BME Heat Transfer 3

Question 1

In transient conduction, the lumped capacitance method is valid when:

Accepted Answer

Bi < 0.1

Answer

The lumped capacitance method assumes uniform temperature within the body and is valid when Bi < 0.1, meaning internal conduction resistance is negligible.

Question 2

The effectiveness of a heat exchanger (ε) is defined as:

Accepted Answer

Actual heat transfer / Maximum possible heat transfer

Answer

Heat exchanger effectiveness ε = Q_actual / Q_max, comparing actual performance to the thermodynamic maximum limited by the minimum capacity rate fluid.

Question 3

Thermal conductivity of metals generally _______ with increasing temperature.

Accepted Answer

Decreases slightly

Answer

For most pure metals, thermal conductivity decreases slightly with increasing temperature due to increased lattice vibrations scattering electrons.

Question 4

In forced convection over a flat plate, the Reynolds number is used to determine:

Accepted Answer

Whether flow is laminar or turbulent

Answer

The Reynolds number Re = VL/ν indicates the flow regime; transition from laminar to turbulent on a flat plate typically occurs around Re ≈ 5×10⁵.

Question 5

Which material has the highest thermal conductivity at room temperature?

Accepted Answer

Diamond

Answer

Diamond has the highest known thermal conductivity (~2000 W/m·K) of any natural material, far exceeding metals like copper (~400 W/m·K).

BME - Bachelor of Mechanical Engineering Practice Test

BME - Bachelor of Mechanical Engineering Practice Test

BME Heat Transfer 3