Thermal Conduction Formula
The thermal conduction is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described by the second law of the thermodynamics.
Thermal conduction = -(heat transfer coefficient)*(Area/length)*(difference of temperature)
The equation is:
Q = -h (A/l) (T2-T1)
With:
Q: Heat or thermal conduction
h: The heat transfer coefficient
A: area of the emitting body
l: the length of the material.
T2: Temperature in hot state
T1: Temperature in cold state
Thermal Conduction Formula Questions:
1) A 2mm thick glass sheet is being used for a window. The heat transfer coefficient is 1.7J/(m K s). The area of the glass is 1m2. The temperature outside is 10°C and that inside is 20°C.What is the conduction of heat of the glass?
Answer:
The difference of temperature is ΔT = T2 - T1 = 20°C - 10°C = 10°C = 283 K.
The thermal conduction is given by the formula:
Q = -k (A/l) (ΔT)
Substituting the values of the heat conductivity coefficient, the area, the length and the difference of temperature between the hot and cold,
Q = -1.7 J/m K s (1 m2/0.002 m) (283 K) = -240550 J/s
2) Hot air at 80°C is blown over a 2 m by 4 m flat surface, of 1 cm width, at 30°C. If the average heat transfer coefficient is 55 W/m°C, determine the rate of heat conducted from the air to the plate.
Answer:
The difference of temperature is ΔT = T2 - T1 = 80°C - 30°C = 50°C
The thermal conduction is given by the formula:
Q = -k (A/l) (ΔT)
Substituting the values of the heat conductivity coefficient, the area, the length and the difference of temperature between the hot and cold,
Q = -55 W/m °C (2 m * 4 m/0.1 m) (50°C) = -22000 W
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