Engineering Letter Glossary - New York Blower

INSTABILITY the point of operation at which a fan or systemwill “hunt” or pulse; common in FC fans and some other fantypes where the point of operation is left of the peak of thestatic-pressure curve.INTERFERENCE FIT specified interference between matingparts requiring either a press fit or a shrink fit.KELVIN see Absolute Temperature.KILOPASCAL Kpa; metric pressure unit; one inch watergauge is 0.24836 Kpa.KILOWATT Kw; measure of power equal to 1.34 horsepower.L-10 BEARING LIFE the theoretical number of hours afterwhich 90% of the bearings subjected to a given set of conditionswill still be in operation; also known as B-10.LAMINAR FLOW gas or fluid in parallel layers with somesliding motion between the layers.LAMINATE the total structure of the FRP part. For nybcorrosion-resistant products it consists of a resin-rich surfaceand a thickness of glass-reinforced resin as required forstructural strength.LITHIUM a soft element in the alkali metal group commonlyused as a lubricant base.LOGARITHM a mathematical term used as a basis of thedecimal system. A logarithm is the exponent of 10 whichproduces a given number. For instance the log of 100 is 2 since:log 10 100 = 2 10 2 = 100LOUVER a device comprised of multiple blades which, whenmounted in an opening, permits the flow of air but inhibits theentrance of undesirable elements.LOWER EXPLOSIVE LIMIT the lowest percentage of anelement in otherwise standard air that will explode whenexposed to a spark.MACH NUMBER a fraction of the speed of sound; used in fanengineering where air moving at a mach number of 0.9, or 9/10the speed of sound, begins to deviate from the fan laws.MAKE-UP AIR a ventilating term which refers to thereplacement of air lost because of exhaust air requirements.MANOMETER instrument for measuring pressure, u-shaped,and partially filled with liquid, either water, light oil, ormercury.MAXIMUM CONTINUOUS RATING the point at which thefan is expected to operate.MICROBAR a unit of pressure equal to one-millionth of anatmospheric pressure; 0.0000 146 PSI.MICRON a unit of measure equal to one-millionth of a meter,commonly used in dust collection and material-handlingapplications to designate particle size.MIL a unit of measure equal to 25 microns or one-thousandthof an inch.MIXED-FLOW FAN a fan where the airflow is primarilyaxial and is changed by the blade shape to induce a small radialflow at the discharge.MOLECULAR WEIGHT the weight of a molecule expressedon a scale in which the carbon isotope weighs exactly 12.0;represents the sum of the weights of all the atoms in a molecule.As air is a gas mixture, it does not have a true molecularweight but an apparent molecular weight determined by thepercentages of the molecular weights of each gas in acomposition.NACE National Association of Corrosion Engineers.NATURAL FREQUENCY the frequency at which a componentor system resonates.NEC National Electrical Code.NEMA the National Electrical Manufacturers Association;the trade association establishing standards of dimensions,ratings, enclosures, insulation, and other design criteria forelectric motors.NOISE CRITERIA a way for an architect to specify themaximum permissible sound-power level in each of the eightoctave bands. NC curves give, in a graphical form, maximumpermissible intensity per octave band.OCTAVE BANDS ranges of frequencies. These octave bandsare identified by their center frequencies (63, 125, 250, etc.).OHM a measure of electrical resistance. A wire in which onevolt produces a current of one ampere has a resistance of oneOhm.OPPOSED-BLADE DAMPER a type of damper whereadjacent blades rotate in the opposite direction.OSHA Occupational Safety and Health Administration.OSI ounces per square inch; a unit of pressure equal to onesixteenthPSI or 1.733 inches of water.PARALLEL-BLADE DAMPER a type of damper where theblades rotate in the same direction.PARALLEL FANS two or more fans which draw air from acommon source and exhaust into a common duct or plenum. Aparallel fan arrangement is generally used to meet volumerequirements beyond that of single fans. Two identical fans inparallel will effectively deliver twice the rated flow of any oneof the fans at the same static pressure.PERMANENT SPLIT CAPACITOR MOTOR very low startingtorque. Performance and applications similar to shaded polebut more efficient, with lower line current and higher horsepowercapabilities.pH a symbol as part of a logarithmic designation to indicateacidity or alkalinity on a scale from 0 to 14; pH7 is taken asneutral, 6 to 0 increasingly acid, 8 to 14 increasingly alkaline.Page 5