DEFINATIONS

Air Cleaner: A device designed for the purpose of removing, atmospheric air-borne impurities such as dusts, gases, vapors, fumes and smokes (Air cleaners include air washers, air filters, electrostatic pre-capacitors and charcoal filters.)

Air Filter: An air cleaning device to remove light particulate loadings from normal atmospheric air before introduction into the building. Usual range: Loadings up to 3 grains per thousand cubic feet (0.003 grains per cubic foot). Note: Atmospheric air in heavy industrial areas and in-plant air in many industries have higher loadings than this and dust collectors are then indicated for proper air cleaning.

Air Horsepower: The theoretical horsepower required to drive a fan if there were no losses in the fan, that is, if its efficiency were 100%.

Air Standard: Dry air at 10 7 and 20.02 in (Ng) barometer. This is substantially equivalent to 0.075

lb/cu it. Specific heat of dry air = 0.24 BTU/1b/F.

Brake Horsepower: The horsepower actually required to drive a fan. This includes the energy losses in the fan and can he determined only by actual test of the fan. (This does not include the drive losses between motor and fan).

Capture Velocity: The air velocity at any point in front of the hood or at the hood opening necessary to overcome opposing air currents and to capture the contaminated air at that point by causing it to flow into the hood.

Coefficient of Entry: The actual rate of flow caused by a given hood static pressure compared to the theoretical flow which would result if the static pressure could be converted to velocity pressure with 100% efficiency. It is the ratio of actual to theoretical flow.

Comfort Zone (Average): The range of effective temperatures over which the majority (50 per cent or more) of adults lee) comfortable.

Convection: The motion resulting, in a fluid from the differences in density and the action of gravity. I heat transmission this meaning, has been extended to include both forced and natural motion and circulation.

Density: The ratio of the mass of a specimen of a substance to the volume of the specimen. The mass of a unit volume of a substance. When weight can be used without confusion, as synonymous with mass, density is the weight of a unit volume of a substance,

Dust: Small solid particles created by the breaking up of larger particles by processes such as crushing, grinding, drilling, explosions, etc. Dust particles already in existence in a mixture of materials may escape into the air through such operations as shoveling, conveying, screening, sweeping, etc.

Dust Collector :  An air cleaning device to remove heavy particulate loadings from exhaust systems before discharge to outdoors. Usual range: Loadings 0.003 grains per cubic foot and higher.

Entry Loss: Loss in pressure caused by air flowing into a duct or hood. (Inches H20).

Fumes: Small solid particles formed by the condensation of vapors of solid materials.

Gases: Formless fluids which tend to occupy an entire space uniformly at ordinary temperatures and pressures.

Specific Gravity: The ratio of the mass of a unit volume of a substance to the mass of the same volume of standard substance at the same temperature. For gases, dry air, at the same temperature and pressure as the gas, is often taken as the stand-and substance.

Hood: A shaped inlet designed to capture contaminated air and conduct it into the exhaust duct system.

Absolute Humidity: The weight of water vapor per unit volume, pounds per cubic foot or grams per cubic Centimeter

Relative Humidity : The ratio of the actual partial pressure of the water vapor in a space to the saturation pressure of pure water at the same temperature.

Inch of Water: A unit of pressure equal to the pressure exerted by a column of liquid water one inch high at a standard temperature.

Lower Explosive Limit: The lower limit of flammability or explosibility of a gas or vapor at ordinary ambient temperatures expressed in per cent of the gas or vapor in air by volume. This limit is assumed constant for temperatures up to 250 F. Above these temperatures, it should be decreased by a factor of 0.7 since explosibility increases with higher temperatures.

Manometer: An instrument for measuring pressure; essentially 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.

Micron: A unit of length, the thousandth part of 1 mm or the millionth of a meter, (approximately 1/25,000 of an inch).

Minimum Design Duct Velocity: Minimum air velocity required to move the particulates in the air stream, fpm

Mists: Small droplets of materials that are ordinarily liquid at normal temperature and pressure.

Plenum: Pressure equalizing chamber.

Atmospheric Pressure: The pressure due to the weight of the atmosphere. It is the pressure indicated by a barometer.

Standard Atmospheric Pressure or Standard Atmosphere is the pressure of 29.92 inches of mercury.

Static Pressure: The potential pressure exerted in all directions by a fluid at rest. For a fluid in motion it is measured in a direction normal to the direction of flow. Usually expressed in inches water gauge when dealing with air. (The tendency to either burst or collapse the pipe.)

Total Pressure: The algebraic sum of the velocity pressure and the static pressure (with due regard to sign).

Vapor Pressure: The pressure exerted by a vapor. If a vapor is kept in confinement over its liquid so that the vapor can accumulate above the liquid, the temperature being held constant, the vapor pressure approaches a fixed limit called the maximum or saturated, vapor pressure, dependent only on the temperature and the liquid. The term vapor pressure is sometimes used as synonymous with saturated vapor pressure.

Velocity Pressure: The kinetic pressure in the direction of flow necessary to cause a fluid at rest to flow at a given velocity. Usually expressed in inches water gauge.

Thermal Radiation: The transmission of energy by means of electromagnetic waves of very long wave length. Radiant energy of any wave length may, when absorbed, become thermal energy and result in an increase in the temperature of the absorbing body.

Slot Velocity: Linear flow rate of contaminated air through slot, fpm.

Smoke: An air suspension (aerosol) of particles, usually but not necessarily solid, often originating in a solid nucleus, formed from combustion or sublimation.

Effective Temperature: An arbitrary index which combines into a single value the effect of temperature, humidity and air movement on the sensation of warmth or cold felt by the human body. The numerical value is that of the temperature of still, saturated air which would induce an identical sensation.

Wet-Bulb Temperature: Thermodynamic wet-bulb temperature is the temperature at which liquid or solid water. by evaporating into air, can bring the air to saturation adiabatically at the same temperature. Wet-bulb temperature (without qualification) is the temperature indicated by a wet-bulb psychrometer constructed and used according to specifications.

Threshold Limit Values (TLV): The values for air borne toxic materials which are to be used as guides in the control of health hazards and represent time weighted concentrations to which nearly all workers may be exposed 8 hours per day over extended periods of time without adverse effects.

Transport Velocity: Minimum Design Duct Velocity.

Vapor: The gaseous form of substances which are normally in the solid or liquid state and which can be changed to these states either by increasing the pressure or decreasing the temperature.