Heat Flux Formula and Sample Example

Heat Flux Formula :

Heat flux formula is conductive heat flux JHc(w/m-1) in watts per meter-1 is equal to the product of thermal conductivity costant = λ(wm-1/K-1) in watts per meter-1 per Kelvin-1 and multiply the temperature dT(0c) in degree Celsius and divided by the dz .Hence the Heat Flux Formula can be written as

JHc(w/m-1) = λ(wm-1/K-1)* dT(0c)/dZ

JHc =Conductive heat flux in w/m2

T→ Temperature in 0c

λ → thermal conductivity constant in wm-1 /K-1

Heat Flow Rate Formula,

The heat flow rate is defined as the amount of heat transferred per unit time in the material. The heat flow rate in a rod depends on the cross-sectional area of the rod, the temperature difference between both the ends and the length of the rod. Following is the formula used to calculate the heat flow rate of any material:

Q=-K(wm-1/k-1)* (A(m2)/l(m))*( ΔT)

Where,

 Q → heat transfer per unit time  in j/s

k → thermal conductivity in wm-1 K-1

A→ cross-sectional area in m2

l → length of the material in m

∆T→ temperature difference

Sample Problems :

Example 1 :

Calculate the heat transferred through the plate? One face of a copper plate is 4 cm thick and maintained at 400C, and the other face is maintained at 100C.

Solution :

Given parameters are

Coefficient of thermal conductivity of copper λ=385

dT=400-100=300

dx=4cm

Substitute the values in the given formula

JHc = λ* dT/dZ

JHc=385*300/4

JHc= 28.875 Mw

Example 2 :

Calculate the heat transferred through the plate? One face of a copper plate is 6 cm thick and maintained at 600C, and the other face is maintained at 100C.

Solution :

Given parameters are

Coefficient of thermal conductivity of copper λ=385

dT=600-100=500

dx=6cm

Substitute the values in the given formula

JHc = λ* dT/dZ

JHc=385*600/6

JHc= 38.500Mw

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