BME Heat Transfer 2

Question 1

The Prandtl number is defined as the ratio of:

Accepted Answer

Momentum diffusivity to thermal diffusivity

Answer

Prandtl number Pr = ν/α = momentum diffusivity / thermal diffusivity, indicating the relative thickness of velocity and thermal boundary layers.

Question 2

In a counter-flow heat exchanger, the maximum possible temperature change of the cold fluid is limited by:

Accepted Answer

The hot fluid inlet temperature

Answer

In counter-flow, the cold fluid can theoretically be heated up to the inlet temperature of the hot fluid, giving the highest thermodynamic efficiency.

Question 3

Stefan-Boltzmann law states that radiation heat flux is proportional to:

Accepted Answer

T⁴

Answer

The Stefan-Boltzmann law states E = εσT⁴, meaning emissive power is proportional to the fourth power of absolute temperature.

Question 4

The LMTD method for heat exchanger analysis stands for:

Accepted Answer

Log Mean Temperature Difference

Answer

LMTD (Log Mean Temperature Difference) is the effective driving temperature difference for heat transfer in a heat exchanger.

Question 5

Which dimensionless number governs natural (free) convection?

Accepted Answer

Grashof number

Answer

The Grashof number Gr = gβΔTL³/ν² represents the ratio of buoyancy forces to viscous forces and governs natural convection.

BME - Bachelor of Mechanical Engineering Practice Test

BME - Bachelor of Mechanical Engineering Practice Test

BME Heat Transfer 2