• Adsorption: The binding of fluids on the surface of a solid or liquid. It is important to note that adsorption differs from absorption, which is the process of a substance dissolving into another substance.
  • Aftercooler: A heat exchanger that cools the air that passed through a turbocharger and makes the air denser.
  • Air Handler: A device used for heating and air conditioning systems. Air is blown across heating/cooling elements to attain a desired temperature and is then sent throughout the building.
  • Alternator: The part of the generator that produces electrical output from the mechanical input supplied by the engine.

  • B

  • Back Work Ratio (bwr): The ratio of total turbine power to the power that was used to operate the compressor.
  • Blowdown: The removal of liquid or solid contaminants from a process or storage vessel by the use of pressure.

  • C

  • CHP (Combined Heat and Power system): Systems that produce multiple forms of useful energy from sequential and simultaneous generation derived from mechanical and thermal loads, also known as cogeneration.
  • Compression Ratio: The ratio of the maximum volume formed in the cylinder to the minimum volume.
  • Compressor Choke Point: When the flow in the compressor reaches Mach 1 at the blade throat, a point where no more flow can pass through the compressor.
  • Condensate Pump: A type of pump used to pump the condensate produced in a thermodynamic system.
  • Condenser: A device used to condense vapor into liquid, usually through cooling or pressurization.
  • Counterflow: When two fluids in a heat exchanger run parallel to each other in different directions.
  • Crankshaft: The part of an engine that translates linear piston motion into rotation.
  • Crossflow: When two fluids in a heat exchanger run perpendicular to each other.

  • D

  • Deaerator: An apparatus that removes oxygen and other dissolved gases from feedwater.
  • Dew Point: The temperature at which humidity in the air condenses to liquid water.
  • Diffuser Passages: Passageways within a centrifugal compressor that convert kinetic energy into static pressure. The passageways are narrow at the beginning and then widen.
  • Dry Bulb Temperature: The ambient air temperature measured by a thermometer.

  • E

  • Economizer: A heat exchange device incorporated into a system/process to increase overall efficiencies. Economizers can be found on both chillers and boilers though they operate differently.

  • F

  • Feed Pump: A pump that supplies feedwater to a boiler.
  • Feedwater: Water supplied to a boiler.
  • Feet Water: Unit of pressure (in H2O at 4 degrees Celsius). It is converted to the standard SI unit Pa by multiplying its value by 249.082.
  • Flash Chamber: A tank located between the expansion valve and evaporator in a refrigeration system that separates liquid from the gas formed in the expansion valve.
  • Flue Gas: Combustion gases from the burning of a fuel within a boiler.
  • Flue Gas Recirculation: The diversion of some of the flue gas exiting the furnace of a boiler back into the combustion chamber to reduce emissions.

  • G

  • Generator: A device that converts mechanical energy, obtained from an external source, to electrical energy.

  • H

  • HRSG (Heat Recovery Steam Generator): A heat exchanger that uses the hot exhaust from a gas turbine to generate steam.

  • I

  • IGV (Inlet Guide Vanes): Pitch variable blades used to ensure that the air enters the first stage rotors at the desired flow angle.
  • Impeller: A rotating component within a centrifugal compressor that draws in refrigerant and accelerates it.

  • J



  • Louvers: A set of horizontal slats that can be adjusted to keep out rain, direct sunlight, and noise while permitting air into a structure.
  • Low Water Condition: When a boiler is not receiving the amount of feedwater necessary to keep it running safely. This condition can cause the boiler pressure to rise considerably and make the boiler explode.

  • M

  • Mach Number: A dimensionless number that represents the speed of an object divided by the local speed of sound. The speed of sound is known as Mach 1 (768mph).
  • Makeup Water: Water that is supplied to compensate for lost water in the system due to evaporation and/or leakages, etc.
  • MBTUH: Sometimes referred to as MMBTUH, is a measure for the rate of heat transfer commonly used in boiler applications. 1 MBTUH is equal to 1,000,000 Btu/h.
  • Mud Drum: The lower drum on a water tube boiler where the feedwater will enter.

  • N

  • No. 2 Fuel Oil: One of the fuel options used for combustion in boilers. It is also referred to as diesel fuel oil or distillate fuel oil.
  • NOx (Nitrous Oxides): A product formed during combustion that is composed of nitrogen and oxygen.

  • O


  • Peak Shaving: Decreasing the amount of energy purchased from a utility company during peak usage hours when charges are highest.
  • Pitting: Local corrosion that can create holes in metal.
  • Pressure Relief Valve: An inline device on a pipe used to reduce the pressure of a fluid to a desired level.
  • Prime Mover: A machine that transforms energy into work.
  • Psia (Pounds per square inch absolute): The measurement of pressure relative to a vacuum.
  • Psig (Pounds per square inch gage): The measurement of pressure relative to atmospheric pressure (psig=psia-14.7).
  • Psychrometrics: Ways of determining physical and thermodynamic properties of gas-vapor mixtures.
  • Pump Head: A specific measurement of liquid pressure. Pump head is the height at which the pump can deliver.

  • Q


  • Risers and Downcomers: Tubes connecting the steam drum and mud drum on a water tube boiler.
  • Rotor: A row/rows of rotating blades in a compressor.

  • S

  • SCR (Selective Catalytic Reduction): A process in which NOx emissions from a turbine are reduced through reaction with ammonia to produce nitrogen gas and water.
  • Shell and Tube Heat Exchanger: A device that consists of an outer pressure vessel containing one fluid with bundles of tubes inside of it that contains a different (usually) fluid at a different temperature.
  • Sootblower: A system for removing the soot that has built up on the furnace tubes of a boiler.
  • SOx (Sulfur Oxides): A product consisting of sulfer and oxygen formed during combustion.
  • Spud Burner: A device used to bring in fuel to a furnace.
  • Stator: A row of stationary airfoils in a compressor.
  • Steam Drum: The upper drum on a water tube boiler from which the saturated steam exits.
  • Steam Traps: Devices inline with a steam pipe that will allow only condensate to pass.
  • Superheater: A device that converts saturated steam to superheated steam to decrease the chances that the steam will condense inside the steam turbine.

  • T

  • Ton: A measure of energy transfer. A ton is often used for performance ratings of refrigeration systems. 1 ton equals 12,000 Btu/h.
  • Turbocharger: A centrifugal compressor, driven by a small turbine powered by exhaust-gas from an engine or turbine, which boosts the air intake pressure.

  • U


  • Volute: A chamber on the outskirts of a centrifugal compressor in which the compressed vapor is collected.

  • W

  • Wet Bulb Temperature: The lowest temperature to which an object may be cooled solely through the process of evaporation.
  • Wet Deck: A series of cascading metal sheets that increase the exposed surface area over which water flows to increase the cooling rate.

  • X