Power Engineering Dictionary

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MAGNESIUM - A scale forming element found in some boiler feed water.

MAGNETIC FIELD - The region within which a body or current experiences magnetic force.

MAGNETIC FLUX - The rate of flow of magnetic energy across or through a surface.

MAGNETIC IRON OXIDE (Fe3O2) - Partially oxidized iron.

MAGNETIC PARTICLE INSPECTION - A nondestructive method of inspection for determining the extent of surface cracks and similar imperfection in ferromagnetic materials.

MAGNETIC POLE -The area on a magnetized part at which the magnetic field leaves or enters the part. It is the point of maximum attraction in a magnet.

MAGNETIC REFRIGERATION - Where very low temperatures are obtained by using paramagnetic salts with magnets.

MAKEUP WATER - Water fed to a system to replace that which is lost - for example, water fed to a boiler to replace that lost as steam or condensate; water fed to a cooling tower to replace that lost by evaporation, drift, or other causes.

MALLEABILITY - The characteristic of metals that permits plastic deformation in compression without fracture.

MANGANESE - A metallic element occasionally found in very small amounts as an impurity in well-water supplies.

MANIFOLD, SERVICE - Chamber equipped with gauges and manual valves, used by service technicians to service refrigerating systems.

MANIFOLDING - A method of circulating the refrigerant through separate rows of tubes and mostly used with direct-expansion or dry evaporators.

MANOMETER - An instrument for measuring pressures: especially a U-tube partially filled with a liquid, usually water, mercury, or a light oil, so constructed that the amount of displacement of the liquid indicates the pressure being exerted on the instrument.

MANUAL FROST CONTROL - Manual control used to change operation of refrigerating system to produce defrosting conditions.

MASS - The quantity of matter in a body as measured by the ratio of the force required to produce a given acceleration, to the acceleration.

MASTER (CENTRAL) CONTROL - Control of all outlets from one point.

MCM - Thousand circular mill used to describe large wire sizes.


MECHANICAL SEALS - A mechanical device used to control leakage from the stuffing box of a pump. Mechanical seals are usually made of two flat surfaces, one of which rotates on a shaft. The two flat surfaces are of such tolerances as to prevent the passage of water between them.

MECHANICAL WEAR - Removal of material due to mechanical process under conditions of sliding, rolling, or repeated impact. Included are abrasive wear, fatigue wear and adhesive wear, but not the corrosive and thermal wear.

MELTING POINT - For a given pressure, the temperature at which the solid and liquid phases of the substance are in equilibrium.

MELTING POINT - Temperature at atmospheric pressure at which a substance will melt.

MEMBRANE - A barrier, usually thin, that permits the passage only of particles up to a certain size or of special nature.

MEMBRANE - A thin sheet or layer.

MERCAPTAN - A compound chemically similar to alcohol, with sulfur replacing the oxygen in the chemical structure. Many mercaptans have an offensive odor and are used as deodorants in natural gas.

METALLURGICAL FACTOR - The condition of the metal, such as inclusions, chemical segregationís, cold work and others, which have an impact upon the rate of electrochemical corrosion rates.

MICA - A silicate material used with high pressure gauge glasses on boilers.


MICROBAR - A unit of pressure equal to 1 dyne/cm2 (one millionth of the pressure of the atmosphere).

MICRO FILTRATION - A membrane filtration process, which forces water through a porous barrier. Pores are usually between 0.1 to 20 m m, when used for water purification. For filtering purposes, pore sizes are .045 m m.

Micron - A unit of length, the thousandth part of 1 mm of the millionth of a meter.

Microprocessor - A small computer used in load management to analyze energy demand and consumption such that loads are turned on and off according to a predetermined program.

MILD STEEL - A low-carbon steel of ordinary production.

MILL SCALE - A natural black iron oxide coating loosely adhering to the interior of new piping or tubes.

MINERAL - A naturally occurring inorganic substance having specified chemical composition and crystalline structure.

MISCIBILITY - The ability of two liquids, not mutually soluble, to mix.

MIX BED DEMINERALIZER - Having a mixture of cation and anion exchange resin in the same housing.


MIXTURE - A physical blend of two or more substances.

MODULATING - Type of device or control which tends to adjust by increments (minute changes) rather than by either "full on" or "full off" operation.

MODULATING CONTROL - A mode of automatic control in which the action of the final control element is proportional to the deviation, from set point, of the controlled medium.

MODULATING REFRIGERATION CYCLE - Refrigerating system of variable capacity.

MODULUS OF ELASTICITY (E) - The measure of rigidity or stiffness of a material.

MOISTURE INDICATOR - Instrument used to measure moisture content of a refrigerant.

MOLLIER DIAGRAM - An enthalpy-entropy or enthalpy-pressure chart showing the thermodynamic properties of a fluid.

MONOMER - A molecule, usually an organic compound, having the ability to join with a number of identical molecules to form a polymer.

MOTOER CONTROL CENTER - A single metal enclosed assembly containing a number of motor controllers and possibly other devices such as switches and control devices.

MUD DRUM - A pressure chamber of a drum or header type located at the lower extremity of a water tube boiler and fitted with blowoff valve.

MULLION HEATER - Electrical heating element mounted in the mullion. Used to keep mullion from sweating or frosting.

MULTIPLE STAGE COMPRESSOR - Compressor having two or more compressive steps. Discharge from each step is the intake pressure of the next in series.

MULTIPLE SYSTEM - Refrigerating mechanism in which several evaporators are connected to one condensing unit.

MULTI-SHAT GAS TURBINE - A gas turbine having more than one shaft, like the dual shaft arrangement.

MULTISTAGE COMPRESSION REFRIGERATION SYSTEM - Where the refrigerant is vaporized and condensed alternately and is compressed in the vapor phase.

MULTISTAGE THERMOSTAT - A thermostat which controls auxiliary equipment for heating or cooling in response to a greater demand for heating or cooling.

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