1. Presented By: Pritesh K Jaradi
Subject : Heat & Mass Transfer Topic: Conduction Lecture No: 3 Date: 8 – Feb
Presented By:
Pritesh K Jaradi

2. Some Expectations
Respect others
Respect the college
Humility

3. Work Ethic
DO participate and ask questions. For order in class, raise your hand when asking a question.
BRING all specified books.
HAND IN all homework ON TIME!
SHOW CARE and concern for each other. Help one another in homework. BUT NO COPYING OF ENTIRE ASSIGNMENTS!

4. Lecture 3 by Pritesh Jaradi
Topics Covered
Fourier’s Law of heat conduction
Effect of temperature
On thermal conductivity of metal
On refractories & building material
On gas
Liquid
General heat conduction equation
8 February 2013
Lecture 3 by Pritesh Jaradi

5. Fundamentals of Heat Transfer
Conduction, Convection, and Radiation Heat Transfer Mode
Heat transfer (or heat) is thermal energy in transit due to a temperature difference
8 February 2013
Lecture 3 by Pritesh Jaradi

6. Fourier’s Law of heat conduction
Rate of heat flow is directly proportional to area of section at normal to heat flow.
Rate of heat flow is directly proportional to temperature gradient.
8 February 2013
Lecture 3 by Pritesh Jaradi

7. Fourier’s Law of heat conduction (Contd.)
Assumptions
steady state condition.
No internal heat generation
Homogeneous and isotropic material
Unidirectional heat flow (1-D)
8 February 2013
Lecture 3 by Pritesh Jaradi

8. Conduction Heat Transfer
First mechanism - molecular interaction (e.g. gas)
Greater motion of molecule at higher energy level (temperature) imparts energy to adjacent molecules at lower energy levels
Second mechanism – by free electrons (e.g. solid)
8 February 2013
Lecture 3 by Pritesh Jaradi

9. Thermal Conductivity of Gas
Smaller than solid.
Intermolecular space is much large.
Continuous random motion.
K increases as increase of temp.
At high temp collision increase.
8 February 2013
Lecture 3 by Pritesh Jaradi

10. Thermal Conductivity of Metal
Due to migration of free electrons and molecular vibration.
At high temp vibration becomes violent and obstruct free flow of electrons.
Thus reduces HT by movement of free electrons.
For alloys TC is less than pure metals.
8 February 2013
Lecture 3 by Pritesh Jaradi

11. Thermal Conductivity of Liquid
Close spacing molecules + strong molecular attraction force.
Heat exchange via collision process.
Lies between gases and solid.
As temp increases reduction in molecular attraction….. Leads to decrease in K
8 February 2013
Lecture 3 by Pritesh Jaradi

12. Conductivity of refractories and building materials
Very low thermal conductivity.
Known Insulating materials
Porous structure with trapped air / liquid.
At increased temp, conductivity of gases increases ………….leads to increase in thermal conductivity of building materials.
8 February 2013
Lecture 3 by Pritesh Jaradi

13. General heat conduction equation:
8 February 2013
Lecture 3 by Pritesh Jaradi

14. General heat conduction equation (Contd.):
8 February 2013
Lecture 3 by Pritesh Jaradi

15. THE END