Air pressure measurement

Optimum atomization is achieved by fine adjustment of the air cap and atomization air pressure measured at the nozzle. The binder solution is delivered to the nozzle port through a spray lance and tubing. The peristaltic- or positive-displacement pump is commonly used to pump the binder solution. The pneumatically controlled nozzle needle prevents the binder liquid from... 

The unit used to compare the computer line s pressure measurement readings with equipment air pressure measurements has not been calibrated. Additionally there has been no periodic maintenance to assure that the unit is operating appropriately. The issue becomes even more critical because the. .. computer system is not validated. It is essential that this unit. .. be accurate and reliable. [FDA Warning Letter, 1999]... 

Atmosphere A metric unit of measurement of pressure equal to 1.013250 x l.OE+06 dynes/cm or 1.013250 X l.OE+05 pascals, which is the air pressure measured at mean sea level. It has a dimension of unit of force per unit of area. Used to denote the pressure of gases, vapors, and liquids. Also called atm, standard atmosphere, and std atm. 

Pressure Measurements, Methods, Fig. 2 (a) Schematics of liquid pressure measurement, (b) Schematics of air pressure measurement, (c) Snapshot of liquid pressure measurement in microchannel P = 7,000 Pa), (d)... 

Snapshot of air pressure measurement in microchannel P = 78,559 Pa) (Reprinted from [12], with permission from The Royal Society of Chemistry)... 

The measurement of furnace pressure on both pressurized and suction-type units is required to assure that design pressures of the casing or containment are not exceeded. Some form of differential gas- or air-pressure measurement, in conjunction with time lapse, is required as an indication that the setting has been adequately purged prior to firing. This is a necessary operating guide to assure a proper fuel-air ratio at the burners. 

To illustrate the air pressure measured by a meteorologist, consider what happens when you fill a bottle with water by totally immersing it under the water in a sink, then pull the bottle up and out of the water bottom first, as illustrated in Figure 9.5. 

Air pressure measurements can be done by any kind of sensors that provide a signal for the data acquisition system. The relative error of pressure sensors is very small because its absolute inaccuracy is related to relatively high absolute measures. There is no need for a very sophisticated instrument - it has just to be recalibrated several times within a year. 

RVP is a vapor pressure measurement at a fixed air/Hquid ratio of 4 and a temperature of 38°C. It is measured under conditions of water saturation. For samples which contain water-soluble components such as alcohols, ASTM D4953 is used. 

Air Permeability. Air permeabiUty is an important parameter for certain fabric end uses, eg, parachute fabrics, boat sails, warm clothing, rainwear, and industrial air filters. Air permeabiUty of a fabric is related to its cover, or opacity. Both of these properties are related to the amount of space between yams (or fibers in the case of nonwovens). The most common method for specifying air permeabiUty of a fabric involves measuring the air flow per unit area at a constant pressure differential between the two surfaces of the fabric. This method, suitable for measuring permeabiUty of woven, knitted, and nonwoven fabrics, is described in ASTM D737. Units for air permeabiUty measured by this method are generally abbreviated as CFM, or cubic feet per square foot per minute. 

Langmuir-Blodgett was the first technique to provide a practical route for the constmction of ordered molecular assembhes. These monolayers, which provide design dexibiUty both at the individual molecular and at the material levels, are prepared at the water—air interface using a hiUy computerized trough (Fig. 1). Detailed discussions of troughs (4) and of surface pressure, 7T, and methods of surface pressure measurements are available (3,6). 

A minimum volatihty is frequently specified to assure adequate vaporization under low temperature conditions. It can be defined either by a vapor pressure measurement or by initial distillation temperature limits. Vaporization promotes engine start-up. Fuel vapor pressure assumes an important role particularly at low temperature. For example, if fuel has cooled to —40°C, as at arctic bases, the amount of vapor produced is well below the lean flammabihty limit. In this case a spark igniter must vaporize enough fuel droplets to initiate combustion. Start-up under the extreme temperature conditions of the arctic is a major constraint in converting the Air Force from volatile JP-4 to kerosene-type JP-8, the military counterpart of commercial Jet Al. 

Vacuum pump capacity is conventionally based on the total cycle and expressed as mVh-m" (cfi7i/ft ) of filter area measured at pump inlet conditions. Thus, the gas volumes per unit area passing during each dry period in the cycle are totaled and divided by the cycle time to arrive at the design air rate. Since air rate measurements in the test program are based on pressure drop across the cake and filter medium only, allowance must be made For additional expansion due to pressure drop within the filter and auxiliary piping system in arriving at vacuum pump inlet conditions. 

Deflagration pressure can be reduced substantially by suppression. Figure 26-30 shows the pressures measured in an ethylene-air explosion and a sodium bicarbonate-suppressed ethylene-air explosion. Fike Corporation, Blue Springs Missouri, and Fenwal Safety Systems, Marlborough, Mass., supply explosion suppression systems. 

Air flow/air permeability Measure of the amount of air that flows through a filter - a variable of the degree of contamination, differential pressure, total porosity, and filter area. Expressed in either cubic feet/minute/square foot or liters/minute/square centimeter at a given pressure. 

TTie ability of the ventilation system to protect the worker efficiently can readily be determined by personal samples. The PIMEX method (see Chapter 12) can be used to determine the worker s exposure during various work phases. The capture efficiency as well as the supply air fraction can be measured using tracer gas techniques. Simple evaluation is carried out visually with smoke tube or pellet tests. Daily system evaluation is recommended using airflow or static pressure measurements at appropriate parts of the system. The air velocities, turbulence intensities, air temperature, mean radiant temperature, and air humidity should also be measured to provide an assessment ol thermal comfort. 

A number of units are used to express a pressure measurement. Some are based on a force per unit area for e.xample, pound (force) per square inch (psi) or dyne per square centimeter (dyne/enr). Otliers are based on a fluid height, such as inches of water (in H O) or millimeters of mercury (iimiHg) units such as these are convenient when tlie pressure is indicated by a difference between two levels of a liquid, as in a imuiometer or barometer. Barometric pressure is a measure of the ambient air pressure. Standard barometric pressure is 1 atm and is equivalent to 14.696 psi and 29.921 in Hg. 

The roentgen is the international unit of quantity for both x-rays and y-rays. It is the quantity of this radiation which will produce, as a, result of ionization, one electrostatic unit of charge, of either sign, in one cubic centimeter of dry air (as measured at 0° C and standard atmospheric pressure). 

Measurements are always accompanied by errors, which depend on the design of the instrument as well as external factors, such as change of air pressure, variation of temperature, etc. 

Differential Pressure Measurement Differential manometers are instruments that measure the difference in pressure between two adjacent rooms. Cleaner environments must have a higher pressure than adjacent, less clean environments to prevent flow of relatively dirty air into the cleaner environment. This differential pressure must be monitored and controlled. 

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