Blockage mechanisms

In order to illustrate the method, we can take the example of a pump as a component. It may fail to start or to stop when requested, provide too low a flow rate or too low a pressure, or present an external leak. The internal causes for pump failure may be mechanical blockage, mechanical damage, or vibrations. The external causes may be power failure, human error, cavitation, or too high a head loss. Then the effect on the operation of the system and external systems must be identified. It is also useful to describe the ways for detecting the failure. This allows establishing the corrective actions and the desired frequency of checks and maintenance operations. 

Deactivation of catalysts, LaY, LaP, ASA and SZR, used in isobutane/1-butene alkylation occurs by pore blockage mechanism. The amount and the chemical nature of organic... 

Figure 3. Emulsion blockage mechanism. (ti and T2 are the radii of curvature at the trailing and leading edges of the drop, respectively.) (Reproduced with permission from reference 9. Copyright 1973 Society of Petroleum Engineers.)...

The mechanism of antiperspinant action has not been fully estabHshed but probably is associated with blockage of ducts leading to the surface by protein denaturation by aluminum salts. The FDA has mandated that an antiperspinant product must reduce perspiration by at least 20% and has provided some guidelines for testing finished products. Some antiperspinant chemicals are Hsted in Table 14 (63). 

In the case of multiparticle blockage, as the suspension flows through the medium, the capillary walls of the pores are gradually covered by a uniform layer of particles. This particle layer continues to build up due to mechanical impaction, particle interception and physical adsorption of particles. As the process continues, the available flow area of the pores decreases. Denoting as the ratio of accumulated cake on the inside pore walls to the volume of filtrate recovered, and applying the Hagen-Poiseuille equation, the rate of filtration (per unit area of filter medium) at the start of the process is ... 

A mechanic was instructed to fit a steam supply at a gauge pressure of 200 psi to a process line in order to clear a blockage. By mistake, a steam supply at a gauge pressure of 40 psi was connected. Neither supply was labeled the 40 prsi supply was not fitted with a check valve resulting in backflow of process material into the steam supply line. Later the. steam supply caught fire when used to disperse a small leak. 

One-shot metered lubrication is eminently suited to oiling systems and can be employed either in an all-loss arrangement or as part of a circulatory system. Sight-glasses or other indicators should be incorporated since such lubricating mechanisms are nowadays so reliable that a blockage or other failure might not be suspected until too late. 

The opposite scenario also may occur, whereby a localized pre-boiler water chemistry problem can affect the downstream, mechanical operation of a boiler. As an example, difficulties in the control of pretreatment equipment may lead to treated MU water instability, causing downstream after-precipitation, leading to FW line blockages, and finally resulting in boiler cutout as a result of low water. 

The development of the two-phase flow in a heated capillary at different Peclet number is illustrated in Fig. 9.13. It shows that different mechanisms of two-phase flow formation may occur depending on the value of Peu. At small Pcl the fine bubble formation (on the micro-channel wall) plays a dominant role. Growth of these bubbles leads to a blockage of the micro-channel, to a sharp change of the hydraulic... 

Ensemble or Third-Body Ejfects. These effects concern the selective blockage of a particular adsorption site by adatom deposition. This can be advantageous when the reaction mechanism contains parallel paths that can be affected differently by blocking particular sites. In some cases, the undesired reaction needs more than one free adjacent site (ensemble), and can be inhibited by blocking particular sites without decreasing the reactivity of the surface for the catalyzed reaction. 

Mechanism of Action The mechanism of action of lamotrigine appears to involve blockage of ion channels and effects on glutamate transmission, although the precise mechanism in bipolar disorder is not clear.33... 

Possible causes—blockage, valve failure (mechanical or power), failure of steam supply (fracture of main, boiler shut-down). 

The ion-channel blocking mechanism has been widely tested and found to be important in both pharmacology and physiology. Examples are the block of nerve and cardiac sodium channels by local anesthetics, or block of NMDA receptor channels by Mg2+ and the anesthetic ketamine. The channel-block mechanism was first used quantitatively to describe block of the squid axon K+ current by tetraethylammonium (TEA) ions. The effects of channel blockers on synaptic potentials and synaptic currents were investigated, particularly at the neuromuscular junction, and the development of the single-channel recording technique allowed channel blockages to be observed directly for the first time. 

This is an important result. The simple open-channel block mechanism predicts that the total open time per burst is the same as the mean open time in the absence of blocker (Neher, 1983), even though openings are now chopped up by channel blockages. In fact, for channels that give bursts of openings in control recordings, the total open time per burst is constant in the presence or absence ... 

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