Temperature & Humidity

8/18/2019 Temperature & Humidity

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EMPERA URE

& HUMIDI Y


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EMPERA URE


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Temperature is a degree of

hotness or coldness measuredon a definite scale


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TERMINOLOGIES

• Mean Daily Temperature – the average

of the daily maximum and minimum

temperature

• Normal Daily Temperature – the average

daily mean temperature for a given date

computed for a specific 30-year period.


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• Daily Range Temperature – the

difference between the highest and the

lowest temperatures recorded on a

particular day

• Mean Monthly Temperature – the

average of the mean monthly maximum

and minimum temperatures


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• Mean Annual Temperature – the average

of the monthly means for the year

• Degree-day – a departure of one degree

for one day in the mean daily temperature

from a specified base temperature


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MEASUREMENT OF

TEMERATURE

• In order to measure air temperature

properly, T!ERMOMETER must be

placed where air circulation is

relatively unobstructed and yet

protected from the direct rays of thesun and from precipitation.


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"a#i$ Type# o% Thermometer#

&' Traditional Thermometer

- designed for at home use for measuring the

temperature of the air or water in both F or . !hese

should not re"uire much maintenance, but they may

have a varied accuracy, range and resolution.


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(' Re#i#tan$e Thermometer

- designed to measure temperatures between

-#$0 and %00 degrees elsius by noting the

resistance change of a li"uid by a currant flowingthrough the platinum wire inside.


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*' Dual Sen#or Thermometer - designed for professional use as they

provide dual readings of environments that can

remain steady for long periods of time. !he main

reader of this thermometer can be mounted to ades) or wall and the probes can be inserted into

a variety of environments for readings.


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+' Fi,ed and ired ro.e Thermometer

*robe thermometers are designed to provide

accurate readings of temperatures in foods,

li"uids or semi-solids in retail or laboratory

settings. !hese are mainly designed for hygienetesting, and they will vary in si+e and focus on

providing solid, accurate readings to ensure user

safety.


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/' 0-type Thermometer

- designed to measure extreme temperatures in

the air, li"uids or surfaces within a professional

environment. !he specific temperature range willvary by brand but they wor) to provide a non-slip

grip that is manoeuvrable for use in a variety of

environments without compromising accuracy.


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1' Data Logging Thermometer

!hese provide temperature results in real time that

can be downloaded to a computer to note the

temperature history of an environment to chec) forvariances. !his can be used to provide graphical data

and accurate readings that are suitable for

professional use.


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2' In%rared Thermometer !hese can measure very high or low surface

temperatures without the need to ma)e contact with

the item in "uestion, which is ideal for spot chec)ing

temperature settings within an environment.owever, there can be up to a 30 percent error

reading due to this lac) of contact, but this can be

corrected with a traceable accuracy setting.


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3' "imetal Thermometer - designed to note temperature changes as the

metal in the base expands and contracts. !hese

are typically used on thermostats or dial

thermometers to note the temperature at aspecific time by allowing the dial in the face to

rotate as necessary.


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&4' Li5uid-$ry#tal Thermometer

!hese thermometers will change colors due to the

li"uid crystals in the face to reflect the temperature on

the forehead or other substance where this is placed.

!he designated temperature will become dar)er on theface to designate a reading that also provides a digital

reading.


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&&' Ga# Thermometer

!hese are a very common type of industrial

thermometer that are used to )eep the

temperature of stored gas constant within aconfined area. !he pressure of this gas will be

measured to determine the temperature inside.


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Ma,imum Thermometer –

has a constriction near the bulb

which prevents the mercuryfrom returning to the bulb as

the temperature falls and thus

registers the highest

temperature since its last

setting

Minimum Thermometer –

of alcohol in glass-type

has an index which

remains at the lowest

temperature occurringsince its last setting


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Thermograph – with either a

bimetallic strip or a metal tube

filled with alcohol or mercury forits thermometric element, ma)es

an autographic record on a chart


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/orlds 1argest

!hermometer is

in alifornia


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LASE RATES

Lap#e Rate vertical temperature gradient

– the rate of change of temperature with

height in the free atmosphere.

Temperature Inversion – an increase of

temperature with altitude in the surface

layer


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• Dry-adia.ati$ Lap#e Rate ' degree

elsius per '00 m – the rate of

temperature change of unsaturated air

resulting from expansion or compressionas the air rises lowering pressure or

descends increasing pressure without

heat being added or removed


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• Super-adia.ati$ Lap#e Rate exceeding

' degree elsius per '00 m – an

unstable condition since any parcel of air

lifted dry-adiabatically remains warmerand higher than the surrounding air and

thus has a tendency to continue rising.


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• Saturated-adia.ati$ Lap#e Rate – if any parcel

of saturated air is lifted adiabatically, the

temperature decreases and its water vapor

condenses, releasing latent heat of ofvapori+ation

• #eudo-adia.ati$ Lap#e Rate – if the moisture

in the rising air is precipitated as it is condensed,

the temperature of the air will decrease


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Neutral Equilibrium – condition when a

layer of saturated air having a saturated or

pseudo-adiabatic lapse rate


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Land and 7ater ma##e#

In the interior of the large islands and

continents, temperatures are higher in

summer and lower in winter than on

coasts at corresponding latitudes.


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Topography

!emperatures at high elevations are

colder than at low levels and southern

slopes have warmer temperatures than

northern slopes.


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8egetation

Forested areas have higher daily

minimum and lower daily maximum

temperatures than barren areas


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TIME 8ARIATIONS OF

TEMERATURE

• In continental regions, the warmest and

coldest points of the annual temperature

cycle lag behind the solstices by about '

month. In 45, 6anuary is usually thecoldest month and 6uly the warmest.

•

7t oceanic stations, the lag is nearer #months and the temperature difference

between the warmest and coldest months

is much less.


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• !he daily variation of temperature lags

slightly behind the daily variation of solar

radiation.

• !he daily range of temperature is affected

by the state of the s)y. 8n cloudy days, the

maximum temperature is lower because ofreduced insolation and the minimum is

higher because of reduced outgoing

radiation.


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HUMIDI Y


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Type#

• A.#olute humidity

It is the total amount of water vapor present in a given volume

of air. It does not ta)e temperature into consideration. 7bsolute

humidity in the atmosphere ranges from near +ero to roughly

30 grams per cubic meter when the air is saturated at 30 9. 7bsolute humidity is the mass of the water vapor mw divided

by the volume of the air and water vapor mixture Pnet , which

can be expressed as2


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• Relati9e humidity

!he relative humidity : of an air-water mixture is defined

as the ratio of the partial pressure of water vapor #8

ew

in the mixture to the saturated vapor pressure ofwater e;w at a given temperature. !hus the relativehumidity of air is a function of both water content and

temperature.


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ropertie# o% ater 8apor

• 8apori:ation or e9aporation – the

process whereby a solid is transformed

directly to the vapor state

• Su.limation meteorology – direct

transformation from ice to vapor and vice

versa

• 6onden#ation – process by which vaporchanges to the li"uid or solid state


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• 8apor re##ure – the partial pressure

exerted by water vapor

• Saturation 8apor re##ure – the

pressure exerted by the vapor in saturated

space which is the maximum vapor

pressure possible at a given time


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8apori:ation removes heat from

the li"uid being vapori+ed while$onden#ation adds heat.


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• Latent !eat o% 8apori:ation – the amount of

heat absorbed by unit mass of a substance

without change in temperature while passing

from the li"uid to the vapor state

v ? #.$0 – 0.00#3(!

where T is the temperature in degree Celcius and

Hv is in kilooules per gram


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• Latent !eat o% Fu#ion for water, 0.33% )6@g

at 0 A – is the amount of heat re"uired to

convert ' g of ice to li"uid water at the same

temperature

• Latent !eat o% Su.limation - for water,

#.B3 )6@g at 0 A – is the amount of heatre"uired to convert ' g of ice into vapor at the

same temperature without passing through

the intermediate li"uid state


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• !he #pe$i%i$ gra9ity of water vapor is 0.(##

times that of dry air at the same temperature

and pressure

• !he density of water vapor in g@cm3

Cv ? (.## e


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• !he density of dry air in grams per cubic

meter g@m3 is2

Cd ? '0 Cd


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• !he density of moist air is e"ual to the

mass of water vapor plus the mass of dry

air in a unit volume of the mixture.

Ca ? '0 Ca x ' – 0.3%B e


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• 8apor re##ure – the basic element in

practically al expressions of air density and

vapor content

• De7point – the temperature at which space

becomes saturated when air is cooled under

constant pressure and with constant water

vapor content. It is the temperature having a

saturation vapor pressure es e"uals to the

existing vapor pressure e.

TERMINOLOGIES


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• Relati9e !umidity – is the percentage

ratio of the actual to the saturation vapor

pressure and is threfore a ratio of the

amount of moisture in a given space to theamount the space could contain if

saturated, f ? '00 x e@es


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• Spe$i%i$ !umidity – is the mass of water

vapor per unit mass of moist air expressed

in grams per )ilogram

"h ? (## e (## e

*a – 0.3%B e * a


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• Mi,ing Ratio – the mass of water vapor

per unit mass of perfectly dry air in a

humid mixture

wr ? (## e

*a - e


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S;6!ROMETER uses the difference in

readings between two thermometers, one

having a wet bulb and the other having a drybulb, to measure the moisture content or

relative humidity of air.

MEASUREMENT OF

!UMIDIT;


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• !air !ygrometer – ma)es use of

the fact that the length of a hair

varies with relative humidity

•

!air !ygrograph – a hairhygrometer operating a pen

mar)ing a trace on a chart

• !ygrothermograph – combining

the features of both the hairhygrograph and thermograph that

records both relative humidity and

temperature on one chart


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• De7point !ygrometer – measures dewpoint

directly and is used mostly for aboratory

purposes

• De7-$ell !ygrometer – measures the

dewpoint by regulating the temperature of a

saturated a"ueous lithium chloride solution sothat the water vapor pressure of the solution

is e"ual to that of the surrounding atmosphere


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• Spe$tral !ygrometer – measures

selective absorption of light in certain

bands of the spectrum by water vapor.

Deasurement of humidity is one of the

least accurate instrumental procedures in

meteorology


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GEOGRA!I6 DISTRI"UTION OF

!UMIDIT;

• 7tmospheric moisture tends to decrease

with increasing latitude but relative

humidity, being an inverse function of

temperature, tends to increase.• It is greatest over oceans and decreases

with distance inland.

• It also decreases with elevation and isgreater over vegetation than over barren

soil.


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• In actual water vapor content,


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END OF

DIS6USSION


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*repared by2

DAR;L GRA6E 6' ADUA

E55-$7

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Temperature & Humidity