Thermal Conduction Formula

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

Related Links: