Internal loops

External and internal loop air-lifts and bubble column reactors containing a range of coalescing and non-Newtonian fluids, have been studied (52,53). It was shown that there are distinct differences in the characteristics of external and internal loop reactors (54). Overall, in this type of equipment... 

Eig. 23. Airlift reactors (a) spHt cylinder internal loop, (b) draft tube internal loop, and (c) external loop (94). 

When considering the availability of nutrients, it is also necessary to examine the significance of nutrient re-use within the waterbody. These internal sources amount not to an additional load, but a multiplier on the recyclability of the same load. This nutrient recycling and the internal stores from which they are recycled are often misunderstood, but there is a dearth of good published data about how these recycling mechanisms operate. Microbial decomposition in the water column is one of several internal loops recognized in recent years, but these are not closed and the flux of nutrients recycled through them is delayed rather than retained. 

There are two types of sample valve commonly used in LC, the internal loop valve and the external loop valve. In order to improve the seating and eliminate leaks, the valve faces are sometimes made from appropriate ceramics. The internal loop valves are largely used with small bore columns, that is to say columns having internal diameters of less than 1.5 mm. The external loop valves are used for larger diameter columns up to semi-preparative columns. 

The sample volume of the internal loop valve is contained in the connecting slot of the valve rotor and can range in capacity from 0.1 pi to about 0.5 pi. The dispersion that... 

Table 2. Variance of Solute Bands Resulting from Two Internal Loop Valves...

The peaks shown were obtained using a low dispersion UV detector (cell volume, 1.4 pi) in conjunction with a sample valve with a 1 pi internal loop. All tubes were of... 

Svendsen, H. F., et al., Loeal flow struetures in internal-loop and bubble eolumn reaetors, Chem. Eng. Sci., 47, 3297, 1992. 

The gas is circulated by means of pressurised air. In airlift bioreactors, circulation is caused by die motion of injected gas through a central tube, with fluid recirculation through the annulus between die tube and the tower or vice versa. Figure 6.1 shows an airlift bioreactor widi an internal loop cycle of fluid flow. 

Fig. 6.1. Gas and liquid flow pattern with internal loop cycle.

There are basically two types of LC sample valve, those with an internal loop and those with an external loop. Valves with an internal loop are normally designed to deliver sample volumes of less than one microliters. Valves with external loops can deliver sample volumes ranging from a few microliters to several milliliters or more. In general, LC sample valves must be able to sustain pressures up to 10,000 p.s.i., although they are likely to operate on a continuous basis, at pressures of 3,000 p.s.i. or less. 

As already stated, the valve system can take two basic forms, the internal loop sampling valve and the external loop sampling valve. A diagram of the internal loop valve which utilizes only four ports is shown in figure 14. 

Spatial Profiles of Gas Holdup in a Novel Internal-loop Airlift Reactor... 

Internal-loop airlift reactors (ALRs) are widely used for their self-induced circulation, improved mixing, and excellent heat transfer [1], This work reports on the design of an ALR with a novel gas-liquid separator and novel gas distributor. In this ALR, the gas was sparged into the annulus. The special designed gas-liquid separator, at the head of the reactor, can almost completely separate the gas and liquid even at high gas velocities. 

In this model, energy balances are set up for the reactor and the separator tube separately, and two equations are obtained. The gas holdup can then be obtained from combining these two equations. Details can be found in Zhang et al. [7]. The comparison between the measured and calculated cross-sectional mean gas holdups is shown in Fig. 5. It can be seen that there is a satisfactory agreement between the experimental and calculated gas holdup in the different operating conditions. Therefore, it is reasonable to conclude that the energy balance model used in this work can describe the circulation flow behavior in the novle internal-loop airlift reactor proposed in this work. 

A specially built conductivity probe was used to investigate the gas holdup in a novel internal-loop airlift reactor. The gas holdup generally increases with increasing solid holdup due to increased flow resistance. A model based on energy balance was developed that can be used to predict the average gas holdup in this novel interal-loop airlift reactor. 

The sample is loaded at atmospheric pressure into an external or internal loop, or groove in the valve core and introduced into the mobile phase stream by a short rotation of the valve. The volume of sample injected is normally V2u ied by changing Ute volume of the sample loop or by partially filling a sample loop with a fraction of its nominal volume. External sample loops have volumes from about 5 microliters up to about 1 ml. 

For smaller samples, four port valves with an internal loop can be used. In these, the sample loop is an engraved slot in the body of the valve. With both types, the volume of sample that has to be used to flush out and fill the loop is about ten times the loop volume. Fig. 2.2g shows the operating principle of each type. 

Poelma, F. G. J., Tukker, J. J., Evaluation of the chronically isolated internal loop in the rat for the study of drug absorption kinetics, J. Pharm. 

Abstract This chapter embodies two sections. In the first section a survey of the state of the art of azo-dye conversion by means of bacteria is presented, with a focus on reactor design and operational issues. The relevance of thorough characterization of reaction kinetics and yields is discussed. The second section is focused on recent results regarding the conversion of an azo-dye by means of bacterial biofilm in an internal loop airlift reactor. Experimental results are analyzed in the light of a comprehensive reactor model. Key issues, research needs and priorities regarding bioprocess development for azo-dye conversion are discussed. 

Figure 5 shows a sketch of the experimental apparatus. It consists of a bench scale internal loop airlift, gas and liquid flow control units and a gas humidifier. 

Geometric details of the reactor are reported by [41], The volume of the liquid phase in the internal loop airlift, hence the reaction volume V, could be changed by varying the level of an overflow duct. 

Fig. 6 Acid orange 7 and phenol concentration in the internal loop airlift reactor operated with Pseudomonas sp. 0X1 biofilm on natural pumice. (A) Aerobic phase. Gas air. Liquid continuous feeding of phenol supplemented synthetic medium. (AN) Anaerobic phase. Gas nitrogen. Liquid batch conditions, dye supplemented medium...

The reactor flow pattern is that of an internal loop airlift with pneumatic mixing of both the liquid and the solid phases [61], the latter consisting in biofilm supported by granular solids. The reactor was assumed uniformly mixed. 

Another perspective for production simulation is automatic capacity utilization optimization of multi-product systems. As discussed, this task may be very difficult because of the many different variables and boundary conditions. In an environment integrating optimization and simulation, the optimizer systematically varies the important decision variables in an external loop while the simulation model carries out production planning with the specified variables in the internal loop (see Gunther and Yang [3]). The target function, for example total costs or lead times, can be selected as required. The result of optimization is a detailed proposal for the sequence of the placed orders. 

Internal loop airlift bioreactors, 1 742 Internal manifolding method, 12 200 Internal microwave field, 16 513 Internal olefins, sulfonation of, 23 527 Internal-pair formation (IPF),... 

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