Horizontal laminar flow

Horizontal laminar flow clean air benches are not BSCs (Section 10.3.4). They discharge HEPA-filtered air across the work surface and toward the user. These devices only provide product protection. They can be used for certain dean activirie.s, such as the dust-free assembly of sterile equipment or electronic devices. These benches should never be used when handling potentially infectious materials. The worker can be exposed to materials on the clean bench. Horizontal clean air benches should never be used as a substitute for, i biological safety cabinet. 

Vertical laminar flow clean benches also are not BSCs. They may be useful, for example, in hospital pharmacies when a clean area is needed. Although these units generally have a sash, the air is usually discharged into the room under the sash, resulting in the same potential problems as the horizontal laminar flow clean benches. 

A quantity sufficient to carry out the required tests, generally in duplicate, are filled into the containers. Most substances for which there are no concerns for either toxicity or stability are filled by weighing the appropriate quantity into antibiotic vials in a horizontal laminar flow work station. These operations are carried out in a self-contained cubicle to avoid cross-contamination. The vials are then closed with butyl rubber stoppers and sealed with an aluminium crimp seal using an automatic crimping and labelling machine. 

Horizontal laminar flow cabinets used for product protection, for example, in the pharmaceutical industry, exhaust directly into the face of the operator. This equipment must never be used as a biological (microbiological) safety cabinet. 

In the early days of laminar flow, the idea of entire rooms being protected by laminar flow was greeted with enthusiasm. They are now rarely found in connection with aseptic filling. They arc far more expensive to construct than conventional turbulent flow clean rooms, because of the need for more filters and greater engineering capabilities to move a lot of air at high velocity. Moreover, a horizontal laminar flow wall provides unidirectional air flow only as far as the first work station. Thereafter it is no different from a conventional clean... 

Last but not least, best practice is for aseptic changing rooms to be equipped with horizontal laminar flow protection, providing a gradient of air cleanliness from the filter bank situated at the cleanest end (access to the aseptic filling room) of the room to exit registers at the entrance. 

A unit sometimes confused with a Class I biological safety cabinet is a horizontal laminar flow cabinet or work table. This type of unit serves precisely the opposite function of a class I cabinet. Clean air which has been HEPA filtered is blown across the work surface toward the worker so that the research or product materials are protected against contamination, but the worker is not protected at all. Such a unit is unsuited for microbiological work, except for applications which would cause no harm to the users, such as a work involving noninfectious or non-aUergenic materials. 

Figure 18.2. Air flows for vertical and horizontal laminar flow hoods.

It is good practice to cool all sterilized items in an operating horizontal laminar flow hood or in a dust- and draft-free area to avoid drawing contamination back into the cooling container. Bottles should have screw caps left... 

Cleanbenches use horizontal laminar flow of filtered air from the back to the front of a hooded table. Care must be taken to ensure that the laminar flow is not disrupted by equipment on the bench, which can bring particles into the work area by turbulent exchange with the non-filtered room air. 

The preceding equation automatically allows for the effect of the number of vertical rows of horizontal tubes as proposed by Kem and cited later in this discussion. The flow should be streamlined (laminar) flow, with a Reynolds Number of 1,800- 2,100 for the condensation, see Figures 10-67Aand 10-67B. 

Show that the volumetric flowrate of this fluid in a horizontal pipe of radius a under isothermal laminar flow conditions with a pressure gradient —AP/l per unit length is ... 

Filtered air may be used to purge a complete room, or it m be confined to a specific area and incorporate the principle of laminar flow, which permits operations to be carried out in a gentle current of sterile air. The direction of the airflow may be horizontal or vertical, depending upon the type of equipment being nsed, the type of operation and the material being handled. It is important that there is no obstruction between the air supply and the exposed product, since this may resnlt in the deflection of microorganisms or particulate matter fiom a non-sterile surface and canse contamination. Airflow gauges are essential to monitor that the correct flow rate is obtained in laminar flow units and in complete suites to ensure that a positive pressure fiom clean to less clean areas is always maintained. 

A laminar flow enclosure provides a means for environmental control of a confined area for aseptic use. Laminar flow units utilize HEPA filters, with the uniform movement of air along parallel lines. The air movement may be in a horizontal or vertical direction and may involve a confined area, such as a workbench, or an entire room. Laminar flow modules are suspended above filling lines, vial- and stopper-washing equipment, and other processes to provide an aseptic and particulate-free environment. 

The Nusselt Equations apply to laminar flow of the condensing film. For horizontal condensation the equations... 

This regime is characterized by the presence of two continuous fluid phases and an interface which can easily be described. The term separated flows is frequently employed to describe these situations in both horizontal and vertical systems. Some flow patterns in Regime I are advantageous for transferring heat between the tube wall and the fluid mixture or for carrying out two-phase reactions. The special case of laminar-laminar flow is included in this regime, and two studies seem to be of interest, Byers and King (B7) and Bentwich and Sideman (B3). 

Figure 5. Exact (numerical solution, continuous line) and linearised (equation (24), dotted line) velocity profile (i.e. vy of the fluid at different distances x from the surface) at y = 10-5 m in the case of laminar flow parallel to an active plane (Section 4.1). Parameters Dt = 10 9m2 s-1, v = 10-3ms-1, and v = 10-6m2s-1. The hydrodynamic boundary layer thickness (<50 = 5 x 10 4 m), equation (26), where 99% of v is reached is shown with a horizontal double arrow line. For comparison, the normalised concentration profile of species i, ct/ithe linear profile of the diffusion layer approach (continuous line) and its thickness (<5, = 3 x 10 5m, equation (34)) have been added. Notice that the linearisation of the exact velocity profile requires that <5,

A Newtonian liquid in laminar flow in a horizontal tube emerges into the... 

Determine the shear stress distribution and velocity profile for steady, fully developed, laminar flow of an incompressible Newtonian fluid in a horizontal pipe. Use a cylindrical shell element and consider both sign conventions. How should the analysis be modified for flow in an annulus ... 

An interesting study of entrainment from horizontal liquid films has also been carried out by Van Rossum (VI). On the basis of a liquid film in laminar flow with a flat and smooth surface, he found that the mean actual film thickness was about 0.6 times the theoretical one. The critical Weber number corresponding to the onset of atomization was determined for five different liquids, with Weber number defined as... 

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