NCEES Heat Transfer 3

Question 1

For the lumped capacitance method, the temperature response of a body cooling in a fluid follows which mathematical form?

Accepted Answer

Exponential decay with time constant τ = ρVcp/(hAs)

Answer

Linear decrease with time

Answer

Parabolic decrease with time

Answer

Step change at time t = τ

Question 2

A blackbody at 1000 K emits thermal radiation at what power per unit area? (σ = 5.67 × 10⁻⁸ W/m²·K⁴)

Accepted Answer

56,700 W/m²

Answer

5,670 W/m²

Answer

567 W/m²

Answer

5,670,000 W/m²

Question 3

In the NTU-effectiveness (ε-NTU) method for heat exchanger analysis, effectiveness ε is defined as:

Accepted Answer

Actual heat transfer rate divided by maximum possible heat transfer rate

Answer

Outlet temperature divided by inlet temperature of the hot fluid

Answer

Number of transfer units times Cmin/Cmax

Answer

Total surface area times overall heat transfer coefficient

Question 4

For fully developed laminar flow inside a circular tube with a constant heat flux boundary condition, the Nusselt number is approximately:

Accepted Answer

4.36

Answer

3.66

Answer

6.28

Answer

8.00

Question 5

Which dimensionless number characterizes the ratio of buoyancy forces to viscous forces and is the key parameter in natural convection analysis?

Accepted Answer

Grashof number (Gr = gβΔTL³/ν²)

Answer

Reynolds number (Re = VL/ν)

Answer

Nusselt number (Nu = hL/k)

Answer

Stanton number (St = h/(ρVcp))

Question 6

For a semi-infinite solid initially at uniform temperature Ti, suddenly exposed to a new surface temperature Ts at t = 0, the temperature distribution T(x,t) involves which mathematical function?

Accepted Answer

Complementary error function erfc(x/2√(αt))

Answer

Fourier series expansion

Answer

Bessel function of the first kind

Answer

Legendre polynomial

Question 7

The radiation view factor F₁₂ is defined as the fraction of:

Accepted Answer

Radiation leaving surface 1 that is intercepted by surface 2

Answer

Total radiation incident on surface 2 that originated from surface 1

Answer

Emissive power of surface 1 relative to a blackbody at the same temperature

Answer

Radiation absorbed by surface 2 divided by radiation emitted by surface 1