ENADE Engenharia Química flashcards

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

Extent of reaction

Variable ξ quantifying how far a reaction proceeds; species moles equal initial moles plus stoichiometric coefficient times ξ. Closes reactive mass balances with several simultaneous reactions.

Carnot efficiency

Maximum thermal efficiency between two reservoirs, equal to one minus the ratio of cold to hot absolute temperatures. Any real heat engine performs below this limit.

Fugacity equality

At phase equilibrium each component has equal fugacity in every phase present. For ideal mixtures it reduces to Raoult's law relating partial pressure and mole fraction.

Reynolds number

Dimensionless ratio of inertial to viscous forces, density times velocity times diameter divided by viscosity. Pipe flow is laminar near 2100 and turbulent above about 4000.

Darcy-Weisbach equation

Pressure drop in a pipe equals friction factor times length over diameter times dynamic pressure. Friction factor comes from the Moody chart or Colebrook equation.

Chilton-Colburn analogy

Links momentum, heat, and mass transfer through j-factors: friction factor over two equals jD equals jH. Valid for turbulent flow over common geometries.

NPSH and cavitation

Available net positive suction head must exceed the pump's required value. Otherwise local pressure falls below vapor pressure, forming bubbles that collapse and damage the impeller.

Arrhenius equation

Rate constant equals pre-exponential factor times exponential of minus activation energy over gas constant times temperature. Plotting log k against inverse temperature gives activation energy.

CSTR design equation

Reactor volume equals molar feed rate times conversion divided by the reaction rate evaluated at outlet conditions. Because it operates at outlet composition, it needs more volume than a plug flow reactor.

Half-life first order

Time for reactant concentration to halve equals natural log of two divided by the rate constant. It is independent of initial concentration, unlike higher-order reactions.

Thiele modulus

Dimensionless number comparing intrinsic reaction rate to intraparticle diffusion rate. Large values mean strong diffusion limitation and effectiveness factor well below one.

Relative volatility

Ratio of equilibrium constants of two components; measures ease of distillative separation. Values near one require many stages or alternative separation methods.

Fenske equation

Gives minimum theoretical stages at total reflux from relative volatility and product compositions. Used as a first estimate before rigorous distillation design.

Kremser equations

Analytical relations for absorption and stripping stages assuming constant flow rates and equilibrium line. Estimate stage count or outlet composition quickly.

Cake filtration equation

Constant-pressure filtration obeys a quadratic relation between filtrate volume and time. Plotting time over volume against volume yields cake and medium resistances.

PID controller

Output combines proportional, integral, and derivative action on error. Proportional band equals one hundred divided by controller gain, expressed in percent.

FOPDT model

First-order plus dead time transfer function has gain, time constant, and delay. Ziegler-Nichols and other tuning rules use these three parameters.

Integral windup

Integral term accumulates while actuator saturates, causing overshoot when control resumes. Prevented by clamping or back-calculation anti-windup schemes.

Cascade control

Inner loop controls a fast secondary variable while outer loop sets its setpoint. Requires inner loop to be substantially faster than the outer loop.

PREN

Pitting resistance equivalent number computed from chromium, molybdenum, and nitrogen content. Higher values indicate better resistance to chloride pitting in stainless steels.

Cathodic protection

Makes the protected structure the cathode using sacrificial anodes or impressed current. Prevents corrosion of buried and submerged steel equipment.

Stress corrosion cracking

Cracking requiring susceptible alloy, tensile stress, and specific corrosive environment simultaneously. Chlorides plus austenitic stainless steel is a classic case.

Corrosion allowance

Extra wall thickness added to equipment design to compensate for expected metal loss over service life. Determined from corrosion rate and inspection interval.

HAZOP study

Systematic review applying guide words to process parameters to identify deviations and their consequences. Requires multidisciplinary team and accurate piping and instrumentation diagrams.

Inherent safety hierarchy

Order of preference: minimize, substitute, moderate, simplify. Eliminates hazards at the source rather than relying on add-on protective systems.

LOPA

Layer of protection analysis quantifies risk reduction from independent protection layers. Compares mitigated frequency against tolerability criteria for each scenario.

Pinch analysis

Composite curves identify minimum hot and cold utility targets and the pinch temperature. Heat recovery is maximized by avoiding transfer across the pinch.

Haber-Bosch process

Ammonia synthesis from nitrogen and hydrogen over iron catalyst at high pressure and moderate temperature. Exothermic equilibrium favors low temperature and high pressure.

Michaelis-Menten kinetics

Enzyme rate equals maximum rate times substrate concentration divided by Michaelis constant plus substrate. Lineweaver-Burk linearization estimates both parameters.

Monod growth model

Specific growth rate equals maximum rate times substrate concentration over half-saturation constant plus substrate. Analogous to Michaelis-Menten enzyme kinetics.

Transesterification biodiesel

Triglycerides react with methanol using basic catalyst to form fatty acid methyl esters and glycerol. Glycerol recovery affects process economics.

Precautionary principle

Absence of full scientific certainty does not justify postponing cost-effective measures against serious or irreversible environmental harm. Central to environmental regulation debates.

Life Cycle Assessment stages

Standardized phases are goal and scope, inventory, impact assessment, and interpretation. Used to compare environmental burdens of products and processes.

Polluter-pays principle

Party responsible for contamination bears prevention and remediation costs. Basis for environmental liability and effluent charge schemes.

Validity and soundness

A valid argument's conclusion follows from premises; soundness additionally requires true premises. Deductive validity concerns form, not factual truth.

Correlation versus causation

Statistical association does not prove one variable causes another. Confounders, reverse causality, and chance must be excluded before causal claims.

Cohesion and coherence

Cohesion links sentences through pronouns and connectives; coherence is overall logical consistency with purpose. Both are required for readable technical text.

Conflict of interest

Situation where a secondary interest could improperly influence professional judgment. Disclosure and recusal are standard remedies in engineering practice.

Whistleblowing conditions

Disclosure is ethically justified when it prevents imminent serious harm and internal channels failed or are unsafe. Documentation and proportionality guide the action.

Informed consent

Affected parties must understand risks, alternatives, and uncertainties before agreeing. Communication must match the audience's language and literacy.

Excess air

Percentage of oxygen supplied beyond stoichiometric requirement for complete combustion. Measured from flue gas analysis and affects efficiency and emissions.

Degrees of freedom

Difference between independent equations and unknown variables in a balance problem. Zero means solvable; negative means over-specified or inconsistent.

Lumped capacitance method

Valid when Biot number is below about 0.1; assumes uniform body temperature. Temperature decays exponentially toward ambient with a time constant.

Fouling resistance

Additional thermal resistance from deposits on heat transfer surfaces. Adds in series with wall and film resistances, lowering overall coefficient over time.

Levenspiel plot

Graph of reciprocal reaction rate against conversion. Area under the curve gives plug flow volume; rectangle gives continuous stirred tank volume.

Runaway reaction

Thermal instability when heat generation grows faster than heat removal. Prevented by cooling capacity, feed control, and emergency relief design.

Azeotrope

Mixture whose vapor and liquid compositions are equal at equilibrium. Cannot be separated by simple distillation; requires pressure swing, extraction, or membranes.

Concentration polarization

Solute buildup at membrane surface reduces driving force and flux. Mitigated by higher crossflow velocity and periodic cleaning.

Gain and phase margin

Stability measures from Bode plots indicating how much gain or phase change causes instability. Positive margins indicate a stable closed loop.

Sequential modular simulation

Simulation approach solving unit modules one at a time, tearing recycle streams. Contrasts with equation-oriented methods that solve all equations simultaneously.

Galvanic corrosion

Dissimilar metals in contact in an electrolyte cause the more active metal to corrode faster. Avoid by selecting compatible materials or electrical isolation.

Creep

Time-dependent deformation under sustained load at high temperature, significant above about 0.4 of melting temperature. Design uses creep-rupture data.

Flammability limits

Lower and upper concentration bounds of fuel in air that support combustion. Operation outside these limits or inerting prevents fire and explosion.

Net present value

Sum of discounted future cash flows minus initial investment. Positive value at the hurdle rate indicates an economically viable project.

Chemostat operation

Continuous bioreactor at steady state where growth rate equals dilution rate. Washout occurs when dilution exceeds maximum specific growth rate.

Anaerobic digestion stages

Hydrolysis, acidogenesis, acetogenesis, and methanogenesis convert organic matter to methane-rich biogas. Each stage has distinct microbial populations and optimal conditions.