Thermal Conductivity and the Fourier Equation

This quiz contains multiple-choice problems on various properties of Fourier’s heat equation, heat conduction equation and thermal conductivity of different materials.

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Which of the following is the unit of thermal resistance?

degree/kcal hour degree s degree/kcal degree/W

Thermal conductivity is defined as the heat flow per unit time

When the temperature gradient is unity Across the wall with no temperature Through a unit thickness of the wall Across unit area where the temperature gradient is unity

Which one of the following forms of water have the highest value of thermal conductivity?

Boiling water Steam Solid ice Melting ice

The average thermal conductivities of water and air conform to the ratio

50:1 25:1 5:1 15:1

Most metals are good conductor of heat because of

Transport of energy Free electrons and frequent collision of atoms Lattice defects Capacity to absorb energy

The heat energy propagation due to conduction heat transfer will be minimum for

Lead Water Air Copper

The famous Fourier series is named after

Diller and Ryan

J.B. Joseph Fourier

Stefan-Boltzmann

Wein

Fourier’s law of heat conduction is best represented by

Q = -k A(dt/dx)

Q = k A(dt/dx)

Q = -k A

Q = k(dt/dx)

Here are some assumptions made for Fourier’s heat conduction law. Identify the wrong one.

No internal heat generation

Steady state heat conduction

Non-linear temperature profile

Isotropic and homogenous material

Consider the following statements:
The Fourier heat conduction equation Q = -kA(dt/dx) 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?

i, ii and iii

i, ii and iv

i, iii and iv

Transmission of heat, i.e., molecular is smallest in case of

Gases

Liquids

Alloys

Solids

The negative sign in the Fourier heat conduction equation indicates

Heat always flows is in the direction of positive temperature gradient

Heat always flows in the direction of negative temperature gradient

No heat flow is there