1. Teaching Innovation - Entrepreneurial - Global
DTEL(Department for Technology Enhanced Learning)
The Centre for Technology enabled Teaching & Learning D M I E T R , Wardha
Teaching Innovation - Entrepreneurial - Global

2. DEPARTMENT OF MECHANICAL ENGINEERING
V -semester
Heat transfer
UNIT NO. 01
INTRODUCTION TO BASIC MODES OF HEAT TRANSFER

3. CHAPTER 1:- SYLLABUS Introduction to Heat Transfer
Modes of Heat Transfer
Laws of Heat Transfer
General Heat Conduction Equation in Cartesian, Cylindrical and Spherical Coordinate.
One dimensional steady state heat Conduction Equation.
Thermal resistance
Critical thickness of insulation.
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4. LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
Conduction, Convection, and Radiation
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5. LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
Heat Energy
Energy is what makes things happen.
All materials are made of tiny particles called molecules.
Molecules are always moving.
Molecules in motion
The movement creates heat.
The amount of heat depends on how fast the molecules move.
As the molecules move faster, they take up more space and make the object expand.
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6. LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
Heat Transfer
Heat can be transferred from one object to another in 3 different ways:
Conduction
Convection
Radiation
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7. LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
Conduction
Heat traveling through solids.
Two objects must touch or have direct contact.
As molecules heat up they move faster and expand.
When you touch one hot surface to another, the hot molecules bump into the other molecules which makes them start to move faster.
An object gets hotter from the movement of the molecules.
All solid objects conduct heat, some are better conductor than others.
Metals are good conductors.
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8. LECTURE 01:- INTRODUCTION TO HEAT TRANSFER Examples of Conduction
MODES OF HEAT TRANSFER
LECTURE 01:- INTRODUCTION TO HEAT TRANSFER
Examples of Conduction
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9. LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
Convection
Heat traveling through liquids or gases
As molecules heat up, the heat makes the molecules move more rapidly and expand.
Creates currents in liquids or gases – hot air rises and cold air sinks.
Uneven heating of our ocean creates ocean currents.
Uneven heating of our atmosphere produces huge convection wind currents.
Scientists use global and local wind patterns to predict weather.
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10. LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
Examples of Convection
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11. LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
Radiation
Release of invisible heat energy waves from the sun or fire.
No movement of molecules to transfer heat.
Feel warm without touch – heat radiates.
Radiators got their name from this type of heat.
When the radiant energy from the sun hits the earth, the earth soaks up the energy and changes it into heat.
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12. LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
Examples of Radiation
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13. LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
MODES OF HEAT TRANSFER
LECTURE 02:- INTRODUCTION TO HEAT TRANSFER
Balance
Whenever a hot object is placed near a cold object, the hot object will transfer heat to the cold object until they reach a state of balance.
Balance happens when the temperatures of both objects are the same.
The fast moving molecules mix with the slow moving molecules until they are all mixed and balanced.
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14. LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
LAWS OF HEAT TRANSFER
LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
Fourier’s Law
A rate equation that allows determination of the conduction heat flux
from knowledge of the temperature distribution in a medium
Its most general (vector) form for multidimensional conduction is:
Implications:
Heat transfer is in the direction of decreasing temperature
(basis for minus sign).
Fourier’s Law serves to define the thermal conductivity of the
medium
Direction of heat transfer is perpendicular to lines of constant
temperature (isotherms).
Heat flux vector may be resolved into orthogonal components.
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15. LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
LAWS OF HEAT TRANSFER
LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
Cartesian Coordinates:
Cylindrical Coordinates:
Spherical Coordinates:
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16. LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
LAWS OF HEAT TRANSFER
LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
In angular coordinates , the temperature gradient is still
based on temperature change over a length scale and hence has
units of C/m and not C/deg.
Heat rate for one-dimensional, radial conduction in a cylinder or sphere:
Cylinder
or,
Sphere
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17. LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
LAWS OF HEAT TRANSFER
LECTURE 03:- INTRODUCTION TO HEAT TRANSFER
Stefan-Boltzmann formula
Surface area (m2)
HEAT REAT
(watts)
Q = E s A T4
Absolute temperature
(K)
Stefan-Boltzmann constant
5.67 x 10-8 watts/m2K4)
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18. LECTURE 04:- INTRODUCTION TO HEAT TRANSFER
Thermophysical Properties
LECTURE 04:- INTRODUCTION TO HEAT TRANSFER
Thermophysical Properties
Thermal Conductivity K: A measure of a material’s ability to transfer thermal
energy by conduction.
Thermal Diffusivity a : A measure of a material’s ability to respond to changes
in its thermal environment.
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19. LECTURE 04:- INTRODUCTION TO HEAT TRANSFER
Thermophysical Properties
LECTURE 04:- INTRODUCTION TO HEAT TRANSFER
Thermal response of a plane wall to convection heat transfer.
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20. LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
HEAT CONDUCTION EQUATION
LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
GENERAL HEAT CONDUCTION EQUATION
In the last section we considered one-dimensional heat conduction and assumed heat conduction in other directions to be negligible.
Most heat transfer problems encountered in practice can be approximated as being one-dimensional, and we mostly deal with such problems in this text.
However, this is not always the case, and sometimes we need to consider heat transfer in other directions as well.
In such cases heat conduction is said to be multidimensional, and in this section we develop the governing differential equation in such systems in rectangular, cylindrical, and spherical coordinate systems.
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21. LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
HEAT CONDUCTION EQUATION
LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
Rectangular Coordinates
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22. LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
HEAT CONDUCTION EQUATION
LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
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23. LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
HEAT CONDUCTION EQUATION
LECTURE 05:- INTRODUCTION TO HEAT TRANSFER
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24. LECTURE 06:- INTRODUCTION TO HEAT TRANSFER
HEAT CONDUCTION EQUATION
LECTURE 06:- INTRODUCTION TO HEAT TRANSFER
Cylindrical Coordinates
Relations between the coordinates of a point in rectangular and cylindrical coordinate systems:
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25. LECTURE 07:- INTRODUCTION TO HEAT TRANSFER
HEAT CONDUCTION EQUATION
LECTURE 07:- INTRODUCTION TO HEAT TRANSFER
Spherical Coordinates
Relations between the coordinates of a point in rectangular and spherical coordinate systems:
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26. LECTURE 08:- INTRODUCTION TO HEAT TRANSFER
BOUNDARY CONDITION
LECTURE 08:- INTRODUCTION TO HEAT TRANSFER
The description of a heat transfer problem in a medium is not complete without a full description of the thermal conditions at the bounding surfaces of the medium.
Boundary conditions: The mathematical expressions of the thermal conditions at the boundaries.
The temperature at any point on the wall at a specified time depends on the condition of the geometry at the beginning of the heat conduction process.
Such a condition, which is usually specified at time t = 0, is called the initial condition, which is a mathematical expression for the temperature distribution of the medium initially.
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27. LECTURE 08:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 08:- INTRODUCTION TO HEAT TRANSFER
Boundary Conditions
Specified Temperature Boundary Condition
Specified Heat Flux Boundary Condition
Convection Boundary Condition
Radiation Boundary Condition
Interface Boundary Conditions
Generalized Boundary Conditions
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28. 1- Dimensional Heat Conduction
ONE DIMENSIONAL HEAT CONDITION
LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
1- Dimensional Heat Conduction
The Plane Wall : … … k
T∞,2
Ts,1
Ts,2
x=0
x=L
Hot fluid
Cold fluid
Const. K; solution is:
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29. LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
Thermal resistance (electrical analogy)
OHM’s LAW :Flow of Electricity
V=IR elect
Voltage Drop = Current flow×Resistance
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30. LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
Thermal Analogy to Ohm’s Law :
Temp Drop=Heat Flow×Resistance
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31. LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
1 D Heat Conduction through a Plane Wall … … k
T∞,2
Ts,1
Ts,2
x=0
x=L
Hot fluid
Cold fluid
T∞,1
T∞,1
Ts,1
Ts,2
T∞,2 qx A h 2 1 A k L A h 1
(Thermal Resistance )
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32. LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 09:- INTRODUCTION TO HEAT TRANSFER
Resistance expressions
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33. LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
Composite Walls : A B C
T∞,1
T∞,2 h1 h2
K A
K B
K C
L A
L B
L C
q x
T∞,1
T∞,2 A h 1 2
Overall heat transfer coefficient
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34. LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
Overall Heat transfer Coefficient
Contact Resistance : A B TA TB
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35. LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
Series-Parallel : A B D C T1 T2
K c
K D
K A
K B
AB+AC=AA=AD
LB=LC
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36. LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 10:- INTRODUCTION TO HEAT TRANSFER
Series-Parallel (contd…) T1 T2
Assumptions :
Face between B and C is insulated.
(2) Uniform temperature at any face normal to X.
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37. LECTURE 11:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 11:- INTRODUCTION TO HEAT TRANSFER
Critical Insulation Thickness : r0 ri T∞ Ti h
Insulation Thickness : r o-r i
Objective : decrease q , increases
Vary r0 ; as r0 increases ,first term increases, second term decreases.
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38. Critical Insulation Thickness (contd…)
BOUNDRY CONDITION
LECTURE 11:- INTRODUCTION TO HEAT TRANSFER
Critical Insulation Thickness (contd…)
Maximum – Minimum problem
Set at
Max or Min. ? Take :
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39. LECTURE 11:- INTRODUCTION TO HEAT TRANSFER
BOUNDRY CONDITION
LECTURE 11:- INTRODUCTION TO HEAT TRANSFER
Critical Insulation Thickness (contd…)
Minimum q at r0 =(k/h)=r c r (critical radius)
good for steam pipes etc.
good for electrical cables
R c r=k/h r0
R t o t
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40. THANK YOU
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