dr. emad m. saad - fayoum transfer mechanisms.pdf · dr. emad m. saad mechanical engineering dept....
TRANSCRIPT
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Fayoum University
Faculty of Engineering
Mechanical Engineering Dept.
Dr. Emad M. Saad Mechanical Engineering Dept.
Faculty of Engineering
Fayoum University
Heat Transfer Mechanisms
Lecture (9)
on
By
2015 - 2016
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms - Conduction
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
For Plane wall
For Cylinder
For Sphere
To find the general form of one-dimensional heat transfer by conduction through plane wall and temperature distribution
Heat Transfer Mechanisms - Conduction
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms - Conduction
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Internal Forced Convection
External Forced Convection
Convection Mechanism
Forced Convection Natural or Free Convection
Heat Transfer Mechanisms - Convection
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Forced Convection
Natural or Free Convection
Heat Transfer Mechanisms - Convection
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Natural or Free Convection
Heat Transfer Mechanisms - Convection
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms - Convection
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms - Radiation
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Heat Transfer Mechanisms - Radiation
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Thermal Resistance Concept
Conduction Thermal Resistance
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Thermal Resistance Concept
Convection Thermal Resistance
Radiation Thermal Resistance
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Thermal Resistance Concept
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Thermal Resistance Concept
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Lecture (1) – Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Example 1: Heat transfer by Conduction
Solved Examples
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Lecture (1) – Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Example 2: Heat transfer by Convection
Solved Examples
A 2-m-long, 0.3-cm-diameter electrical wire extends across a room
at 15°C, as shown in the following figure. Heat is generated in the
wire as a result of resistance heating, and the surface temperature
of the wire is measured to be 152°C in steady operation. Also, the
voltage drop and electric current through the wire are measured to
be 60 V and 1.5 A, respectively. Disregarding any heat transfer by
radiation, determine the convection heat transfer coefficient for
heat transfer between the outer surface of the wire and the air in
the room.
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Lecture (1) – Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Example 2: Heat transfer by Convection
Solved Examples
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Lecture (1) – Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
Example 3: Heat transfer by Radiation
Solved Examples
Consider a person standing in a room maintained at 22°C at all times. The
inner surfaces of the walls, floors, and the ceiling of the house are observed to
be at an average temperature of 10°C in winter and 25°C in summer.
Determine the rate of radiation heat transfer between this person and the
surrounding surfaces if the exposed surface area and the average outer surface
temperature of the person are 1.4 m2 and 30°C, respectively. Take the
emissivity of a person is 0.95
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Mechanical Engineering (2) – 2nd year – Electrical Power Dept.
A transistor with a height of 0.4 cm and a diameter of 0.6 cm is mounted on a circuit
board. The transistor is cooled by air flowing over it with an average heat transfer
coefficient of 30 W/m2·°C. If the air temperature is 55°C and the transistor case
temperature is not to exceed 70°C, determine the amount of power this transistor can
dissipate safely. Disregard any heat transfer from the transistor base.
Quiz
Homework
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