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Thermod Temperature

发布时间:2013-12-13 12:02:13  

Thermodynamics I

Temperature

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?Thermal Equilibrium and Temperature. Temperature scalesAbsolute Temperature Scale. The Ideal-Gas LawThe Kinetic Theory of Gases. Pressure and TemperatureHeat

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?Heat. Heat capacity and Specific HeatChange of Phase and Latent HeatThermal expansion and Phase DiagramsHeat TransferTransport Laws

References: Tipler; wikipedia, Britannica

Thermodynamics II

The First Law of Thermodynamics

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?Heat and Work. First Law of ThermodynamicsHeat and Work on Quasi-Static Processes for a Gas. The Second Law of Thermodynamics

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?Heat Engines and the Second Law of ThermodynamicsRefrigerators and the Second Law of ThermodynamicsThe Carnot EngineHeat PumpsIrreversibility and disorder. Entropy

References: Tipler; wikipedia,…

Temperature

Thermal Equilibrium and Temperature. Temperature scales Our sense of touch can usually tell us if an object is

hot or cold. Usually we need get in touch –physical

contact-to appreciate if a body is hot or cold.But our perception is very subjective.measure of hotness

and coldness in

terms of any

arbitrary scales and

indicating the

direction which

energy

spontaneously flows

(from a hotter body

to a colder one)A thermometeris any of class of instrument that measures the temperature. Temperature is the physical magnitude that is measured by thermometers. A physical property that changes with the temperature is called a thermometric property-most solids an liquids expand when they are heated-electrical resistance change when is heated-in a gas pressure and volume change when it is heated -radiation from the surface of a body depends on the surface temperature

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References: Tipler; Britannica

Temperature

?Thermal Equilibriumand Temperature. Temperature scales

Thermal contact: Heat energy is transferred between

the bodies in thermal contact

Thermal equilibrium: When the thermometric

properties of the bodies in thermal contact do not change

If two objects are in thermal equilibrium with a

third, then they are in thermal equilibrium

each other

(Zeroth Law of thermodynamics)

Two objects are defined to have the same

temperatureif they are in thermal equilibrium with each other. TemperatureTemperature is one of the seven basic physical

quantities in term of which all other physical

quantities are defined. It is an “intensive” property,

as pressure or density. Length, mass are

“extensive”

Thermodynamics. Temperature

?Temperature scales

Calibration of a thermometer: Reproducibility

and Reliability.

When the thermometric property changes

lineally with the temperature, two fixed points

can be used to calibrate the thermometer.

Ice point temperature (normal

freezing point of water)

Steam-point temperature : normal boiling point of water

Centigrade Temperature Scale

(Celsius scale)

Fahrenheit Temperature Scale

Absolute Temperature Scale

tF?tC?32

5

CCFDerive and check the above expressions to convert Fahrenheit degrees temperature to centigrade degrees temperature and the inverse relationship. The same to convert Kelvin scale to centigrade. Apply to obtain the Fahrenheit normal human temperature if it is 36.5 Celsius degrees 9t?(t?32)T?t?273.15

Thermodynamics. Absolute Temperature Scale. Kelvin Scale.

A constant-volume gas It is possible to define a temperature scale in a

independent way of the used thermometric substancethermometerTemperature of the boiling point of sulfur measured with

constant-volume gas thermometers . P100 is the pressure of the

gas at 100oC

Plot of pressure versus

temperature for a gas,

as measured by a

constant-volume gas

thermometer. When

extrapolated to zero

pressure, the plot

intersects the

temperature axis at the

showed value of -

273.25 oCThe ideal-gas temperature scaleis defined so that the temperature of the triple point state is 273.16 kelvins, K.The triple point of wateris the unique temperature and pressure at which water, water vapor and ice coexist in equilibrium. [0.01 oC and 4.58 mmHg]T

Thermodynamics. Ideal Gas LawThe properties of gas samples that have low densitiesled to the definition of the ideal-gas temperature scales. The behavior of

gases at this low densities was described

(1) by Boyle′s Law (1661)

PV = constant (for a constant temperature)

(2) by Charles and Gay-Lussac Law (about 1800)

P = C1T (for a constant volume)Ideal Gas-LawPV?nRT

V = C2T absolute temperatures; C1 and C2 constantsn= amount of gas expressed in moles

R :Universal gas constant

= 0.082 atm ? L/(mol ?K)

The temperature of 0o (273.15 K) and

the pressure of 1 atm are often referred

as standard condition.

Amole(mol) of any substance is the

amount of substance that contains the

Avogadro number, NA, of atoms or

molecules, defined as the number of

carbon atoms in 12 g of 12C.R= 8.314 J/(mol ?K) =

Thermodynamics. Dealing with theIdeal Gas Law

PV?nRTIdeal Gas-Lawn= m/ M[mass of the substance in g/molecular mass] mol

R= 8.314 J/(mol ?K) = 0.082 atm ? L/(mol ?K)P??RT

?Mdensity??RT?The mass per mole of a substance is called its molar mass. (The terms molecular massor molecular weightare sometimes used

A gas has a volume of 2 L, a temperature of 30oC, and a pressure of 1 atm. When the gas is heated to 60oC and compressed to a volume of 1.5 L, what is the new pressure What is the density of dry air at standard conditions of pressure and temperature?. The same at 20oC; The same at 20oC and 933 mb. Molecular mass of dry air: 28.97 g.

An automobile tire is filled to a gauge pressure of 200 kPa when its temperature is 20oC. After the car has been driven at high speeds, the tire temperature increases to 50oC. (a) Assuming that the tire volume does not change, find the gauge pressure in the tire (b) Calculate the gauge pressure if the volume of the tire expands by 10%.

Thermodynamics. The Kinetic Theory of Gases. Molecular Interpretation of Pressure and Temperature

Goal : To relate macroscopic point of view aboutt pressure

and temperature with the microscopic motion.

For a solid, these microscopic motions are principally the

wiki/Image:Translationa

l_motion.gif

Crystalline

Solidstemperatureis a measure of the average kinetic energyof the molecules.

Thermodynamics I

Temperature

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?Thermal Equilibrium and Temperature. Temperature scalesAbsolute Temperature Scale. The Ideal-Gas LawThe Kinetic Theory of Gases. Pressure and TemperatureHeat

?Heat. Heat capacity and Specific Heat

?Change of Phase and Latent Heat

?Thermal expansion and Phase Diagrams?Heat Transfer

?Transport Laws

References: Tipler; wikipedia, Britannica

Thermodynamics. Heat. Heat capacity and Specific HeatHeatis the energy that is being transferred from one system to another as a result of difference in temperature.

If two bodies at different temperature are brought together, energy is

transferred –i.e. heat flows-from the hotter body to the colder. The effect of

?oC)= 1kcal/(kg?oC)= molar specific heat* The exceptionsoccurs during a change of phase

Thermodynamics. Heat. Heat capacity and Specific HeatHeat capacity: The amount of heat energy Q necessary to raise the temperature of a substance by one degree.

The Heat capacity per unit mass is called specific heat

The Heat capacity per amount of substance (mol) is called the molar specific heat

Specific Heat kJ/(kg?K)kJ/(mol?K)

Water

Air

cP= 29.19 J/(mol?K); cV= 20.85 J/(mol?K). M=28.84 gcP= 1.012 kJ/(kg?K); cV = 0.723 kJ/(kg?K); 4.184 75.3

Thermodynamics. Heat. Heat capacity and Specific HeatHeat Capacity and Specific HeatThe amount of heat energy Q needed to

raise the temperature of a substance is

proportional to the temperature change

and to the mass of substance.Q?C?T?mc?TCheatcapacity;cspecificheat

c?cwater: 1 cal/(g?oC)= 1kcal/(kg?oC)=

4.184 kJ/(kg?oC) = 4.184 kJ/(kg?K)

How much heat is required to change 1.5 kg of ice at -20oC and 1 atm into steam.Typical volumetric heat capacity of a soil is 2.1 MJ/(m3K). Estimate the absorbed heat energy by a layer of 1 m of depth when its temperature is increased by10oC. Calculate the specific heat of the soil if the bulk density of the solid is 1.7 Mg/m3.

A great part of the soil are pores that can be filled by water. Then the volumetric heat capacity of a soil will vary with its content of water. Explain the behavior when the content of water increase.

Thermodynamics. Change of Phase and Latent Heat

Common types of phase changeinclude fusion(liquid to solid), melting(solid to liquid), vaporization(liquid to vapor or gas); condensation (gas or vapor to liquid), and sublimation(solid directly to vapor).

When a phase change appears there is no temperature change when the thermal energy is being transferred to the body in which the phase

change is occurring. In the case of a phase change the specific heat (or capacity) is infinitum.

Latent Heat

Qf?mLfLatent heat of fusion [or melting], Lf. At a pressure of 1 atm, the latent heat of fusion for water is

Lf=333.5 KJ/kg

Latent heat of vaporization, LV. For water at a

pressure of 1 atm, the latent heat of vaporization is Lf= 2.25 MJ/kg (at boiling point). QV?mLV

?3Latent heat of vaporization of water depends ??2.501?(2.361x10)twateron the temperature. ?1?latentheatofvaporization[MJkg]Latent heat of water at 20oC is 2.45 MJ/kg.

A common relationship is: ttemperature[ C]

Thermodynamics. Change of Phase and Latent Heat

Common types of phase changeinclude fusion, freezing, (liquid to solid), melting(solid to liquid), vaporization(liquid to vapor or gas); condensation (gas or vapor to liquid), and sublimation(solid directly to vapor and vapor to solid –in some places the last process is called deposition-).

When a phase change appears there is no temperature change when the thermal energy is being transferred to the body in which the phase

change is occurring. In the case of a phase change, the specific heat (or capacity) is infinitum.

http://www.usatoday.com/weather/wwatphse.htm

Thermodynamics. Change of Phase and Latent Heat. Water

http://hyperphysics.phy-

astr.gsu.edu/hbase/thermo/phase.html

Thermodynamics. Evaporation

Evaporation

Ordinary evaporation is a surface phenomenon-some molecules have enough kinetic energy to escape. If the container is closed, an equilibrium is

reached where an equal number of molecules return to the surface. The pressure of this equilibrium is called the saturation vapor pressure

.

In order to evaporate, a mass of water must collect the large heat of vaporization, so evaporation is a potent cooling mechanism. Evaporation heat loss is a major climatic factor and is crucial in the cooling of the human body.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html

Thermodynamics. Evaporation vs. Boiling

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html

Thermodynamics. Thermal expansionThermal expansion. When the temperature of an object increase, the object usually increase

?L

LdV???TV???T?:coefficientoflinearexpansion?:coefficientofvolumeexpansion

Do holes

expand?

Thermodynamics. Thermal Expansion. Case of Water

Volume of 1 g of water at atmospheric pressure versus temperature. The minimum volume, which corresponds to the maximum density, occurs at 4oC. [ Supercooled water is water that is cooled below the normal freezing point without solidifying. It is showed in the figure]

Discuss the expansion of water in the case of freezing (or fusion) -liquid to solid (ice)-. See the density of ice and the density of liquid water

Thermodynamics. Phase Diagramas. Case of Water

The diagram P-T for water at a constant volume. The pressure and temperature scales are not linear.

Thermodynamics. Heat Transfer

Heat Transfer

The spontaneous transfer of heat energy is from a high temperature object to a lower temperature object. Heat Transfer focus on the energy rate that is being transferred and on the mechanism of transport.

Thermal energy is transferred from one place to another by three types of processes. The driving force of heat transfer flow is always the difference of temperature:

?Conduction, In this case, the mechanism of heat energy transport is the interactions among atoms or molecules (collisions), although there is no mass motion. It is the case of heat transfer in opaque solids

?Convection, heat energy is transported by direct mass transport. Convective currents are in charge of the transport

?Radiation; heat energy is transferred through space in the form of

electromagnetic waves [ or photons] that move at light speed. Sun′s energyIn all cases we can write:

rate of net heat transfer = difference of temperatures/ resistance

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