Presented By: Pritesh K Jaradi Subject : Heat & Mass Transfer Topic: Conduction Lecture No: 3 Date: 8 – Feb - 2013 Presented By: Pritesh K Jaradi
Some Expectations Respect others Respect the college Humility
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!
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
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
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
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
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
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
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
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
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
General heat conduction equation: 8 February 2013 Lecture 3 by Pritesh Jaradi
General heat conduction equation (Contd.): 8 February 2013 Lecture 3 by Pritesh Jaradi
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