Power Eng 2nd Class cheat sheet

Sensible heat: Q = m·c_p·ΔT; latent heat: Q = m·h_fg. Steam tables give h_fg = h_g − h_f at the saturation pressure.

Steam quality x = (h − h_f)/h_fg; for a throttling calorimeter, x = (h_2 − h_f1)/h_fg1 where state 2 is the superheated sample.

Rankine cycle efficiency = (h_1 − h_2) − (h_4 − h_3) divided by (h_1 − h_4), where 1 is turbine inlet, 2 turbine exhaust, 3 pump inlet, 4 pump discharge.

Conduction: q = kA·ΔT/L; cylindrical wall resistance R = ln(r_o/r_i)/(2πkL). Convection: q = hA·ΔT.

LMTD = (ΔT_1 − ΔT_2)/ln(ΔT_1/ΔT_2); counterflow is always equal to or better than parallel flow for the same terminal temperatures.

Overall heat transfer coefficient 1/U = 1/h_i + R_fouling,i + t/k + R_fouling,o + 1/h_o, referred to the same area.

Nozzle/steam flow: velocity increases and pressure falls in a converging-diverging nozzle once flow is choked at the throat (M = 1).

Second law: no cyclic device can convert all heat to work; Carnot efficiency = 1 − T_L/T_H with absolute temperatures.

Heat balance check: heat in (fuel × HHV + air enthalpy) minus stack loss, radiation loss, and blowdown loss equals useful steam output.

Centrifugal pump affinity laws: Q ∝ N, H ∝ N², P ∝ N³; for impeller trim, Q ∝ D, H ∝ D², P ∝ D³.

NPSH available = (p_suction − p_vapor)/(ρg) + static head − friction losses; cavitation occurs when NPSH_a falls below NPSH_r.

Pump operating point is the intersection of the pump curve and the system curve; throttling moves the system curve, VFD changes the pump curve.

Reciprocating compressor volumetric efficiency drops with high clearance volume, high compression ratio, and low suction temperature.

Compressor clearance volumetric efficiency ≈ 1 + C − C·(P_discharge/P_suction)^(1/n).

Steam turbine stage efficiency = actual enthalpy drop / isentropic enthalpy drop; use the Mollier chart between inlet and exhaust conditions.

Critical speed is the shaft speed where operating speed equals a natural frequency; run through it quickly and avoid continuous operation near it.

Diesel engine indicated power = P_mep × L × A × N × cylinders, with N in power strokes per second; mechanical efficiency = brake/indicated.

Governor droop = (no-load speed − full-load speed)/full-load speed × 100; isochronous governors have zero droop.

Theoretical air is the stoichiometric air for complete combustion; excess air = (actual air − theoretical air)/theoretical air × 100.

Flue gas CO₂ falls and O₂ rises as excess air increases; optimum excess air is the point where stack loss plus unburned loss is minimum.

Combustion air requirement: for a fuel with mass fractions C, H, S, O, air mass = 11.5C + 34.5(H − O/8) + 4.32S kg air per kg fuel (approx.).

Drum level shrink and swell occur on load increase and decrease respectively; low-water trip is a mandatory boiler safeguard.

Safety valve capacity must equal or exceed maximum boiler steaming capacity; set pressure is at or below design pressure.

Three-element feedwater control uses drum level, steam flow, and feedwater flow; it corrects level before the swell/swell transient misleads a single-element controller.

Boiler efficiency by the indirect method = 100 − (dry flue gas loss + moisture loss + unburned carbon + radiation + blowdown losses).

Furnace purge: prove airflow for the manufacturer's specified time before ignition, and prove flame by scanner before admitting fuel.

4–20 mA transmitter: measured span maps to 4 mA at zero and 20 mA at full scale; live zero allows open-circuit detection.

Control modes: proportional output = K_p·error; integral removes offset; derivative anticipates rate of change and amplifies noise.

PID tuning rules: Ziegler-Nichols ultimate gain method uses K_u and P_u; PID settings are K_p = 0.6K_u, T_i = P_u/2, T_d = P_u/8.

A control valve fails closed, open, or last position depending on actuator/spring arrangement; select fail-safe direction to match process hazard.

Three-way valve: mixing valve has two inlets and one outlet; diverting valve has one inlet and two outlets.

RTD resistance rises with temperature; thermocouple output is a small millivolt EMF and requires cold-junction compensation.

Interlocks must be proof-tested at defined intervals; a bypassed trip must be logged, time-limited, and approved by the responsible authority.

Flame scanner must discriminate between burner flame and hot refractory; a flame-out trip closes the fuel valve within the proven response time.

Three-phase power P = √3 × V_L × I_L × power factor for a balanced load; single-phase P = V × I × PF.

Synchronous speed N_s = 120f/P; induction motor slip = (N_s − N)/N_s and rises with load.

Motor full-load current is taken from the nameplate; conductor and overload sizing uses the applicable code percentage of FLC.

Star-delta starting reduces starting current and torque to one third of the direct-on-line values.

A VFD controls motor speed by varying frequency and voltage; below base speed it maintains constant V/f ratio to hold flux.

Motor protection: overload relay protects against sustained overcurrent, while short-circuit protection is provided by fuses or a circuit breaker.

Insulation resistance testing uses a megohmmeter; a falling trend across periodic tests is more meaningful than a single reading.

Lockout/tagout must isolate and prove de-energized every energy source, including control circuits and stored energy such as capacitors.

pH scale: below 7 acidic, above 7 alkaline; boiler water is held alkaline to protect steel, typically with coordinated phosphate/pH control.

Conductivity is used to estimate dissolved solids; blowdown rate is set to hold boiler water TDS within the manufacturer's limit.

Scale-forming ions (Ca, Mg) are removed by softening (ion exchange) or demineralization; hardness is expressed as mg/L as CaCO₃.

Oxygen pitting is controlled by mechanical deaeration plus chemical oxygen scavenger; the scavenger residual is measured and held in the specified range.

Caustic embrittlement (stress corrosion cracking) is avoided by maintaining a protective phosphate-to-alkalinity ratio and avoiding concentrated caustic in crevices.

Corrosion rate is often expressed in mils per year (mpy); 1 mpy equals 0.001 inch per year of metal loss.

Condensate return corrosion is usually caused by carbonic acid from CO₂; neutralizing amines or filming amines are used to control it.

Silica carryover into steam is limited by boiler pressure and steam purity; high-purity steam requires low silica and low carryover.

Refrigeration capacity: 1 ton = 12,000 Btu/h = 200 Btu/min = 3.517 kW.

Coefficient of performance, COP = refrigeration effect / work input; for a Carnot refrigerator COP = T_L/(T_H − T_L) with absolute temperatures.

Vapor-compression cycle: evaporation at low pressure absorbs heat; the compressor raises pressure and temperature; the condenser rejects heat.

Superheat at the evaporator outlet protects the compressor from liquid slugging; subcooling at the condenser outlet increases refrigeration effect.

High discharge pressure causes: high condensing temperature, fouled condenser, non-condensable gases, or overcharge.

Compressed air: free air delivery is measured at standard intake conditions; pressure drop in piping wastes energy because compressor power rises with discharge pressure.

Air dryer dew point must be below the lowest ambient temperature of the piping to prevent condensate; refrigerated dryers give about 2–10 °C dew point.

Psychrometrics: relative humidity = partial pressure of water vapor / saturation pressure at the same dry-bulb temperature.

Root cause analysis tools: 5 Whys, fishbone (Ishikawa), and fault tree; the goal is the underlying cause, not the immediate symptom.

Vibration analysis: imbalance shows 1× running speed; misalignment shows 2× and axial 1×; bearing defects show high-frequency impacts.

Preventive maintenance is calendar/usage based; predictive maintenance is condition based (vibration, thermography, oil analysis, ultrasound).

Oil analysis reports wear metals, water content, viscosity, and particle count; rising iron with stable viscosity suggests wear, not contamination.

A pump that loses discharge pressure with rising vibration should be checked for cavitation, air ingress, and a closed suction valve before overhaul.

Alignment: dial indicator or laser alignment to the manufacturer's tolerance; thermal growth must be compensated when the machine is at operating temperature.

Permit-to-work systems require isolation, gas testing, and a signed handover before hot work or confined-space entry.

Trending is the primary diagnostic tool: compare current readings against baseline and alarm limits rather than judging a single value.

Boiler and pressure vessel rules are typically enforced by the jurisdiction adopting a recognized code; the owner must know which edition is in force.

Periodic inspection intervals for boilers and pressure vessels are set by the jurisdiction and by the insurer; certificates must be current.

Safety valve set pressure, capacity, and testing records must be retained and traceable to the equipment file.

Relief valve discharge piping must be sized so that back pressure does not reduce valve capacity below the required flow.

Environmental permits define emission limits, monitoring methods, and reporting deadlines; exceedances require notification within the permitted time.

Refrigerant handling is regulated; technicians must hold the required certification and record recovery, leak checks, and disposal.

Confined-space entry requires atmospheric testing for oxygen, flammables, and toxics before entry and continuously during occupancy.

Management-of-change procedure: any alteration to equipment, process, or setpoints must be reviewed and approved before implementation.

Atmospheric hazards in confined spaces: oxygen below 19.5% or above 23.5%, flammable gas above 10% LEL, and toxic gas above exposure limit require entry prohibition.

Flash point is the lowest temperature at which a liquid gives off enough vapor to ignite; it is not the ignition temperature.

Flammable range is bounded by the lower and upper explosive limits (LEL/UEL); inerting or ventilation keeps the concentration outside that range.

Emergency shutdown sequence: trip fuel, isolate steam, maintain feedwater to protect the boiler, and alarm/evacuate per the site plan.

Spill response: stop the source, contain with booms or absorbent, notify per the plan, and prevent entry to drains and waterways.

Personal protective equipment is the last line of defense; engineering controls and administrative controls rank higher in the hierarchy of controls.

Fire classes: A ordinary combustibles, B flammable liquids, C electrical, D metals; the extinguishing agent must match the class.

Incident investigation: preserve the scene, record facts, interview witnesses separately, and report to the regulator within the required time.

Shift handover must record equipment status, open permits, abnormal conditions, and outstanding work orders; both parties sign.

Competency records for each operator must show training, authorization, and date; unqualified staff may not operate independently.

Key performance indicators for a plant include availability, heat rate, forced outage rate, and maintenance backlog.

Work order prioritization: safety-critical first, then production-critical, then planned maintenance; deferral requires documented risk acceptance.

Budget variance analysis compares actual against budget by cost center; labor, fuel, chemicals, and maintenance are typical line items.

Regulatory reporting calendar tracks inspection dates, emission reports, and certification renewals with assigned owners.

Effective toolbox talk covers the specific task hazard, the controls in place, and the stop-work authority of every worker.

Succession and cross-training plans reduce single-point dependency; each critical role should have a named backup.