UPDA Chemical flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Reynolds number

Re = ρvD/μ = vD/ν; determines flow regime: laminar below 2100, transitional 2100–4000, turbulent above 4000 in pipe flow.

Bernoulli equation

For steady, incompressible, frictionless flow along a streamline: P/ρ + v²/2 + gz = constant, relating pressure, velocity, and elevation.

Buckingham Pi theorem

Number of independent dimensionless groups equals n variables minus m fundamental dimensions; used to derive correlations from dimensional analysis.

Fick's law

Diffusive molar flux J_A = −D_AB dc_A/dx; the proportionality constant D_AB is the binary diffusion coefficient.

LMTD

Log mean temperature difference = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2); used with q = U A F ΔT_lm for heat exchanger sizing.

Effectiveness-NTU method

Effectiveness ε = q/q_max and NTU = UA/C_min; used when outlet temperatures are unknown, avoiding iterative LMTD solution.

Dittus-Boelter correlation

Nu = 0.023 Re^0.8 Pr^n for turbulent flow in smooth tubes; n = 0.4 for heating and 0.3 for cooling of the fluid.

Fenske equation

N_min = log[(xD/(1−xD))((1−xB)/xB)]/log α_avg; estimates minimum distillation stages at total reflux.

Kremser equation

Relates number of equilibrium stages to absorption factor A = L/(mV) for absorption and stripping calculations.

CSTR design equation

V = F_A0 X / (−r_A); the reactor operates at exit conditions, giving the lowest conversion per volume for positive-order kinetics.

PFR design equation

V = F_A0 ∫₀^X dX/(−r_A); plug flow assumes no axial mixing and gives higher conversion than a CSTR of equal volume.

Arrhenius equation

k = A exp(−E_a/RT); a plot of ln k versus 1/T has slope −E_a/R and intercept ln A.

Space time

τ = V/v0, the reactor volume divided by volumetric feed rate; its reciprocal is space velocity, used to compare reactor throughput.

Raoult's law

Partial pressure of component i equals x_i P_i^sat; valid for ideal liquid mixtures, modified by activity coefficient γ_i for non-ideal systems.

Clausius-Clapeyron equation

ln(P2/P1) = −(ΔH_vap/R)(1/T2 − 1/T1); relates vapor pressure to temperature for a pure substance.

Gibbs phase rule

F = C − P + 2 gives degrees of freedom from number of components C and phases P at equilibrium.

Carnot efficiency

η = 1 − T_C/T_H for a reversible heat engine operating between absolute temperatures T_C and T_H.

NPSH available

NPSH_A = (P_atm − P_vap)/(ρg) + z − h_f,suction; must exceed the pump's required NPSH to avoid cavitation.

Darcy-Weisbach equation

hf = f (L/D)(v²/2g); the Darcy friction factor f equals 64/Re for laminar pipe flow.

Ergun equation

Predicts pressure drop through packed beds combining viscous (150) and inertial (1.75) terms using void fraction ε and particle diameter.

Pump affinity laws

For a centrifugal pump at constant impeller diameter: Q ∝ N, H ∝ N², and power P ∝ N³ with rotational speed N.

PID controller

u(t) = K_p e + K_i ∫e dt + K_d de/dt; proportional, integral, and derivative actions correct error in a feedback loop.

First-order process

Transfer function G(s) = K/(τs + 1); after a step input the response reaches 63.2% of final value at time t = τ.

Ziegler-Nichols tuning

Ultimate gain method: K_p = 0.6 K_u, integral time τ_I = P_u/2, derivative time τ_D = P_u/8 for a PID controller.

Routh-Hurwitz criterion

Determines closed-loop stability from the characteristic equation coefficients without solving for roots; all first-column entries must be positive.

Six-tenths rule

Capital cost scaling: C2 = C1 (Q2/Q1)^n with n approximately 0.6, used for preliminary equipment cost estimates.

Net present value

NPV = Σ CF_t/(1 + r)^t − initial investment; a positive NPV at the hurdle rate indicates an acceptable project.

Payback period

Fixed capital divided by annual cash flow; simple measure that ignores the time value of money and cash flows after payback.

HAZOP study

Systematic hazard review applying guide words (no, more, less, reverse, as well as, part of, other than) to process nodes and parameters.

Flash point

Lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture near its surface; key flammability indicator.

Inherent safety hierarchy

Priority order: minimize, substitute, moderate, simplify; reduces hazards by design rather than adding protective layers.

Fault tree analysis

Top-down deductive method combining basic event probabilities through AND (product) and OR (sum) gates to estimate top event frequency.