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Temperature,Heat, and Energy Transfer
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Temperature,Heat, and Energy Transfer

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    Temperature,Heat, and Energy Transfer Temperature,Heat, and Energy Transfer Presentation Transcript

    • Temperature, Heat, and Energy Transfer Wx 201 Henry Robinson
    • Philosophy
      • It is mused that in physics, when you know the mass, momentum (including rotational) and energy changes in a system, you have the problem solved.
    • Energy - Definitions
      • Energy - Ability to do work.
      • Work - move matter over some distance
      • Potential Energy – the ability to do work because of position (usually height)
      • PE = mgh : m = mass g = gravity h = height
      • Kinetic Energy – the energy of a mass because of its motion: v = velocity
    • Potential Energy Maximum Kinetic Energy Maximum
    • Conservation of Energy
      • Energy can not be created or destroyed
      • Energy is changed from one form into another.
      • Since the atmosphere is a big heat engine, most of our discussions of energy will center around heat transfer
      • Heat and Temperature are not the same thing
    • Temperature
      • Temperature is the average kinetic energy of the air molecules.
      • High temperature – faster molecules.
      • Low temperature – slower molecules.
      • animation
    • Fahrenheit Scale
      • Developed in early 1700s by G. David Fahrenheit.
      • Zero is the lowest temperature that salt water will freeze.
      • 32 F o is freezing point of pure water.
      • 100 F o was to be body temperature (slight mistake)
      • 212 F o is boiling point of pure water.
      • F scale used in US for surface temperature except in METARS.
      • Absolute scale is the Rankine scale
    • Celsius Scale
      • Developed in late 1700s
      • Also called Centigrade scale.
      • Zero is the freezing point of pure water.
      • 100 is the boiling point of pure water at sea level.
      • A change of 1 C o = 1.8 F o
      • 1.8 C = F - 32
    • Kelvin Temperature Scale
      • Absolute zero – molecules stop moving.
      • Lowest possible temperature.
      • Zero K. = –459 degrees F.
      • Zero K. = -273 degrees C.
      • 1 degree K = 1 degree C.
      • o K= o C+273
      • Kelvin scale used for all scientific equations, such as gas law, etc.
    • Temperature Scales 311 38 100 300 27 80 289 16 60 277 4 40 273 0 32 266 -7 20 255 -18 0 244 -29 -20 233 -40 -40 K C F
    • US Meteorology Temperature Units
      • Most of the world uses Celsius (metric unit)
      • U.S. uses F for surface air temperature.
      • U.S. uses C for air temperature above surface
    • Kinetic Theory of Gases
      • Perfect Gas Law (animation)
    • Heat
      • In the absence of chemical or phase changes, Heat is the total Kinetic Energy of the molecules. (Temperature is the average kinetic energy of the air molecules.)
      • First law of thermodynamics.
      • Animation
    • Heat
      • Transfer of heat energy to a mass changes its temperature and its dimensions.
      • Specific Heat – amount of heat needed to raise one gram of material one degree Celsius.
      • 1 calorie of heat will raise 1 gram of water one degree C.
    • First Law of Thermodynamics
      • Add heat to something and it goes into raising the temperature AND expanding the something
      • Adiabatic means not adding heat so compress a gas means the temperature goes up
      • The adiabatic lapse rate for air is 10 degrees C per kilometer (5.5 F/ 1000 ft)
    • Specific Heat of Substances Sand Dry Air Clay Ice Water Substance 0.19 0.24 0.33 0.5 1.0 Specific Heat 5.2 C 4.2 C 3.0 C 2.0 C 1.0 C Temp rise for 1 calorie of heat added to one gram of material
    • Radiation
      • Incoming solar radiation is important to life, weather
      • We receive 2 cal/cm min to warm us during daylight hours Area = 2  r
    • Surface absorption of heat
      • Sunlight not reflected by clouds or surface moves molecules in surface to increase total and average kinetic energy of molecules
      • Some heat moves downward but the rest warms the air just above the surface
      • Primary reason for the climatological lapse rate of 3.5 degrees F/1000 ft
    • Cooling the Earth
      • All warm bodies emit infrared radiation
      • Earth radiates heat through infrared all the time from entire surface Area =  r 2
    • Balance
      • When incoming solar radiation equals outgoing infrared, the climate is in balance
      • If it is not in balance, the climate warms up or cools down.
      • We have had periodic imbalances in the past
      • We are probably going through a change right now
    • Greenhouse Effect
      • In the news - but it is a natural process in the atmosphere
    •  
    • At Issue
      • If the balance is changing, what sort of weather will result
      • Consensus seems to be Global Warming will result in
        • Sea level rise
        • Increased bacterial activity
        • Stronger storms
        • Faster winds
    • Radiation Transfers
      • Greenhouse effect is only one transfer
      • Reflection from clouds
      • Reflection from the oceans, lakes, etc.
      • Reflection from the surface
      • Direct absorption of air
    • Radiation Effects on Matter
      • Absorption
      • Conduction
      • Convection
      • Latent Heat conversion
    •  
    • Some Consequences of Specific Heat
      • Land areas warm up more rapidly than water areas for same heat input.
      Average air temperature near sea level in July ( o F)
    • Latent Heat
      • Latent heat is the heat required to change state (solid to liquid or liquid to gas)
      • Latent heat of fusion (melting or freezing)
      • Water latent heat of fusion = 80 cal/g.
      • Latent heat of evaporation (or condensation)
      • Water latent heat of evaporation = 600 cal/g
    • Latent Heat Transfer to/from Environment
      • When water evaporates it takes heat from the environment (example: sweating cools body). When it condenses it releases heat to the environment.
      • Latent Heat of evaporation/condensation is an important sink/source of atmospheric energy
      • Latent heat drives hurricanes and thunderstorms.
    • Heat Transfer in Atmosphere
      • Conduction – transfer of heat from molecule to next molecule. Slow process.
      • Air is a poor conductor of heat.
      • Convection –vertical transfer of heat by fluid motions. (warm air rises by buoyancy)
      • Advection – horizontal transfer of heat by fluid motions.
      • Mixing of air is more efficient process of heat transfer than conduction.
    • Buoyancy
      • If a parcel is lighter than the fluid it displaces, it will rise. Gravity causes the heavier fluid to sink which forces the lighter parcel to rise.
      • Recall gas law PV=RT.
      • If all the air at a level warms, nothing will happen. Buoyancy requires localized differences in density caused by temperature differences.
    • Thermals
      • Differences in ground temperature caused hot and cool spots.
      • Warm air is forced up by cool air.
      • Rising air parcel goes to lower pressure.
      • Air parcel expands and cools (gas law).
      • If air parcel is still warmer (buoyant) than environment, it will continue to rise.
      • If air parcel is the same (or cooler) temperature than environment, it will stop rising.
    • Thermals and Clouds Clouds are cause by rising air parcels.
    • Thermals and Latent Heat
      • Rising parcel cools. If the air temperature reaches the dew point temperature (later chapter), droplets will condense out of the air.
      • Condensation will release latent heat (600 calories/gram).
      • Latent heat will warm air parcel making it buoyant relative to surrounding air.
    • Summary
      • Definitions:
      • Energy - Ability to do work.
      • Work - move matter over some distance
      • Kinetic Energy – mass moving =1/2 mv 2
      • Temperature - average kinetic energy of the air molecules.
    •  
    •  
    •  
    •  
    •  
    •  
    •  
    • Summary (cont 1)
      • Temperature Scales – Kelvin ( o K) Fahrenheit ( o F), and Celsius ( o C) scales
      • 0 o K = -273 o C = -459 o F absolute zero
      • 273 o K = 0 o C = 32 o F water freezing
      • 373 o K = 100 o C = 212 o F water boiling
      • C=5/9(F-32) ; o K= o C+273
    • Summary (cont 2)
      • Heat -transfer of energy to a mass which changes its temperature.
      • Specific Heat – amount of heat needed to raise one gram of material one degree Celsius.
      • 1 Calorie of heat will raise 1 gram of water one degree C.
      • Specific heat: water=1.0; air=.24; sand=.19
    • Summary (cont 3)
      • Latent heat is the heat required to change state (solid to liquid or liquid to gas)
      • Water latent heat of fusion = 80 cal/g.
      • Water latent heat of evaporation = 600 cal/g
      • Latent heat drives hurricanes and thunderstorms
      • Convection –vertical transfer of heat by fluid motions. (warm air rises by buoyancy)
      • Buoyancy requires localized differences in density caused by temperature differences.
      • Advection – horizontal transfer of heat by fluid motions.