# 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) (T_{2}-T_{1})

With:

Q: Heat or thermal conduction

h: The heat transfer coefficient

A: area of the emitting body

l: the length of the material.

T_{2}: Temperature in hot state

T_{1}: 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 1m^{2}. 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 = T_{2} - T_{1} = 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 m^{2}/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 = T_{2} - T_{1} = 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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