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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