Fluid management

Cassettes Cassette is a term used to describe two different cross-flow membrane devices. The less-common design is a usually large stack of membrane separated by a spacer, with flow moving in parallel across the membrane sheets. This variant is sometimes referred to as a flat spiral, since there is some similarity in the way feed and permeate are handled. The more common cassette has long been popular in the pharmaceutical and biotechnical field. It too is a stack of flat-sheet membranes, but the membrane is usually connected so that the feed flows across the membrane elements in series to achieve higher conversion per pass. Their popularity stems from easy direct sc e-up from laboratoiy to plant-scale equipment. Their hmitation is that fluid management is inherently veiy hmited and inefficient. Both types of cassette are veiy compact and capable of automated manufacture. 

Prepare a treatment plan with clearly defined outcome criteria for a hypovolemic shock patient that includes both fluid management and other pharmacologic therapy. 

IL-2 may cause capillary leak syndrome with profound hypotension and patients may require vasopressor support and aggressive fluid management. Patients should be cared for in an intensive care setting... 

Duration of Illness Hours, or days to weeks. Treatment is mainly limited to supportive care, but assisted ventilation may be necessary in serious cases, and fluid management is necessary. No antitoxin is available, and antibiotics provide no benefit. 

Since the successful exploitation of these membranes has been largely dependent on effective fluid-management techniques, it seemed appropriate for this symposium to review developments in this field over the last twenty years. 

Currently, the most common fluid management technique used in industry is "cross-flow" through tubes or channels with the fluid velocity tangential to the membrane surface (Figure 5). 

Figure 5. Crossflow fluid management in tubular membrane conflguration...

It should be obvious from the above that fluid-management techniques which Improve the mass-transfer coefficient (k) with minimum power consumption are most desirable. However, in some cases, low-cost membrane configurations with inefficient fluid management may be more cost effective. In any case, it is important to understand quantitatively how tangential velocity and mem-brane/hardware geometry affects the mass-transfer coefficient. 

The basic membrane/hardware geometries-tubes, plate and frame, and hollow fibers can of course all be operated with fluid management techniques which are relatively efficient or non-efficient. The remainder of this paper will adress itself to novel fluid-management techniques which utilize the basic membrane/hardware geometries but which seek to augment the mass-transfer coefficient even further. 

The cross-flow electrofilter has not been commercially exploited so far. However, it should find applications for suspensions or solutions of negatively charged species which have a low background ionic strength. Indeed, for shear sensitive particles, it may be advisable to dispense with cross-flow fluid management and to depend on eletrofiltratlon exclusively. 

Flux. The film model (Equation 6.6) illustrates that increasing flux has an exponential effect on CP. If we accept that fouling is a consequence of CP the impact of excessive flux is obvious. As a result high flux membranes tend to be short lived and foul unless improved fluid management is able to enhance k. Selection of the appropriate flux and crossflow velocity is a trade-offbetween capital and operating costs (see cost of fouling below). 

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