Series-parallel Arrangement Research Articles

Hollow fiber solvent extraction of pharmaceutical products: A case study

Dispersion-free solvent extraction using Celgard® microporous hydrophobic hollow fibers and flat membranes has been utilized for extraction/purification of fermentation-based pharmaceutical products. Extraction as well as back extraction has been studied using a pH swing procedure. Problems of emulsion formation, inherent in current processes, have been avoided to obtain stable dispersion-free operation. Very high solute recoveries and mass transfer rates have been obtained in the hollow fiber devices. Modular plant design using a series-parallel arrangement of this type of extractors and cost of existing dispersion-based devices indicate that these novel devices can compete effectively with commercial extractors.

Simulation and control of a 20-kHz spacecraft power system

A detailed computer representation of four Mapham inverters connected in a series-parallel arrangement has been implemented. System performance is illustrated by computer traces for the four Mapham inverters connected to a Litz cable with parallel resistance and DC receiver loads at the receiving end of the transmission cable. Methods of voltage control and load sharing between the inverters are demonstrated. The computer representation is used to design and demonstrate the advantages of a feedforward voltage-control strategy. It is shown that with a computer simulation of this type, the performance and control of spacecraft power systems can be investigated with relative ease and facility. >

Duct and pipe losses in solar energy systems

The effect of the heat loss from the piping system of a solar collector field of a large size is measured and the effect of this loss on the effective collector efficiency is evaluated. The data are used to develop a model that can be used to evaluate the effect of piping loss on collector efficiency for solar field of different areas. The collector field used in this study consists of 1064 evacuated tube collectors; each one has an absorber area of 1.75 m2. They are connected in a series–parallel arrangement and designed in a U-shape. Measurements of the heat loss in the piping system indicate that a drop in the collector efficiency occurs due to this heat loss. The effect of the heat loss on the collector efficiency was found to depend on the collector x-parameter with higher x corresponding to larger efficiency drop. The standard Hottel–Whillier–Bliss (HWB) equation for the collector efficiency was modified so that the form of the equation is maintained while the parameters change due to the inclusion of piping loss in the equation. The modified parameters were estimated for the collector field based on measurement and the data were used in the model to generalize the results for field with different piping to collector area ratios.

A variable low frequency high voltage generator using valves with fibre optic light guide control

Describes a new method of generating low frequency high alternating voltages by modulating two high voltage DC supplies of opposite polarity. The modulation is accomplished by the use of triode valves situated at high voltage whose grids are supplied by control signals, transmitted from the control circuit through fibre optic light guides. The first generator built is capable of driving a 1 nF load at 10 kV peak over the frequency range DC-50 Hz, or a 0.1 mu F capacitor at up to 0.1 Hz. In order to increase the voltage and current ratings of the generator, a series-parallel arrangement of valves may be used, with the appropriate control signals fed to the grid of each valve. Because the generator is relatively free from any electrical noise, it can be used to energize insulation samples in connection with partial discharge detection investigations.

The electrical interaction between artificial pacemakers and patients, with applications to electrocardiography

Eleven artificial pacemakers were calibrated prior to surgery. The current delivered by these units to human hearts was then measured at surgery with a current probe. Body surface pacemaker voltages were recorded subsequently in nine cases. The amplitude and shape of the current pulse depends upon the patient load impedance. Patient load impedance consists of myocardial electrode polarization impedance and tissue resistance. For the pacemaker and myocardial electrodes employed, the patient load impedance is well represented by an equivalent circuit consisting of a series parallel arrangement of two capacitors and two resistors. Values of these circuit parameters were determined in nine cases. Tissue resistance is represented by a fraction of the series resistor in the equivalent circuit. The remainder of the equivalent circuit is attributable to polarization. The voltage pulse measured at the body surface is related to the current pulse delivered to the myocardium by a transfer impedance. Since details of the current pulse, which had a rise time of less than a microsecond, were present in surface voltages, the transfer impedance is approximately resistive and independent of frequency up to a megacycle per second. It is concluded that no significant frequency distortion of electrocardiograms is caused by the electrical characteristics of body tissues. The value of the maximal scalar transfer impedance from these studies has been cast into the vectorial form employed by others in torso model studies. Under the conditions discussed, the vectorial transfer impedance has comparable magnitude whether obtained from model studies or from the present pacemaker study.

Optimizing simple circuitry for reliability and performance by failure mode

MANY PAPERS have been written about redundant circuits in which components can undergo either open-circuit or short-circuit failure. John von Newmann studied the problem in connection with abstract automata.1 Shannon and Moore showed that any given reliability could be achieved by using redundancy, however, as the reliability approaches 1, the number of parts involved approaches infinity.2 Other papers have been written that derive the formulas for mean time to failure and/or reliability for series-parallel and parallel-series type arrangements, that is, for n items in series and m such arrangements of n items in parallel, or n items in parallel and n such arrangements of n items in series.3,4 In applications to either ground-based equipment or microminiaturized parts such analysis is sufficient. However, there is not a true optimization until all circuits are considered. In systems with tight size, weight, and power requirements, all circuits must be considered. This paper discusses all circuits containing four components or less. Graphs are presented showing the circuit's optimizing reliability for any component reliability distribution. Then the exponential distribution is assumed, and the circuits maximizing the expected life are found. In both these optimization procedures, there will be optimal circuits which are not of the parallel-series or series-parallel type.