11. temperature and heat transfer
TRANSCRIPT
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Temperature and Heat
TransferJ.T.II Olivar
Faculty of Arts and Letters
University of Santo Tomas1st Semester AY 2011-2012
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Outline of the Lecture
Temperature and Heat
Temperature Scales
Latent Heat
The Hidden WarmthSensible Heat
Daily Temperature Variations
Basic Processes in Heating andCooling the Atmosphere
The Controls of Temperature
Air Temperature Data
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Temperature and Heat
Temperature
Is the quantity that tells us how hot orcold something is relative to some set
standard value.Kinetic energy is the energy of motion
Is a measure of the atoms and
molecules
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Temperature Scales
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Latent Heat The HiddenWarmth
Water vapor is an invisible gas thatbecomes visible when it changes intolarger liquid or solid particles.
This process of transformation is knownas a change of state (phase change).
The heat energy required to change a
substance, such as water, from onestate to another is called latent heat.
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Sensible Heat
The heat we can feel and measurewith a thermometer.
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Daily Temperature Variations
Daytime Warming
Sunlight warms the ground, and theground warms the air in contact with it
by conduction.
Nighttime Cooling
As the sun lowers, its energy is spread
over a larger area, which reduces theheat available to warm the ground.
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Basic Processes in Heating andCooling the Atmosphere
Radiation
Absorption
ReflectionScattering
Transmission
ConductionConvection
Adiabatic Cooling and Warming
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Radiation is the process by whichheat energy is emitted from a body.
It involves the flow of radiant energy
out of the body through the air.
The hotter the object the more intenseits radiation.
A body that emits the maximum amountof radiation possible at everywavelength is called a blackbody.
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Absorption
When insolation strikes an object and isabsorbed, the temperature of the object
increases.
Good radiator is also a good absorberand poor radiator is a poor absorber.
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Reflection is the ability of an objectto repel waves without altering eitherthe object or the waves.
Reflection is the opposite of absorption.If the wave is reflected, it cannot beabsorbed.
An object that is good absorber is apoor reflector.
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Scattering
Particulate matter and gas molecules inthe air sometimes deflect light waves
and redirect them.This deflection involves a change in the
direction of the light wave but no
change in wavelength.
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Transmission is the process wherebya wave passes completely through amedium.
As when light waves are transmittedthough a pane of clear, colorless glass.
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Conduction is the movement of heatenergy from one molecule to anotherwithout changes in their relative
positions.This process enables heat to be
transferred from one part of a
stationary body to another or from oneobject to a second object when the twoare in contact.
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Convection is the transfer of heatfrom one point to another by amoving liquid or gas.
In convection the molecules physicallymove away from the heat source.
Advection is the horizontal movement of
liquid or gas.
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Adiabatic Cooling and Warming
Whenever air descends, its temperaturechanges.
Adiabatic cooling is is cooling byexpansion in rising air.
Adiabatic warming is warming by
compression in descending air.
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The Controls of Temperature
Factors that cause variations intemperature from one place toanother.
1. Latitude
2. Land and Water distribution
3. Ocean currents
4. Elevation
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Air Temperature Data
Daily (diurnal) range of temperature
Mean daily temperature
Annual range temperatureMean (average) annual temperature
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Daily (diurnal) range of temperature
The difference between the dailymaximum and mean temperatures
Mean daily temperature
The average of the highest and lowesttemperature for a 24-hour period
The average temperature for eachmonth is the average of the daily meantemperatures for that month
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Annual range temperature
The difference between the averagetemperature of the warmest and coldest
months
Mean (average) annual temperature
The average of the twelve monthly
average temperatures