1) The document discusses three main modes of heat transfer: conduction, convection, and radiation. Conduction involves heat transfer through direct contact within a solid medium. Convection refers to heat transfer by fluid motion in either forced or natural situations. Radiation transfers heat through space or matter without conduction or convection. 2) It describes how the thermal conductivity of solids, liquids, and gases is affected by temperature changes. The thermal conductivity of most solids and liquids decreases with increasing temperature, while the conductivity of gases generally increases with temperature. 3) The document derives a generalized heat transfer equation for three-dimensional Cartesian coordinates, assuming a homogeneous, isotropic solid with constant physical parameters under steady-state conduction

1. Heat Transfer (2151909)
Mechanical Department
Sem.: 5th
D (D2)
Fundamentals
Guided By: Jyotin Kateshia
Prepared By: Dubey Manish S. (160123119009)

2. Content
1.Modes of Heat Transfer
2.Effect of Temperature on Thermal
Conductivity of different solids,Liquids and gases
3.Derivation of genralized equation in Cartisan

3. Modes of Heat Transfer
• The Literature on heat transfer generally Recognizes three distinct
modes of heat transfer;
1) Conduction
2) Convection
3) Radiation
• Heat always flow from higher temperature to lower temperature.

4. Conduction
 Heat transfer through a solid medium via direct contact
 It is the micro form of heat transfer. The basic law which govern heat
transfer by conduction is Fourier's law.

5. Fourier’s Law
k = thermal conductivity (W/ mK)
dt/dx = temperature gradient: C/m
dt= temp. difference on both side of walls:*c
dx= thickness of body in the direction of heat flow:
m
q” = rate of heat transfer per unit area (W/m2)

6. Energy transfer by fluid motion
Two kinds of convection
 Forced convection: Fluid is forced
 Natural or free convection: fluid is induced by temperature
difference
Convection

7. Radiation
 ‘Radiation’ is the transfer of heat through space or matter by means other than
conduction or convection.
Examples:
The solar energy incident upon the earth

8. Effect of Temperature on Thermal Conductivity of Different
Solids
• Thermals conductivity of pure metals is due to migration
of three electrons (Ke) and lattice vibrations (Kl).
• K = Ke + Kl
• In pure metals, heat is transferred due to movement of
free electron in clouds and also due to vibrational energy
in lattice structure.
• Thermal conductivity of pure metal is decreases with the
increasing in temperature.

10. Effect of Temperature on Thermal Conductivity of Gases
• Thermal conductivity of gases is smaller then that of solids
because there intermolecular spacing is much larger.
• The thermal conductivity of all the gases increases with
increases with increases in temperature.
• This is because at high temperature collision among gas
particles increases and heat transfer increases.
• K = 0.006 to 0.05 W/mK

12. Effect of Temperature on Thermal Conductivity of
Liquids
• Heat conduction in liquids is also same as in gases.
• In case of liquids, close spacing of molecules and strong
molecular attraction force compare to gases cause more heat
exchange via collision.
• So the thermal conductivity of liquids usually lies between those
of gases and solids.
• In most of the liquids value of thermal conductivity tends to
decrease with increase in temperature.

14. Cartesian co-ordinates
 Three Dimensional heat transfer equation analysis (Cartesian co-ordinates)
 Assumptions
 The solid is homogeneous and isotropic
 The physical parameters of solid materials are constant
 Steady state conduction
 Thermal conductivity k is constant