exist in liquid, solid or gaseous (vapor) phases Transformations between these phases (called phase changes) are accompanied by the release or absorption of heat, referred to generally as latent heating condensation or freezing evaporation or melting } } heat is released to surroundings heat is removed from surroundings ● Vapor in the atmosphere is thus a hidden way of transferring heat, with the heat realized once condensation (or freezing) occurs condensation in clouds releases latent heat to the surroundings, thus warming the air ● Over most of the atmosphere, shortwave radiation from the sun passes straight through, without being absorbed - Exceptions: UV absorption in the stratosphere (by ozone) and X-ray and gamma-ray absorption in the thermosphere (by O 2 ) ● Question: If not the sun, then where does the atmosphere get its energy from? ● Over most of the atmosphere, shortwave radiation from the sun passes straight through, without being absorbed - Exceptions: UV absorption in the stratosphere (by ozone) and X-ray and gamma-ray absorption in the thermosphere (by O 2 ) ● Question: If not the sun, then where does the atmosphere get its energy from? Answer: Most of the atmosphere's energy comes from from the Earth below ● Over most of the atmosphere, shortwave radiation from the sun passes straight through, without being absorbed - Exceptions: UV absorption in the stratosphere (by ozone) and X-ray and gamma-ray absorption in the thermosphere (by O 2 ) ● Question: If not the sun, then where does the atmosphere get its energy from? Answer: Most of the atmosphere's energy comes from from the Earth below (Of course, the Earth gets its energy from the sun, so ultimately it does all come from the sun....just not directly) Warming the Atmosphere from Below Step 1: Shortwave passes through and is absorbed by the ground, causing the ground to warm (radiation) Warming the Atmosphere from Below Step 1: Shortwave passes through and is absorbed by the ground, causing the ground to warm (radiation) Step 2: Air in the lowest few cm is warmed by contact with the ground and moistened by evaporation Warming the Atmosphere from Below Step 1: Shortwave passes through and is absorbed by the ground, causing the ground to warm (radiation) Step 2: Air in the lowest few cm is warmed by contact with the ground (conduction) and moistened by evaporation Warming the Atmosphere from Below Step 3: Warm air rises, transferring heat upwards Warming the Atmosphere from Below Step 3: Warm air rises, transferring heat upwards (convection) Warming the Atmosphere from Below Step 3: Warm air rises, transferring heat upwards (convection) Step 4: As air rises it cools, leading to condensation.... Warming the Atmosphere from Below Step 3: Warm air rises, transferring heat upwards (convection) Step 4: As air rises it cools, leading to condensation and latent heat release Warming the Atmosphere from Below Of course, we also have absorption of radiation...... it's just IR from the Earth instead of shortwave from the sun. Warming the Atmosphere from Below Putting it all together: the input energy stream Some (roughly 30%) of the incoming solar radiation is reflected or scattered back to space, and some (roughly 19%) is absorbed directly by the atmosphere. Net result: About 51% of the incoming radiation is absorbed by the ground. Putting it all together: the Earth's total energy budget The exchanges of energy by radiation, conduction, convection and latent heat can be quite complex, but in the end they all balance