MECH 352 HEAT TRANSFER I FINAL CRASH
PART 1- Basic Concepts and the Heat Conduction
Equation Concordia University
,Basic Concepts
Basic Nomenclature
• Q is the heat energy
• q is the heat flux, which is Q/A
Note that in general, heat flows from higher temperatures to lower temperatures.
Basic Modes of Heat Transfer
Conduction
Conduction occurs when heat is transferred through a solid medium. In some cases where a fluid is
stagnant and is confined to a small area, heat transfer can be said to go through conduction. The general
equation is:
∂T
Q́ =−kA
∂x
• k is the conduction heat transfer coefficient, which is dependent on the material.
Convection
Convection occurs when heat is transferred from a fluid to another body. The fluid can either be moving
or not. The general equation is:
Q́ =hA (T w −T ∞ )
The complexity with this equation is trying to find the convection heat transfer coefficient h, which
depends on many factors. (MECH 452)
Radiation
Radiation occurs when heat is transferred through energy-carrying wavelengths from one hot body to
another that are not in direct contact. The general equation is:
Q́ =σεFA (T 4−T 4 )
b surr
• σ = 5.67 x 10-8, is the Stefan-Boltzmann constant
• ε is the emissivity of the body, (= 1 for a black body)
• F is the view factor.
2
, 1. The inner and outer surfaces of a 4-m X 7-m brick wall of thickness 30 cm and thermal conductivity
0.69 W/m-K are maintained at temperatures of 26°C and 8°C, respectively. Determine the rate of heat
transfer through the wall, in W.
Given:
∆T
A = 28 m2 Q́ cond =−kA
Δx = 0.30 m ∆x
8−26
k = 0.69 W/m-K Q́ =−0.69(28)
cond
T1 = 26°C 0.30
T2 = 8°C Q́ cond=1159.2 W
3
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