Enclosure methods

Figure 8.1 Installing underlayment over older flooring as a suitable lead-based paint enclosure method.

Dust Enclosure Methods of partial and total enclosure at transfer points of mechanical type conveyors are employed by many industries to control fugitive dust and material spillage. The total enclosure of flammable-type material should be practiced with care because of potential explosions of the generated dust. Proper safety precautions should be incorporated in the design of the total enclosure devices. 

EC = Eddy covariance DEC = disjunct eddy covariance vDEC = virtual disjunct eddy covariance REA = relaxed eddy accumulation EM = enclosure method CBL = conveaive boundary layer budgeting MEG = mixed layer gradient MLV = mixed layer variance. 

In the standard method, the metal enclosure (called the air chamber) used to hold the hydrocarbon vapors is immersed in water before the test, then drained but not dried. This mode of operation, often designated as the wet bomb" is stipulated for all materials that are exclusively petroleum. But if the fuels contain alcohols or other organic products soluble in water, the apparatus must be dried in order that the vapors are not absorbed by the water on the walls. This technique is called the dry bomb" it results in RVP values higher by about 100 mbar for some oxygenated motor fuels. When examining the numerical results, it is thus important to know the technique employed. In any case, the dry bomb method is preferred. 

Most continuous pressure filters available (ca 1993) have their roots in vacuum filtration technology. A rotary dmm or rotary disk vacuum filter can be adapted to pressure by enclosing it in a pressure cover however, the disadvantages of this measure are evident. The enclosure is a pressure vessel which is heavy and expensive, the progress of filtration cannot be watched, and the removal of the cake from the vessel is difficult. Other complications of this method are caused by the necessity of arranging for two or more differential pressures between the inside and outside of the filter, which requires a troublesome system of pressure regulating valves. 

The principal use of LDPE and LLDPE in building products is as a film water barrier under below-grade doors as a wall vapor barrier, though PVC is typically preferred and as temporary enclosure film during constmction. The film is made either by extmding a thin-waHed tube, which may be sHt or wound up direcdy, or by extmsion through a slot die and cast direcdy on to a cold roU, cooled, then wound up. The former method is more widely used. A much smaller use for low density polyethylene is in piping. 

To reduce the amount of dust produced, water can be added to the abrasive from a circular water sprayer around the no22le. Chemical corrosion inhibitors must be dissolved in the water to prevent flash msting of the steel. Newer methods to reduce dust include the use of ice, soHd carbon dioxide (dry ice), or plastic beads as abrasives. Blasting with dry ice is inexpensive and effective, but the accumulation of carbon dioxide must be avoided in enclosures. Plastic beads are inexpensive, but the cutting efficiency is low and paint removal is slow the beads can be cleaned of paint particles and reused. 

Process-variable feedback for the controller is achieved by one of two methods. The process variable can (I) be measured and transmitted to the controller by using a separate measurement transmitter with a 0.2-I.0-bar (3-15-psi pneumatic output, or (2) be sensed directly by the controller, which contains the measurement sensor within its enclosure. Controllers with integral sensing elements are available that sense pressure, differential pressure, temperature, and level. Some controller designs have the set point adjustment knob in the controller, making set point adjustment a local and manual operation. Other types receive a set point from a remotely located pneumatic source, such as a manual air set regulator or another controller, to achieve set point adjustment. There are versions of the pneumatic controller that support the useful one-, two-, and three-mode combinations of proportional, integral, and derivative actions. Other options include auto/manual transfer stations, antireset windup circuitry, on/off control, and process-variable and set point indicators. 

Environmental Enclosures Enclosures for valve accessories are sometimes required to provide protection from specific environmental conditions. The National Electrical Manufacturers Association (NEMA) provides descriptions and test methods for equipment used in specific environmental conditions in NEMA 250. Protection against rain, windblown dust, hose-directed water, and external ice formation are examples of environmental conditions that are covered by NEMA standards. 

We have defined the various types of enclosures adopted by various manufacturers to suit different locations and environmental conditions in Tables 1.10 and 1.11. Here we briefly discuss methods for testing these enclosures to check their compliance with defined requirements. 

Mankoff, L.L.. Sverdlow, N. and Wilson, W.R., An analogue method for determining losses in isolated-phase bus enclosures , Trans. IEEE, 82, August, 532-542 (1963). 

In the cinematic method the airflow in the aperture is understood to be the result of interaction of the air curtain jet and the incident flow. Some of the cinematic methods that were developed did not apply the laws of conservation of the impulse and mechanical energy. These methods did not correspond satisfactorily to test results and were not developed further. In these cases the determination of the jet trajectory does not take into account the effect of the enclosures and the interaction of the jets, and the division of airflows between the room and the outer atmosphere is performed with an arbitrary geometrical construction. The above-mentioned facts lead to divergence of design results and existing test results as to both the release speed and the initial temperature of the air curtain."... 

In the following we apply the dynamic method of air curtain design (see Fig. 7.92). The basic dependency is illustrated for a one-sided air curtain that is supplied at angle a and developed on the plane surface XOY. Since the jet of the air curtain is bent by the effect of differential pressure from outside and inside (P ) the building, the jet of the air curtain flows to the opposite side of the aperture and splits into two parts. After the division, one part of the jet flows along the outer surface of the enclosure and the other one enters the room at an angle (i to the plane surface of the aperture. We isolate the... 

The first step in designing an exhaust hood is to select the geometry of the hood. As described above, the hood should enclose the process as much as possible. Where enclosures are not possible the hood should be located as close as possible to the source. The next step is to select an appropriate hood flow rate. The most common methods are... 

A visual evaluation of ventilation system performance can be performed by injecting smoke into the jet. No quantitative evaluation methods for these systems have been reported, but it should be possible to measure the containment of a hood with side walls (partial enclosure) using one of the containment indices (see Sections 10.2.1 and 10..5). Additional information may be obtained by measuring capture efficiency. 

Most of the combined systems could be designed using information provided in Sections 10.2 and 10.3 and taking into account the mutual influence of the supply and the exhaust system. Many of these local ventilation systems for small enclosures are very similar to general ventilation systems for rooms and could be designed using the methods described in Chapter 8. 

For exterior hoods and enclosures, the measurement of the breathing zone concentration provides a method of comparing the effects of changes in the supply and exhaust airflow rates,... 

Different protection factors have been defined. One method is to define it as the ratio of the concentration of a contaminant in the exhaust duct (CJ to the concentration in the breathing zone (C[,) of a person standing in front of the enclosure, for example, a laboratory fume hood ... 

Ion chromatography (see Section 7.4). Conductivity cells can be coupled to ion chromatographic systems to provide a sensitive method for measuring ionic concentrations in the eluate. To achieve this end, special micro-conductivity cells have been developed of a flow-through pattern and placed in a thermostatted enclosure a typical cell may contain a volume of about 1.5 /iL and have a cell constant of approximately 15 cm-1. It is claimed15 that sensitivity is improved by use of a bipolar square-wave pulsed current which reduces polarisation and capacitance effects, and the changes in conductivity caused by the heating effect of the current (see Refs 16, 17). 

Dust from release agents (chalk stearate or talc) Substitution of wet methods Enclosure and local exhaust ventilation... 

Table 13.16 sets out the major waste disposal methods, and potential hazards from toxic waste deposition are indicated in Table 13.17. The range of precautions required at land tips depends upon the risk, e.g. the nature and degree of contamination and the work to be undertaken. It will, however, encompass personal protective equipment a high standard of personal hygiene enclosure, possibly pressurization, and regular cleaning of vehicle cabs vehicle washing facilities site security, and control of designated dirty areas. Air monitoring and medical surveillance may be required.

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