# 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

• 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 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 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.

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