Laminar Flow Installations

To ensure that laminar flow meets the specification 

The quality control manager is responsible for following the procedure. The quality assurance manager is responsible for SOP compliance. 

Initial validation at the time of installation Revalidation once per year 

Use smoke cartridges to determine the air stream profile of the used laminar flow system. Measure the air velocity of at least 15 different locations below the LAP installation with the help of an anemometer. 

There should be undisturbed laminar air flow above the machinery and exhaust of the air. The average air velocities should be as follows 0.4 to 0.5 m/s with a lower limit of 0.4 m/s at each measure point. 

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Achievement of satisfactory air velocities is imperative to laminar flow installations. The laminarity and the sweeping effects that are essential to their effective operation are functions of air velocity. The standard within the pharmaceutical industry is an average velocity of 90 ft/min with a plus or minus 20% tolerance. 

In general, extreme care has to be taken when LB films are prepared, since tire quality of the resulting films depends cmcially on tire preparation conditions. The best place for an LB trough is a laboratory where tire surroundings, i.e. temperature, humidity and atmosphere, are completely controlled. Often it is placed in a laminar flow box. Also, tire trough should be installed in a shock-free environment. 

Enough space must be available to properly service the flow meter and to install any straight lengths of upstream and downstream pipe recommended by the manufacturer for use with the meter. Close-coupled fittings such as elbows or reducers tend to distort the velocity profile and can cause errors in a manner similar to those introduced by laminar flow. The amount of straight pipe required depends on the flow meter type. For the typical case of an orifice plate, piping requirements are normally Hsted in terms of the P or orifice/pipe bore ratio as shown in Table 1 (1) (see Piping systems). 

See Benedict, loc. cit., for a general equation for pressure loss for nozzles installed in pipes or with plenum inlets. Nozzles show higher loss than venturis. Permanent pressure loss for laminar flow depends on the Reynolds number in addition to p. For details, see Alvi, Sri-dharan, and Lakshamana Rao, J. Fluids Eng., 100, 299-307 (1978). 

Intuitively, GSD can be considered to be inversely related to the efficacy of installed engineering controls. A GSD of 1.0 means that all exposures are identical, a condition nearly realized in some laminar flow clean rooms. When GSD > 2.5, as may be the case for some kinds of maintenance work, it is likely that there are no functioning engineering controls. The exposure variability for most American workers is characterized by a GSD lying between 1.2 and 2.5 (3). 

Understandably, the baffles do not influence the power characteristics within the laminar flow region, where viscosity forces prevent rotation of the hquid. However, their influence is extremely strong at Re > 5 X IO". Here, the installation of baffles under otherwise unchanged operating conditions increases the power consumption of the stirrer by a factor of 20 ... 

Fig. 11 Self-contained terminal HEPA filtration modules installed in a T-bar suspended plenum ceiling in a laminar-flow application. (Courtesy of American Air Filter, Inc., Louisville, Kentucky.)...

To avoid possible contamination from atmospheric particles during sample manipulation and analysis, the equipment is installed in a clean chemistry laboratory, inside a Class 100 laminar flow area, or, during oceanographic cruises, under a laminar flow area in a clean ehemistry laboratory container (ISO20) available on board. 

Airborne particles are one important source of sample contamination. Therefore, the laboratory must enable samples to be treated and measurements to be carried out in a satisfactorily dust-free environment. Improvements in existing laboratories can be obtained by installing a laminar flow hood, but optimal improvement involves the design of clean rooms in which air is pumped through a dust-stop prefilter and then forced by a blower through an absolute filter inside the working... 

The helical ribbon stirrer is particularly favorable for homogenizing in the laminar flow range, but has two serious drawbacks, namely, the high cost of manufacture and the complicated introduction and installation in the tank. These disadvantages... 

These interesting devices consist of a tube or duct within which static elements are installed to promote cross-channel flow. See Figure 8.5 and Section 8.7.2. Static mixers are quite effective in promoting radial mixing in laminar flow, but their geometry is too complex to allow solution of the convective diffusion equation on a routine basis. A review article by Thakur et al. (2003) provides some empirical correlations. The lack of published data prevents a priori designs that utilize static mixers, but the axial dispersion model is a reasonable way to correlate pilot plant data. Chapter 15 shows how Pe can be measured using inert tracers. 

Figure 6.21 shows such a plot. It can be used to rapidly select the economic pipe diameter for laminar flow, subject to the restriction that the economic data on the line to be installed must be the same as those shown on the plot. Figure 6.21 has nomenclature similar to that of Fig. 6.13, and the comments on the latter are applicable here. Figure 6.21 also shows the economic diameter for turbulent flowJ... 

Contamination oocurs in petri dishes after pouring media but before inoculation. High contaminant spore load in lab. Clean, paint lab. Install laminar flow hood. 

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