Aaberg entry loss


Similar questions can be addressed by the P-RISM (polymer reference interaction site model) theory of Curro and Schweizer [36]. This integral equation theory generalizes the Omstein-Zemike equation to polymeric systems in order to account for the fluid-like packing structure. Details of the molecular architecture enter via the single-chain structure factor. The P-RISM approach yields a detailed description of the phase behaviour and the local structure and has been applied to models with various degrees of structural detail. In the limit that the chains are modelled as infinitely thin Gaussian paths the results are very similar to the Flory-Huggins theory. The theory has been applied to fairly realistic chain models taking the experimentally measured single-chain structure factors as input. More recently, this approach has been applied self-consistently to calculate the change of the molecular confonnation upon blending.  [c.2368]

Fluid and spouted beds offer ideal conditions for drying provided the feed material is consistently suitable for fluidization or spouting however, if the drying operation is preceded by mechanical Hquid separation, eg, centrifugation, use of these dryers should be considered with caution. Fluid and spouted beds do not tolerate sticky materials and oversize lumps. Successful appHcations are particulate and pelleted polymers, grain, sand, coal, and mineral ores, appHcations whereia the physical size and character of the feed material is known and controllable 100% of the time. Fluid and spouted beds are attractive for iaert gas and organic Hquid drying because the vessels are stationary. Superheated steam drying is carried out ia fluid beds. This is an attractive alternative environmentally, but a process which was stalled for many years because of the lack of a suitable process vessel. The volumetric drying capacity of a fluid bed is many times that of a rotary dryer. The reason is that gas flowing through the latter moves between a series of parallel particle curtains ia which the gas must be entrained and mixed to contact particle surfaces. In the former, small bubbles of gas enter through the distributor and immediately penetrate and mix with a cloud of particles. Figure 14 shows that whereas the dryer efficiency of a cocurrent rotary dryer and fluid bed may be comparable, because both are siagle-stage vessels, the vessel size requirements are quite different. To approach the dryer efficiency of a countercurrent rotary dryer, two or more fluid beds with countercurrent gas flow must be operated ia series. Figure 15 shows one form of a two-stage fluid bed.  [c.250]

Both the metaboHsm of a material and its potential to cause toxic injury may vary with the route of exposure, although the magnitude of the dose and duration of dosing may influence this relationship. For example, materials that are metaboHcally activated by the Hver are likely to exhibit a comparatively greater degree of toxicity when given peroraHy than when absorbed in the lung or across the skin. This is largely related to the anatomical routes of transport. Thus, the greatest proportion of material absorbed from the gastrointestinal tract passes via the portal vein direcdy to the Hver. In contrast, materials absorbed as a result of respiratory exposure or skin contact initially pass to the lung and then into the systemic circulation, with only a small fraction of the cardiac output being deHvered to the Hver through the hepatic artery (Fig. 3). By similar reasoning, materials that are detoxified by the Hver may be significantly less toxic by swallowing than by either inhalation or penetration across the skin. An example of the influence of route on toxicity is presented in Table 3. When assessing the relevance of metaboHsm in acute toxicity testing, and particularly when comparing toxicity by different routes of exposure, both the magnitude of the dose and the time period over which it is given must be considered. For example, when a single large dose (a bolus) of a metaboHcally activated material is given by gavage, it may be almost completely metabolized, resulting in the rapid development of acute toxic injury. When the same material is given orally at a slower rate, eg, by continuous inclusion in the diet, then there is a slow and continual absorption and metaboHsm of the material, and in these circumstances the rate of generation of the toxic species may approach that which occurs from the continuous absorption resulting from persistent exposure to an atmosphere of the material. The influence of dose magnitude—time relationships also apply to the interpretation of results with materials detoxified by the Hver. With such materials, slow continuous peroral adininistration of the material results in slow titration to the Hver and a high proportion of the material being detoxified. In this instance, the anticipated differential toxic effect between the oral and inhalation routes of exposure occurs. However, if a bolus of the material is introduced into the stomach, then the endogenous hepatic detoxification mechanisms may be exceeded, and unmetaboHzed material may enter the systemic circulation and initiate toxic injury.  [c.231]

Sizing the enclosure is more important than might first appear. If the enclosure walls are close to the compacting pile of material, material splash effects will cause losses through openings in these wails. Therefore, the use of a larger enclosure allows the velocity of these air streams to decrease before reaching the walls. Since quantitative estimates cannot be made as to the magnitude of the material splash effects, field observations of an existing system and experience are the only guides. Air entrainment becomes a factor when the enclosure has large areas or complete sides that must remain open. Winds or local air currents can then enter and exit the enclosure, thereby removing dust. The flow rate can be calculated in a straightforward manner from the wind velocity, open area, and loss coefficient of the opening. However, the ingress airflow rate is usually found to be quite large so that it may not be practical to attempt to counteract it by enclosure exhaust alone. Positioning the exhaust off-take dose to the active zone of dust generation may capture the most concentrated portion of airborne dust before recirculation and mixing with entrained air can occur. This approach reduces the exhaust volume needed for air induction and control velocity.  [c.905]


See pages that mention the term Aaberg entry loss : [c.1687]   
Industrial ventilation design guidebook (2001) -- [ c.1448 ]