Tong quan ve truyen nhiet - DH CN.PDF

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  • Ly Ngoc Minh, Senior Lecturer 1

    TRNG AI HOC CONG NGHIEP TPHCMKHOA CONG NGHE HOA HOC VA MOI TRNG

    CHNG ITNG QUAN V TRUYN NHIT

  • Ly Ngoc Minh, Senior Lecturer 2

    VAI TRO CUA TRUYEN NHIET

    MY HI NC THI C I

    ong c hi n cthi Hy-lap coai

  • Ly Ngoc Minh, Senior Lecturer 3

    Mt hnh nh TB Nhit trong thc t

  • Ly Ngoc Minh, Senior Lecturer 4

    Cu hi tho lun: cho bit nhng hnh thctrao i nhit xy ra trong hnh nh ny?

  • Ly Ngoc Minh, Senior Lecturer 5

    Hy m t cc qu trnh TN xy ra trong hnhnh di y?

  • Ly Ngoc Minh, Senior Lecturer 6

    NOI HI ONG LO ONG LA NAM

  • Ly Ngoc Minh, Senior Lecturer 7

    TRUYN NHIT

    NHIT BAO GI CNG CTRUYN T NI C NHIT CAON NI C NHIT THP.

  • Ly Ngoc Minh, Senior Lecturer 8

    3 DNG TRAO I NHIT C BN

    DN NHITDN NHIT

    BC X NHITBC X NHIT

    I LU NHITI LU NHIT

  • Ly Ngoc Minh, Senior Lecturer 9

    The Nature of Heat

    Definition: Heat is the internal kinetic energy ofthe atoms and molecules that make up asubstance. Since it is a form of energy, it is measure in thestandard unit of a Joule.

    More commonly, it is measured in the following units: calorie heat energy needed to raise 1 gram of water by 1degree Celsius. 1 calorie = 4.186 Joules.

    Calorie commonly used to measure energy content of food.1 Calorie = 1000 calories.

    British Thermal Unit (BTU) heat energy needed to raiseone pound of water by 1 degree Fahrenheit. 1 BTU = 252calories = 1,054 Joules.

  • Ly Ngoc Minh, Senior Lecturer 10

    Properties of Heat

    Two liters of boiling water has more energythan one one liter of boiling water.

    Heat will not flow between two objects of thesame temperature.

    Heat is energy in the process of beingtransferred from one object to another becauseof the temperature difference between them

  • Ly Ngoc Minh, Senior Lecturer 11

    Heat Capacity

    Definition: Heat capacity is the amount of heatrequired per unit increase in temperature. It is a measure of how well the substance stores heat. Heat added = heat capacity x (change in temperature) Materials with large heat capacities hold heat well.

    Their temperatures will not rise much for a given amount ofheat.

    Example: water

    Materials with small heat capacities do not hold heatwell. Their temperatures will rise quickly for a given amount ofheat

    Example: air

  • Ly Ngoc Minh, Senior Lecturer 12

    Mechanisms of Heat Transfer

    Conduction Convection Advection Radiation

  • Ly Ngoc Minh, Senior Lecturer 13

    Conduction

    Conduction is the transfer of heat within asubstance, molecule by molecule

  • Ly Ngoc Minh, Senior Lecturer 14

    TRUYN NHIT DN NHIT

    T1

    T2

    d

  • Ly Ngoc Minh, Senior Lecturer 15

    TRUYN NHIT DN NHIT

    DT1 DT2 DT3

  • Ly Ngoc Minh, Senior Lecturer 16

    Conductivity of Various Substances

    427Silver80Iron2.7Granite2.1Ice2.1Wet Soil0.63Snow0.60Water at 20 C0.25Dry Soil0.023Still air at 20 CHeat ConductivitySubstance

  • Ly Ngoc Minh, Senior Lecturer 17

    Convection

    Convection is heat transfer by the movement ofa fluid in the vertical direction

  • Ly Ngoc Minh, Senior Lecturer 18

    Advection

    Advection is the movement of heat in thehorizontal (north/south/east/west) direction.

    Any measurable property of air can beadvected.

  • Ly Ngoc Minh, Senior Lecturer 19

    TRUYN NHIT I LU

  • Ly Ngoc Minh, Senior Lecturer 20

    Khi nim v tun han

    HI RA

    NC CAP

    O NGN

    C

    X UO NG

    ONG NC LENONG NC XUONG

    S lun chuyn canc trong ni hi

  • Ly Ngoc Minh, Senior Lecturer 21

    Radiation

    Radiation allows heat to be transferred throughwave energy

    These waves are called electromagnetic wavesbecause the energy travels in a combination ofelectric and magnetic waves

    The energy a wave carries is related to itswavelength (distance from crest to crest)

  • Ly Ngoc Minh, Senior Lecturer 22

    Electromagnetic Spectrum

  • Ly Ngoc Minh, Senior Lecturer 23

    Stephan-Boltzmann Law

    All things with a temperature above absolute zero emitradiation.

    As the temperature of an object increases, moreradiation is emitted each second

    E = T4

    where is a constant, T is the temperature of an objectin Kelvin and E is the maximum rate of radiationemitted per square meter.

  • Ly Ngoc Minh, Senior Lecturer 24

    Weins Law

    Weins law states that the wavelength of maximumemission of an object is related to the objectstemperature.

    max = /Twhere max is the wavelength in micrometers (m) atwhich the maximum radiation emission occurs, is aconstant equal to 2897 m K, and T is the temperaturein Kelvin.

  • Ly Ngoc Minh, Senior Lecturer 25

    Emission Spectrum ofan Object with

    Constant Temperature

  • Ly Ngoc Minh, Senior Lecturer 26

    Summary

  • Ly Ngoc Minh, Senior Lecturer 27

    Weins Law

    Weins law states that the wavelength of maximumemission of an object is related to the objectstemperature.

    max = /Twhere max is the wavelength in micrometers (m) atwhich the maximum radiation emission occurs, is aconstant equal to 2897 m K, and T is the temperaturein Kelvin.