Power Eng 2nd Class key terms

A measure of the total energy in a fluid that combines its internal energy with the flow work needed to push it through a system. Used to track energy changes across boilers, turbines, and heat exchangers.

The amount by which steam temperature exceeds its saturation temperature at a given pressure. Superheated steam contains no entrained moisture and is used to protect turbine blades from erosion.

The temperature at which a liquid boils at a given pressure, or at which vapor condenses. It rises as pressure rises, so a boiler's steam temperature is fixed by its operating pressure.

The energy absorbed or released when a substance changes phase without changing temperature, such as water boiling into steam. It is much larger than sensible heat for the same mass.

The idealized thermodynamic cycle describing steam power plants, comprising pumping, boiling, expansion through a turbine, and condensation. Efficiency gains come from higher steam pressure and temperature and lower condenser pressure.

A number expressing how readily heat moves between a fluid and a surface per unit area and temperature difference. It depends on fluid velocity, properties, and whether flow is laminar or turbulent.

Heat transfer through a solid material by molecular vibration, without bulk movement of the material. It is the dominant path for heat loss through boiler insulation and tube walls.

An allowance added to heat exchanger design calculations for deposits that build up on surfaces and reduce heat transfer. It represents the extra resistance expected over time between cleanings.

A pump that adds energy by spinning fluid outward from an impeller, converting velocity into pressure in the casing. It is the standard choice for high-volume boiler feed and cooling water service.

The margin of absolute pressure above a liquid's vapor pressure at the pump suction. Insufficient NPSH causes cavitation, which damages impellers and erodes performance.

The formation and collapse of vapor bubbles in a liquid when local pressure drops below vapor pressure. It produces noise, vibration, and pitting damage on pump impellers and turbine blades.

A graph of head versus flow rate for a given pump at a fixed speed. The operating point is where this curve intersects the system resistance curve.

An unstable condition in compressors or fans where flow reverses cyclically because discharge pressure exceeds what the machine can sustain. It causes violent vibration and can damage bearings and blades.

A bearing designed to carry axial loads along a rotating shaft, common in turbines and compressors. Failure causes rotor shift, which can trigger high-vibration trips and severe internal damage.

A rotational speed at which a shaft's natural frequency matches running speed, producing resonance and amplified vibration. Operators must pass through these bands quickly during startup and shutdown.

A boiler feedwater control strategy using steam flow, feedwater flow, and drum level signals. It compensates for shrink and swell so feedwater responds to true mass balance rather than level illusion.

Apparent changes in boiler drum level caused by pressure shifts that alter steam bubble volume in the water. Level can read falsely high or low even when water mass is unchanged.

The final control element regulating flow from the feed pump into the boiler. It must withstand high differential pressure and provide tight, stable positioning to keep drum level within limits.

An industrial computer that executes ladder or function-block logic to control equipment and interlocks. It reads sensors, drives outputs, and enforces permissives that protect boilers and rotating machinery.

A hardwired or programmed condition that prevents or forces an action to protect equipment and people. Examples include low-water cutoff trips and flame failure shutdowns.

A sensor that verifies a burner flame is present by detecting ultraviolet or infrared radiation. It signals the burner management system to trip fuel if flame is lost.

The safety system that sequences burner startup, monitors flame, and shuts off fuel on unsafe conditions. It enforces purge, light-off, and trip requirements defined by code.

A forced airflow period before ignition that clears combustible gases from the furnace and gas passages. It must run at specified airflow for a set time to prevent explosion on light-off.

Burning fuel with exactly the theoretical amount of air needed for complete oxidation. In practice boilers run with excess air to ensure complete combustion and limit carbon monoxide.

Air supplied beyond the theoretical requirement for complete combustion. Too little produces carbon monoxide and smoke; too much wastes heat by raising stack losses.

Measurement of oxygen, carbon monoxide, and carbon dioxide in exhaust gases to judge combustion efficiency. Oxygen readings are used to trim excess air to the optimum.

The sub-atmospheric pressure maintained in a steam condenser by removing air and condensing steam. Better vacuum lowers turbine exhaust pressure and raises cycle efficiency.

Unwanted entry of air into a condenser or vacuum system through seals, joints, or fittings. It degrades vacuum, raises dissolved oxygen, and increases back pressure on the turbine.

A vessel that heats feedwater and strips dissolved oxygen and other gases by steam scrubbing. Removing oxygen protects boiler tubes and downstream piping from corrosion.

Localized corrosion caused by dissolved oxygen attacking steel at discrete points, forming deep pits. It is prevented by deaeration and chemical oxygen scavengers.

Hard mineral deposits such as calcium carbonate that form on heat transfer surfaces. Scale insulates tubes, raises metal temperatures, and can cause overheating failures.

Deliberate removal of boiler water to control dissolved solids and sludge concentration. Excess blowdown wastes energy; too little leads to carryover and foaming.

Contamination of steam by boiler water droplets or foam, carrying dissolved solids into superheaters and turbines. It causes deposits, corrosion, and loss of superheat.

The temperature rise of refrigerant vapor above its saturation point at the evaporator outlet. It confirms complete evaporation and protects the compressor from liquid slugging.

The amount by which liquid refrigerant at the condenser outlet is cooled below its saturation temperature. It indicates adequate charge and ensures solid liquid reaches the expansion device.

Operating multiple compressor stages or units in series or parallel to match load and pressure ratio. Staging improves efficiency and avoids surging at low demand.

A procedure that isolates energy sources and applies locks and tags before maintenance, preventing accidental startup or release of stored energy. It is a core requirement for safe equipment work.

Entry into a space with limited access and poor ventilation that may contain hazardous atmosphere. It requires testing, permits, attendants, and rescue provisions before entry.

Continuous or periodic measurement of machine vibration to detect imbalance, misalignment, bearing wear, and looseness. Trending allows faults to be corrected before failure.

A networked control platform with distributed processors and operator workstations that manages plant loops and alarms. It provides centralized monitoring while keeping control local to equipment areas.