Heat Transfer Flashcards
6 cards from real BME practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Heat Transfer flashcards as text
In transient conduction, the lumped capacitance method is valid when:
Answer: Bi < 0.1
The lumped capacitance method assumes uniform temperature within the body and is valid when Bi < 0.1, meaning internal conduction resistance is negligible.
The effectiveness of a heat exchanger (ε) is defined as:
Answer: Actual heat transfer / Maximum possible heat transfer
Heat exchanger effectiveness ε = Q_actual / Q_max, comparing actual performance to the thermodynamic maximum limited by the minimum capacity rate fluid.
Thermal conductivity of metals generally _______ with increasing temperature.
Answer: Decreases slightly
For most pure metals, thermal conductivity decreases slightly with increasing temperature due to increased lattice vibrations scattering electrons.
In forced convection over a flat plate, the Reynolds number is used to determine:
Answer: Whether flow is laminar or turbulent
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.
Which material has the highest thermal conductivity at room temperature?
Answer: Diamond
Diamond has the highest known thermal conductivity (~2000 W/m·K) of any natural material, far exceeding metals like copper (~400 W/m·K).
The NTU method in heat exchanger analysis stands for:
Answer: Number of Transfer Units
NTU (Number of Transfer Units) = UA/C_min is a dimensionless parameter representing the heat exchanger size relative to the minimum fluid capacity rate.