Test: Fourier Equation
10 Questions MCQ Test Heat Transfer | Test: Fourier Equation
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He gave this theory in 1824.
According to Fourier law of heat conduction, Q = -k A d t /d x.
Here are some assumptions that are made for Fourier law. Identify the wrong one
It has constant temperature gradient and a linear temperature profile.
Consider the following statements:
The Fourier heat conduction equation
Q = -k A d t /d x
Presumes
i) Steady state conditions
ii) Constant value of thermal conductivity
iii) Uniform temperature at the wall surface
iv) One dimensional heat flow
Which of these statements are correct?
Thermal conductivity is different for different materials.
The surface temperature of body 475 K and it radiates heat to the surroundings at 335 K. If thermal conductivity of the material is 12.5 W/m degree, find the temperature gradient. Let convective coefficient be 80 W/m2 degree and radiation factor is 0.9
Heat conducted through the plate = convection heat losses + radiation heat losses. So, d t /d x = – 13155/12.5 = – 1052.4 degree Celsius.
Negative sign in Fourier heat conduction equation indicates
The ratio d t/d x represents the change in temperature per unit thickness i.e. the temperature gradient. So it represents heat flow in the direction of negative temperature gradient.
In gases atoms are arranged loosely, there is less molecular transmission of heat as compared to solids, liquids and alloys.
The unit kcal/m hr K could also be specified as J/m s K or W/m s K and this is actually done while quoting the numerical values of thermal conductivity.
“Thermal conductivity represents the amount of heat conducted across unit area when a temperature difference of one kelvin”. True or false
It is across unit area and through unit distance.
Thermal resistance is expressed in the unit’s hr degree/kcal, degree/W and s degree/J.
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