External pumps

Ca.rdia.c-AssistDevices. The principal cardiac-assist device, the intra-aortic balloon pump (lABP), is used primarily to support patients before or after open-heart surgery, or patients who go into cardiogenic shock. As of the mid-1990s, the lABP was being used more often to stabilize heart attack victims, especially in community hospitals which do not provide open-heart surgery. The procedure consists of a balloon catheter inserted into the aorta which expands and contracts to assist blood flow into the circulatory system and to reduce the heart s workload by about 20%. The disposable balloon is powered by an external pump console. 

The second class of grinding equipment is used to prepare dispersions. Typical of this class are baU and pebble mills, ultrasonic mills, and attrition mills. SoHds, eg, sulfur, antioxidants, accelerators, and zinc oxide, are generaUy ground on this equipment (see Size reduction). BaU mill action is assisted in some mills by a combination of dispersion circulation by an external pump and mechanical osciUation of an otherwise fixed nonrotary mill chamber. Where baU mill chambers are rotated it is necessary to experimentally estabHsh an optimum speed of rotation, the size and weight of the baU charge, and ensure the mills do not overheat during the grinding period. 

The fluid dehvery in an air-spray system can be pressure or suction fed. In a pressure-fed system, the fluid is brought to the atomizer under positive pressure generated with an external pump, a gas pressure over the coating material in a tank, or an elevation head. In a suction system, the annular flow of air around the fluid tip generates sufficient vacuum to aspirate the coating material from a container through a fluid tube and into the air stream. In this case, the paint supply is normally located in a small cup attached to the spray device to keep the elevation differential and frictional pressure drop in the fluid-supply tube small. 

Jet Mixers Continuous recycle of the contents of a tank through an external pump so arranged that the pump discharge stream appropriately reenters the vessel can result in a flow pattern in the tank which will produce a slow mixing aciion [Fossett, Trans. Jnst. Chem. Eng., 29,322 (1951)]. 

In the reactor shown in Fig. 23-41, a stable fluidized bed is maintained by recirculation of the mixed fluid through the bed and a draft tube. An external pump sometimes is used instead of the built-in... 

Figure 17.10 shows metal loss on the throat of the pump housing. External pump housing surfaces were also affected (Fig. 17.11). Note the large tubercles. (Tubercles are knoblike mounds of corrosion products. They typically have a hard, black outer shell enclosing porous reddish-brown or black iron oxides) (see Chap. 3, Tuberculation ). The metal surface beneath these tubercles had sustained graphitic corrosion, in some cases to a depth of Vi in. (0.6 cm) (Fig. 17.12).

The DTB, crystallizer has a relatively slow-speed propeller agitator located within a draft-tube which draws a fine-crystal suspension up to a boiling zone of wide cross-sectional area, as shown in Figure 3.3(i). The fine-crystal magma then passes through an annular zone in which an additional baffle is located. Liquor flow continues upwards at low velocity while crystals settle out and fall to the base of the vessel. Liquor from the external pumped loop provides an up-... 

Reactors with a packed bed of catalyst are identical to those for gas-liquid reactions filled with inert packing. Trickle-bed reactors are probably the most commonly used reactors with a fixed bed of catalyst. A draft-tube reactor (loop reactor) can contain a catalytic packing (see Fig. 5.4-9) inside the central tube. Stmctured catalysts similar to structural packings in distillation and absorption columns or in static mixers, which are characterized by a low pressure drop, can also be inserted into the draft tube. Recently, a monolithic reactor (Fig. 5.4-11) has been developed, which is an alternative to the trickle-bed reactor. The monolith catalyst has the shape of a block with straight narrow channels on the walls of which catalytic species are deposited. The already extremely low pressure drop by friction is compensated by gravity forces. Consequently, the pressure in the gas phase is constant over the whole height of the reactor. If needed, the gas can be recirculated internally without the necessity of using an external pump. 

As will be shown later the equation above is identical to the mass balance equation for a continuous stirred-tank reactor. The recycle can be provided either by an external pump as shown in Fig. 5.4-18 or by an impeller installed within the reaction chamber. The latter design was proposed by Weychert and Trela (1968). A commercial and advantageously modified version of such a reactor has been developed by Berty (1974, 1979), see Fig. 5.4-19. In these reactors, the relative velocity between the catalyst particles and the fluid phases is incretised without increasing the overall feed and outlet flow rates. 

The role of mixing in heterogeneous reactions is obvious. In multiphase processes mixing imposed by a stirrer or an external pump is necessary to increase the interface through which reactants pass to meet their partner in the other phase and/or to intensify mass transfer between phases. Mixing can also play a significant role in the case of homogeneous reactions. Chemical reactions occur at the molecular level. Reactant molecules introduced into a reactor encounter the environment in the vicinity of the inlet. The composition of the mixture there is obviously... 

Flow boiling is distinguished f rom pool boiling by the presence of fluid flow caused by natural circulation in a loop or forced by an external pump. In both systems, when operating at steady state, the flow appears to be forced no distinction will be made between them, since only the flow pattern and the heat transfer are of interest in this section. 

Slurry reactors may take on several physical forms they may be simple stirred autoclaves they may be simple vessels fitted with an external pump to recirculate the liquid and suspended solids through an external heat exchanger or they may resemble a bubble-tray rectifying... 

Fig. 7. Systemic (a) human insulin concentration and (b) glucose response following infusion of human insulin from external pump, 5 months postimplantation (Dziubla et ai, 2002).

The gaseous 3He, removed from the still by the external pumping system at room temperature (see Fig. 6.10), is purified and again cooled at 4.2 K by the 4He bath. 

The different adsorption and desorption events are controlled via the flow rates adjusted by the means of 3 or 5 external pumps and the column switch times, Fig. 3. The key element for success is the proper selection of the respective flow rates, which must be chosen in such a way that the extract front between zones I and II and the raffinate front between zones III and IV are stabilized, while the separation between zones II and III is assured. A simple trial-and-error approach to such an optimization of the system parameters is unlikely to be successful. Instead, the chromatographic behavior of all compounds has to be modeled and simulated. 

Figure 14.21. Forced circulation evaporator with an external pump...

Methods that utilize external pumps or pressure to inject concentrate into the water stream at a fixed ratio (balanced pressure systems). 

A more complicated behavior of the system (3) is manifested if the time-dependent driving field and damping are taken into account. Let us assume that the driving amplitude has the form /1 (x) =/o(l + sin (Hr)), meaning that the external pump amplitude is modulated with the frequency around /0. Moreover,/) = 0 and Ai = 2 = 0. It is obvious that if we now examine Eq. (3), the situation in the phase space changes sharply. In our system there are two competitive oscillations. The first belongs to the multiperiodic evolution mentioned in Section n.D, and the second is generated by the modulated external pump field. Consequently, we observe a rich variety of nonlinear oscillations in the SHG process. 

In this section we consider a model of interactions between the Kerr oscillators applied by J. Fiurasek et al. [139] and Perinova and Karska [140]. Each Kerr oscillator is externally pumped and damped. If the Kerr nonlinearity is turned off, the system is linear. This enables us to perform a simple comparison of the linear and nonlinear dynamics of the system, and we have found a specific nonlinear version of linear filtering. We study numerically the possibility of synchronization of chaotic signals generated by the Kerr oscillators by employing different feedback methods. 

Let us consider the driving field amplitude in the form 3F = "0(1 + sin fix), meaning that the external pump amplitude is modulated with a frequency ... 

Circulation and shear of the liquid in a vessel can be accomplished with external pumps and appropriate location of suction and discharge nozzles, but a satisfactory combination of vertical and lateral flows is obtained more economically by internal impellers, baffles, and draft tubes. Some general statements about dimensions, proportions, and internals of a liquid mixing vessel can be made. 

Jeandidier N, Boullu S, Busch-Brafin MS, Chabrier G, Sapin R, Gasser F, Pinget M. Comparison of antigenicity of Hoechst 21PH insulin using either implantable intraper-itoneal pump or subcutaneous external pump infusion in type 1 diabetic patients. Diabetes Care 2002 25(l) 84-8. 

Vessel Type Compressed Air Internal Moving Parts External Pumping ... 

Fig. 6.21 Column fermenters (a) bubble column, (b) tapered bubble column, (c) sieve-tray bubble column, (d) sieve-tray column with external pumping, and (e) packed-bed column with external pumping.

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