Walls clean areas

Soft wall clean area (cleaning) A clean area defined by hanging plastic drapes so that the filtered air flows from the ceiling downward and out under the drapes. The drapes may be in the form of strips (strip curtains). 

Clean and aseptic areas must be adequately illuminated lights are best housed above transparent panels set in a false ceiling. Electrical switches and sockets should fit flush to the wall. When required, gases should be piped into the area from outside the unit. Pipes and ducts, if they have to be brought into the clean area, must be effechvely sealed through the walls. Additionally they must either be boxed in (which prevents dust accumulation) or readily cleanable. Alternatively, pipes and ducts may be sited above false ceilings. 

The cleanroom facility should be carefully designed to control the ingress of contaminants, and be positively pressurized to the surrounding area in accordance with industry standards. The core and anterooms are positively pressurized by varying the amount of incoming make-up air. ° In the case of soft wall clean space facilities, such pressurization (potential outflow) is not possible, and a sufficient amount of constant, active outflow (kinetic outflow) should occur to prevent ingress of contaminants. 

Components, bulk-product containers, equipment, and any other articles required in a clean area where aseptic work is in progress should be sterilized and, wherever possible, passed into the area through double-ended sterilizers sealed into the wall. 

To prevent the shedding or accumulation of dust and other particulate matter, ceilings, floors, and walls in the aseptic area, and floors and walls in the clean area, have smooth impervious surfaces that permit the repeated application of cleaning and disinfecting agents. 

Walls, floors, ceilings, and equipment in a clean area are cleaned and, when required, disinfected in accordance with a written program. The program differentiates between the daily procedures and those undertaken when a different drug is fabricated. 

The interior surfaces (ceilings, walls and floors) shall be smooth and crackless, shall neither shed nor hold particulate matters, and shall stand washing and disinfecting. The joinings between walls, floors and ceilings in clean areas are preferably constructed into rounded corners. 

To reduce accumulation of dust and to facilitate cleaning, there should be no hidden difficult-to-clean recesses and a minimum of projecting ledges, shelves, cupboards, equipment, fixtures and fittings. Covin c should be used where walls meet floors and ceilings in sterile areas and other clean areas. 

Vessels of large volume aud limited surface area to be cleaned are not adapted to fill-and-empty or flow-through methods. Qeaning reagents have been applied in the form of a gel. Also, the interior surface may be cleaned by using automated spray devices that do not require personnel to remain inside the vessel. In some instances, reactants, both alkalis and acids, have been put into the hollow space by means of steam and allowed to condense on the interior walls. Cleaning tank exteriors chemically has not met with great success. 

In general, the test object caimot be heated above its operating temperature in space. As free molecular conditions are obtained around the object, it outgases and, if solar-spectmm photons impinge on the object, increases the release of gas. Because the object is in a vessel and the area of the hole lea ding to the gas pump is small compared with the projected interior area of the vessel, molecules originating from the test object can return to the test object provided that they do not interact in some manner with the vessel walls and the other components of the molecular environment. The object inside the vessel estabhshes an entirely different system than the clean, dry, and empty vacuum vessel. The new system no longer has the capabiUty to reach the clean, dry, and empty base pressure within a reasonable time. 

Work in connection with desahnation of seawater has shown that specially modified surfaces can have a profound effect on heat-transfer coefficients in evaporators. Figure 11-26 (Alexander and Hoffman, Oak Ridge National Laboratory TM-2203) compares overall coefficients for some of these surfaces when boiling fresh water in 0.051-m (2-in) tubes 2.44-m (8-ft) long at atmospheric pressure in both upflow and downflow. The area basis used was the nominal outside area. Tube 20 was a smooth 0.0016-m- (0.062-in-) wall aluminum brass tube that had accumulated about 6 years of fouhng in seawater service and exhibited a fouling resistance of about (2.6)(10 ) (m s K)/ J [0.00015 (fF -h-°F)/Btu]. Tube 23 was a clean aluminum tube with 20 spiral corrugations of 0.0032-m (lA-in) radius on a 0.254-m (10 -in)... 

The overall heat-transfer rate is almost entirely dependent upon the film coefficient between the inner jacket wall and the solids, which depends to a large extent on the solids characteristics. Overall coefficients may range from 30 to 200 J/(m s K), based upon total area if the diyer walls are kept reasonably clean. Coefficients as low as 5 or 10 may be encountered if caking on the walls occurs. 

To control air and contaminant movement between zones, different construction, process-related, and ventilation techniques are used. Clean and dirty areas can be separated using solid walls, curtains, or partitions (Fig. 7.109(2). Ventilation techniques used to separate zones include... 

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