Closed-loop configuration

Open-loop systems have inherently long residence times which may be detrimental if the retentate is susceptible to degradation by shear or microbiological contamination. A feed-bleed or closed-loop configuration is a one-stage continuous membrane system. At steady state, the upstream... 

There are also special cells for use with USP Apparatus 4 in a closed-loop configuration. Using a 100 mL bottle, a total volume of dissolution media ranges from 25 to 100 mL. For very low volume assembly, a test tube with a rubber stopper allowing for inlet and outlet tubing can be used. However, with the need for even smaller volumes, internal modifications should be made to the apparatus to minimize the impact on functionality due to a change in the internal tubing volumes. Also, the additional volume of the flow cell must be considered. For example, the implant... 

An 8 column SMB with a 2-2-2-2 closed-loop configuration is considered. Available for the controller are the on-line concentration measurements at the two outlets of extract and raffinate. The substances to be separated are A and B, where A adsorbs stronger than B. Linear adsorption behaviour has been assumed (qj=Hi-Ci). The Henry constants Hi have been chosen as Ha=4 and Hb=2. The controller is able to adjust the external flow rates in order to change the internal flow rates in the four sections of the SMB, which are the manipulated variables. Since all 4 internal flow rates cannot be directly controlled via the external flow rates, one internal flow rate has to be directly controlled by an additional pump, which... 

The experiments using sprays were performed in both open and closed loop configurations. In the closed loop configuration, the experiments eould be performed with varying total system pressures and air partial pressures. 

S. M. Ramasamy and H. A. Mottola, Flow Injection (Closed-Loop Configuration) Catalytic Determination of Copper in Human Serum. Anal. Chim. Acta, 127 (1981) 39. 

Distillation column models are well known to be nonlinear. This implies that a +10% step perturbation in the feed composition could display different dynamics and nonsymmetrical responses to a -10% step perturbation. Six different input sequences were studied and in each case, the computational time for computing the process transient was recorded, for both the open- and closed-loop configurations. 

The closed-loop configuration (Fig. 4) is used when the parts to deliver are placed inside a container or a pallet which has to be returned (empty) to the loading station. This configuration can also be used when the parts have to be recirculated before unloading, in order to create a sort of a storing buffer (in the same way which occurs in the baggage claim area of the airports). 

Membrane bio-reactor (MBR) A system for simultaneous reaction and separation with a membrane. Could be conducted in the same physical enclosure or in separate enclosiures if the reaction vessel and membrane unit are coupled in a semi-closed-loop configuration. 

Escobar et al (2001) did a complete study in which pilot plant trials were conducted in a corn wet mill with a 7000-L membrane recycle bioreactor (MRB) that integrated ceramic microflltration membranes in a semi-closed loop configuration with a stirred-tank reactor. Residence times of 7.5-10 h... 

In these cases, the configuration is called a closed-loop configuration. Three important closed-loop configurations are ... 

Fig. 5 Transimpedance amplifier based on a closed-loop configuration forcing the input current /( to flow in the feedback resistor Rfeed while keeping at virtual ground the negative input node.

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