NCEES Heat Transfer

Question 1

According to Fourier's Law of heat conduction, the heat flux q" is proportional to which of the following?

Accepted Answer

Negative temperature gradient

Answer

Fourier's Law states q" = -k(dT/dx); the negative sign shows heat flows in the direction of decreasing temperature.

Question 2

A flat wall has thermal conductivity k = 2 W/(m·K), area A = 5 m², thickness L = 0.2 m, and surface temperatures of 100°C and 20°C. What is the conductive heat transfer rate?

Accepted Answer

4 kW

Answer

Using q = kA(ΔT/L) = 2 × 5 × 80/0.2 = 4,000 W = 4 kW.

Question 3

The thermal resistance for convection from a surface with area A and convection coefficient h is expressed as:

Accepted Answer

1/(hA)

Answer

The convective thermal resistance is R_conv = 1/(hA), analogous to Ohm's law with Q = ΔT/R.

Question 4

Which dimensionless number represents the ratio of convective heat transfer to conductive heat transfer at a surface?

Accepted Answer

Nusselt number

Answer

The Nusselt number Nu = hL/k quantifies convective enhancement over pure conduction across the same fluid layer.

Question 5

For a composite plane wall with three layers in series, the total thermal resistance is:

Accepted Answer

Sum of individual resistances

Answer

Thermal resistances in series add directly: R_total = R₁ + R₂ + R₃, analogous to electrical resistors in series.

NCEES Practice Test

NCEES Practice Test

NCEES Heat Transfer