Air leakage

This leakage air must be taken into account in the specification of the compressor since it is lost from the system and is not available for conveying. Manufacturers of rotary valves will generally provide this data. It would always be recommended that rotary valves should be vented, as shown, to prevent the leakage air from interfering with the smooth fiow of material into the pipeline. The rotary valve is a positive displacement type feeder and so for a given valve and speed of rotation the material feed rate will be almost directly proportional to the bulk density of the material. 

If the leakage air does interfere with the material feed it could result in a significant reduction in the bulk density of the material, and hence affect the material fiow rate. It is important, therefore, to ensure that the vent is correctly designed and maintained. On start-up, after a shut down, the bulk density of the material in the hopper could increase considerably and this could result in pipeline blockage at this time due to over feeding. If this is a possibility the material in the supply hopper should be aerated prior to start-up. 

Convective-section air leaks reduce the thermal efficiency of the heater by mixing cold ambient air with hot flue gas. The resulting energy debit may be expressed as follows  

= percent oxygen in combustion zone, i.e., just below the shock tubes at the inlet to the convective section 

Just for practice, let us suppose we have a stack temperature of 600°F, ambient air is 100°F, the convective section has 10 percent 02, and the firebox has 6 percent 02 measured just below the shock tubes. What percentage of fuel fired (AF in our equation) is being wasted by cold air leaking into the convective section  

Suppose we put the air registers back as they were and pinch on the stack damper instead. So let s suppose we restrict airflow via the stack damper until the firebox oxygen goes down from our base case value of 6 percent, to 3 percent. The oxygen in the convective section will also be reduced to, say, 5 percent. In this case, we see that the A02 is also much 

To suppress afterburn and minimize energy losses caused by in-leakage of cold ambient air, any holes in the heater walls, convective section, ducts, etc. should be patched. Also make sure that inspection ports are closed. Leaks can be detected on stream to a certain extent by visual inspection (crumbling chalk dust or dropping a little baking powder past a suspected leak will pinpoint the leak). 

What percentage of fuel fired (AF in our equation) is being wasted by cold air leaking into the convective section  

Suppose we put the air registers back as they were and pinch on the stack damper instead. So let s suppose we restrict airflow via the stack damper until the firebox oxygen goes down from our base case 

Standards have been developed by the Heat Exchange Institute for rates of air leakage into commercially light systems. Their chart is represented by the equation 

The size of ejector and its steam consumption depend on the rate at which gases must be removed from the process. A basic portion of 

Three Stage Compression with Intercooling and Pressure Loss between Stages 

Ethylene is to be compressed from 5 to 75atm in three stages. Temperature to the first stage is 60°F, those to the other stages are 100°F. Pressure loss between stages is 0.34 atm (5 psi). Isentropic efficiency of each stage is 0.87. Compressihihties at the inlets to the 

Values of Pj will be assumed until the value of P2 calculated by equating the first two terms equals that calculated from the last two terms. The last entries in the table are the interpolated values. 

After the required system pressure has been defined, flow rates of condensables and noncondensables must be estimated. 

Air can leak into a system around flanged joints, valve stems, pump and agitator shaft seals, instrument connections, and the like. Leakage can also occur through metal porosities and cracks along weld seams. Air leakage is unavoidable in commercial systems. 

In almost all design situations, air leakage rates cannot be accurately predicted. The only real accuracy necessary is that extremes be avoided. The designer is in reality specifying a maintenance level for the system when he estimates air leakage. All vacuum systems will have a finite leakage which 

Various methods have been proposed for estimating air-leakage rates  

The largest portion of condensable vapor load is generally product since noncondensable gases are generally saturated with product vapors at process vent conditions. The amount of condensable that enters the vacuum system should be minimized for several reasons  

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The amount of inerts which has to be removed by a pumping system after the pump-down stage depends on the in-leakage of air at the various fittings, connections, and so on. Air leakage is often correlated with system volume and pressure, but this approach introduces uncer-... 

Deflagration of vapor caused by air leakage into equipment operating under vacuum. Possibility of fire/explosion. 

The enclosure must be tested for one minute, with an inside air pressure equal to a head of about 1 in of water. No air should leak during the lest. Air leakage may be detected by submerging the enclosure in water, with the Just covering the enclosure. 

Watertightness and air leakage test for isolated phase bus systems. 

Seal problems can give rise to high leakages and thrust problems. The high leakages reduce the efficiency of the unit and can also lead to contamination of the lubricant. Thrust problems are created by air leakage past seals, causing an unbalance of the thrust forces on the system. 

If the air leakage is greater than the load for which the jet was designed, the alternatives are to correct the leaks or to use a larger ejector. The ejector must be large enough to handle not only the leaks but the normal load from the process. 

A reverse philosophy in sizing ejectors is occasionally applicable to a system in which even a small quantity of air leakage will upset the operation or contaminate the product. In such a system it may be desirable to install an ejector having a deliberately limited air handling capacity, so that the system cannot be operated until an injurious rate of air leakage is corrected. 

In order to maintain gas purity, it is desirable to select a positive suction pressure in order to minimize air leakage into the loop. Apart from the need to minimize inlet density and, hence, test power, the selection of test inlet pressure is a matter of convenience. 

In general, the air leakage rate through a building envelope is dependent... 

The airflow rate infiltrating and exfiltrating through each air leakage pass, Q , due to the combined effect of wind, stack, and mechanical ventilation system perfotmance can be calculated ftom the mass balance equation... 

The airflow rate Q, for each air leakage path is expressed with Eqs. (7.237), (7.242), and (7.243) using the infotmation on effective leakage area, CjA, and a pressure difference across the path. The total pressure acting on an opening from the outside is the sum of the pressure due to wind, gravity forces, and mechanical ventilation performance, and the static pressure inside the building results from Eq. (7.244). 

ASTM E783-84. 1984. Standard Method for Field Measurement of Air Leakage through Installed Exterior Windows and Doors. American Society for Testing and Materials, Philadelphia. 

It is of prime importance to keep air and gas leakage from ductwork at a minimum, as it represents increased fan running cost and the waste of treated air. Leakage into extract ductwork reduces the efficiency of the collection system. 

The leakage factor is the rate of air leakage at a given static pressure per m- of duct surface area ... 

TABLE 9.10 Airtightness Classes as Defined in the EUROVENT Guidelines HI Air Leakage Rate in Sheet Metal Air Distribution Systems... 

If the air leakage rate does not comply with the class requirement, the test shall be extended to include an additional equal percentage of the total surface area. 

Eurovent 2/2. Air leakage in sheet metal air distribution systems. 

The problem of unknown amounts of air leakage in the cold season in an industrial hall can be calculated by multizone airflow models during the whole year with local meteorological data. 

HEPA filters consist of a filter pack sealed into a case. The filter pack or core is made by pleating a continuous web of fiberglass paper back and forth over corrugated separators. The filter pack is sealed into a full-depth wood or steel casing using a elastomeric sealant. Gasketing is a critical item to ensure that the filter passes the air leakage tests. 

Air leakage rate The leakage of air through an enclosure such as a building or ductwork, expressed as air loss in L/s per m run, or as a percentage loss of the total volume. 

Airlock A two- or three-door enclosure providing access to a clean room that reduces the air leakage of external pol luted air into the clean room. 

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