Stagnation region

In the stagnation region shown in Fig. 10.54, contaminants will move m an irregular and often unpredictable manner. This means that production with exposed products in stagnation regions gives rise to contamination risks. 

FIGURE 10.54 An example of observed stagnation region in a bench with vertical unidirectional airflow. 

In order to reduce the influence ol unfavorable stagnation regions and vortex structures with their risk for accumulation of contaminants, tests should be carried out to characterize the functioning of the bench. In connection with these tests, induction tests should also be performed. Here smoke (particles) generated outside the bench and the probe of a particle counter placed inside the bench in the critical regions can give valuable information. 

Fig. 17.5 Illustration of the Tsuji and Yamaoka diffusion flame in the forward stagnation region of a porous cylinder [410,411].

H. Tsuji and I. Yamaoka. The Structure of Counterflow Diffusion Flames in the Forward Stagnation Region of a Porous Cylinder. Proc. Combust. Inst., 12 997-1005,1969. 

Fig. 4. Mass transfer from an impinging jet electrode. (From ref. 48 by permission of the publisher, The Electrochemical Society, Inc.). I, Potential core region II, established flow region III, stagnation region IV, wall-jet region.

The increased platelet adhesion onto HCP surfaces is mainly due to the high surfacial concentration of fibrinogen associated with immobilized heparin. Therefore one of the solutions to the problem could have been provided by simultaneous immobilization of heparin and proteolytic enzymes which could hydrolyze the adsorbed fibrinogen. The immobilized enzyme could also provide the lysis of the fibrin clot, in case it was formed, for instance in stagnation regions of the complicated devices. 

Figure 7-1. Schematic side view of differentially pumped cluster beam apparatus and quadrupole mass spectrometer. The temperature of the nozzle in the stagnation region is regulated by a circulating chiller. Reprinted with permission from Vaidyanathan et al. 1991b. Copyright 1991 American Institute of Physics.

Flow considered in integral equation solution for stagnation region. 

The nose cone can be made of refractory material, in which case the material must be capable of withstanding the final temperature attained by absorbing the heat from the stagnation region. 

Fig. IV.2. Flow system for studying reaction systems. Note Mixing nozzles are usually arranged to enter the vessel tangentially in order to avoid stagnation regions and also give some rotary mixing to the flow stream.

Within the stagnation region, the surface shear stress Try is given by... 

SOLUTION To analyze the problem, consider particle deposition on a single cylinder placed normal to an aerosol flow. The Reynolds number for the flow, based on the cylinder diameter, is 2320, which is sufficiently large to use the potential flow approximation for the stagnation region. We know that the critical Stokes number for the cylinder is... 

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