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Large aluminum electrolytic capacitors are usually selected by considering factors such as cost effectiveness (more ripple current or capacitance per dollar), space effectiveness (less volume per dollar), and performance (more useful life at actual application temperature and voltage). These factors have been addressed in recent years as most major manufacturers have responded with improvements in ripple current ratings, new electrolyte systems, high capacitance foils, and rigorous cost controls. The focus of this paper is some of the constructional and application factors affecting the performance of large electrolytic capacitors. An aluminum electrolytic capacitor must be considered as a complete system since the internal failure mechanisms are multiple and complex in their interactions. It is also shown that the choices made by the circuit designer can be informed and improved by understanding the tradeoffs between different capacitor series, circuit design parameters and equipment design enhancements. This understanding can result in designs that are both reliable and cost-effective.

SummaryIntroduction Flow volume loops (FVLs) are considered part of the workup of patients with thyroid enlargement presenting to the endocrinology clinic. They are used to detect upper airway obstruction (UAO) secondary to tracheal compression (TC) from a goitre. Surgical assessment in contrast tends to focus on clinical evaluation supplemented when required by imaging. The aim of this study was to investigate whether FVLs influence the decision to operate in patients with a goitre. Methods We identified patients with a goitre referred by the department of endocrinology for FVLs between 2006 and 2011. The results of the FVL were collated, and their impact on patient management was assessed. Results Ninety-six patients were referred for FVL. In 38 patients, the indication was specifically to evaluate the effects of a goitre. Of these, 33 were reported as normal. Five FVLs were reported as abnormal (3 suggesting lung pathology and 2 TC). Both patients with TC on FVL presented no CT evidence of TC and underwent surgery due to abnormal cytology. Of the 33 normal FVLs, 7 underwent surgery: 2 for local compression, 4 for abnormal cytology and 1 for Graves' disease. None of the FVLs influenced the decision to operate. Conclusion FVLs may detect subradiological TC, but rarely influence management in patients with a goitre. In view of this and the cost of £235 per investigation, FVL should be reserved for goitre patients with suspected primary lung pathology, where the distinction between large and small airway compression is likely to influence management.

Marx generators have been built with a wide span of physical size and output capability, ranging from circuit board scale devices of a few stages up to systems capable of producing many Megavolts and occupying entire buildings. Our focus in this paper is the development of a capability to explore compact Marx generator (CMG) devices, where we arbitrarily define a CMG to be an apparatus consuming less than 0.5 m/sup 3/ (excluding the charging and control systems). We report the development of a laboratory system that incorporates a shielded test stand with battery-powered high voltage charging supplies and a computer based control system with a graphical user interface. We briefly discuss a demonstration of the test bed capability with results from a modular CMG we have constructed.

Thermal models for large can aluminum electrolytic capacitors have existed for a number of years for screw terminal products. These models have various shortcomings in their ability to handle the effects of package size, roll diameter and the mechanical details of assembly. An improved model was introduced recently which more accurately accounts for these internal parameters. This paper extends the use of that model to improved constructions which allow much more ripple current with no more internal heating than standard capacitors. An approximate empirical relationship has been developed to estimate conduction of heat from the roll to the terminals. In addition, the external environment of the capacitor has been considered since dissipation of heat necessarily involves transfer of the energy away from the capacitor. Studies have been conducted on the effect of air flow on the package-to-ambient thermal resistance. The use of external heat sinking is shown to be effective, especially when air flow is available and the heat sinks are integrated with the capacitor package to minimize the thermal resistances in the heat flow path. In these cases, the external thermal resistances can be reduced by more than 50%.

In prior studies we have reported considerable progress in improving the heat dissipation due to ripple current for large aluminum electrolytic capacitors [elcaps]. Due to these enhanced thermal construction techniques, elcaps are now commercially available with very high ripple current ratings at moderate cost. In those same studies, some effort was devoted to the improvement of the heat dissipation from the elcap into the external environment. This paper extends that work. A number of attempts have been made to enhance the removal of heat from the exterior of large elcaps with varying degrees of acceptance. We describe several approaches to external heat removal including an active heat removal system, which can deliver total thermal resistances around 1 C/Watt with a minimum of additional required space. It is believed that these approaches will be useful to those equipment designers who place a high priority on achieving the greatest possible circuit densities without resorting to liquid cooling.

The principal purpose of this case study of the Sumikawa Geothermal Field is to document and to evaluate the use of drilling logs, surface and downhole geophysical measurements, chemical analyses, and pressure transient data for the assessment of a high temperature volcanic geothermal field. The work accomplished during Year 1 of this ongoing program is described in the present report. A brief overview of the Sumikawa Geothermal Field is given. The drilling information and downhole pressure, temperature, and spinner surveys are used to determine feedzone locations, pressures and temperatures. Available injection and production data from both slim holes and large-diameter wells are analyzed to evaluate injectivity/productivity indices and to investigate the variation of discharge rate with borehole diameter. Finally, plans for future work are outlined.