Transport Phenomena (Fluid Mechanics, Heat Transfer, Mass Transfer)
Core concepts
Transport phenomena unifies momentum, energy and mass transfer through the same shell-balance logic. For fluids, know the continuity and Navier–Stokes equations, Newtonian and non-Newtonian rheology (power law, Bingham), Reynolds number regimes, friction factor (Moody chart, Colebrook), and pressure drop in pipes and fittings. Bernoulli and mechanical energy balances, pump curves, NPSH and cavitation, packed and fluidised beds (Ergun equation), and flow measurement (orifice, venturi, rotameter) are recurring. For heat transfer, master conduction (Fourier, resistance networks, fins), convection (dimensionless groups Nu, Re, Pr, correlations), radiation (Stefan–Boltzmann, view factors), and heat exchanger design (LMTD, effectiveness–NTU, fouling). For mass transfer, know Fick's law, diffusivity, film and penetration theories, mass transfer coefficients, and analogies (Reynolds, Chilton–Colburn).
Traps
Units and dimensional consistency dominate errors. In LMTD, switch to NTU when temperatures are not both specified. Remember effectiveness ≤ 1 and counterflow exceeds parallel. For packed beds, Ergun blends viscous and inertial terms; check which dominates. Distinguish overall and individual heat/mass transfer coefficients with resistances in series.
Worked rule of thumb
For turbulent pipe flow, use Darcy–Weisbach: ΔP = f·(L/D)·(ρv²/2). For smooth pipes, f ≈ 0.079·Re^(−0.25) (Blasius) up to Re ≈ 10⁵. A quick check: doubling velocity quadruples frictional loss (roughly, since f varies weakly).
Exam strategy
Always sketch the control volume and list assumptions (steady, incompressible, fully developed) before selecting a correlation.