Chapter12: Temperature Chapter12: Temperature and Heat

COMMON TEMPERATURE SCALESCOMMON TEMPERATURE SCALESC l i t F h h itCelsius to Fahrenheit

T (F) = [1.8 x T (C)] + 32

Fahrenheit to Celcius

T (C) T (F) 32 / 1 8T (C) = T (F) – 32 / 1.8

Celsius to KelvinCelsius to Kelvin, Kelvin to Celsius

T (C) = T (K) – 273

T (K) = T (C) + 273

LINEAR THERMAL EXPANSION OF A SOLID

• The increase in any one dimension f lid i ll d li iof a solid is called linear expansion.

• The change in length is directly The change in length is directly proportional to the change in temperature : ∆L ≈ ∆T

• The length of an object changes when its temperature changes:p g

TLL oΔ=Δ α• Common Unit for the Coefficient of

Linear Expansion: ( ) 1CC1 −= o

oC

APPLICATIONS OF LINEAR THERMAL EXPANSION OF SOLIDSEXPANSION OF SOLIDS

VOLUME THERMAL EXPANSIONVOLUME THERMAL EXPANSION

Th l f bj t h • The volume of an object changes when its temperature changes:

TVV oΔ=Δ β

coefficient of volume expansion

• Common Unit for the Coefficient of Volume Expansion: ( ) 11Expansion: ( ) 1C

C1 −

= o

o

APPLICATIONS OF VOLUME THERMAL EXPANSION

HEAT AND INTERNAL ENERGYHEAT AND INTERNAL ENERGY• Heat is energy that flows from a Heat is energy that flows from a

higher- temperature object to a lower- temperature objectp jbecause of a difference in temperatures.

• SI Unit of Heat: joule (J)j ( )

• The heat that flows from hot to • The heat that flows from hot to cold originates in the internal energy of the hot substance.energy of the hot substance.

Heat and Temperature Change: Specific Heat Capacity

S ifi H t C it i th h t th t t b li d • Specific Heat Capacity: is the heat that must be supplied or removed to change the temperature of a substance.

• The amount of heat needed to cause a temperature change p gdepends on the mass of the object, size of the temperature change, and the substance of which an object is made

TQ Δ• Common Unit for Specific Heat Capacity: J/(kg·Co)

TmcQ Δ=p p y /( g )

Example: A Hot Jogger

In a half-hour, a 65-kg jogger can generate 8.0x105J of heat. This heat is removed from the body by a variety of means, including th b d ’ t t l ti h i If th h t the body’s own temperature-regulating mechanisms. If the heat were not removed, how much would the body temperature increase?

TmcQ Δ=

( ) ( )[ ]o

oC 5.3

CkgJ3500kg 65J100.8 5

=⋅

×==Δ

mcQT ( ) ( )[ ]

Sample problemSample problem

• How much heat is needed to increasethe temperature of 200 g of waterp g5.0°C? (cwater1.0 kcal/(kg.C°)

• How much heat is needed to increasethe temperature of 200 g of lead5.0°C? (c lead = 0.030cal/g °C)5.0 C? (c lead 0.030cal/g C)

Heat Units other than JouleHeat Units other than Joule• Kilocalorie

– The amount of heat needed to raise the temperature of 1kg of water by one Celcius degree TmcQ Δ=

– c = 1.0 kcal/(kg.C°)

B iti h Th l U it (Bt )• British Thermal Unit (Btu)– Amount of heat needed to raise the temperature of one pound

of water by one Fahrenheit degree.

• Joule– There is a relationship between energy in work and energy in There is a relationship between energy in work and energy in

heat.– 1kcal = 4186 joules or 1 cal = 4.186 joules

Also known as mechanical equivalent of heat– Also known as mechanical equivalent of heat

HEAT AND PHASE CHANGE : LATENT HEATHEAT AND PHASE CHANGE : LATENT HEAT• Phase changes require large

amounts of energy compared amounts of energy compared to the energy needed for temperature changes.

• Energy used to cause a phase change does not cause a temperature change temperature change.

• The amount of energy grequired is proportional to the number of molecules in the object and to the forces

ti b t l lacting between molecules.

CONCEPTUAL EXAMPLECONCEPTUAL EXAMPLE• Suppose you are cooking spaghetti and the instructions say “boil

pasta in water for 10 minutes.” To cook spaghetti in an open pot withp p g p pthe least amount of energy, should you turn up the burner to itsfullest so the water vigorously boils, or should you turn down theburner so the water barely boils?

LATENT HEATLATENT HEAT• Latent Heat: is the heat supplied or removed in changing the pp g g

phase of a mass (m) of a substance

mLQ =• SI Units of Latent Heat: J/kg

Q

• Latent heat of fusion (Lf): change between solid and liquid phases

t t h t f i ti ( ) h b t li id d • Latent heat of vaporization (Lv): change between liquid and gas phases

• Latent heat of sublimation (Ls): change between solid and gas a e ea o sub a o ( s): c a ge be ee so d a d gas phases

Chapter 13

The Transfer of Heat

CONVECTIONCONVECTIONConvection is the process Convection is the process

in which heat is carried from one place to

another by the bulk movement of a fluid.

CONDUCTIONCONDUCTION• Conduction is the process

h b h t i t f d whereby heat is transferred directly through a material, with any bulk motion of the material playing no role in the transfer.

• Movement of heat by atomic • Movement of heat by atomic collisions; transfer of heat through stationary matter by

h i l t tphysical contact

• Materials that conduct heat well Materials that conduct heat well are called thermal conductors, and those that conduct heat poorly are called thermal poorly are called thermal insulators.

The amount of heat Q that is conducted through the bardepends on a number of factors:

1. The time during which conduction takes place.2. The temperature difference between the ends of the bar.3 Th ti l f th b3. The cross sectional area of the bar.4. The length of the bar.

RADIATIONRADIATIONR di ti i th i hi h • Radiation is the process in which energy is transferred by means of electromagnetic waves.

• A material that is a good absorber is also a good emitteris also a good emitter.

• A material that absorbs completely p yis called a perfect blackbody.

DIAGNOSTIC AND THERAPEUTIC USES OF HEAT

• Thermography: indication of blood supplyg p y pp y– Decreased: deficiency in blood flow to a specific region

(clotting, stroke)– Increased: malignant tumor g

• Heat pads: relaxation of muscles and increased blood flow• Infrared radiation: premature or newborn babiesInfrared radiation: premature or newborn babies• Microwave or radio diathermy (controlled to affect only

intended area)• Ultrasound diathermy (energy carried by the sound can be Ultrasound diathermy (energy carried by the sound can be

converted as thermal energy)

• Therapeutic Uses of Cold: lowered temperatures as local Therapeutic Uses of Cold: lowered temperatures as local anesthetic – Ice packs– Cryosurgery (treatment of warts, tumors, Parkinson’s) g ( )

CLINICAL APPLICATION: THERMOMETERSCLINICAL APPLICATION: THERMOMETERS• A thermometer is used in health care to measure and monitor body

temperature temperature.

• It allows a caregiver to record a baseline temperature when a patient is admitted patient is admitted.

• Repeated measurements of temperature are useful to detect deviations from normal levels and also useful in monitoring the effectiveness of current medications or other treatments.

• Thermometers are usually made of a thin glass tube containing a liquid.

• The temperature is measured by observing how far up the tube the liquid rises. Different liquids have different nonlinear expansions.

TYPES OF CLINICAL THERMOMETERS -DIRECTDIRECT

• LIQUID EXPANSION : Liquid-in-glass q gthermometers are devices consisting of a bulb attached to glass chamber filled with liquid;

Clearglassglass chamber filled with liquid;

columns are marked with a measurement scale.

glass

• PRINCIPLE: Liquid-in-glass Lensfront

thermometers rely on the principle that a liquid changes its volume relative to its its volume relative to its temperature. White

backingCapillary

TYPES OF LIQUID EXPANSION THERMOMETERSQ• Mercury in-glass: a thermometer consisting of

mercury in a glass tube. • Calibrated marks on the tube allow the

temperature to be read by the length of the mercury within the tube, which varies according to the temperature.

• ADVANTAGES

– Mercury has large and uniform expansion abilities, its silvery appearance allows for easy reading, & stability.

• DISADVANTAGES

– When liquid mercury is spilled, it forms droplets that accumulate in the tiniest of spaces and emit vapors into the air. It is odorless, colorless,

d t i and very toxic. – Occur by breathing vapors, by direct skin

contact or by eating food or drinking water contaminated with mercury contaminated with mercury.

TYPES OF LIQUID EXPANSION THERMOMETERSQ• ALCOHOL-IN-GLASS: Similar to mercury-in-

glass thermometer but contains colored glass thermometer but contains colored alcohol.

• ADVANTAGE: less toxic than a mercurial thermometer

• DISADVANTAGES: Alcohol has a smaller density of 0.79 g/cm3 [compared to the densit of merc r 13 6 g/cm3] With density of mercury = 13.6 g/cm3]. With alcohol, there is greater increase in volume, requiring either a longer stem or a wider capillary tube.

TYPES OF CLINICAL THERMOMETERSTYPES OF CLINICAL THERMOMETERS• CHEMICAL - DOT MATRIX OR PHASE CHANGE: Plastic strips

or adhesive patches that indicate a temperature or adhesive patches that indicate a temperature in response to the thermal change in chemical dots.

• These devices vary in usefulness depending on y p gtheir resolution.

• DOT MATRIX: Each dot contains a different combination of a chemical mixture that will melt and change color from beige to bright blue at a specific temperature.T t di i di t d b th • Temperature readings are indicated by the number on the thermometer that corresponds with the last blue dot.

• The device registers a temperature within 60 • The device registers a temperature within 60 seconds and can be read after waiting an additional 10 seconds for a stable measurement; the last dot to turn blue constitutes the body temperature.

TYPES OF CLINICAL THERMOMETERS -DIRECT

• LIQUID CRYSTAL DISPLAY: A LIQUID CRYSTAL DISPLAY: A chemical thermometer made by impregnating spots of liquid crystal material onto a spatula crystal material onto a spatula.

• If mixed with suitable dyes the ytransition from solid to liquid phase is demonstrated by the color of the spot. the spot.

• Liquid crystal paints are also available which can be used to demonstrate temperature distribution by color over parts of the body.

TYPES OF CLINICAL THERMOMETERS -INDIRECT

• THERMOCOUPLE: A thermocouple consists of THERMOCOUPLE: A thermocouple consists of two junctions at two different metals. If the two junctions are at different temperatures, a voltage is produced

Thermocouplep g p

that depends on the temperature difference

• DIGITAL : Electronic digital thermometers are well-known and widely used. They have several advantages including fast have several advantages including fast response time, ease of reading and the lack of mercury or other potentially harmful liquidsq

• PACIFIER• ORAL, RECTAL, AXILLARY

http://www.digitalthermometers.net

TYPES OF CLINICAL THERMOMETERS -INDIRECT

• INFRARED: Infrared thermometers • INFRARED: Infrared thermometers measure temperature using electromagnetic radiation such as i f d itt d f bj t B infrared emitted from object. By knowing the amount of infrared energy emitted by the object and its emissivity

• Tympanic• Temporal Tympanic• Temporal Tympanic

http://www.digitalthermometers.net