HKIE Professional Assessment - Chemical Discipline flashcards

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

Carnot efficiency

Maximum thermal efficiency of a heat engine operating between hot and cold reservoirs: η = 1 − T_C/T_H, with absolute temperatures. No real cycle can exceed this limit.

Exergy destruction

Lost work due to irreversibility equals T0·S_gen, where T0 is the dead-state temperature and S_gen is entropy generation. It locates inefficiency in a process network.

Azeotrope

A mixture whose liquid and vapour compositions are identical at a given pressure, so ordinary distillation cannot separate it further. Example: ethanol–water at about 95 wt% ethanol.

Levenspiel plot

A graph of 1/(−r_A) versus conversion X. The area under the curve gives PFR volume; a rectangle gives CSTR volume for the same conversion.

Thiele modulus

Dimensionless ratio of reaction rate to diffusion rate in a porous catalyst: φ = L·√(k/D_eff). Large φ means strong pore-diffusion limitation.

Weisz–Prater criterion

C_WP = (−r_A,obs·L²)/(D_eff·C_As). A value much less than 1 indicates kinetic control, allowing intrinsic kinetics to be measured reliably.

Effectiveness factor

Ratio of observed reaction rate to the rate if the entire catalyst pellet were at surface conditions. For a first-order slab, η = tanh φ/φ.

Darcy–Weisbach equation

Pressure drop in pipe flow: ΔP = f·(L/D)·(ρv²/2), where f is the Darcy friction factor. For laminar flow, f = 64/Re.

Dittus–Boelter equation

Turbulent convective heat transfer correlation: Nu = 0.023·Re^0.8·Pr^n, with n = 0.4 for heating and 0.3 for cooling. Valid for Re > 10^4.

Ergun equation

Predicts pressure drop through a packed bed, combining viscous (Blake–Kozeny) and inertial (Burke–Plummer) terms as a function of porosity, particle size, and velocity.

Fenske equation

Gives minimum theoretical stages at total reflux: N_min = ln[(x_D/(1−x_D))·((1−x_B)/x_B)]/ln α, using relative volatility α and distillate/bottoms compositions.

Kremser equation

Calculates theoretical stages for absorption or stripping using the absorption factor A = L/(mV), relating inlet and outlet gas and liquid compositions.

Underwood equations

Two equations using relative volatilities and feed composition to find minimum reflux ratio and the distribution of components at minimum reflux.

Pinch analysis

Method using composite curves to find minimum hot and cold utility targets. Heat transfer across the pinch is forbidden, as it increases both utility duties.

Rachford–Rice equation

Iterative flash calculation that solves for vapour fraction using equilibrium K-values and overall composition. Used inside process simulators for flash drums.

Scale-up similarity

Matching geometric, kinematic, dynamic, thermal, and chemical similarity. Full similarity is rarely achievable, so the controlling mechanism must be identified and matched.

HAZOP guide words

Standard prompts applied to node parameters: No/Not, More, Less, As well as, Part of, Reverse, Other than. Each deviation is examined for cause, consequence, and safeguard.

ALARP principle

Risk must be reduced until further reduction is grossly disproportionate to the benefit. Tolerable risk is not zero risk; it lies between broadly acceptable and intolerable.

LOPA

Layer of protection analysis: initiating event frequency multiplied by the probability of failure on demand of independent protection layers gives the mitigated event frequency.

SIL levels

Safety integrity levels per IEC 61511 for low-demand mode: SIL 1 PFD 10^-1 to 10^-2, SIL 2 10^-2 to 10^-3, SIL 3 10^-3 to 10^-4, SIL 4 10^-4 to 10^-5.

Le Chatelier mixing rule

Estimates the lower flammability limit of a gas mixture from the LFLs and volume fractions of its components, using the reciprocal of the weighted sum.

BLEVE

Boiling liquid expanding vapour explosion: sudden catastrophic failure of a vessel containing pressurised liquid above its atmospheric boiling point, producing a fireball or blast.

EIA Ordinance Cap. 499

Hong Kong legislation requiring environmental impact assessments for designated projects. An Environmental Permit from EPD is needed before construction or operation.

Occupational exposure limit

Concentration of airborne contaminant averaged over a reference period (8-hour TWA or 15-minute STEL) that is believed safe for nearly all workers.

Hierarchy of controls

Order of preference for hazard control: elimination, substitution, engineering controls, administrative controls, then personal protective equipment as the last resort.

Ziegler–Nichols tuning

Closed-loop tuning using ultimate gain K_u and period P_u: K_c = 0.6·K_u, τ_I = P_u/2, τ_D = P_u/8 for a PID controller.

FOPDT model

First-order plus dead time transfer function K_p·e^(−θs)/(τs+1). The ratio θ/τ indicates controllability; higher values are harder to control.

Safety instrumented function

A protective loop comprising sensor, logic solver, and final element that brings the process to a safe state on demand. Its PFD is often dominated by the final element.

PREN formula

Pitting resistance equivalent number: %Cr + 3.3·%Mo + 16·%N. Values above 40 indicate suitability for aggressive chloride or seawater service.

Chloride SCC

Stress corrosion cracking of austenitic stainless steel in chloride environments, typically above about 60 °C. Mitigate with duplex grades, lower stress, or coatings.

Scope 1 emissions

Direct greenhouse gas emissions from sources owned or controlled by the organisation, such as fuel combustion in boilers, process emissions, and company vehicles.

HKIE Code of Conduct

Professional obligations: integrity, competence, confidentiality, disclosure of conflicts of interest, and placing public safety above commercial or personal interest.